HullScant is the Wolfson Unit's Hull Scantlings program. It has been developed in collaboration with the International Sailing Federation and Royal Yachting Association.

HullScant is used to evaluate the scantlings for motor and sailing vessels under 24 metres.

The program calculates the actual scantling structural properties of a vessel and can compare this with the requirements set out in the ISO standard 12215, Part 5, which deals with pressures and scantling equations for fibre reinforced plastic, metal and wood monohull boats.

The HullScant software is specifically designed for all builders and designers conducting a scantling assessment and will greatly simplify the process of design category assessment for pleasure craft under the Recreational Craft Directive.

A demonstration version, showing the general capabilities of the software can be downloaded from here

HullScant ISO 12215-5

 HullScant & the ISO 12215 standard

As HullScant is based on the ISO standard and the ‘design categories’ I presume that the pressures it calculates are based on the maximum wave heights for those categories.  Does this mean that if I enter a speed of 25 knots for Category B the pressures are based on 4m waves at that speed, or does it appreciate the vessel cannot be driven at that speed in that sea state ?

When writing HullScant the Wolfson Unit used the standard that is created by ISO working group 18, we do not write this standard. We understand there is an inherent consideration of reducing speed in waves - section 3.1 of the standard describes this –and there is consideration of this fact in the design pressure for certain types of vessel (e.g. see the Notes in section 8.1). If you would like a full and comprehensive technical answer to this question it would be best placed to the convener of the ISO working group. HullScant is an assessment of the provided particulars against the ISO 12215 standard, NOT an assessment of the vessels suitability for a specific environment.

Have you ever think about producing a more general software without the ISO limits? That is, have you considered adding an option into HullScant to add design pressure directly – say a design load on deck or the load from a block? This could be called 'user load' with direct input of design pressure. The material and laminate stack build could be the same, but without the ISO limits while calculating the characteristics of a ply or stack, and instead the general theory can be used.

HullScant will never be able to go outside the ISO limits as this has never been validated and could lead to many user errors. In terms of your suggestions this may be difficult as there are intrinsic safety factors in the material properties etc. that are then accounted for in the ISO 12215 prediction of loading and pressure. One cannot work without the other. However, the user is able to obtain the stiffener and laminate strengths in the program without doing a full ISO calculation using the Results, Stiffer Properties or Results, Laminate properties menu items respectively. All in all, the software should not be considered to be a design tool; it checks conformity to the ISO standard, which in turn is a ‘sizing rule’. i.e. no part of the standard should be used in isolation.

What version of the ISO 12215 standard is used in the software ?

The program is in accordance with the April 2008 publication (2008-04-15) of 12215 part 5. We have released updates after every version change of the standard, free of charge to existing customers. The version of the standard used within a given version of HullScant is listed in the Report section, as well as the About screen. If you need to update your existing copy, please go to our Customer Download Area

 Is the program verified by a third party ?

The program has not gone through an official third party verification process and certification but it is endorsed by both the RYA (a Notified Body) and ISAF.

 Does HullScant cover multihulls?

No, HullScant currently only covers monohulls, as per Part 5 of the ISO 12215 standard. Part 7 of the ISO 12215 standard is currently (June 2009) deleted, and hence there is no standard upon which to base the software.

Material properties

When I define material in the Material library, the program shows me the material properties. But in the data sheet of material I have much different values. Which is correct?

The values pre-defined in HullScant are those ‘approved’ and selected within the ISO 12215 standard. Actual material values will clearly vary according to manufacturing process, base materials, quality assurance etc. The ISO materials can be seen as the ‘average’ material, and there will be a great number of more specialised materials with higher strength or modulus, etc. There is also the underlying reason that the ISO values are relatively conservative, due to the requirement that they cover the materials produced by all manufacturers, as they can be used (via evaluation level c) without any material test data checks. You have the ability to enter your own materials into the database (and indeed, racing yacht designers do so regularly) by adding (‘Test Data Material’) to the materials database. Be aware though that there are separate rules and regulations covering a structure where you are using manufacturers test data properties rather than the default ISO values; The Wolfson Unit strongly advise reading Annex C of ISO 12215 part 5 (and any other associated Annex) before using test data values in your structural assessment.

In the boat particulars dialogue should I be using EL-b, measured fibre content by mass, or EL-c, ISO fibre content by mass? The latter gives a lower strength result.

If there is no explicit test data for the material then it should be EL-c. This is clearly described in Table C.1 of the ISO 12215-5 standard. There is a 0.8 factor on all mechanical properties calculated on the standard where there is not explicit actual measurement of the fibre content.

I’ve observed inequalities in the material property calculation between the ISO standard 12215-5 and the presented solutions in the HullScant application. The presented values are only 80% of the default values coming from the ISO standard. Why is this?

The default setting for the material properties are specified to be the “default data (Tables C.4 to C.7) with a multiplication factor of 0.8”, as per evaluation level EL-c , specified in Annex C, C.1.1,  General. Therefore you are correct to state that the values are 0.8 of the values specified. If you want to use EL-b (default data), select the required value in the boat particulars dialog. Be aware of the implications of the different evaluation levels and their requirement for quality assurance checks.


HullScant does not seem to calculate carbon properly. If, for this boat, I insert a glass laminate with the same weight as one of the tested carbon laminates and check 'Calculate', the glass layup will pass but the carbon layup will fail - at the same weights. The carbon needs to be significantly beefier and heavier than the glass laminate in order to pass!

Check what orientation you have the carbon in. The material properties are determined in accordance with ISO (annex C, Table C.5 in particular). For example, double bias (DB) properties are very low in tensile and compressive strength. If for example you switched the outer layer (both inner and outer skins) to woven roving (300g/m) instead of DB (300) then the panels pass.

IF the NA is close-ish to the crown AND you have any 90 UD's (by which I mean UD running perpendicular to stiffener axis) AND you've entered this as an individual ply then HullScant will home in on its poor tensile failure strain of 0.45% or there abouts. It's a FPF (first ply failure) method.  If you have got this, try deleting these plies - if this is the problem then the M_offered will increase massively as the increase in limiting strain massively outweighs the minor loss in EI. This is why I model the inner skin/outer skin as two individual plies. My motto - never let HullScant see a 90 deg UD in tension!

“Does EL c also take into account that the higher resin content inferred by the 0.8 factor would create a slightly thicker laminate?”

The laminate thickness is the same as ISO data; only the material mechanical properties are altered (down to 0.8). This is an additional safety factor and the reduction in mechanical properties does not infer different resin content than the default values.

In the Material Library, when adding a GRP Multiple Laminate, what does “Multiplied or Crossplied Fabric” mean exactly? Is it a double axial 0/90° stitched fabric, a quadriaxial +/-45°/0/90° stitched fabric or still something else?

Multi or Crossplied fabric refers to bi-axial (0/90) fabric. If you need in the future to apply a double bias (+/-45) or quadriaxial fabric, you will need to add the material in the material library from: {Material Library => Add =>GRP Laminate} and then build your layup in the laminate library.


What is the difference between double bias and multidirectional fabric? Both are unidirectional fibres that lay on top of each other in different angles and are stitched together. Am I mistaken?

1) Double bias is +-45 degrees, Multidirectional (Crossplied) is +-90 degrees.

2) You cannot use DB or Quadraxial cloth in the "multiple laminate" because these have quite different properties from the more basic CSM, WR etc. where these are treated as a homogenous material with a thickness. Therefore you have to use laminate analysis for these.


In the Panel Results, what is the second column? Is it the minimum requested thickness or the minimal dry fibre weight as defined in 10.6.2 for FRP. The results don’t quite tally with what I expect them to be.

For FRP single skin panels HullScant calculates the equivalent required thickness from the dry fibre weight specified in ISO12215-5 Part 10.6.2 and examines this against the actual thickness. So HullScant does compare thickness against thickness. Check that you are not using a ‘laminate’ sandwich. You should be using a “Multiple GRP laminate” via the materials library (these (single skin & sandwich) are assessed in different ways


I would like to use Coremat type materials in the webs of some stiffeners to increase web stability. If I use “add>>core material” in the materials Library window, there is no option for this type of material. If I insert it as one of the options show or as a test data material there is no option that makes it work as a material that increases shear web stability. Do you have a workaround for this?

 Coremat thick is typically only half of total thickness of laminate and E value is much higher than real cores. This means treatment as a 'thin' sandwich (i.e. make as laminate in HullScant) is probably not correct. It is probably only ever used with CSM & WR which means normally the user would model panel as a multiple GRP laminate (i.e. a material). This uses flexural properties, not in plane. For example if you make up a multiple GRP material (see “6 x CSM MATERIAL” in the Materials dialog below) which gives a thickness compliance factor of 1.058. If the same 6 plies of CSM600 are modelled as a sandwich then it fails. This is because ISO defaults to in-plane properties for sandwich and UTS CSM < UFS. The problem is therefore how you get the laminate to use flexure properties, not in plane.

Define the Coremat as a material (‘Test Data’); It is probably best not to model COREMAT as a core material; use E glass instead, entering the relevant material properties (see screen grab below). Next add the other plies used (CSM, WR) as ‘Test Data’ as well, using flexural properties only the user can then build a laminate with Coremat in.

Finally, it might be worth doing a manual shear strength check at the neutral axis.


CSM, using ISO material properties                                                                                                          CSM, entered as ‘Test data’, and specifying flexural properties only                                   COREMAT as a ‘Test Data’ (note material type)


An example laminate



I am adding materials to the material library.  I am stuck as to how to add Soric flexible core.  I can’t add it as a core because none of the choices in the drop down menu are even close, and I have the same problem trying to add it as a reinforcement.  Do I add it as a “test data material”?

Entering the information as test data is the correct approach, but this isn't going to be that straightforward.......

If you treat it a sandwich (i.e. SORIC entered as a core in test data) HullScant will recognise it as a core and will employ thin sandwich theory as per ISO.  The core will have a zero E value and the program will do both a core shear strength and EI check in addition to BM check. This is wrong. The E value of the SORIC is much, much higher than a normal marine core AND these aren't really cores but 'bulkers' and are typically 2-4mm thick so thin sandwich approach is violated.

The best way to deal with this type of product is to treat it as a single skin (but using the laminate stack Annex H) - i.e. SORIC is entered as a laminate in test data. Without the magic word, 'core' HullScant will treat as any other ply and include the SORIC E value. BUT it won't however do a shear or EI check.

Recommendation:  Treat as single skin.  If it is just 2-4mm thick bulker the SF and stiffness are probably not going to be a problem.  If they are thought to be so then you will need to model it as a sandwich AS WELL or do a manual check. Finally, if entering as a core (as a 2nd check), make sure shear elongation (<35% or 35%) is correct for the material - work out USS/G from the type approval certificate.


In your choice of core material what is the difference between PVC I and PVC II? Both are listed as cross linked.

There are three broad classifications for rigid PVC compounds: Type I, Type II, and CPVC. Type II varies from Type I due to greater impact values, but lower chemical resistance. CPVC has greater high temperature resistance. You should match manufacturer’s data to the type set in HullScant. Typically most would be Type I.


I’ve used Quadraxial ply as a single skin, with the results giving a 0 required thickness and failing. When I looked closer at the results, quad (and UDWR) shows zero for flexural strength in the material properties. Why is this?

This data is derived from Table C.7. There is no ability to derive flexural strength from this table and members of the Working Group suggest that only actual test data should be used for flexural as it is very difficult to predict. If you convert this to a Laminate then you can get an answer out of HullScant (laminates use in plane strengths whereas single ply constructs use flexural). It is clear that HullScant is quite conservative when a single ply is used as a laminate. So two solutions... Use a laminate instead of single ply and increase the material to comply. Or get some test flexural data for the Quadraxial material and add this material as a “Test Data Material” in the Materials dialog using the other properties derived from ISO 12215-5.


When you create the material stack is the gel coat side at the top or bottom of the list, and does it make any difference anyway?

A laminate is created as if laying onto a female mould with the outer most ply first and inner most ply last. This applies to a schedule made using the laminate option. Using the multiple GRP material option it doesn’t matter (If you try the up/down buttons and check say flexural strength (which is the key property here) nothing changes). However, for best practise do it in the order of laying down (and the Wolfson Unit would tend to specify each individual ply rather than lump them together) is for audit purposes and so as not to confuse the builder in the unlikely event he needs to see the HullScant output.


I’ve got a CSM layup (which I was using as ‘single skin’ in Hullscant), but when I converted to using a laminate stack and added some WR, it starts to fail. What’s going on?

IN GENERAL: When you use the laminate option 12215-5 uses in-plane properties. The UTS of a CSM is about 68-80 MPa. When you use a MATERIAL stack (only available for CSM/WR/BX plies) it uses the Flexural strength - more like 130 MPa. Hence the different answers. The flexural strength is probably more correct for GRP single skin but data not so available for complex laminates hence LAMINATE option. Good for sandwich but for clever layups the user really should test the material properties. So if you have a WR/CSM/BX in roughly alternating plies or at least evenly distributed, use MATERIAL method and only use a laminate stack for cored layups

Back to the case in point: If you turn on stress ratios in results, and look at your hand lay bottom laminate, the problem is the WR ply in compression.  This is due to the low failure strain of WR compared with CSM.


I have created 2 different laminates, and used them alternatively for the same stiffener. However the stronger laminate is failing in HullScant, whereas the weaker one passes. What’s happening?


The stronger laminate (which fails according to HullScant)-

The weaker laminate -


HullScant/ISO-12215-5 is a first ply to fail method (FPF).  This means if a ply is introduced which has a much lower failure strain than any other of the plies, it will generally be that ply that triggers failure. This is what happens whenever a 90 degree UD is introduced as is the case for the panel with 195gsm 90 deg ply. When this is used in a stiffener as attached plating, the attached plate is in tension (12215 assumes built- in ends).  The tensile failure strain in the 90 deg ply is about 0.5% whereas it is nearly 2% in the other plies, so the 90 ply triggers failure.  

Sometimes it is possible to get away with this but if as in this case the weight of crown UD's moves the neutral axis well away from the plate then the problem is compounded.  Simply by deleting the two 90 plies from the laminate, the stiffener S1 one part becomes stronger (i.e. about the 14.3 kN.m given in the passing file). The same thing happens when you use aramid (unless you use a lot of it).


I’m considering using "Strongplank" material. What is the best way to model it in HullScant, particularly the "webs" in terms of cross linking the plies. Test data is a bit sparse. How can the cross linking of the skins that comes with Strongplank betaken into account?

The laminate analysis method assumes there is a bond between the skins and core. It would be necessary to input this as a material from test results to be sure. It should be analysed as a laminate for the purposes of the program.

If you have test data, and the shear properties are for the complete structure, then I would enter the properties as specified, and view the structure as one entity, i.e. skins included with the Strongplank 'core'.

It is understood this is a composite style strip-plank, i.e. used for hull, with the inner and outer faces glassed over with epoxy. Assuming that the radiused edges get filled with epoxy AND a top-notch secondary bond is produced, structurally we would have:

1. Outer and inner skin = horizontal flanges of Strongplank plus sheathing.

2. 'Core' material consisting of actual PVC core (assuming this has a decent density and it therefore structural) plus the vertical web.

It is suggested that a single pseudo-core having the actual thickness of the PVC be created but with properties derived as follows:

a) Calculate minimum strain from web and core (probably the GRP component)

b) Calculate the E value (or G value for shear) using:

G(effective) = (2 x tweb x Gweb + width PVC x G PVC)/(2 tweb + width PVC)

c) Calculate USS from G effective x min strain.

The actual laid up inner and outer skins should then be added to the laminate, but not the strong plank skins as they are already accounted for in the 'Strongplank' core.


I have a wooden yacht construction which is a combination of plank on frame, but with a double veneer of cold moulding over the top. Is this catered for in the program? I can see how to use normal plank on frame, and also full cold moulding, but not the combined.

First thing first – it is best to start reading all of Annex E!

There are two possible methods. The first is an Annex H laminate stack.  You need to set up two offered panels, one //, one #, corresponding to with or across the grain. This is a more conservative but more scientific method. It is very dependent in panel AR and it is suggested to use # to the grain.  The Wolfson Unit suggest you set up wood # to grain yourself to see what's going on. The alternative method is to treat the whole stack as a pseudo single material. Handle with care!  See the attached BST file for examples of both of these methods.


General hints & helpers in the use of HullScant

1. Avoid UD's for panels in HullScant - this is a first ply to failure method and not a laminate analysis program - always try to combine a multidirectional ply using the closest possible combination of WR, DB and QX

2. If UD's must be modelled (and this will mostly give lower strengths) then it is necessary to use the option to produce a 90 deg laminate (option available in the laminate toolbar - this automatically creates a second laminate at 90 degrees where UD0's become UD90's and vice versa.  QX/BX/WR/DB are unaffected) and within the second tab of the panel layup offer this new laminate in the long direction.

3. A much better approach is to use the material library option of defining test material and calculate the properties of the single ply in both directions using CLT (outside the scope of HullScant) but avoiding the ply by ply trap.  This avoids the problem - even a BX (same strain in two principal directions) always comes out better that a two ply layup of one UD0 and one UD90. E's are the same - strengths are different.

4. Even better - use test data - not a lot of point going to the trouble of vacuum bagging only to use EL-C or even B really. 


What are the various abbreviations (e.g. Wos)?

Wos = outer skin weight

Wis = inner skin weight

EI b is as per equation 42 of the standard, combining 2nd moment of area with modulus. The subscript b indicates in the shorter direction (see BML & BMb for corresponding bending moment values for long & short directions).


In the panel requirements dialog screen, what is meant by “The % panel area in bottom location specifies the percentage of an area of a side panel that extends into the bottom”?

The answer to your question is based on section 6.2 of the ISO 12215 - Part 5. The input you are required to enter into HullScant is the area of a side panel (for the hull) that extends to the bottom, in percentage term. For example, if your panel area is 100% above the waterline, then this value is 0% (i.e. a side panel). If, say 70% of the panel area is above the waterline and 30% of it is below, then the value to enter is 30% (i.e. a side panel that extends to the bottom of the hull). If the panel area is 100% below the waterline, then this is defined as a bottom panel in the dialog.


The K2 and K3 (aspect ratio) coefficients don’t appear to be correct comparing against table 5 in 12215-5:2008. With an aspect ratio of 1.67 the K2 & K3 values must lie between 0.468 / 0.476 and 0.025 / 0.026 respectively, but HullScant is providing much smaller values.

Check if you are using different material properties in the short direction as opposed to the long direction. Table 5 is for isotropic panels. For an orthotropic panel the function to Calculate K2 & K3 gets passed the effective aspect ratio based on the stiffness:

Effective aspect ratio, EAR:=(Length/spacing)*power(DS/DL,0.25), where DS:=short laminate EI, DL:=long laminate EI

This EAR is then directly used in the calculation of K2 & K3. Hence the different factors

This is as per Annex H.2.1.12, & table H.3


But ….Effective Aspect Ratio is only used in the calculation of alpha, beta b and beta l, and therefore in the calculation of Mdb (maximum design bending moment in the b direction, Nmm/mm), Mdl (maximum design bending moment in the l direction, Nmm/mm) and y/b (maximum relative deflection, mm/mm) for orthotropic panel calculations at Annex H (normative). It is never used in the calculation of K2 or K3, even if in the standard Table 5 is clearly indicated to be used for isotropic panels because orthotropic panels don't use it.

Table H.3, α and βb equations are curve fits to K2 and K3 as may be found in ABS guides.  To convert from α to K3 multiply by 12. To convert from βb to K2 multiply by 6.  Hence as high aspect ratio, α= 0.00237 or 0.028 as K3 and βb = 0.0833 or 0.5 as K2. This a minor difference, as in Table 5, the original Timoshenko coefficients were plotted on a more complicated basis. This is all true for AR or EAR. It was decided within HullScant to use α= K3/12 and βb= K2/6 in order to avoid minor differences when analysing either using Annex H or main body of the standard. The difference is trivial but might have caused some confusion with users. The equations in H.3 were checked against FE plate models to check their validity and also to develop βl.  There is no main body equation equivalent to βl so this is programmed as per Table H.3.  The FE plate models apply to especially orthotropic layups (e.g. plywood). DO NOT USE FOR COMPLEX ANGLE, NON-SYMMETRICAL LAYUPS - USE CLASSICAL LAMINATE THEORY (CLT). The presumption is that the stiffest direction is parallel to the short side as this is the logical way to layup a panel (having said that the equation will cope with minor (only minor) deviations from this presumption). As such by laying up the stiffest material in short direction, EAR > AR.  This makes sense as the panel is receiving less support from the long direction and so the panel more nearly corresponds to 'cylindrical bending' for which transverse strain is zero.


General hints & helper

The user doesn’t need to check the panel in both directions (short side and long side) in panel requirements if your laminates are CSM/WR. You only need to do this if you have a different offered material in that direction (e.g. 90 degrees to a unidirectional or a bias fabric).


The Results report shows a bending moment. Is that the maximum value that the stiffener can support?

Yes the ‘offered BM’ is the greatest BM the stiffener can support using the safety factors on materials as per the ISO standard.

 Transverse and longitudinal stiffeners: do I have to specify a stiffener length as the gap between the crossing bonds ?

It depends on the stiffener and what it is expected to support. Usually transverse stiffeners are fully supporting the panels either side. Refer to Section 9.2. of ISO12215:5

 Scantling bulkheads: do I have to input a bulkhead as a beam, divide it into longitudinal frames, and define it with the local height ?

Yes this is the method required. Refer to Section 9.2 of ISO12215:5

In the calculation result for stiffeners, is the “offered” values for the stiffeners base on exact values of section modulus or values from table in Annex G?

The section modulus for stiffeners is calculated from first principles, not interpolated or derived from the tables of Annex G.

Is the effective plate width automatically adjusted if the stiffener spacing is less than that width?

If the stiffener is set up as a hybrid/laminate stiffener it will adjust the plating size accordingly and automatically.

If the stiffener is set up as a complex stiffener then the plating size must be set in the stiffener builder. It will use this size to calculate mechanical properties.

Our current design has a large webframe without any longitudinal framing in the area of interest. Hence some of the stiffener is below the water line and some above. If I enter this as a bottom web, HullScant finds a design pressure of 20.5 kN/m2. If I calculate it as a combined bottom/side web, HullScant gives a design pressure of (only) 10.5 kN/m2.I also calculated it as a side web, and HullScant also gives 10.5 kN/m2.

In other words, it appears that HullScant assumes that most of the web is above the waterline, while in fact it is for more than 2/3 under the waterline.

What’s happened is the % of frame in the bottom zone has been set to zero (see highlighted input parameter in dialog box below).  So HullScant thinks it's all in the side shell zone and gives a 100% side shell pressure.  If you enter a figure of 80% in the bottom zone in the amended input, then Hullscant calculates according to part 5, 6.2.5. As the minimums govern, 10.5 kPa (side) and 20.5 kPa (bottom), HS calculates pressure as 0.2 x 10.5 + 0.8 x 20.5 = 18.5 kPa.


As I read the rule, if a bulkhead does not meet the structural requirements for a water tight bulkhead, it can be regarded as a stiffener. However, as I read it, you can only regard the bulkhead as a stiffener with a height of 7 time its thickness. In other words, it we have a bulkhead from 12mm plywood, it only counts as a stiffener 84mm high?

Not quite, no. A structural non-watertight bulkhead is handled under 7D (D = depth of hull in metres), as defined in Section 11.8.1 of the standard. The thickness of the bulkhead cannot be less than 7 times the depth of the hull in that area. See also the comments from a member of the working group to the question below

I didn’t see anything regarding the definition of non-watertight structural bulkheads, wood or sandwich (ref ISO12215-5 chap 11.8), in Hullscant. How are these accounted for?

Structure that is not classified as a bulkhead but provides structural support can be viewed as a stiffener (ISO 12215 part 6 is probably worth re-reading). Table 20 (sect 11.7.2) limits the height to thickness ratio (h/tw) to 10 for a flat bar plywood stiffener (thereby giving 120mm height for a 12mm ply structure).It is also worth reading section 11.8 of the standard.

And some words of wisdom from a member of the ISO 12215 working part – “a structural non-watertight bulkhead is handled under 7D (D = depth of hull in metres).  It's a semi-empirical equation, with some simple plate theory behind it, but not much. If you wish to analyse a ply or cored bulkhead as a stiffener, I believe that this should only be done in the case of cut-outs which produce a beam-like 'transverse frame', i.e. the span/depth > 5.  If this is the case then the dw/tw limits (to prevent shear buckling under in plane bending) become meaningful. I wouldn't try to analyse a deep ply bulkhead by just considering an artificial depth based on 12t or similar. An in-plane stress analysis of a deep bulkhead is not practical using simple equations.  The 7D seems from experience to give adequate racking stiffness so I'd leave it at that.  There have been various efforts to develop an equivalent stiffener but these predate the 7D.”


What is the best way of defining full height longitudinals and bulkheads i.e. those which are attached to both the hull and deck? At the moment I am treating them as a “T” type, but this poses the question of how much inner plate to use.  What is the usual method?

If the vessel is a small boat feature such as a RIB where the depth between bottom shell and deck is sufficiently small that the 'web' is attached to both deck and bottom so as to make an I-beam, then we then have an I-beam under deck pressure and bottom pressure.  There are a number of issues here, some 12215-5, some HullScant. The approach is to make a complex stiffener, i.e. manually enter the effective deck plating at 20 (t_i+t_o) deck + presumably cored web thickness and likewise for the bottom shell.  It is probably best to treat this as bottom stiffener as this gives the largest pressure. HullScant will then give you the compliance factors.

However, there are a few other things to consider. The first is web buckling.  Assuming a not untypical couple of plies either side of a H80, 20-30mm core, the ISO slenderness limits (based on 'hollow/PU' cores, albeit with a shear force compliance factor >>1) may need some additional investigation outside HullScant.

In the past, faced with these it is sometimes better to use an 'artificial' span since if you have a series of full-deck transverses and girders (i.e. egg-box style - see ISO-12215-6) you can't be sure what's supporting what. As the beam theory only really works for span/depth > 5, the user might also treat a floor web as an unstiffened WT bulkhead (even though it's not designed as such) since for a typical small boat head of 0.5-0.7m it ought to be able to survive no problem. Of course if this is a RIB or similar then the floor design point (built-in) is at the shallow ends under ISO - this might be a problem - one option might be to treat as simply supported and look for a minimum CF at the keel of 1.5 in bending from HS (assumption depends on deadrise).  However you still have to model the shallow depth at the deck extremes for shear and this could be a problem. A detailed analysis of this is beyond the scope of Hullscant and this FAQ; the user should speak to a structural engineer with a knowledge of the standard, relevant small craft structures and the requirements of the notify body.


For topside stiffeners, is there anywhere were the neutral axis for the top-hat-stiffener/hull-flange combination can be seen?

You should be getting this shown as a black dotted line in the laminate view window, as shown below.

When creating a stiffener can I insert pad layers (inner-skin reinforcements) separately form the hull laminate, or of width other than the hull plating effective width?

Yes, just insert layers in. Remember you will need to do this as a ‘complex’ laminate, rather than the standard off the shelf top hat etc.


Table 21 shows the value of Table 20 being multiplied by the square root of the actual BM over the BM design (hopefully less than unity). This then further increases the minimum thickness required for a given web or crown dimension which seems strange - is this correct or have I misunderstood the standard?

Ksm and Kas cannot be less than 1.0.  They are the ratio of the offered value to the required value.  So if you have more section modulus than required then KSM > 1 and so the applied compressive stress in the flange will be lower.  This means dividing by the 1% ultimate strain is making the flange unnecessarily stiff, hence the root Ksm factor.


Hullscant doesn’t appear to evaluate the slenderness ratios of stiffener web & flanges in much rigor. Also using a value of 35 for carbon laminates (Table 20) is a bit of an assumption since for basic GRP - covering the majority of craft - the value is 30 for webs and 21 for flange. What is the reasoning behind all this?

The crown slenderness ratio is loosely based on the Euler plate buckling equation which for an isotropic material is 3.62 E(tf/d)^2 where t = thickness and b = width of crown. The requirement is for this stress to be (roughly) twice the applied stress.  It is easier to write this in terms of strain so: d/tf = (3.62 /(2 x 0.5 ultimate strain))^0.5 (Note 0.5 is the allowable stress factor, and this is valid when the BM or SM compliance factor is 1.0000)

For GRP the ultimate strain in compression varies a lot between CSM and WR but using 1%, this equation would yield  (3.62 /(2*0.5 x 0.01))^0.5 = 19 (NOTE for all CSM using this logic, the factor would be more like 14). The figure of 21 is the ABS figure - it is in line with the above derivation (which was used for all the other materials) and 21 was kept to give agreement with ABS (ISO 12215 pt 5 tried to look a bit like ABS ORY).

Coming up with a slenderness for the web is even more difficult.  The web is actually under combined in plane bending and shear.  This requires a quadratic interaction equation which is too complex for use in a simple rule formula. The web limit is loosely based on shear stress only (and some comparisons with existing rules).

In addition, the methods assume a totally non-effective former. Even with a PU32 it is not certain if this behaves exactly the same as a genuine hollow pre-moulded/bogged down stiffener. For a 80 kg/m3 core, the slenderness ratios are probably meaningless. Also, many crowns have UD's (sometimes carbon UD300) with glass over bonding.  This is not only a mixture of two different materials but the orthotropic buckling equations are different from the isotropic ones.

No simple rule can do everything!

So because of the uncertainties, it was decided that the check should be a 'yellow box' warning only.  Many RIBS have very tall thin webs and it would be misleading if Hullscant was showing failures when these aren't happening in practice.

Finally, remember that ISO-12215-5 is one of a number of methods permitted under Recreational Craft Sectoral Group (RSG) guidelines.


Can I be sure the Offered Bending Stiffeness from the HullScant Report is correct ?

HullScant has been validated over a number of reference cases. Based on examplemotoryacht.bst (reference case which comes with the installation package), here is a detailed calculation for the "Deck Stiffener 1"/"Coachroof Stringer" attached to the "Coachroof Sandwich" laminate.
The calculation was performed based on ISO Standard 12215-5 chapter 11.
(In addition to the following, a worked example can also be found in Annex H which contains the full analysis for a Top Hat stiffener)



The difference of 0.5% is due to roundings and the true length of the webs used in HullScant software.


General hints & helpers

Effective width: The 20 (ti+to) (from LR SSC) really hits thin skinned cored panels with typically 20-30mm NOMEX 'former' L's. This is big reduction from the ABS ORY equivalent 't' .

If struggling to understand why the stiffener is failing

a), create it using the hybrid method - make a copy and then convert - this gives a nice graphic showing position of NA.  Makes it easy to see how highly loaded the plate v crown is and allows simply deletion/editing - it is also necessary for b) below.

b) If all else fails and only thing left is to pull NA closer to plate -  insert 'pad' of typically 200-300mm wide 3/4 plies of EUD0 under stiffener and over inner skin. 


Release notes: 

Release changes are cumulative.

Release Notes for Hullscant Version 14.10.16

  • Corrected link to HTML help files

Release Notes for HullScant Version: 03.08.16

  • Modified skin stiffness equation for cases where skin wrinkling occurs.

Release Notes for HullScant Version: 30.06.15

  • Help system and context-sensitive help upgraded to Microsoft HTML Help (.chm) format.

Release Notes for HullScant Version: 25.05.15

  • Removed bug in calculation of torque carried by a ‘combined’ stock and blade rudder.

  • Clarified and improved metal material property selection and usage in rudder module.

Release Notes for HullScant Version: 14.03.12

  • The ‘Pass Warning Ratio’ parameter found in the ‘Boat Particulars’ dialog was not saved to .bst. This has now been fixed.

Release Notes for HullScant Version: 01.08.11

  • Under some Windows 7 font settings the ‘Material Name’ column in the Laminate window was not shown. This has now been fixed.

Release Notes for HullScant Version: 31.05.11

  • The aspect ratio shown in the ISO Scantling Report was found to be inconsistent with the actual aspect ratio used in the scantlings calculations. This has now been corrected.
  • For cored panels with aspect ratios greater than 4, the calculated kSHC was incorrect. This has now been fixed.

Release Notes for HullScant Version: 05.04.11

  • If converting a hybrid wood/FRP stiffener to a complex stiffener a warning will now appear indicating the effective breadth factor is 20.
  • In calculating the web thickness for an FRP stiffener in the Stock Stiffener dialog the formula uses 0.3 default for the fibre content. This has now been changed so it uses the actual FRP fibre content.
  • In calculating the minimum thickness requirement, tmin, for hull and sides with an offered laminate, Hullscant would use FRP calculations even for wood sheathed with FRP, for example. A further option has been added to the Reinforcement Type dropdown on the Offered tab of the Panel Requirements dialog to set this to wood. Hullscant will then use the wood equations accordingly. For a laminate of wood type, Hullscant will also remove the weight requirements for the outer and inner skins.
  • In calculating KSHC, Table 12 for cored panels, this value was limited to 0.465. Hullscant now includes an additional curve for 2<(l/b)<4.

Release Notes for HullScant Version: 29.09.10

  • For large panels (section 8.4 of ISO12215-5) located over the bottom and the side, Hullscant will not apportion the pressure for the bottom and side accordingly.

Release Notes for HullScant Version: 09.09.10

  • For structural bulkheads the transverse position may now be entered and displayed in the boat view window and the water head is also shown by a blue line.
  • Section 8.4 of ISO 12215-5 for very large panels has been added to HullScant. The results will show a warning if this Section has been invoked.
  • For a single skin laminate built using the laminate builder the tmin in some circumstances could be presented as the minimum weight. This has now been fixed.
  • The kar value in the results were generally displayed for the displacement mode only, this has now been changed so it reflects the value for displacement, planing or cored panels.

Release Notes for HullScant Version: 30.07.10

  • The k6 option for the sandwich minimum skin care factor has been added to the program. This can be set in the Boat Particulars dialog.
  • Hullscant Rudder: for the main rudder stock type, the option would not be set when reloading a file. This has now been fixed.

Release Notes for HullScant Version: 06.07.10

  • For a particular set of circumstances related to the Undo function HullScant can encounter a library indexing problem. This has now been fixed

Release Notes for HullScant Version: 05.05.10

  • For Hullscant Rudder a laminated stock was not recognised if it did not have a corresponding laminated rudder blade. This has now been fixed.
  • For laminates without a core on rare occasions the skin wrinkling stress can cause what looks like a non-compliance even though it should not be considered for non-sandwich laminates. This has now been fixed.
  • For a stock L shaped stiffener the web area included the angle. This has now been changed to remove this thickness.

Release Notes for HullScant Version: 09.02.10

  • Optional Hullscant Rudder module now available. Hullscant Rudder calculates the structural properties of a vessel’s spade rudder, and compares it to the requirements of ISO 12215 Part 8.

Release Notes for HullScant Version: 07.01.10

  • The frp ply thickness, tMIN, calculated from the weight of the fibre was based on an assumed resin specific gravity of 1.2. This calculation has now been changed to be the ratio of the required fibre weight over the actual fibre weight times the actual thickness of the ply to remove the reliance on resin density.
  • The reverse laminate order option in the Laminate dialog can create an error in some circumstances. This has now been fixed.
  • In rare circumstances the wrinkling stress ratio of the inner skin of a sandwich laminate may not be recognised as the lowest stress ratio. This has now been fixed.

Release Notes for HullScant Version: 02.12.09

  • The frp ply thickness, tMIN, calculated from the weight of the fibre had an error that could affect the calculation. This has now been fixed.

Release Notes for HullScant Version: 03.06.09

  • The Longitudinal pressure distribution factor, KL, was not shown for deck panels and stiffeners. This has now been corrected.
  • The kar factor for sandwich panels in a unique set of circumstances could be greater than the 1.0 limit. This has now been corrected.

Release Notes for HullScant Version: 30.04.08

Relates to ISO 12215-5:2008, Date 2008-04-15

  • Updated titles and footers in program to match title of final ISO 12215-5:2008, Date 2008-04-15 International Standard.

Release Notes for HullScant Version: 21.04.08

Relates to ISO 12215-5:2008(E), Date 2008-01-04

  • Updated program to match changes in new ISO 12215-5:2008(E), Date 2008-01-04 International Standard.
  • Updated HullScant to match ISO 12215:5 Table 3.
  • Updated HullScant to match ISO 12215:5 Table 18.
  • Added curvature correction to ISO 12215:5 Table H3 to match equations 38 and 39. This is an omission in the standard.

Release Notes for HullScant Version: 29.11.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • In factors for the minimum thickness and skin fibre mass requirements there is a speed dependency. This has now been set to 2.36*LWL1/2 for sailboats.
  • If the neutral axis of a stiffener moves into the plate or the flange then the offered shear force results can be too high. The offered shear force form formulation has therefore been changed and relies on the web only. For hybrid or complex stiffeners there is now a drop down box in the corresponding dialog/window that describes the stiffener configuration to aid the calculation for a shear force factor. If more precise information is required regarding this formulation then please contact the Wolfson Unit.
  • The HullScant file format has been changed (FV20), older HullScant files will work with no problem but new files cannot be used with older versions of HullScant.

Release Notes for HullScant Version: 14.09.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Following a request for intepretation the addition of a requirement for the laminate weight of the inner and outer skin for the superstructure and deckhouses location has been added back in to HullScant. There is also a requirement for tmin for other material types for superstructure and deckhouses.
  • Every time the stiffener properties results are calculated for a hybrid/laminated stiffener and there is a bondwith set, the height of the web laminate will be subtracted from the height of the stiffener. This has now been fixed.

Release Notes for HullScant Version: 12.09.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Added view scroll buttons to cycle through the views on the boat view window.
  • The wrinkling stress calculation for the laminate analysis can be incorrect for some circumstances. This has now been fixed.
  • When using sandwich laminates for locations other than bottom, side and deck, Hullscant wrongly shows a requirement for the weight of the inner and outer skin. There is no requirement for other locations. This has now been fixed.
  • Laminates in the laminate library cannot be deleted, even if they are not referenced in a panel or stiffener. This has now been fixed.

Release Notes for HullScant Version: 18.07.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • There is now the facility to copy the boat view to the clipboard. The view will be copied at the size and aspect ratio of the boat view window. See the Edit, Copy View to Clipboard menu item when the boat view window is selected.
  • The top hat stiffener weights in the weight estimate now include the additional weight of the panel at the base of the stiffener as this is not included in the adjacent panels.
  • The panel and stiffener weights in the weight estimate now include an additional curvature factor. The shape of the panel or stiffener is assumed to be a circular arc.
  • Additional important information has been added to the weight estimate report. Please see Help, Process Description, Weight Estimate for more information.
  • For Hybrid/Laminated stiffener types with a bond laminate width set, the mechanical properties can be marginally overestimated as the bonding laminate thickness is not removed from the web overall height. This has now been fixed.

Release Notes for HullScant Version: 24.05.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • The off face grain angle in the plywood dialog was not enabled when plywood on edge is selected. This has now been fixed.

Release Notes for HullScant Version: 22.05.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • The output thickness of complex stiffeners can be missing the last layer if that layer is a web part. This does not affect the Hullscant calculations. This has now been fixed.
  • Wrinkling stress ratios for laminates were calculated on the basis of individual ply modulus, this should be the thickness weighted modulus of the whole inner skin. This has now been fixed.
  • In the panel stress ratio results the minimum ply was displayed in the failure colour. This has confused some users and therefore has been changed to not display a colour.

Release Notes for HullScant Version: 17.04.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • For floating stiffeners there is an error in the ISO standard equation (51) such that the kSA factor should always be 5 for hybrid/laminated or complex stiffeners using the required shear force and shear flow methods. This has now been corrected in Hullscant.
  • There are some indexing errors that can occur for particular circumstances when editing sitffeners or materials. This has now been fixed.

Release Notes for HullScant Version: 16.04.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • An indexing error can occur if you have more laminates than materials and they are offered to a plating requirement. This has now been fixed.
  • The required web thickness for complex stiffeners can sometimes be 0 in error. This has now been fixed.
  • The hardwood shear properties in Table E.1 of the curerent ISO standard version are rounded to integer values. These have been changed in HullScant to reflect the values.

Release Notes for HullScant Version: 23.03.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Added non-ISO12215 capability for adding wood properties perpendicular to the grain direction. See the Wood dialog. Please note the following disclaimer: The perpendicular-to-grain values are for indicative purposes only and are not taken from ISO-12215 as the standard provides no data. It is strongly recommended that actual test values be used for design purposes. The Wolfson Unit MITA accepts no liability for the use or accuracy of these values.
  • Added non-ISO12215 data for Wood shear modulus data. Wood Shear Modulus = 1.6 x density. This is required when wood is used in a hybrid/laminated or complex stiffener.
  • Added icons to the Panel and Stiffener requirements windows to indicate the offered material or stiffener type. This is only available when in the "Details" view of the window.

Release Notes for HullScant Version: 06.03.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Added a copy button to the GRP multiple laminate dialog for copying previously created layers in the laminate.
  • Added a weight estimate tool button on the Main window.
  • Changed the layout of some dialogs, particularly Plywood dialog as users are not finding the Plywood on Edge option for building stiffeners.
  • If you use the sorting in the Materials library, Stiffener library or Laminates library and then select "No" to saving the changes to the library, there can sometimes be an indexing error in the respective referenced items. This has now been fixed.

Release Notes for HullScant Version: 27.02.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • The results now include a full web shear buckling check as per section 11.7.2 and Tables 20 and 21. A warning will appear in the results if the web is likely to buckle in shear.
  • The results window and various library windows now retain their sizing and window state (normal,maximised or minimised) after closing and reopening in a single program session.
  • There are extra sorting options for the required panels, required stiffeners and materials library windows using the layout menu or move up/move down tool buttons.
  • There are now sorting options for the Laminate library and Stiffener library using the layout menu or move up/move down tool buttons.
  • Added a weight per unit area column in the Materials Library and Laminate Library Windows.
  • Updated the Boat View window, changed presentation of selected structure and overall presentation differences.

Release Notes for HullScant Version: 20.02.07

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • The area pressure reduction coefficient kAR has been added to the results in the ISO Calculations columns for panels and stiffeners.
  • In the laminate window, for some symmestrical layups the minimum bending moment can appear as zero. This has now been corrected.
  • In certain dialogs the materials drop down box can sometimes be too small for certain types of materials. These have been increased in width where appropriate.
  • If a stock stiffener is FRP and it is first in the list it will not show the Stiffness - (EI) requirements for FRP stiffeners in the results. This has now been corrected.
  • For single skin panels designated as "bottom and side" there was no required tmin. This has now been corrected and requires tmin as for a bottom panel.
  • Added the ability to enter wood material shear modulus data in the Materials Library dialog. This is requred for hybrid/laminated or complex stiffeners or sandwich panels with wood.

Release Notes for HullScant Version: 27.11.06

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Corrected units output for EI and BM in Laminate Window when editing a stiffener.
  • If a stock stiffener is not FRP the ISO report will indicate that it is a pass/fail warning when it actually passes. This is now corrected.
  • Hullscant relies on an HTML browser plug-in for the results page. There has been no indicated problems using the new Internet Explorer 7

Release Notes for HullScant Version: 09.11.06

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • For stock stiffeneres, plate effective width - be, has been updated in HullScant to correctly reflect Table 19 based on material type rather than stiffener shape.
  • If a stock stiffener is specified as floating or other arrangement then the effective plate width will be 0 such that there is no contribution to area, section modulus or inertia from the attached plating.
  • In the materials properties results, individual GRP multiple laminate schedules are tabulated below the materials properties.
  • In the laminate window the inner and outer plys are indicated on the laminate diagram.

Release Notes for HullScant Version: 13.09.06

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-08-24

  • Checked to include newly released standard equations and nomenclature as version stated above "Final FDIS Draft"
  • When adding strip planking, material title includes sheathing details

Release Notes for HullScant Version: 04.08.06

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-06-15

  • When loading a file with Carbon double-bias or quadraxial in the materials library, the weave will return to woven roving or crossplied fabric. This has now been fixed.

Release Notes for HullScant Version: 25.07.06

Relates to ISO/FDIS 12215-5:2006(E), Date 2006-06-15

  • For a hybrid stiffener effective plating width only used calculated effective plating width (20tp + bb) and not the lesser of this or the stiffener spacing. This is now corrected
  • Inner skin wrinkling stress (Section 10.5.3 of ISO Standard) is now displayed in the Panel Stress ratios in the Results window
  • Panels may be analysed now in long direction (Annex H). Refer to offered tab on panel requirement dialog, also Orthogonal Panels in the Process Description section of the Help File
  • Added data for shear modulus of Quadriaxial and Double-bias Glass and Carbon as it is unavailable in the ISO Standard, this is required for stiffeners.
  • Laminates may be re-orientated by 90 degrees using the Add menu in the Laminates Library window. Refer to Orthogonal Panels in the Process Description section of the Help File
  • The decimal separator has been hard set to a point (.) to avoid errors with compiler when windows regional settings has a comma (,).
  • The curvature label in the ISO stiffener report and weight estimate report had the units of metres when it should actually be labelled in mm (millimetres). This is corrected.