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Author Topic: thickness of a GRP hull?  (Read 6837 times)

TurboTyne

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thickness of a GRP hull?
« on: July 18, 2014, 01:16:08 pm »

Hello
Can someone please give me an idea of how thick a GRP hull needs to be. Size presumably affects this and the hull in question would be about 70 ins long by 7 in beam.

I've searched a bit on this site and elsewhere and probably  missed this info. I've found references to how many layers of varous grades of fibre etc should be applied but this does not give me any idea about the overall thickness when finished. I am hoping that this will allow me to roughly estimate the weight of the GRP hull. I can estimate hull surface area and have found data on GRP density - although this seems to depend to some extent upon composition. If anyone knows of a better way to predict finished weight then that would be very useful.

Thanks  Mike
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Subculture

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Re: thickness of a GRP hull?
« Reply #1 on: July 18, 2014, 02:20:53 pm »

Very much open to preference.

Some people like thicker hulls, others thinner. I tend to prefer a thinner hull, with localized reinforcement and if required a bit of bracing here and there.

I would say for a 70" long hull, three layers of 300 gram CSM or two of 450gram with tissue over the gelcoat would sufficient, with the option of an extra layer if you want to something super stout.

TurboTyne

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Re: thickness of a GRP hull?
« Reply #2 on: July 18, 2014, 04:01:21 pm »

Very much open to preference.

Some people like thicker hulls, others thinner. I tend to prefer a thinner hull, with localized reinforcement and if required a bit of bracing here and there.

I would say for a 70" long hull, three layers of 300 gram CSM or two of 450gram with tissue over the gelcoat would sufficient, with the option of an extra layer if you want to something super stout.

Thanks Subculture, so for the standard and stouter regions in your example, what would the actual total thicknesses be, i.e. in mm (or ins) ?
Regards Mike
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John W E

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Re: thickness of a GRP hull?
« Reply #3 on: July 18, 2014, 04:29:02 pm »

hi there Mike
 
not wanting to rain on your parade or put you off in any way - but judging by your questions - (model boating) - may be a very new hobby to your goodself - with totally new methods and ways of construction.  I would strongly advise that you sought ought Tynemouth Model Boat Club or South Shields model boat club - have a good nosey around and ask all the questions.  Although any forum members are brilliant at answering questions - you cannot beat a 1 : 1 where you are looking at something you wish to construct and also you will see other problem areas & have a person there advising of how to get over them.   Hey, its a lot easier doing it that way than over a forum.
 
To give you an example - how are you going to construct a hull from fibre glass - build a 2 part mould first?   Or, are you going to use a foam block system? where you create the shape of a hull from a block of foam and then cover that with fibre glass and over the fibre glass you put a filler/sand to shape the hull?   There are other methods of building hulls using fibre glass and as has already been suggested there are several ways of stiffening hulls and building them lighter.
 
I have put a link on here http://www.modelboatmayhem.co.uk/forum/index.php/topic,33734.0.html this is of a hull of HMS Exeter.   Although its at 1:96 scale; its dimensions are 72 inches long.   So the beam to length ratio will be exactly the same as you wish to build at 1:48 scale.
 
aye
 
john
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Neil

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Re: thickness of a GRP hull?
« Reply #4 on: July 18, 2014, 05:19:41 pm »

but to answer your question simply my 72" hull of the Clyde class lifeboat was about 1/16th inch ( 2mm) thick, and it and it's two sister models sailed Loch ness in rough weather without any problems with the hull

the boats are on page 6.


http://www.modelboatmayhem.co.uk/forum/index.php/topic,28576.msg281241.html#msg281241
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TurboTyne

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Re: thickness of a GRP hull?
« Reply #5 on: July 18, 2014, 07:08:37 pm »

hi there Mike
 
not wanting to rain on your parade or put you off in any way - but judging by your questions - (model boating) - may be a very new hobby to your goodself - with totally new methods and ways of construction.  I would strongly advise that you sought ought Tynemouth Model Boat Club or South Shields model boat club - have a good nosey around and ask all the questions.  Although any forum members are brilliant at answering questions - you cannot beat a 1 : 1 where you are looking at something you wish to construct and also you will see other problem areas & have a person there advising of how to get over them.   Hey, its a lot easier doing it that way than over a forum.
 
To give you an example - how are you going to construct a hull from fibre glass - build a 2 part mould first?   Or, are you going to use a foam block system? where you create the shape of a hull from a block of foam and then cover that with fibre glass and over the fibre glass you put a filler/sand to shape the hull?   There are other methods of building hulls using fibre glass and as has already been suggested there are several ways of stiffening hulls and building them lighter.
 
I have put a link on here http://www.modelboatmayhem.co.uk/forum/index.php/topic,33734.0.html this is of a hull of HMS Exeter.   Although its at 1:96 scale; its dimensions are 72 inches long.   So the beam to length ratio will be exactly the same as you wish to build at 1:48 scale.
 
aye
 
john

Hello John

Thanks very much for your comments and, yes you are quite right about me being new to model boating. The Heaton club is closest to me and I do intend to make contact with them. Actually, the reason I asked about the GRP thickness is that I am thinking of building a hull out of tinplate - as described here:
http://www.modelboats.co.uk/news/article/model-shipbuilding-in-steel/480
and also described in the book "Scale Model Warships" by John Bowen and in old articles by Norman Ough that I have.

I have numerous years experience of hobby-working with metals and using soldering methods etc and this approach for making the hull (of what I hope will be a R-class destroyer) really appeals to me for a number of reasons. I have obtained the lines drawings, body plans, shell-expansion drawings etc which will be needed for this project. A complication is that the hull has a small degree of tumblehome, but that means the former will have to made in a cunning way.

I am asking about the GRP thickness because I have read that tinplate hulls are no heavier than GRP and I wanted to do some calculations to check this out for myself.  As discussed in the thread on displacment, weight will be critical since I plan to install steam.

I have not seen any posts on this site concerning tinplate construction, so I guess that this method is not very common  - I'll be interested to hear if that is the case.

Thanks for the link to your Exeter build - I must say that looks really impressive and certainly demonstrates well the need to seek advice and guidance locally.

Thanks again   Mike
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TurboTyne

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Re: thickness of a GRP hull?
« Reply #6 on: July 18, 2014, 07:11:43 pm »

but to answer your question simply my 72" hull of the Clyde class lifeboat was about 1/16th inch ( 2mm) thick, and it and it's two sister models sailed Loch ness in rough weather without any problems with the hull

the boats are on page 6.


http://www.modelboatmayhem.co.uk/forum/index.php/topic,28576.msg281241.html#msg281241

Thanks very much Neil

Thats exactly the info I need.

Regards,  Mike
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John W E

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Re: thickness of a GRP hull?
« Reply #7 on: July 18, 2014, 07:14:28 pm »

hi ya Mike
 
right, you have to make a bee line to South Shields Club - they literally have loads of tin built hulls; and that is their speciality - the steam lads - some of the models go back to the 1800s of some of the hulls.
 
aye
john
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John W E

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Re: thickness of a GRP hull?
« Reply #8 on: July 18, 2014, 07:53:06 pm »


Hi Mike - if this link works - it should take you to the North East Show and if you scroll down through the photographs about two-thirds down the page - you may see something which interests you; these are from South Shields Model Yacht Club :-)



http://www.modelboatmayhem.co.uk/forum/index.php/topic,27986.msg294001.html#msg294001




aye


john


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Subculture

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Re: thickness of a GRP hull?
« Reply #9 on: July 18, 2014, 09:29:23 pm »

I have my doubts that a tinplate hull is going to be lighter than a GRP hull unless the latter is very poorly made.

Tinplate is roughly six times heavier than a GRP laminate, so to be equal in weight the tinplate would have to be an eighth of the GRP thickness. What sort of gauge is usually used to make these hulls?

If weight is of primary importance I would consider using epoxy resin and glass cloth layup, or maybe kevlar and/or carbon fibre. This will produce a very light and strong laminate indeed, much stronger and lighter than polyester resin and chopped matt.

John W E

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Re: thickness of a GRP hull?
« Reply #10 on: July 18, 2014, 10:26:32 pm »

hi Mike if you go to the shields model boat club this is the gentleman you need to speak to
http://www.onthewire.co.uk/wkirtly.htm
 
aye
john
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TurboTyne

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Re: thickness of a GRP hull?
« Reply #11 on: July 18, 2014, 10:37:12 pm »

Hi Mike - if this link works - it should take you to the North East Show and if you scroll down through the photographs about two-thirds down the page - you may see something which interests you; these are from South Shields Model Yacht Club :-)



http://www.modelboatmayhem.co.uk/forum/index.php/topic,27986.msg294001.html#msg294001




aye


john

Hi John
I guess you mean the fantastic model of HMS Gloworm (H92) and the close-up shots. Very impressive. A somewhat larger ship than the R-class.
Thanks for that link.

Mike
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TurboTyne

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Re: thickness of a GRP hull?
« Reply #12 on: July 18, 2014, 11:02:13 pm »

I have my doubts that a tinplate hull is going to be lighter than a GRP hull unless the latter is very poorly made.

Tinplate is roughly six times heavier than a GRP laminate, so to be equal in weight the tinplate would have to be an eighth of the GRP thickness. What sort of gauge is usually used to make these hulls?

If weight is of primary importance I would consider using epoxy resin and glass cloth layup, or maybe kevlar and/or carbon fibre. This will produce a very light and strong laminate indeed, much stronger and lighter than polyester resin and chopped matt.

Thanks Subculture.
I gather that tinplate 0.25 mm thick is frequently used.  I've found values for density of 7850 Kg/m3 for mild steel and 1750 Kg/m3 for GRP.  That indicates steel density is 4.5 fold greater but it is at least 8-fold thinner because it is stronger material. But we have to allow for extra weight of the lapped joints in tinplate and the weight of stiffening strips etc. So it seems there may not be too much difference in weight for the same size hull. But I guess the other materials you mention would shift the balance. However, so long as the tinplate hull is not significanlty heavier, the idea of using it appeals to me because I feel more comfortable using metal than resins etc and the tinplate method more closely replicates the material and construction of the prototype. Also, apparently, it is more forgiving if one needs to replace poorly fitting parts during construction. I'm still developing the steam plant so, at this stage, having an idea of the dimensions and weight of the hull (whichever construction method I end up using - O.K.  assuming I get that far  :-) )will give me a target to work towards with regard to weight of boiler, fuel and water pumps and engine etc.
Reagrds  Mike
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John W E

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Re: thickness of a GRP hull?
« Reply #13 on: July 19, 2014, 09:02:30 am »

hi ya Mike
 
HMS Gloworm belongs to a gent from Hull and he was exhibiting his model at the Shields show - the photographs I was referring to begin with the jet-powered Bluebird - amongst the set of photographs you will see the tin-plate liners and the steam plant inside one of the models - these are the models which belong to the Shields steam enthusiasts.
 
aye
 
john
 
 
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Subculture

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Re: thickness of a GRP hull?
« Reply #14 on: July 19, 2014, 11:10:25 am »

1.75kg/m3 for GRP density is right at the top end, with a very glass rich laminate. Usually glass fibre laminates tend to be around 1.2-1.3 kg/m3. Kevlar laminates are lighter still with Carbon fibre somewhere between the two.

However use the material you feel happiest working with.

vnkiwi

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Re: thickness of a GRP hull?
« Reply #15 on: July 19, 2014, 11:27:05 am »

Hi,
I've recently received 5 fibreglass huls from Gibraultar, they range from 20inchx4.25inch to 55inchx8inch.
They all are very well laidup most happy with them.
To answer your question, they are all between 2mm and 2.5mm thick.
And I'd take that as pretty typical for all the fg hulls I have.
cheers
vnkiwi
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TurboTyne

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Re: thickness of a GRP hull?
« Reply #16 on: July 19, 2014, 12:09:50 pm »

Thanks John - I now see what you mean. Yes, before I start actually making a hull (some time away still) I would definitely like to have a look at those hulls and chat with the guys who made them.

Thanks Subculture. Those lower density bvalues clearly affect the relative weights. But even then, from what I've found out so far, it seems that a tinplate hull would not be very much heavier. At present that is all I am concerned about checking. But if I need to save all weight possible, maybe I'll need to look into the Kevlar that you mention.

Thanks vnkiwi, that is very useful confirmation.  These thickness values do not seem to crop up anywhere that I  have searched - except for this commercial site:
http://www.strikemodels.com/products/ships/
But these guys seem to be making hulls for actual combat by firing ball bearings at each others models (!!!?).

Regards

Mike
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