FRP hull thickness

[tdamico]

I have noticed that very few power boat builders (trawlers) state what the thickness of their hulls are below waterline. One proudly points out that theirs is a full 1 inch thick, while another states that their hull ranges from 3/4" to 1.5". But most simply state that the hull is solid FRP below waterline. Is there a standard or a minimum thickness that is considered safe. And will this thickness vary if the boat is a coastal cruiser or a ocean passagemaker

Thanks

[mmd]

There are formulae for calculating skin thickness of FRP boats that take into consideration stiffener spacing and strength, size of vessel, vessel type, usage, etc. Common sources of these formulae are texts produced by organizations such as American Bureau of Shipping (ABS) and Det Norske Veritas (DNV). And, yes, the skin thickness will vary between a coastal cruiser and a blue-water passagemeker - well, at least it should!

This is a new IMO standard for boat structure that can be used as well as those cited above. It can be obtained in the US from ABYC (www.abycinc.org) as well as ISO.

[tdamico]

Thanks, I have visited those sites and the problem is that they are not very easy to navigate and any reference to the information I want, you seem to have to pay for. Before I take $30 out of my pocket for the right to know how thick a hull should be, does anybody out there actually know?

[SailDesign]

Quote:
"Before I take $30 out of my pocket for the right to know how thick a hull should be, does anybody out there actually know?"

"Knowing" how thick a hull should be is not a "right", it is a product of hard-earned, expensive education. At that scale, the outlay of $30 is small potatoes, and well worth it considering the cost of the boat it applies to. Don't be a cheapskate - buy the book.
Steve

[tdamico]

You know, I hadn't thought about it in that way. So I guess that most of the questions that are being asked on this site should be aswered by simply providing the link to the resource where everybody can purchase the appropriate answer. That should make it easier for the admins of the site. All they need to do is to provide a list of links where books, materials, etc are for sale and we all can go and buy the answers. Sheesh. All I'm looking for at this point in time is a simple answer. In FRP boats is a 1" thick solid hull safe? If not what is. I am not asking for the information on how to build a boat, how to be a marine architech in my spare time, and I don't have the time to read several hundred pages of physics that I won't understand just so I can become more confused and still not have the answer. Just a thought...It might be fine to own, and cruise in a boat, without having to know all the physics behind why a 1" hull is not safe and a 1.5" hull is.

[SailDesign]

I just KNEW my post was going ot be taken the wrong way.... Just as I had taken yours beyond it's logical and literal meaning.
What I am getting at is that there is more to it than "Is a 1" thick solid hull safe enough?" You need to provide the size of boat, it's intended use (planing powerboat, we assume), the spacing of the internals, the location on the boat of the panel you're looking at, etc., etc., etc.
Back to what I was getting at, is that you may not want a to become a marine architect in your spare time, but you need one to accurately answer your question.

Steve

[tdamico]

Steve:

Actually my response was tongue in cheek. Or only half serious. I actually have picked up enough knowledge to understand your points, but there has to be a ball park answer. For example, If I buy a Nordhvn 50' Trawler or a Kadey Krogen 48' trawler, I assume that the build is good and that the hull has the proper thickness to ensure a safe boat. Or at least that's what they tell me! Both these boats are FRP, in this example, and if I assume that both are what they appear to be, solid, passagemakers then I find it curious that neither share what the hull thickness is. Now if I change gears to Mirage and their Great Harbor 47' trawler. they go to great extremes to state that their hull is a full 1" thick solid and offer a core to prove it. So I am just trying to get through the marketing hype by asking for a ball park, opinion. Assuming a good quality build, good design, and proven, name recognized boat, is Mirage's claim that their 1" hull is superior a fair statement or not? As nobody probably has knowledge of all these boats I thought I could get to it if there was a standard for hull thickness. But it looks like I can't get to it without a lot of in depth reading that I probably wouldn't understand.

[SailDesign]

tdamico,
Again, whether 1" is enough is going to depend on a lot of things. Is the hull built of multi-axial unis, woven cloth, or sprayed mat (Yeuch!) - are the frames spaced at 3' intervals, or 6' intervals?

[BrettM]

A thick hull sample does not necessarily mean good quality. The sample indicated could have been taken from the hull for a skin fitting such as a raw water pickup in the engine space. Quite often this is done beside/near a major girder such as required for an engine bed meaning that the one inch sample is composed of a 15mm hull and 10mm of girder laminate. Is the sample wedge shaped. You may also be able to see woven rovings within the laminate. Quite often a thick laminate is due to excess use of a chopper gun and excess resin.

However, as others have said it depends on numerous factors for each case. Whilst a thick laminate could generally be considered more damage/impact resistant it does not guarantee overall structural integrity.

Brett

Actually, I thought ABYC got $10 for the standard.

You can also download other standards from ABS, www.eagle.org.

[Dutch Peter]

Originally Posted by Guest

This is a new IMO standard for boat structure that can be used as well as those cited above. It can be obtained in the US from ABYC (www.abycinc.org) as well as ISO.

That's right, and it might just cost 10 USD, but you will need part 5 (design pressures) also, and maybe even some other parts. So, it is expensive!
But on the price of a boat? Peanuts!

[Dutch Peter]

Originally Posted by tdamico

Steve:

..., but there has to be a ball park answer...//.. then I find it curious that neither share what the hull thickness is. ...//....

I think that's just the whole point. You said you picked up enough to understand what the others were posting, but the sales guys from a yard do not know that.
They just assume (my guess) that you want to compair thicknesses of different boats and decide quality on that. And you can't, that's the point being made!

[Sean Herron]

Hello...

Just thought I would 'have a go' at this - I built 142 foot tri deck yachts for some time - and the hull below the waterline was - well - thick...

Whether it was thick enough to be safe - well - I guess that really depends on what you intend to hit - or how fast you want to hit it - also whether what you want to hit is floating partially submerged or floating directly in front of you - particularily I would worry about whether it is soft or hard - or whether it is stationary or just bobbing about...

I highly doubt that there is a designer or an engineer or even a builder who has hicks doing his layups that are willing to put their carreers on the block and not build or design yachts of the size and brand mentioned to at least the going minimimum and most builders (most) like to over build anyway because they don't trust or believe or understand the designers and engineers...

So it comes down to what you want to hit - and perhaps how big your pumps are and what their flow rating might be...

Now - crap all over me - I can take it...

SH.

[FAST FRED]

Simpletst is to only purchase a boat that meets USCG standards for subchapter T.

This will incluse fire retardant resin (only 1 or 2 cennts a pound more than std fireball resin), a collision bulkhead , and "Teacup scantlings.

The CG in looking at GRP hulls views them at empty teacups , no bulkheads , no deck , so requires a string laminate.

Their rule is 400% over max load , which just about creates a hull that does not flex.

Since much flexing is DEATH to GRP over the long run its sensable.

AN "inch" of glass would be fine in a 35 ft wl boat , mighty thin on a 95 ft wl boat ,

Most stock Slave Labor built Chinese boats are thick enough.

FAST FRED