How Thick should a hull be ?

[WorWilly]

I was looking to purchase a 34' motor cruiser and one window was out, (being repaired) I had the chance to see how thick the hull was it looked like 6mm gel coat, and about 10mm glass, I thought it would be a lot thicker than that ?, is that thin or about right ?

Its a 03 Sunseeker (new shape) I'm new to boating, so got a bit of a shock when I seen it so thin !

thanks

Thats about right, the superstructure of a 34 does´nt need more. Even in Plywood or wood Epoxy it would be about 12,5mm only.
Regards
Richard

[WorWilly]

WoW, I thought about 2".....!

[Fanie]

AT 2" or 50mm, have you any idea what that boat would weigh !!

Fiberglass is very strong. A standard pice of PCB is 1.6mm thick. Try breaking a non perforated piece, you'll be surprised what it takes to do.

[ben2go]

That's one thick heavy hull.My boat is maybe .75mm,yes less that a millimeter thick.I have internal structure keeping my hull stiff and light.

[Itchy&Scratchy]

Technically the gelcoat should be only 1.5 mm thick so that it can flex with the laminate, however I work in the boat repair game and regularly see gel that is up to 10mm thick - which in my opinion is too thick , thats why the boats end up full of spidercracks with the smallest impact.

Its also due to not enough supervision on the shop floor, the laminators end up loading the gel into the mould to make their jobs easier, which does make for a bit of a stiffer boat but at a cost both monetarily and structural integrity wise. Some manufacturers even put a filler coat on the back of the gel before the laminate, usually fillite mix which just makes the problem even worse.

Personally in a big boat I would be happy to see no more than 3mm thick.
cheers
Justin

[WorWilly]

Thanks for that, very informative guys

[WorWilly]

I watched a movie too regarding the laminate. They used a cutter gun to blow on the laminate then rolled out the cloth, this happened 3 times each in a different direction of course after rolling that too must have only been about 10mm, as I say I was just surprised at how thick it was, and now how much strength is in it.

So with gel coat the thinner the better for flexability and with laminate is there any thickness or is it the more the stronger.

[CastrolR]

I am with Apex1, 10mm seems to be right, and 1.5mm for gelcoat. The image below is of my 20' sports boat which is my own design and build, hull thickness is 8mm, she reaches a top speed of just over 50 knts, and there are no structure problems. Hope this helps..

[WorWilly]

Very nice Castrolr M8, very nice.

Would the same or maybe a little more for a 40 footer 12mm glass 6mm gel with structual beams of 20mm ?

sorry, was it vac bagged too, still very nice M8

[CastrolR]

Originally Posted by WorWilly

Would the same or maybe a little more for a 40 footer 12mm glass 6mm gel with structual beams of 20mm ?

A 40 footer would not need no more than 10mm. The gelcoat remains at
1.5mm, this allows for flex as mentioned by Itchy&Scratchy.

The stiffness of the hull largely depends on beams (sometimes called formers), the number of them, what material thay are constucted from and how thay are fixed to the hull.

At the design stage of a performance boat, keeping the weight to a minimum is an aim, however during the first sea trial you would rather hope that the structure has been over engineered

was it vac bagged too, still very nice M8

No the whole construction was hand laminated.

[Fanie]

You guys are thumb sucking boat thicknesses

You can calculate the amount of glass required for a specific boat, size and purpose.

[CastrolR]

You can calculate the amount of glass required for a specific boat, size and purpose.

I expect its rather a complex equation, However if you have it I would love to see it.

[Fanie]

There are formulas you can calculate the amount of glass required from. I know a guy who does fiberglass designing for a living, he showed me a couple of things and he gave me a few formulas to work from.

The easiest would be to ask you fiberglass supplier for such information. There is a bit more involved in that different shapes are calculated differently from one another, the glass thickness, type, orientation and process amongst others play a role.

It's not rocket science though, it's just new to someone that hasn't done it before. I ask the guy I know for advice any time I want to make something fiberglass for the boat. Then whatever he calculates I add some 'just in case', althoug from experience I have a pretty good feeling what to expect.

I have a nice pdf called 'Fishing boat construction' if you're interested. It's 2.5M in size, e-mail me I'll return mail it to you.

[WorWilly]

Mail set Fanie cheer's

and thanks for the info guys