# Weight Calculation

Discussion in 'Fiberglass and Composite Boat Building' started by hhhhar, Apr 15, 2014.

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### hhhharHarun

Hello everybody,

I am a student and doing my graduation thesis on a 14 m ( approx. 46 ft.) composite sailing yacht. I need to calculate weight of the boat to determine the balast weight for stability calculations. I have several questions :
- How much mm should i take the avarage thickness of the hull and the deck ?
- What is the approx. resin/fiberglass ratio in the vacuum infusion method ?
- I have found several densities. Are these values correct: e-glass fiberglass: 2.54 g/cm^3 , Vinylester: 1.004 g/cm^3, foam: 3.43 lb/ft^3, gel-coat: 1gr/cm^3, polypropylen honeycomb: 80kg/m^3

Thank you

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### TANSLSenior Member

Hello hhhhar, I'm a little surprised with your questions.
It strikes me ask you the following question. What kind of thesis, what project you want to do?. It seems logical that you should calculate the thickness of the hull with the greatest possible accuracy. You can not make an estimate but a rigorous calculation of scantlings of the ship. Does your boat need to meet any regulation?

3. ### NavygatePrevious Member

I mean they are good questions but shouldn't you know how to find the answers?
When you ask on a public forum, you could get any number of answers, some right, some wrong and most likely many controversial.
How will you know which is which?

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### rwatsonSenior Member

If you are graduating, you can figure this out by now - or ask for a refund of your fees.

...... I love these trolling threads , you get all sorts of interesting responses, often with a lot of useful information

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### gonzoSenior Member

If you designed the boat, it is whatever you say it is according to your calculations. If it is an existing boat, you need to go and survey it.

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### Steve WSenior Member

The most common foam density in recreational craft is going to be H80 (80kg/m3) or 5lb/ft3. With infusion you can figure on 65% fiber fraction.

Steve.

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### hhhharHarun

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### DCockeySenior Member

hhhhar, are you studying naval architecture or another subject?

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### hhhharHarun

I am studying naval architecture bachelor degree

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### PARYacht Designer/Builder

Sweet God this is scarey stuff . . .

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### JSLSenior Member

I have mentored a few 'students' but I have never had questions like this. Get a refund on your tuition.

12. ### NavygatePrevious Member

Agreed, this sounds ridiculous.

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### PARYacht Designer/Builder

I doubt it was the education part that failed this student. Education is what you can take, steal, rob and.or beat out of your course. You paid for it, so you have the right to get your money's worth, though this is dependent on how bad you want it. They can't teach you, so much as you have to take all you can get from them. It does scare the hell out of me that this question, that should have been covered in his first year of study, is from a final thesis student. He should go back and re-read his first text book.

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### rxcompositeSenior Member

Do they teach composites in Naval Architecture? I doubt if this is so that is why the OP is having problems.

They teach steel and aluminum including stress analysis but not composites. As far as I know, composite is only part of a subject in Aerospace Engineering though I have seen some ads on composite marine engineering. Looks like a short course.

His only recourse is to read books on composite fabrication like E Green- Marine Composites, LR- Special Service Craft Rules or other Class rules that have composites fabrication.

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Sometimes it is shocking me, in this great forum some people didnt show respect to others. if some one ask in the forum, just take it as somewhone who needed help. dont judge on other thing. They are seeking helpor having difficulties. It is that simple I think. well I'll try to help

1. About hull thickness, it is depend on soooo many aspect. you must study scantling calculation, try to search your local class society Turk Loydu Foundation ( am I right?) its depend on class you are rely on. Dave Gerr's book is very very damn good start, as I did it several years ago when i was dumb stupid young naval architect graduate who majoring in steel construction. but remenmber, Gerr's book is mainly covering in handlayup method, which is mainly considering by thickness not fiber/reinforcement weight, As it mentioned onthe preface, his book was intended to Every one, but not for "advanced" reader. I really love his writings, very flow and "liquid" just like reading comics. His book is one of my bible.

In my experience, using GL rule, i would like to estimates, again estimates, i did tons of scantling and i dont have time to calculate your request.

hull bottom = outter skin min 1500 gsm, core 80kg/mcub (Pvc) 18mm Thihick, inner skin min 1200 gsm

hull side = outter skin min 1200 gsm, core min 75kg/mcub (Pvc) 15 mm thickness, inner skin 1000 gsm

deck laminate you could use side laminate, on bulkheads, using bottom laminate is preferred.

resin/fiberglass ratio in infusion.
by weight is ranging from 60:40 (glass:resin) upto 70:30 (again glass : resin) above that number there is very high risk on dry spot, BUT

you also need to consider core suction, some 18 mm pvc core, could drink 1 Kg resin per meter square for each face.

you could easyly googling fibercloth density dont make it equal with solid glass on your window, it is big no, it is somehow littlebit lighter because of other materials employed in fiberglass.

vinlyester,it is about the same as polyester resin ranging from 1.1 - 1.2 depend on temperatur, epoxy is little bit heavier.

gelcoat is vary, depending on filler materials. sometimes i use 600 gram/ msq to get 550 micron.

core materials such as foam (pvc, and any other), honey comb, askyour local supplier, it has wide variety of density and type.

I hope it helps

Again, reading Dave Gerr's book is really great start to understand marine composites. and because you've bbeen bullied by other, dont make yourself like a looser, enjoy it. I did enjoyed it once. Theres so many members here are really helpfull, spreading valuable info just like **** cheap... They have various approacing on "teaching". my favourite is Mr. E Sponberg (which is very gentle, straight pointing) another my favourite is Tunnels who havebeen long gone, oh damn i really miss him ( sometimes he is tacky, but really informing).
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