Question About how to calculate Floatation of my design

Discussion in 'Boat Design' started by AdamOMahony, Sep 11, 2017.

1. Joined: Sep 2017
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Hmm that site seem's good for epoxy, do you know a general rule of how many layer's of fibre/ base coat of epoxy I may need? Hoping to order the fibreglass materials soon and from what I've found you need about 1kg per m2 for the first coat, 8m2 for second coat, and fibrelgass 1:1 ratio between epoxy and glass.

source: How much epoxy resin do I need? - epoxycraft http://www.epoxycraft.com/how-much-epoxy-resin-do-i-need-for-my-project/

I wasn't too sure if this meant to do two coats before the fibre or if your using fibre that you only need the 1:1 per amount of cloth your using.

As most video's on youtube show people just laying the cloth and wetting it for application.

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wbp Plywood for correction on type of plywood being used.

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HeimfriedSenior Member

While it depends of the surface quality of the used ply, I can hardly imagine a consumption of 1 kg/m² for just coating. I coated marine grade plywood (ocumé) weeks ago (a bridge deck of 15,5 m²) and did apply 86 g (0,086 kg) per m² for the first coat and 33 g/m² for the second coat (no fibreglass until now, just epoxi coating to seal the plywood).

A consumption of 1 kg/m² would mean the thickness of the epoxi layer would be nearly 1 mm.

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Thanks for the response, that's good news as I was intended to order just a kg more than the 1:1 ratio, surface area for the hull is 36.7 meters squared including the small deck area, was planning to order 4 packs of 6.48 kg resin + hardener packs (almost 100 Euro each unfortunately but I'm sure it would be worth the please of enjoying the canals) the cloth I was looking at was 300g woven roving or 200g fabric cloth and use two layers of either one or possibly one of each if that would give a better result.

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HeimfriedSenior Member

Maybe you should get some information which is provided by a supplier website (free catalogue pdf download in English) http://www.hp-textiles.com/Flyer/Productcatalogue.pdf
It gives for the different glass (and other reinforcing) textiles the average epoxi consumption and so on. Like this:
"Calculated data for hand laminate with 35 vol. % fibres:
resin consumption: 175g/m², laminate thickness: 0,23mm, laminate weight: 388g/m²"

for a 213 g/m² Glass filament fabrics

Last edited: Sep 13, 2017
6. Joined: Apr 2015
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HeimfriedSenior Member

As for floating position etc. of a boat, if you are interested, have a look at this website: Berechnung der Schwimmlage von Booten http://bootsphysik.de/
Use button top right "English" and the "i" buttons for information. If you would do some math to create a file containing the data of the shape of your planned boat, I could try to insert to the website and you could "play" with the behaviour of your boat.

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Thanks for the info and the offer for checking some of this for me, I have the sketch up file that I do not mind sharing if it's possible that it would help although without the final bow in there as a solid unit it may be hard for you to check anything on it really.

I'll have a look into the links you provided and see what I need

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HeimfriedSenior Member

Find a sample for two dimensional behaviour of "your" boat. Two dimensional means it is just a (geometrical) prism, a body 6 m long, 2.5 m beam, all cross sections shaped like your sections, but smaller radius replaced by a straight line, which will not cause much difference.
"www.bootsphysik.de" click link "wechseln zu 2D-Boots-Rechner" in the top line of the sheet, after new screen, click "English", then "choose / alter frames", then click the pic of the freighter frame (3rd line right). Your frame should appear now.

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Thanks HiemFried, I had a look at the site link, followed the instructions you've given and I was unable to see much from it. Sorry to disappoint but really appreciate the help with it, Looks like an interesting site for those who know what they are doing!

The spec sheet for the textiles with epoxy is amazingly good, seem's most glass fabrics take 35% weight of epoxy as you had mentioned which means I'd save on quite a bit of epoxy from my original estimations

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I'll probably still order more epoxy than I need for just the outer hull as I am thinking of the previous comment about watching for rot inside the boat and thinking a coat or two of epoxy without glass may help the prevention of rot for longer than a standard wood treatment.

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HeimfriedSenior Member

Sure, at the first look the site is quite confusing. I will help you to go some first steps, if you don't mind. Did you see your frame (bottom left) ?

It is stronger, lighter and cheaper to try to achieve a glass resin relation with as less resin as possible for a proper result. It may be not easy for a beginner. Read a lot about it and take care.

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SamSamSenior Member

This boat will cost you 10s of thousands of dollars/moneys. The design seems totally wrong for a canal boat, the catamaran type hull giving more draft, less stability and overly complicated construction. Look at other canal boats in the area and copy them for hull shape at least, if not materials and structure design. I would stop construction and buy no more materials until you re-evaluate what you are doing and the design you have created.

I think you have mis-interpreted the statement below, as it is confusing, using volume for the first half of the sentence and weight for the second half...
You say
"Laminate weight" usually means the glass and resin together. Given that interpretation it would seem to say a laminate weight of 49 grams would need 24 grams of resin. A glass/resin weight ratio of 50/50 is about normal for hand lay-up with woven cloth, if you were using mat it would be more like 30% mat and 70% resin by weight. So that's just for the cloth and resin. Priming the wood with extra coats before the glass laminate is extra resin and filling in the weave after glassing, for smoothness and fiber protection, is more extra resin.

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SamSamSenior Member

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gonzoSenior Member

It seems insane to start cutting stations for a boat before having finalized the design.

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TANSLSenior Member

Many things can be done without completing the project. We do not know what state the project is in right now. More information would be needed to give an opinion. Unless you know something that others do not know.

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