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Oct 24, 2019, 11:32 AM
Boaters are nice people.
Quote:
Originally Posted by Jansvast
1. Question: what weight of fibreglass cloth to choose for a hull (im guessing something in between 150-200g/m2 will do)
2. Question: do i need to use gelcoat for the hull or plain polyester will do? I assume that it will be necessary for the mold, but not for the hull itself.
3. Where should the bow curve start (50%, 30% at the cg?) and should it start at the same point from the side and the top?
4. How about the size of the strakes in relation to hull size?
Hi Jan,

By the numbers:

1) I'm using 160gr/m² twill woven glasscloth (usually two layers, wet in wet, depending on hullsize) and the thin 48gr/m² from HK.

2) As weight is an issue, I don't use polyester for raceboats hulls; the laminate needs to be thicker than the same strength epoxy/glasscloth laminate, polyester gets bone hard and doesn't flex, hence the need for thicker laminate to avoid cracks and breaking.
Bigger hulls are often made with polyester due to the higher cost of epoxy (and cloth like carbon or kevlar), but companies like MHZ and H&M use epoxy for their lightweight hulls.

3) That depends a lot on the design, usually the last third of the keel line needs to be straight to avoid a hopping bunny.

4) As a rule of thumb the last third of the hull doesn't have strakes, also depending on deadrise and amount of power installed (running attitude at speed).

Regards, Jan.
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Oct 24, 2019, 12:43 PM
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Thank you! I Can easily get cheap 160gr cloth from my LHS. And when a hull is made of epoxy gelcoat cannot be used am i right? For the strakes i meant the width of the strake compared to lenght or beam of the hull. I plan on using a smoothed 3d printed plug, then a polyester mold and as you say epoxy hull (if i can get the right epoxy)

If i can make a good hull, i might try to sell some.

I found multiple laminating resins i can get locally, but i find my polyester pretty flexible, but ive never held an epoxy one in my hands, so i cant compare. However, there are different types of epoxies (i can get chs 455, chs 521 and chs 531, but i dont have information about flexibility)

I have a 26" mono in my head, 26°deadrise this time Its gonna be my next project powered by a 3660 motor

Jan
Last edited by Jansvast; Oct 24, 2019 at 03:09 PM.
Oct 24, 2019, 08:55 PM
RELAX. You'll live longer
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You might want to consider a bit more of a droop on the deck from the windshield to the tip.
There is a lot of aero lift under the front of the hull.
A bit of downward droop helps keep the nose down at speed.

This pic might show you a sense of proportion.
Last edited by 785boats; Oct 24, 2019 at 10:32 PM.
Oct 25, 2019, 12:02 AM
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That is a great picture! Ive been looking for something like that. I will make the curve begin a bit later (longer flat section, cirrently 50% flat) an make the bow rise a bit less (i hope i used the correct term..?)

I contacted my local epoxy seller for more information

Regards, Jan
Oct 25, 2019, 01:59 AM
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Based on your suggestions, here is the new design. I like it a lot

I will 3d print the plug and make 2 fibreglass molds
Last edited by Jansvast; Oct 25, 2019 at 05:34 AM.
Oct 25, 2019, 09:08 AM
Boaters are nice people.
Hi Jan,

Your second drawing looks a lot like our Arowana's, they tend to get flighty when running into a strong headwind.

Regards, Jan.
Oct 25, 2019, 09:32 AM
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Quote:
Originally Posted by Jansvast
Thank you! I Can easily get cheap 160gr cloth from my LHS. And when a hull is made of epoxy gelcoat cannot be used am i right? For the strakes i meant the width of the strake compared to lenght or beam of the hull. I plan on using a smoothed 3d printed plug, then a polyester mold and as you say epoxy hull (if i can get the right epoxy)

If i can make a good hull, i might try to sell some.

I found multiple laminating resins i can get locally, but i find my polyester pretty flexible, but ive never held an epoxy one in my hands, so i cant compare. However, there are different types of epoxies (i can get chs 455, chs 521 and chs 531, but i dont have information about flexibility)

I have a 26" mono in my head, 26°deadrise this time Its gonna be my next project powered by a 3660 motor


Jan
Theres nothing wrong with making hulls from Polyester. As regards weight versus epoxy etc ive never found it to be an issue all my hulls are polyester although i have owned epoxy hulls .Never have i found an issue quality wise to be honest . If you want to use poly resin and keep things strong use the right cloth , dont use twill weave for large hulls use biaxial cloths much stronger and stiffer , for smaller hulls simply replace one layer of the twill cloth with 1 layer of the same weight carbon cloth and it will be plenty stiff and strong . Will it be heavier than an epoxy hull maybe but then ive always found a little extra weight more of a benefit than a negative . Carbon cloth is around 4 times the cost of glass cloth to buy so not that expensive and using poly resin with it is fine and makes a nice strong laminate . Less strong than epoxy but ive never had too much of a problem with it and i own hulls that have lasted me well over 15 yrs withstanding hard crashes at over 60 mph without too much damage . Also you mentioned gelcoat and epoxy ?, yes you can use gelcoats with epoxy as you can now buy epoxy gelcoats . What you need to remember if using epoxy to make hulls then you really need to use vaccum not hand layup or at least vaccum bagging .
My friend in the UK makes this 32" hull from poly resins in glass and or carbon theyre pretty sturdy and stiff and handle very well indeed far stronger than my pursuit hulls ive had from China ,a tad heavier but so much stronger .
Last edited by Apache Kemosabi; Oct 25, 2019 at 09:39 AM.
Oct 25, 2019, 11:13 AM
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Thanks! I will not use cf, to keep costs reasonable. I found a local laminating epoxy supplier that sells epoxy that can be used for hand layup. And ive never worked with epoxy so it would be nice to learn something new

The supplier also sells epoxy gelcoats but they are quite expensive. Is gel coat really needed (i assume its there to acquire a nice glossy finish, so necessary on a mould). In case you are interested, the site is https://www.havel-composites.com/cs/kategorie

I tried to make my own polyester gelcoat by mixing cornstarch into the resin. It had a great consistency, but the surface is a bit matte, because of the cup.

Jan
Last edited by Jansvast; Oct 25, 2019 at 01:17 PM.
Oct 26, 2019, 10:06 AM
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You cant really use epoxy for hand laminating boats without vaccum because it takes too long to go off and the resin on the sides and on any surface that isnt flat will run down and ruin your hard work . Thats why you must use either vaccum infusion or if using epoxy to laminate by hand you must use a vaccum bag to keep the resin where it needs to be .Laminating epoxy can take a good few hrs to go off which is why its not really suitable for hand layup unless on a flat surface .
You dont need gelcoat with epoxy but be aware epoxy isnt UV safe so it would need painting over .
Oct 26, 2019, 01:35 PM
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The epoxy i would use with a chosen hardener takes 50min to gel up, but i can get 30min ones too. And what if i pressed the plug into the mould after hand layup to squeege excess out?

Regards, Jan
Oct 26, 2019, 04:21 PM
Boaters are nice people.
Hi Jan,

There are more than one way to create a fast electric hull.
I've worked in the polyester industry for five years and for the products I manufactured (layer thickness up to 5-6 mm) polyester workes fine, but gives you a heavy product.
Using airplane grade glass and polyester resin, used correctly, also results in proper hulls, like the JetChopper30 (which I have here as an example.

When I use a mould, it gets waxed and polished up to six times with at least half a day between layers.

When using epoxy, the first layer is the 48 gr/m² glasscloth with as little resin as possible, but I'm not to anal about it, as the second layer of 160gr/m is added wet in wet, so any excess epoxy is being absorbed by that layer (and the next, if I need more strength).

The trick is to use as little epoxy resin as possible; the glasscloth has to become transparant, by tapping the epoxy through the cloth to saturate it.
Excess resin is removed by using kitchen paper towl, puddles of resin are to be avoided, this only adds weight without any strength!

The surface of the laminate has to look dry, clearly showing the weave of the cloth.

If the laminate turns out to be too thin, you can add another layer of glasscloth within 24h, provided you use 24h epoxy, you'll have sufficient chemical bonding without having to sand and degrease the surface.

If the epoxy has fully cured, sanding and degreasing is mandatory to get a good bond.

Regarding using colour; the German manufacturer Hopf made his racing hulls very light by spraying the first coloured layer in the (waxed) mould by using two part paint (a form of epoxy), this layer was thin and light and was allowed to cure until it was slightly sticky. The next (and often only) layer of glasscloth and epoxy was added by hand, using as little epoxy as possible.

These hulls were very light and have won numerous championchips.
Most raceboaters did add an extra layer of glasscloth, carbon, or kevlar on the bottom to make the hull extra rigid.

As I don't have access to two component spraying equipment, I simply (spray)painted my hulls, once they had cured using rattle cans.

Regards, Jan.
Oct 27, 2019, 03:20 AM
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Thanks pompebled. That is a lot of great info there! I will use epoxy because its less stinky and i wanna try it out, ive never worked with it. I assume that the 48gr later is to fill in the details in the mould. As i allready read gelcoat is just to protect the products from uv light? I would use regular epoxy gelcoat for both the mold and the hull. Its time to turn my drawings into a 3d model. Thats not gonna be easy!

Jan
Oct 27, 2019, 06:52 AM
Boaters are nice people.
Quote:
Originally Posted by Jansvast
As i already read gelcoat is just to protect the products from uv light?
Hi Jan,

Gelcoat is to seal the polyester laminate from water, polyester laminate is not watertight.
This is a concern for 1:1 boats which are permanently in the water, read up on osmoses on polyester 1:1 hulls.

For our small boats that only spend a short time in the water, it is of no concern, specially if you paint the hull.

Untreated epoxy will yellow under the influece of UV, hence the painting.

Regards, Jan.
Oct 27, 2019, 02:12 PM
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In that case epoxy gelcoat will yellow too? I wanna buy regular epoxy gelcoat and use it for both the mold and the hull
Oct 27, 2019, 05:58 PM
Boaters are nice people.
I can't say, as I've never worked with epoxy gelcoat.

From what I read about it, it's UV stabilized, so it should not yellow.
The transparant version can be given any colour using epoxy pigment.

Regards, Jan.


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