Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => GRP & Epoxy => Topic started by: Blaven03 on November 02, 2019, 08:54:41 PM

Title: One off fibreglass hull build help please.
Post by: Blaven03 on November 02, 2019, 08:54:41 PM
hello,


Just starting to build a hull for first time but require some advise.
I had planned to make a plug and mould but seen a fella on Facebook make a plug and just skin the outside with thin layer of fiberglass. Itís a one hull I plan to make  so this method would be quicker and easier but Iím new to this so I worry about the strength (Iíve msged him but no reply)


My plan is to make frame and flesh out as though a plug and glass the outer layer with thin layer and apply gel coat. But again how strong do you think it would be cause I would need to remove the flesh and a lot of inner frames. If I applied fiberglass of inside would this pull the hull and distort it. Any suggestions on how to do it would be appreciated.


Regards
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 02, 2019, 09:04:56 PM
I've done a reasonable bit of fibreglass work. the mehtod you mention is often used with a foam core. the plug is carved out of polystyrene foam, then layers of resin snd glass over applied over it. once cured, the foam is dug and melted out (acetone works). The hull requires external finishing by sanding and filling, so it only makes sense for a one-off.

Some builders are a bit sniffy about this method of construction, but it's perfectly acceptable, and the hull will be as strong as other methods.

Most use epoxy resin for this technique, as the resin doesn't attack the polystyrene foam. You can apply a barrier coat of oil paint to the foam if you wish to use polyester resin. If you can give me an idea of the hull size I can give you some pointers on laminate thickness and cloth or matt weights.
Title: Re: One off fibreglass hull build help please.
Post by: sabre on November 02, 2019, 10:15:43 PM
I've been wondering about this myself.    Instead of polystyrene I was thinking of using surplus blocks of insulation foam.
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 02, 2019, 10:47:02 PM
That tends to be polyurethane, and is often partially mixed with ground glass. I've successfuly used that for making masters, but it dings and dents a bit easier than the blue or pink polystyrene foam. Polyurethane foam can be coated directly with polyester resin- no barrier coat required.
Title: Re: One off fibreglass hull build help please.
Post by: Blaven03 on November 03, 2019, 01:02:17 PM
Thanks very much for reply. The ferry is 1/75 scale so is 90cm length and beam is 18cm. It's a fairly shallow hull.
All help and tips appreciated. Would additional fibreglass internally after frame removed destroy the hull
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 03, 2019, 09:00:12 PM
No, but you need to key the existing laminate if you leave it longer than about 48 hours post cure to provide a good bond.
Title: Re: One off fibreglass hull build help please.
Post by: Blaven03 on November 03, 2019, 09:32:43 PM
Sorry, that's wasn't meant to be destroy. It was distort I meant. Thanks. Have you any advise on epoxy and glass.


I had planed to skim a layer of body filler over it.
Sorry for all the question but this is new to me. Rather get right first time


Regards
Title: Re: One off fibreglass hull build help please.
Post by: Charlie on November 03, 2019, 10:07:31 PM
Have you considered making a timber hull and then coating it with GRP cloth and resin?
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 04, 2019, 06:46:00 PM
Lots of tutorials on glassfibre work on the net. The best advice I can give is try something small first, don;t be discouraged if you make a horlicks of your first attempts, you'll soon get the hang of things, and work in warmer weather, or in a warm environment- resin doesn't cure well (or at all) in the cold unless it's specially formulated for it.

Distortion isn't much of any issue I find. Shrinkage is much greater with polyester resins than epoxy, but even then I find it doesn't cause any problems.
Title: Re: One off fibreglass hull build help please.
Post by: Blaven03 on November 04, 2019, 10:24:18 PM
Tried plank and frame a while back, almost broke me. Did not enjoy. Will just need to get the bits and bobs to give it a try
Title: Re: One off fibreglass hull build help please.
Post by: Umi_Ryuzuki on November 04, 2019, 11:47:56 PM
Quote
Polyurethane foam can be coated directly with polyester resin- no barrier coat required.

Yes, Polyurethane foam...But  pink and blue foam insulation foam is extruded Polystyrene.

Pink or blue polystyrene foam should NOT come into contact with Polyester resin. It will melt the foam.
I use epoxy resin and fiberglass directly on the pink or blue foam. I know others that have used polyester resins, but
they coat the pink or blue foam with latex paint, or duct tape to protect the foam from the polyester resin.
Below, pink foam and EPOXY resin and fiberglass.
Title: Re: One off fibreglass hull build help please.
Post by: Tug Fanatic on November 25, 2019, 01:10:52 PM


......................................... If you can give me an idea of the hull size I can give you some pointers on laminate thickness and cloth or matt weights.



Subculture



Yes please.

Blaven03 listed his hull as 90cm x 18cm and shallow whilst mine would be more like 45cm x 20cm x 11cm for a first attempt.

If you are using polyester resin (I know about the smell) do you need to put a gel coat on the outside?
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 25, 2019, 01:59:55 PM
I always use gelcoat with polyester resin. For that size of hull I would use one or two coats of gelcoat, a layer of glass tissue, then a couple of layers of 300gram chopped matt. Make any tool at least twice the thickness of the hull.
Title: Re: One off fibreglass hull build help please.
Post by: Tug Fanatic on November 25, 2019, 02:04:13 PM
........................... Make any tool at least twice the thickness of the hull.

Thank you but what does "make any tool" mean?

I was thinking woven cloth to make the surface smoother for finishing. Am I wrong & if not what weight?
Title: Re: One off fibreglass hull build help please.
Post by: Blaven03 on November 25, 2019, 04:03:51 PM
Tug fanatic, are you doing a tug?
Title: Re: One off fibreglass hull build help please.
Post by: Subculture on November 25, 2019, 05:13:27 PM
Tooling is the mould you take from a master to make a hull from. I would say double the thickness of the finished hull is a minimum, some would say three to five times thicker, especially if you're going to make lots of hulls, but for one or two you can get away with a thinner tool.

Cloth is much more expensive than csm, and offers little benefit for model boat hulls save for where weight is a consideration (e.g. fast electrics yachts etc.), and also is more prone to delamination with polyester resins. It's much more commonly used with epoxy resin, which bonds with greater tenacity, and also has higher mechanical properties.

If you want a smooth finish to your laminate, just add a final layer of glass tissue over the csm before consolidation.
Title: Re: One off fibreglass hull build help please.
Post by: Tug Fanatic on November 25, 2019, 07:49:15 PM
Subculture
Thanks again.

Blaven03
Thinking small work boat type hull as an experiment without being sure that it will be good enough to use for anything!