making plug for fibreglass mould

[ashley needhamParticipant @ashleyneedham69188]

Fellow boaters. The time has come to try and make a fibreglass hull.

The question is….what is the best/easiest way to make a plug for the mould??

​Solid wood, foam, plaster….and after the shape has been made, what do you seal the surface with prior to waxing etc

Thanks,

​Ashley

[ashley needhamParticipant @ashleyneedham69188]

[Bob Abell 2Participant @bobabell2]

Hello Ashley

How about this for an option?……

……….Use an existing boat hull as the plug and make a mould from it?

Any good?

What type of hull are we talking about?

Bob

[Ray Wood 3Participant @raywood3]

Hi Ashley

I guess this is a new boat ? I'd carve the shape in Blue foam, plaster of paris skim, then polyester resin, rubbed down to a fine finish, then 10-15 coats of Bees wax polish, should release ok I did this last year to produce a winged keel for my sailing barge. I did buy a book on GRP moulding from Amazon by Ron Warring but it was very basic and 30 years out of date

Regards Ray

[harry smith 1Participant @harrysmith1]

Hi Guys

The bees wax is OK but, they have a releasing agent which works well!!!

And Ray a winged keel for a sailing barge !!!!

Looks like Rays having a crack at the Americans Cup !!!

By the way, who invented the winged keel !!!!

Harry

[ashley needhamParticipant @ashleyneedham69188]

Chaps. Yes a new boat so unable to use an existing hull, and no clues as to type…..

​I like the foam/plaster/resin idea as foam is easy to carve. I shall be doing a symmetrical hull so only one half is needed which makes things a lot easier to get even.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

I shall be doing a symmetrical hull so only one half is needed

"Que?"

DM

[Paul TParticipant @pault84577]

I think that as it is a symmetrical hull Ashley intends to make it in two halves and glue them together.

It is true to say that a fully symmetrical hull is a very rare beast and knowing Ashley this project will be interesting and very different.

I'm off to google symmetrical hulls and see if I can guess what it is.

Paul

[ashley needhamParticipant @ashleyneedham69188]

The underwater shape is same both ends as is the above water shape. AT LEAST that's what it says. Pictures are hard to come by, but the (probably builders) half model I have seen a picture of shows a possible rudder port at the aft end…its a bad photo. In which case the blurb is lying and it is not quite symmetrical. I would still make two halves and join them, then cut a hole at the stern and do a bit of re-shaping as easier than making a two part mould, especially for a one off.

I have a preliminary sketch and it looks as if it will be a bit heavy and I am wondering about the chosen propulsion system. Mind you the original was very slow so it doesn't matter that much.

​I have made enquiries with the (possible) owner of this model, and we shall see…or at least hopefully we WILL see, and all may be revealed. The National Maritime Museum is of course a good source of material, but a copy plan is very expensive and you don't necessarily get exactly what you were hoping for.. By the looks of things, making the plug, mould and two halves is not going to ne that inexpensive either what with resins, gel coats, wax and so on. The propulsion system will be the cheapest part of the build!

Paul, good luck with that search….

​Ashley

[John W EParticipant @johnwe]

hi there Ashley

couple of golden rules with fibre glass – Get the mix right; i.e. hardener to resin – making sure you have the correct temperature (not too hot – not too cold ) and don't mix batches that are too large. In other words the size batch which you cannot use up within 30 minutes.

With regard to materials from which to make moulds – as has been stated previously; there are 100s of items which can be used. Make sure though that whatever you use doesn't react to the resin. You may even use cling film as a releasing agent; the other thing is watch out for undercuts in your moulding for when you release the moulding from the plug. A lot of folk don't foresee this and they don't realise why the moulding doesn't release properly and they end up breaking it. So you are making a symmetrically based hull? Could this be the Russian circular ship from the 1800s? Have to go and do some Google.

John

Edited By bluebird on 12/07/2017 17:06:40

[Colin BishopModerator @colinbishop34627]

A war canoe – presumably manned by a bunch of hard boarders?

Colin

[Bill Scott 1Participant @billscott1]

I'd still make two halves, will make joining far easier

[Paul TParticipant @pault84577]

I spent the afternoon looking at possible candidates (how sad am I) and without giving the game away my bet is an obscure Soviet MTB from the mid 1930s.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Suggestion from a professional is wood….sealed, acrylic primed and then gloss sprayed.

Gloss required for a smooth finish to take the release wax coats.

​I think this is what I will go for.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Ashley

THE choice for patterns for casting used to be jelutong. It carves like hard soap, has no perceivable grain and can be sanded very easily and smooth using just hand tools. It's not cheap! Pattern makers now use a very hard, high-density foam. That's even less cheap…

Dave M

[Ray Wood 3Participant @raywood3]

Hi Ashley

Are you going into mass production with this mystery vessel ? I just thought the work making a plug and moulding was a lot of effort for a one off . Although it satisfying process to achieve.

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

Ray. No series production, but there are openings in the hull and there will be water inside the vessel, so a plastic/fibreglass hull would be best.

​High density foam sufficient for my hull would be approx. £60. Not yet found out how much Jelutong would be. I rather like the foam idea as it is very easy to sand.

​Given that a half hull is reasonable shallow I wondered if Styrofoam would work. Styrofoam is very cheap (by comparison) and if eze-coted, skimmed with polyester filler and painted??

​A suppliers website recently visited has a series of on-line videos to look at and these are very interesting. He demonstrates making a plug from foam, however it is coated in several different hardeners. For just a one off, this would work out to be very expensive.

​Continuing to asses, and cost up. A wood plug of course would need simple and cheap finishing treatment…..

​Ashley

[ashley needhamParticipant @ashleyneedham69188]

Not got a quote for Jelutong yet, but high density foam would be about 60 quid.

​Its all starting to add up when you look into it, what with wax, gel coat, resin, cloth, loads of mixing pots and large disposable brushes. Ray may be right about mass production (the cost of doing a one off).

​An alternative as suggested by A>N>Other (you know who you are Trevor) is to make a hull from foam, and cover it in fibreglass then cut out such foam as needed leaving a shell . I my case I need an empty hull due to the mechanics of the thing. I initially worried about getting a good enough finish, but if I used medium and then fine matt and took some care, the bare glass hull should only need an overall scrape of P38 and a good wet`n`dry.

JUst possibly if the foam hull was treated correctly it might come out easily and leave a relatively smooth interior.

​The video I saw on the suppliers website had a good method of getting both sides evenly matched (a big CnC machine!!).

Ashley

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