New C5000 build from scratch

[dazzler]

Building a temporary flange

So, because this fiberglas mold will be 2 part (one for the bottom half of the hulln the other for the top half of the hull) I needed the create a temporary barrier (flange) which would be the separation line between the 2 mold halves.

First step was to roughly saw the shape of the hull out of some MDF board, and attaching it to the building board at the exact height (the flange must be set on the widest part of the hull, so that the mold has no negative angles - a part can't be releases from a mold if it has a negative angle)

Then I placed a large piece of thin cardboard on top of that, and used masking tape the eliminate the gap between the hull and flange.

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This piece of cardboard and masking tape was then put on top a a polystyrene panel, it's outlines drawn and sawn and placed over the hull/MDF panel.

This already gave an incredible tight fit, however since your don't want any resin to leak through, I used model clay to fill any remaining space between the hull and flange, making it completely tight!

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[dazzler]

Building the first mold halve

So, what follows is one of the most important steps in the entire process. It's also the least visible thing: making sure the mold will not stick the the part !!

So, one must apply sufficient release agent. This is done be applying several layers of release wax on your working piece. Theoretically 1 good layer of release wax would be sufficient, but because this wax is nearly invisible it's very very easy to forget a small area. That why everybody will tell you to apply at least 5 to 7 coats of wax. It's not because you really need 7 layers, it's to minimize the risk of any spot being left over, as that would mean the mold is glued to the part!

I also applied an additional 2 layers of PVA parting agent (poly vinyl alcohol). This creates a real barrier between your mold and piece, and because I did not use DD lack (2 compontent paint) on my hull, I really need a good barrier, otherwise the styrene damps in the polyester resin would eat right through the wax and attack the paint (and then your mold will look like your finger when you have been in the water to long!!)

But then finally I could start with the gelcoat layer. I applied 2 layers of gelcoat.

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After the gelcoat has set (minimum 3 hours, maximum 24 hours in my case - it really depends on the brand you are using) I started laminating a first layer with fiberglass of 6oz in combination with a vinylester resin.

After that first layer with 6oz fiberglass (with is more flexibel and will follow the corners better) I then continued to apply 4 layers of 13oz. fiberglass in combination with a special polyester resin (specific resin for molds, which has less shrink than regular polyester resin, and also allows for more layers in one session due to lower heat dissipation)

Finally I also added a wooden frame to the mold the reinforce it and make is generally more rigid.

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Then it was time to flip the entire structure upside down, allowing me to remove the original building board as well as the temporary flange that I had installed.

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Building the second mold halve

So, with the building board and temporary flange removed, it was time to build the second halve of this mold. Because the first halve of the mold now already has a proper flange to itself, you can build the second mold directly against this one.

Off course ..... very important .... apply release wax and PVA agent before continuing, or the 2 mold halves will be glued together and to the top of the hull indefinitely!!

Again I first applied 2 layers of gelcoat, after that 1 layer of 6oz fiberglass with vinylester resin and 4 layers of 13 oz fiberglass with special mold polyester resin.

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Separating the molds

I also made a wooden reinforcement frame on this side of the mold. Then came the time to separate to the mold halves from each other and from the hull.

I started by putting wooden spatulas in between the 2 halves to force a bit of an entry. You must be careful not to damage the gelcoat of the mold by using "hard" tools such as screwdrivers and/or chisels.

After some prying the top halve finally came loose very clean. Unfortunately the same thing can not be said for the bottom halve. I could not get the hull out of the bottom mold without completely destroying the hull.
The problem was actually two-fold: while enough release wax and PVA was used not to make the mold and the hull stick together, the mold was actually so tight around the hull that I as not able the get any spatula between the mold and hull the create any form of leverage.... on top of top, the bottom part of the hull has many many corners, the steps, the transom, the lifting strakes... this just makes for a difficult shape and with a mold so tight around it there was no way to get it out undamaged.

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P.S. The "hull" or better, plug is a lost object anyway. Being the emotionally attached guy I probably would have kept this plug sitting on my shelves for eternity and beyond if it had come out undamaged, while at the same time I would have has some self complain for being in my way all the time

[dazzler]

The finished mold parts

So... there you finally have it! 2 finished mold halves, sitting ready to create some nice fiberglass hulls.

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Guess I will take a break now to think about my next steps, on how I shall proceed with the build of the fiberglass hulls. I'm haven't made up my mind on how tick the laminate would have to be, which fiber cloth thickness I will use (and how many layers) and if I would stick to a fiberglass/epoxy resin combination or go for carbonfiber/epoxy or a mix in between....

Any suggestions about layer thickness and fiber cloth weight is appreciated, as I don't really have a clue at this point how many layers or thickness would be good (you don't want the hull to be to thick and heavy, but you do want it to be strong and stiff enough to withstand the forces on the water...)

[srislash]

Excellent work on the molds! I am looking forward to the further steps.
Shawn

[golfito]

How much work I have done! I am impressed and grateful for the images.
Following your construction.
Regards!
Hernán

[CornelP]

Very nice work!
We found out that it is better to reinforce the mold with wooden rails after you get the plug out... this way it has some give and you can fit some tools in the space. Compressed air around 4-5bar works quite well (I heard) but a very good trick is to use some thin plastic stock (0.4mm) and push it as much as it will go under the plug. Some of the best tools for this are also thin plastic aircraft propellers.
As for layers, a light racing hull in this size will probably go for 100g glass + 100g lass +160g carbon + 100g glass, with carbon tow and epoxy thickened with fumed silica applied in the corners before that to avoid bubbles and get sharp corners.
It is usually better to make it lighter and reinforce where needed, at least on the first pull from the mold (which is also the worst looking one, the second will be ok).
Cornel

[dazzler]

Thanks CornelP.... guess it's too late now to reinforce the mold after getting the plug out

I'll try your suggestion for the layup. I have no idea how stiff/strong that will turn out, but calculating the weight of the suggested fiber cloth + required epoxy resin for those cloths, I'm coming up at around 1000-1100 g. which is about the weight I have seen for these size of hull from MHZ and/or HPR boats.

[fweasel]

Wow!

[hughb]

That looks a great project. I wish you all the best in creating your boats