Lightweight Jetski Mold

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#1

Working on a plug for a lightweight jetski hull. Just want to run through what I plan on doing for the tooling phase…
I have wetsanded to 1000 and polished with Aquabuff 2000. I plan on using grey Duratec primer for the tooling surface (applied thick), 4oz cloth for the first 3layers, using PER for the entire mold. I will only layup 3 layers per session to avoid thermal induced “issues”. Then continue to 6oz cloth layers, with a 2mm coremat layer to build up thickness. Follows by 6 or so layers (probably more) of 1.5oz CSM. Then 2 layers of 24oz roving. I also plan on glassing in some 2x4’s to help ensure it retains proper shape, before I pop the mold off.

I am going to wax it 8times with a proper mold release wax. I plan on spraying PVA… I know this is not going to be an easy release WITH PVA, I do not want to chance not using it. I do relize the price I am going to pay with the molds surface finish. I plan on atleast 5-7layers of PVA. I am also going to glass in 2 or 3 metal female/female threaded fittings with 3/8" barb ends. So I can spray air or water into the omld to assist the release and for wetsanding “drains” later.

So far I think I have almost everything covered, but anyone see something I might be missing? Any other advice or suggestions?

***Right now I plan on laying up the mold one week from today as long as temperatures allow.

Here is a fast forward view of the plug construction. The only thing that has changed since these pictures, is that I have glassed over the motor compartment cover and bondo’d it smooth. I will be spraying the compartment cover with duratec and sanding/polishing that section Sunday.

#2

Look out SkiDoo!

Looks real good. Why so many layers of fiberglass, core, mat?

I have never built a mold that large, so possibly you are just trying to eliminate flexing of the mold?

Beware of clamshelling… a large open mold will want to close up on itself a bit. Possibly enough that the bottom hull mold and part won’t line up with the top hull mold/part.

I would build a steel tube frame to keep the mold from changing shape once released from the plug. The frame could be built so the mold will sit flat while doing your lay up work. The framework could also make it so you don’t need so many layers of fiberglass possibly. How thick is your finished hull going to be? Build the mold so it is 2 to 3 times the thickness of the new hull part.

Others here will have some good input on keeping the mold from clamshelling or shape changing. Polyester resin is bad for that. Vinylester will shrink much less than polyester resin… and epoxy tooling will shrink the least.

#3

When you go to seperate the newly cured mold from the plug, use compressed air, and mold release wedges. Take your time when releasing it and just work all around the mold little by little until it releases. … and mold release wax/lightly buff that plug at least 10 times prior to lay up. …just my cheap 2 cents worth.

Do not use PVA if you can at all help it. Buy some NC770 release spray or PolEase 2300 mold release spray. PVA WILL make it harder to release because the pva kinda acts like denture paste LOL.

Don’t those watercraft use sportbike engines? I’m thinking it needs a CBR 1000RR engine! :smiley:

#4

Yes, its my first large mold as well. And I figure better to be safe then have flex…lol I am trying to eliminate ANY flex in the mold. Thats why I am doing so many layers. I hope the mold to be OVER 3times the thickness of the part. I know poly isnt the best, but I already bought 10gallons of it. I was debating doing the entire mold in epoxy, but I just cant afford that right now. I was going to leave the cured mold on the plug for a week, after I am done adding layers.

Thanks for the PVA alternatives! I have never used anything BUT pva on parts I have made in the past and didnt know there were better alternatives. Do the release sprays you mention handle, dry pretty much the same as pva?

Most standup skis run 700-800cc (up to 1200cc) 2smokes. This one will have a 701 or 771cc yamaha powerplant, pending how much money I have left after the glasswork.

#5

the release sprays are dry much faster. Pol-Ease2300 never dries, you just spray it on then start your gel coat on top of it.

NC770 or NC700 you spray on, let sit a few seconds to a minute, then very lightly buff it with a clean cloth. The goal isn’t to buff so much that the material is removed. Both work very well. No dry time involved.

Technical Data for 770-NC:
http://tds.loctite.com/tds5/docs/FREK770-NC-EN.PDF

#6

Use real tooling GELCOAT, not Duratec primer. It’s a surface primer, not a tooling surface.
Back up the gelcoat within 24 hours with two plies of surfacing veil and let it cure. Then a couple of plies of lightweight cloth and let cure. Then build up thickness with heavier material.

#7

I’ll be watching this thread, i had a x-2 thst i modified the body, motor and paint. I just never thought sbout going as far as you have. Good luck!

#8

I think TET is saying use tooling gel coat for the mold construction. I wouldn’t see any problem using Duratec Primer for the finish coat on the plug.

A little secret with tooling gel coat and resins… lol… find a composites frp shop in your area and go there with an empty jug/container… ask them if you can buy a gallon of it from them. I did this and used to get US Composites black tooling gel for $30 a gallon :smiley:

#9

I have used duratec as a tooling surface on the last 3 mold I made. Works surprisingly good for this, and sands/polishes 10x faster then tooling gel. I really hate sanding. Is it the BEST suface to use???..NO. But keep in mind, I am not going to be pulling many parts. If I do 4 or 5, I’d be amazed. Did I say I really hate sanding?

Here is a jetski rideplate mold I did with duratec. Its still covered in PVA…

And here is a kevlar/s-glass rideplate made from above duratec mold.