Infusing with a wood female mold

[Jetboy]

I'm nearing the point I'll be building a set of beams for a small trimaran. I'd like to infuse them in a female mold made of particle board. Can this be done? I'm primarily concerned that the mold may not be 100% air tight. Is there any way of making this work?

Thanks

 

[TANSL]

In my opinion, it would be good that the beams have a closed cross section. Might be preferable to manufacture as a tubular structure.

 

[Jetboy]

This is the design for the mold. It's open on the under side intentionally so that the folding linkage can recess inside it. Of course it could be re-designed to work differently, but that's the original idea. I'd just like to infuse the layup because I think I can do it a lot faster and get potentially a better quality result.

 

[groper]

Sure it can work... Just seal the mold with glass + resin and then something like duratec or some other high gloss and high toughness 2pk paint - the automotive 2k paints should work well to get a high gloss and provide good release.

To ensure its vacuum tight, its better to use a veil cloth of glass when you apply the resin as without it the pinholes will still come through.

Theres a bit of work in it, after the glass and resin layer you will have to apply some fairing compound to fair it all out and get rid of pinholes etc. Once its fair, the final layers of paint should seal any remaining porosity.

Look like the one in the pic is made from ply wood...

 

[SukiSolo]

I'm not sure infusion would give you much advantage over just vacuum applied after a good hand layup. Tansl is right if you had a box section it would be stiffer, or at least a partial return - known sometimes as picture framing. Massive difference in the stiffness, just try it with a bit of cardboard. it would mean making a demountable part of the mould but it is simple and worth the time.

Groper is right, just seal the buck material with epoxy and 2k gloss black preferably to show flaws, polish and wax etc. It will come off, carnauba wax is one of the better waxes.

 

[Jetboy]

My thoughts on why to go with infusion is primarily based on the number of layers of glass that make up the beams. Overall I believe there are about 50 individual pieces of fiberglass that go into each one of these beams. I think it will take a lot of time to wet all of them out and hand layup as compared to just putting them all in dry, and then infusing as a single operation.

 

[SukiSolo]

50 pieces? or 50 layers? If near the latter, I think you need to core the moulding with foam or pre bent timber, maybe even a ply. If you can get a vacuum it would pull it down fine. Might be worth pre impregnating the core dependent on material. Still seems a lot though 50 pieces, if it was just glass I think you could get away with a lot less for main thickness. Better with a core and less glass but stiffer.

What weight glass/carbon or hybrid cloth are you thinking of using?

 

[Jetboy]

It's 50 pieces, not 50 layers. Basically much of the beam is 3 layers, but the areas with high loading (basically the bottom of the webs) have extra strips of reinforcement. Also the areas where the linkages attach also has a bunch of extra layers to reinforce the beam. Some locations will have over a dozen layers.

I keep going back and forth between building these as per the design, or just re-designing in aluminum and welding up a custom set as I have a lot more metal fab experience. If I could infuse them, I think I could just lay in all the glass in an hour or so, then infuse it, and be done in maybe 2-4 hours of work per beam. I think doing it one fiberglass layer at a time will take all day. Maybe I'm wrong about the time to do a hand layup?

 

[groper]

Jobs like this are perfect for infusion for the time factor alone. But you would want some experience before attempting it, otherwise you could end up with a pile of junk... Have you infused before?

 

[Jetboy]

Nope. This will be my first time. I do have a vacuum pump and I've done some limited vacuum bagging.

 

[Tungsten]

I have some plans for some parts in the future and I was just going to use plastic sheeting on the field areas and clear tape over the corners.Guarantee release.Is there any reason why this wouldn't work?All my test infusions have been done on plastic and the finish looks quite good.

 

[petereng]

Hi Tungsten - for a one off piece using film on mdf or timber is the way to go. Use spray tack and tailor the plastic into the mould with good overlaps and flashtape or polyester tape the seams. Then layup the dry stack, infusion stack and bag it. Infuse at your leisure. Be prepared that anything in the bag can get resin on it so make sure edges and bits are well taped or sealed. I've been waiting for a suitable project to test some "wrapping" plastic so I can heat shape and stick the plastic into and around the mdf. Wrapping plastic is available from signwriters and auto detailers. Its like a sticky backed shrink wrap that images get printed on, then you stick it to your car. Cheers Peter s Is that a Kenrick beam? cheers Peter s

 

[Jetboy]

Yes. This is a Scarab/Kendrick design. The open bottom of the beam allows the folding linkages to collapse internally and it really makes a nice system. The alternative of course is to mount the linkages outside the beams, and that can work too.

Whenever I start re-designing parts of this boat, I draw them out in some cad program and start messing around... then I realize why the design choices were made the way they were, and I go back to the original design. So far at least. I will be changing the cabin design, but that's just for more seating room and less interior space due to personal preference.

 

[petereng]

Hi Jetboy,
I did the beam engineering for Ray many years ago. Cheers Peter S

 

[Jetboy]

Hi Jetboy,
I did the beam engineering for Ray many years ago. Cheers Peter S

I've always been curious as to what load inputs you use to calculate a beam design. Maybe that's a closely held secret. Considering the universe of dynamic loads that a beam would experience in real world sailing, how do you go about coming up with some maximum load to plan for?