My 12'6" splash mold process.... here we go.

[bef]

I used to build wind surfer for make money  when I was young and we made them  like you try but after we put urethne the noise that  come from the mold  show allot of presher  inside the mold mast be very strong.

yes I agree.  My molds are NOT strong enough for that, I would have to do partial pours so the foam does not generate back pressure.  Trying to do it all at once or in large sections would be "bad" for my molds.  Thinking bending or busting the flanges right off!  One psi of pressure would give almost two tons of force trying to separate those mold halves!

Good point and a good one to bring up to others who might be contemplating something like this. 

[bef]

A couple of days ago I laid up some rail reinforcements off of the original board.  I had run a scribe around the board once I had removed one of the molds, so I know where the parting line is.  After waxing it up, I put down 3 layers of a 50mm wide glass tape, felt about 4 oz weight but I have not checked it yet.  These popped off the board and fit nicely into the molded section.  Added some microballoons to some resin, brushed both surfaces and put them in place.  Paint sticks help hold them in place and distribute the load of the spring rods.  Be careful NOT to put too much resin in that it oozes up above the parting line.  coming out the bottom is OK, but not the top.  Clean up the top if this happens. 

I mentioned that I forgot to add my cork reinforcement to the edge of the rail on the top piece.  So I decided to use this as an experiment opportunity.  I added in a 1" strip of cork covered by one strip of 6.5 oz glass and used wax paper, paint sticks and the spring rods again to secure it while it cured.  I did not do the other side.  I figure if I am glassing over the foam up to the rail, another layer or two of glass combined with the foam might mean I do not need the cork along the rail.  I hope so, it was not fun putting it in.  The third layer of glass does not go all the way down the edge, I put a line where it stops.  The third layer that is over the plywood in the middle also does not go all the way to the joint, it only covers about 1" beyond where the plywood ends (line drawn)  This set me up for the fun foam experiment!

You can see the channel I am trying to fill with foam in the last picture.  That is 0.040" HIPS plastic treated with a mold release and bearings to try to hold it down.  The arrow shows the formed channel.

[bef]

So I guessed at the foam amount, and guessed high.  It expanded, oozed out the sides and the gap along the rail, then started lifting the plastic and bearings!  Still, it is 3 LB foam so it cleaned up easy enough.  But yes it does generate some back pressure and some heat, the HIPS sheets came out soft like they were ready for vacuum forming! 

So the other side, I mixed up about half as much foam and repeated, much better.  I did have a few voids where it did not fill as shown by the arrows, but these were easy enough to fill with a small amount of foam later and sand back down.  A simple hacksaw blade makes a simple foam carving tool.  Now ready for the internal glass and stringers!

[bef]

Thought I had updated this, but I didn't even take pictures I guess.  So I used some of the 1/2" urethane foam I had around and made stringers up from three layers for 1.5"  I glued these in place with some polyester slurry resin and then shaped them down to the proper height with a belt sander.  I then laminated over them with two layers of 6.5 oz glass all the way to the parting line of the mold.  I cleaned everything up and this morning I joined the two halves together.  I thickened polyester resin with some cabosil and used this to fill the rail doubler.  The rest I put under one of the stringers.  I pre-fitted the stringers so I knew I had about a 1/4" gap to fill, which is pretty big.  The other side I mixed up a little 3 pound foam and poured it before dropping the deck mold onto the bottom mold and clamping.

The 2' piece popped out pretty easy and I ran it through a band saw to clean it up to 24" and give a nice cross section.  It is heavy....  definately heavy and strong.  The 2' piece came out at just over 9 pounds.  Time for a diet.

[bef]

So I really do like the expanding foam for supporting the stringers to the bottom of the hull. It filled in nicely and really supports the bottom skin.  The polyester putty is more of a point load and concentrated.  To fill a 1/4" gap the length of two 8' stringers will take a lot of resin, so the foam seems to be the way to go. 

I put all of my 270 ish pounds on it, stood on one stringer.  Stood on the rails.  Stood on the bottom where the stringers are.  Plenty of strength.  I do not think the bottom would support me right in the middle, it is too flexible.  If I had a middle stringer it would have no problem.  My son is about 160, and he could stand in the middle of the bottom on one foot.  It deformed, but it did not break or crack.

The deck with the 5mm plywood is really strong.  I put the section in the grass and bounced up and down on one foot right in the middle where the handle would go, no problems.  If I stood on the rail with one foot, I could hear cracking.  But that is not a fair test as I can not stand on the rail with one foot as the board would flip.  Even if I could, the load would be spread out to the water underneath and not a concentrated load against the ground.  I think the main thing is, I have too much strength in the deck area.  It is nice how strong it is where I stand, but I could cover that with a 24" piece of the wood, the rest could be lighter.  If I go back too much, the board starts to sink.  Anyone else who can move around on it, will be lighter.

[bef]

I think I am sold enough to try the urethane paint.  One each side, I scuffed up the surface on half of it to see if that would help adhesion.  On polyester resin, it had bad effects as the paint wrinkled on the surface that I went over with sand paper.  The other half came out nice and could use a buff and wax.  Considering that I am going to be using epoxy, i think I will go with the urethane on the first board, but no sanding. 

[surfcowboy]

That section looks good man. I agree, you got a bit much on the deck support but now you can back down from there.

[TallDude]

Maybe 4 stringers through the standing area or so perpendicular blocking?

[bef]

I was going to modify my 24" long paddle board with a middle stringer.  Cut a piece of xps a little short and slide it into place, then secure with the expanding foam.  I am wondering if that would make the bottom layup strong enough to use as a deck layup.  My thinking is it would, then I could go without the plywood piece.

But I would have to leave a blank area where the handle would go, but if I went with two long stringers and two shorter stringers, I think it would really make the middle 4' of the board very solid.  I can still put in a middle stringer in front and behind the quad area, thanks for the idea cowboy!

I am still going to make one with the 6.5' long plywood piece, as it will be left pond side to be used by all and kids as a raft.  So heavy is not an issue I guess and the ply is already cut out.

[bef]

Put the table and molds in my garage to try some layups at home during the evening.  Hoping I have more time in the evenings to work on it.  After cleaning and washing them out, I put down a couple of fresh coats of wax and a layer of PVA.  This morning I rolled out the one part urethane topside marine paint into the mold.  I also grabbed an old model boat mold and put some urethane pain in it without the PVA coating.  I want to do a quick test layup and make sure the epoxy bonds to it well and the urethane releases from the waxed mold without PVA before I mess up my molds. 

So now my oldest son (16) tells me he doesn't like the water sports.  My second son (14) likes the inflatable kayak more.  Guess I do not need so many paddle boards after all....