Got going on the transom core. I got 2- 3/4" sheets of Douglas fir marine grade ab ply from home depo for $80 each. Wanted to use Coosa to save weight but man that stuff is high. To get it I had to buy a minimum of like 10 sheets to get a good price or pay higher price and high shipping on just the 2 sheets. I decided in interest of time (wanting to work over the holidays while I.had off) to go with wood. To me wood is the best transom material anyhow but just hate to make the rear any heavier than needed. Deep vee ride better with more weight just got to get enough forward to get the balance right. I used the skin from the inside of the hull to get a pattern marked on the ply. Once I got that marked I took a pice of scrap and traced the hull bottom of the vdr and marked it on the ply for an exact tight fit. Got both pieces tried out, then scuffed the inside face of them with 80 grit to get the smoothness off the ply and to make it absorb the resin better. I used thinned infusion vinyl ester and applied a good hot coat of resin to the wood face so it could absorb in. Styriene will thin resin better than acidtone and works best. Infusion resin is thin to start with but wood absorb resin better when really dry and when the resin is super thin. I cut two layers of 1708 and two 1700 cloth for the inner core between the two plys. The 1708 will get applied to the wood csm side mating to the ply. That will hold more resin for the wood to absorb and fill any flaws in the wood better. I dug threw the stack so i got two nice sheets so it was flaw free mainly as ab grade is anyhow. I almost wished I got the Douglas fir exterior ac grade ply at $40 a sheet (half the cost). I told myself the ab marine would be better even tho they are basically the same thing. Back to lay up schedule, 1708 to the wood csm side touching the face then a layer of 1700 biaxel second 1700 biaxel then 1708 facing opposite the first so csm is up to lay the outer ply sheet on that way the csm touched the face of that second sheet. I applied each layer one at the time rolling each out well to get any air out between layers. Applied the top sheet down after it soaked up plenty of thinned resin. I did this on a 38-40 degree night with my shop cold. This gave me plenty of working time to lay everything up without the resin kicking off. It took 3-4 hours to do everything and once I had it clamped together and weight on top of it I shut the doors, fired up the heat and set it to 90 degrees. Once the heat climbed the resin started to kick. Baked it all night for 10 hours and removed the clamps and then trimmed the edges. This gave me a 3/16 or better lament between my plys. Supper strong and flat. Now I. Will hot coat the sides edges of the plys and outside that will face the rear of the boats original transom skin. It will get just one layer of 1708 due to the outer boat skin is already 3/8" thick. Once I get it hot coated I will lay csm strips 2) 1.5" & 1) 4 " strips around the edges just to seal them against water asorbshion then drop the 1708 layer on the back of the ply face. Once that sets flip it and lay an layer of 1708 on the other side. This will seal the core 100% and as long as no screws go in it there shouldn't never get water in it to rot it out. Once cured it will get scuffed with 80 grit and bonded in the hull to the rear skin with thicken epoxy and several layers added to the front tabbing it in to the hull sides.



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nice to what you are doing good luck and happy new year george

George, ready to do some overnight camping with the family this spring in the 25', gotta get rolling to make that happen

Few more pics:
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Looking good! How thick are you going to make the inner laminate skin?
Dave

Thanks, The original inner skin looks like it only had one layer of a thicker woven roven with csm under that against the wood. It was barely an eighth inch thick if that thick, probably less. I was surprised just how thin it was for the large transoms is in theses 25's. The outer hull skin is a very thick 3/8" plus but that was the only thick part. The two wood layers were tacked together with nails every 6" or so with no glass between them at all. I will be going back a lot thicker. I know the outboard bracket will need more support than the outdrives did. I may build up about a 1/4" thick of glass on the inside once it is in place. I will start out with a layer of 1708 with 4" ears to lap onto the hull sides and bottom for tabbing. Then two layers of 1700 for thickness on just the core then a second 1708 with 6" ears for tabs then 2 more 1700 layers then a final 1708 with 8" ears for tabbing. That should give me the thickness I need and three over lapping tabs to the hull. I will also come back and add some additional tabbing strips around the edges for additional support. I will be pulling some nice flits in the corners as well to help the tabbing radius as it rolls off of the core. All said and done it will be a lot more than the thin original factory inside layer plus have the 1/8"- 3/16" of glass between the plys as well. I may be over doing it a bit but that is one large 7'x4' span of transom especially with the bracket and outboards hanging on it. I will also add some knees to the transom down to the inner stringers plus when I build the bracket I will try to align the stringers in it to match up with the ones in the hull to the knees so that it all supports off one another.

2k for the pair!!!! wow that is an amazing deal. I'll be watching closely to see how you like the boat with outboards. Keep up the good work.

Thanks, I couldn't believe the price either. He wanted $2200 but got him down to 2k. I expected to find some old motors with burnt piston's but when I did compression checks the lowest hole was 125 and the highest was 129 and that was cold with the throttle closed. I done a leak down as well and they checked out really well. They also still have the serial Id numbers on the freeze plugs so they are original power heads not rebuilds. The only have around 350 hrs on them according to the gauges that came with them. I found a pair of carb 2.5s last week here locally for 3k. If they were EFI like these I would of got that pair too. Still might end up with them due to the guy may trade them for my 23' Proline and trailer. There as been some deals around on motors lately. Keep me in mind if you come across and Hipo 2.5 stuff. Still like to find some 7 petal fronts and some promax blocks if possible. Not for the 25' but for the race boat. The motors on the 25'will remain stock for now.

A bracket will evenly distribute motor loads across the entire transom, so you'll actually have lower concentrated loads and stresses on your rig than you'd have on a conventional outboard or outdrive transom mount!

I think the knees and 1/4" inside thickness are overkill, but I agree that lapping the cloth around into the hull bottom and sides is a good idea. That glass between the plies may add a bit of compressive strength but it adds NO bending strength to the transom because it's at the neutral axis. (When you bend an I-beam, the compressive and tensile stresses are directly proportional to the distance from the neutral axis, which is at the center of a symmetrical part, so there is NO bending stress at the neutral axis. A cored panel is similar to an I-beam, so the max bending stresses are at the outer surface. This is why cored panels can be so stiff and strong with relatively weak and lightweight core materials like foam. As long as you use epoxy or vinylester resin for good bond strength, that transom will be stiff as a brick!

FYI, Don Herman uses lots of Coosa in his brackets, so if you want some for a future project, it might be worth sending him a PM. He might be able to sell you just one piece for less than the retail you'd probably pay at at most places.

You are exactly right! :D

I defiantly tend to over build, I will probably leave out some of the 1700 layers for building thickness and keep it around 3/16". I planned on using some 4" aluminum flat bar on the back side of the bracket mounts to help spread load so there is really no need for any thicker. I also plan on using some foam in the bracket. I have some core cell left from the last one I done. It is not enough so I will be sending that PM. Thanks for the help guys!!!