1987 Bluewater rebuild

engine350400

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Apr 27, 2015
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Hello This is my first time posting, I have a 1987 17' Bluewater open bow, almost every piece of wood is rotten. I got a really good deal on this boat it has a cracked 4.3 cobra, and a rotten deck. the hull has some dings and scratches, but it will shine up pretty good. the interior is not great but not too bad. I have completely removed all the wood, the motor and out drive. The transom and rear section of stringers were replaced by somebody that did not do a good job at all. The wood i removed from the transom was cut in six individual pieces. My dad actually noticed that the transom is not flat, it has a slight curve in it. I have just got to the 90% mark on grinding the hull and looking to do the transom in the next week or so.

The question i have is, with the transom being curved how should i go about putting ply back there? I dont want to cut 6 pieces like the previous people did. I have already bought the two pieces of 3/4 plywood i was going to use but i dont think i can get it to conform to the slight curve in the transom. boat 1.jpg 20150510_175123.jpg
 

zool

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One way to curve your transom is to lay up progressive layers of thin ply...like 4 layers of 3/8 one at a time.

another way is to laminate 2-3/4 pieces of ply, then cut kerfs in it at 1 inch+- intervals, and contour it to the outer hull. fill in the voids with pb. The 1st way is my preference.
 

johnnybgood

Seaman
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Jun 12, 2012
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72
I'm no expert but your transom may be a case to use pourable sea cast, others on here may know more than me
 

sublauxation

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I also know nothing about the stuff but definitely look into Sea Cast, it seems it was meant for these exact situations, and it's a job you only want to do once.
 

sphelps

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Check out archbuilder's Project Fuggly ..
He is doing a Seacast I/O transom now and almost at the pour stage .
The inside of the skins must be completely clean for proper adhesion .. That's why I always recommend taking the inside skin out for accessibility ...
The main drawback for Seacast is the price .A wood transom would be much less expensive ...
 

Woodonglass

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I'm with Zool, 4 layers of 3/8" plywood, IMHO IS the optimum method for fabricating a curved transom. Cutting kerfs in 3/4" can be done but I truly believe the other way yields a stronger build.
 

engine350400

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Apr 27, 2015
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Thanks for all the info, i did some research on sea cast and found it would cost almost 600 after all said and done. From my calculations i would need just shy of 13 gallons, not subtracting the keyhole to account for the spills. I would also be forced to pull the cap, i don't have a good way of doing that.

On the other hand to do plywood i will need 4 full sheets of 3/8 ply since my transom is about 2'4'' in the middle. That's going to leave a lot of waste. All said and don it will be around half the cost. At this point i am leaning towards using 3/8 plywood.

as for the procedure on multiple layers on the transom, I will cut out all my layers and the first layer will sandwiched to the hull using poly pb. should i use a 3/4 oz mat between layers instead of 1.5? Also should i lay them up one at a time or mix it cold do them all at the same time?
 

Woodonglass

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I'd recommend making some transom clamps as shown here...Fabricating Decks, Stringers, and Transoms
Epoxy would be the best glue to laminate the separate pieces of wood together but you could use TiteBond III wood glue, Gorilla glue PL Construction Adhesive or Poly and CSM. Once the first layer is glued and clamped in place and conforms to the shape of the outer skin, the rest should be easy to do. After the 2nd layer is in, you could actually use screws to install the 3rd and 4th layer. I'd do the first two separately and then the last two at the same time. But that's just me!!!
 

sphelps

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I think to use the clamps he would need to pull or cut the cap . If ya can get them in there the clamps work great .
 

Woodonglass

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Yeah, there is that ^^^ to consider but... You can make clamp extensions for I/O's and still use the clamps and not remove the cap!!! ;)
 

sphelps

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Through the key hole ? Over the cap maybe ? Now ya got me curious Woody .... :pop2:
 

engine350400

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Apr 27, 2015
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Would the holes for the gimbal housing and the holes for the transom straps work good enough to hold it together for the first layer? My dad had a good idea of taking a 2x12 and cutting the curve out of it and using it on the inside and outside with a bolt through a hole in the key hole( not cutting out the keyhole just a 1/2 hole)
 

Woodonglass

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Ok, hopefully you can make sense of the drawing and this explanation. If you looked at the link an saw the transom clamps then all you have to do is fashion some rectangular extensions from some2x4 material as indicated in the drawing, (extensions shown in brown) they would need to be big enuf to extend beyond the depth of the cap and your clamps would need to be made from all thread so they could open wide enuf to accommodate the needed width as well. this would allow you to apply the clamping pressure to the transom pieces as needed. I hope this all makes sense.

 
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sphelps

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It just needs one more threaded rod .. A helper would be advised .. Looks like it would work to me . Might could even make the extensions out of some plywood .
 

Woodonglass

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Yeah, you're right Sam, here's and updated drawing with 2 threaded rods...:joyous:
 

engine350400

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Hello all, As the summer is winding down its time to get back to the new boat. We have been out just about every nice weekend on the river in my first boat. It is a 73 sea swirl trihull. every time we were out there I couldn't stop thinking about the Bluewater, but the kid loves being out in the water so i put the boat project off for a bit. I had decided to go with 4 layers of 3/8 plywood for my curved transom. the first layer was almost a disaster. I made two of the clamps woody showed me, I made them way too tall and out of 2x4's, big mistake on my part I built them really poor now that I look back.

The 2x4's flat out did not have the strength to clamp like i needed them too. I am glad i mixed the resin at 3/4 percent as it was a 90 degree day. I had to screw blocks through holes already in the transom to help suck it up tight. I used pb and it squeezed out all the way around. I think it turned out ok despite the panic that set in as i was doing it. This is the point where I left it for the summer.
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engine350400

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Started back on it, I made two new clamps much shorter and out of 4x4 this time. I added the second layer of 3/8 ply with no issue at all. I didn't get a pic of the clamps in place but i will when i put the 3rd and 4th on. I ran out of cabosil and cant get anymore till tuesday. I glued the 3rd and 4th layer together with two layers of 1.5 oz chop strand. I put a screw dead center of the two while sitting on my saw horses and put a cinder block in the middle to give it a curve much like the transom. Then I added about 30 more screws the suck them together.

Does anyone have a sugestion of where to buy 5 gallons of polyester resin that wont break the bank? I ordered a pail from a seller on ebay and the resin was blue and took about 10 to 12hr to cure. I am looking into US composits for my resin.
 

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engine350400

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I got the last two layers of 3/8 in the boat with the help of a buddy. Also Got the key hole rough cut out. The thickness of the transom is just under 2 inches, without the final layers inside. I have not been able to find the specs for this 1987 omc cobra as I only have a selco book and it is lacking in that area. I have more cabosil on order along with 5 yards of 1708.

I am Kind of worried about drilling the holes for the transom plate, anyone have any tip on how to get the angle right?
 

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