Introduction
 

I hope you guys don't mind, I am not a Seacraft owner. Simply a C-Hawk owner. This seems to be the premier forum for rebuilding boats, and my googling brings me back here time and again. I figured it was time to join. I'm putting a new transom in my C-hawk 245 right now. 2 layers of 3/4 Coosa 26, and 4 layers of 1700 planned. Using Raka epoxy.

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Seems like a powerful endorsement of the boat building knowledge of the forum members. Confirms that Seacraft owners are one friendly, talented bunch!

Welcome aboard!
Good selection on the Bluewater Coosa. The same was just installed in my rebuild and I know how much that stuff costs. The good news is that it's worth every penny.

That's a nice looking boat. Welcome to CSC. Bet its going to feel good to get it back on the water.

Rob

Thanks guys, I cut her apart last monday, so I am making good time. Any suggestions on the best way to reattach the stringers? I was thinking cut them at an angle and scarf a piece of coosa to them. Then two pieces of coosa against each side, sistered to the current stringer to provide additional strength.

sounds like a good plan on the stringers looks like your doing a great job

I'd build knees from the bottom of where the deck would be and tie them right to the stringers. An for hells sake cover up that pretty motor with at least a garbage bag before DonV comes and takes it!

Welcome aboard, beautiful boat and nice job there

Thanks guys. Motor is covered now. Maybe I don't understand what a transom knee does. Mine go from above the deck, and are glassed into the stringers. My stringers are full height from the bottom of the deck to the bottom of the hull. If my knees ended at floor height it would just be a bigger stringer. Also, I got ahead of myself worrying about knees and stringers. More importantly how many layers of 1700 bi-axial should I use for the inner skin, and how much should each piece overlap? The previous inner transom skin was about a 1/4", made of woven and mat. I assume 4 or 5 layers of 1700 will be much stronger, but thinner.

This might help - it is a page from my notes about various glass materials:Attachment 14974

Pat that just made me depressed. 9 layers of 1700 to reach 1/4". I don't see that happening for me.

Thick is not necessarily strong and vice versa.

You are using 1700 which has no mat so it wont be as thick and you are using epoxy (I have been very happy w Raka) which is the right answer for biaxial without mat. I used alternating layers of 1708-1808-1708-1808-1708-1808 on the inside of my 1.5" thick Coosa core and it was almost too thick and caused fit problems. Plus it was heavier than I needed and expensive. I wish I had used glass without mat (1700 or 1800) as it would have been lighter, cheaper (much less resin), thinner and almost as strong (mat is not strong but it provides a good adhesion layer and separates the biax layers; kinda like core).

You should do a small test layup - maybe a foot or two square on something like cheap 1/4-3/8" plywood if you want to understand how strong the glass is. Rotate alternating 1700 layers by 45 degrees for a more uniform directional strength. Jump up and down on it and watch the plywood separate if/when you finally get it close to failure - that's one reason you are using Coosa. 6 layers of 1700 is ~0.180(vac layup) - ~0.20(hand layup) and scary strong. A 1.5" core separating the inner and outer layers is like an I beam with strength in all directions.

Thanks Pat. I know it is strong, I only worry about the thickness for the motor mount bolts. The DF300 is 610 lbs, I thought I needed thickness to resist the bolts trying to pull through.

Just got back to my room from the Arlington Cemetery visit and what do I see?? A 300 hp Zuke free for the taking??? :)

Add 3-4 layers where the motor mounts - not the whole transom. :D

And put a Honda box over that motor so Don thinks it weighs about 900 lbs

Transom is in. I went with 4 layers of 1700. When I build the splashwell/transom knees I'll run another layer or two of quadraxial in the center 1/3 of the transom to provide thickness for the motor mounting bolts. Attachment 14979

I`m putting Ficht stickers on the skinny girl`s OP`s.
Those scumbags from Miami will drive right by.

Or paint 'em gray and put HPDI on 'em. It's like a "Force Field".

Maybe a Wish You Were Here album print on the back???
Fire ... dut dut dut.

You have not lived until you have seen a Ficht bomb lose their injectors and launch
a cowling a hundred feet in the air...

Soros is such a POS. His engineers told him not to launch them...
Many generations of hard working shops lost everything to that
asshole.

Your using two 3/4 cossa boards and then 4 layers of 1700 and your worried about bolts pulling threw? I don't think you need to worry.
I have seen too many heavy outboards out there bolted up with four bolts with small washers on two 3/4 layers of pine bc grade exterior ply that only had a few layers of matt only on the back side. Some how they seem to not fall off into the drink.
Yours seems to be well done and if you use large fender washers or large square washers like use in the electrical field on power poles and strut hangers to spread the load out some you will not have an issue.
On my 20's bracket transom ear I used 4"x1/4" anodized aluminum flat bar to help spread the load of the outboard bolts which is over kill.
You can even take the 4" flat bar and cut 4x4 squares out and use them to back the bolts as washers to spread the load out but that coosa is tough stuff and you shouldn't have much compression issues with it.

Thank you
 

Thank you Frizzle. I don't really know how biaxial compares in strength to mat/woven for pull through resistance. I do have backer plates already.

It is stronger - the biax fibers are all straight rather than random curves (mat) or kinked in the weave (woven).

Great thread. Please keep posting pictures of your progress when you tie the stringers into the transom. Thanks.

Bikecop I will hopefully tie them in today. I was attempting to make 12-1 scarf joints and then sister a piece to each side. Unfortunately that is beyond my limited carpentry skills and patience. The current stringers have a 3" step in them for running hoses. I am going to fill this step in with a piece of coosa, and then sister a piece next to it. Everything will be grinded clean ahead of time, tabbed in with 20 oz triaxial, then overlaid with a couple layers of 1700. The pictures are of the mock up only, I want the butt joint to be 20x as long as the stringer is thick, so that sister piece to the side should extend at least 8 inches past the joint.


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Cap glass
 

I was unable to get my transom inner skin to lay gently over the top of the transom. My plan is to grind back the top and of the outer and inner skins, give myself a nice radius on both sides, and lay strips of 1700 over it. I am not planning on grinding enough back that it will be seamless. It's a 25 year old chawk and I value strength over looks. If this or the stringers in the above post look to be a mistake please speak up.
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I got the first stringer glassed in today. Tabbed it with a layer of 12" triaxial, then 6" biaxial. Covered the whole thing with a single layer of 1700. I struggled with air bubbles today for some reason. I'm not sure if it was the high humidity, overconfidence, or if I just didn't prep enough.

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Update
 

All stringers are in, I added splashwell walls and glassed them to the transom and main stringers, effectively making them huge transom knees also. Floor is mocked up. The only problem I am running into is the floor has to span a large distance without support. About 35". I was debating between doubling the coosa in that section to stiffen it, or adding a mini bulkhead. The bulkhead would be a 6" tall piece of 3/4 coosa tabbed into both main stringers. The bulkhead would hurt my bilge access so i am hoping to avoid that.

Put some 28x4 pieces of Coosa (ribs) with the edges beveled at 25-30 degrees (yeah - the shallow angle that is hard to cut with a circle saw) on the bottom of the 36 inch coosa panel after you put 2 layers of 1700 on it then put 2-3 more layers of 1700 over the ribs. make sure all the layers of 1700 go completely to the edge and tie together. It is a good idea to put a layer of glass wrapped around the edges of the 36 inch panel first or to wrap the top layers around so you don't end up with the edges in shear with no structure.
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Thank you Pat.