My tri-hull transom replacement w/ pics

[ezmobee]

Re: My tri-hull transom replacement w/ pics

Those drains are nice but having to flair them seems like a pain. I used the plastic ones on mine and properly sealed with 5200 they seem like they'll work great.

Nice work on the patches.

 

[Chuck Gibson]

Re: My tri-hull transom replacement w/ pics

Drepster,
I love the looks of your fiberglass work. In the near future I will be rebuilding my tri-hull and I dream of mine looking as good as yours.
Where did you get your aluminum fiberglass roller? All I have seen are plastic.

 

[drewpster]

Re: My tri-hull transom replacement w/ pics

I bought mine at a local supply store. But you can find them online. I have seen them on many of the fiberglass supply websites.

The place I bought mine is actually a manufacturer that sells to the public here in town. The interesting thing about them is that they are a small business that specializes in making baptismal tubs for churches. (Kick-Shaw if any locals are reading)

 

[Mickla]

Re: My tri-hull transom replacement w/ pics

Hi drewpster,

Great thread, I'm brand new to iboats and have gotten a lot of good info. If I did the attachment right you should be able to see I'm working on the same issue so I'll be revisiting this thread a lot. It's an old 15' Bonito that belongs to my father in law, he said if I fix it I can have it so here I go. I have never owned a boat let alone rehabbed one.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

I'm sure you probably addressed this, so I apologize in advance for asking this, but what type of plywood did you use?

I've got a '70 Thunderbird tri-hull and found a soft spot in the deck yesterday. I'm going to replace the whole deck, given the boat's age, but I don't know where to start. I've heard recommendations for marine grade, pressure treated, and CDX.

Also, as I'm a complete novice, what does CSM stand for?

 

[tallcanadian]

Re: My tri-hull transom replacement w/ pics

Marine grade or outdoor grade plywood is what you should use. CSM is chopped strand mat. It's a fiberglass cloth and is good to use on decks as well. If your going to replace the deck, check your stringers (main beams under deck) and your transom.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

Regarding the stringers: how are they attached to the hull? Glued? If so, what type? Do you then screw the plywood decking to the stringers, or attach in another fashion. The transom seems very solid to me, so I'm reluctant to go drilling into it.

I'm good with my hands, so I'll take on any task, but I feel way over my head on this one. Never even seen it done.

 

[tallcanadian]

Re: My tri-hull transom replacement w/ pics

Regarding the stringers: how are they attached to the hull? Glued? If so, what type? Do you then screw the plywood decking to the stringers, or attach in another fashion. The transom seems very solid to me, so I'm reluctant to go drilling into it.

I'm good with my hands, so I'll take on any task, but I feel way over my head on this one. Never even seen it done.

The stringers are fiberglassed to the hull. I know most fellas here say to use pl premium on the bottom of the stringer where it meets the hull, then fiberglass them. You will know once you get the deck up if they are rotten or not. Chances are, they are. I screwed my deck to my stringers. Some guys do, some don't. Some just PL Premium them. I screwed them before I glassed the deck. I also ran a strip of fiberglass on top of the stringer before i put my deck on. I should be good for years to come. As far as your transom goes just check for soft spots or cracking. Mine cracked at the top where the engine sits. It was also soft. And it was rotten for sure. Hope this helps.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

Thanks a ton. I presume you seal the stringers, just like you would the decking? What do you recommend for that? How many coats? And I presume you can use regular building lumber for the stringers?

 

[tallcanadian]

Re: My tri-hull transom replacement w/ pics

I used mat (csm) and sealed the stringers. The old saying is more is stronger but that's really up to you. I used just one layer on my stringers. My stringers were 2x4's and 1 2x6 down the middle. Most stringers are just plywood, some layered together. I was lucky enough to get kiln dried lumber. They were lighter and all the water removed. You won't know what you have for stringers until you remove the deck.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

By "mat (csm)" you mean you just fiberglassed the stringers? What about sealing the plywood decking before glassing?

 

[tallcanadian]

Re: My tri-hull transom replacement w/ pics

Your mat/resin mixture will seal the wood. Water will not get in.

 

[drewpster]

Re: My tri-hull transom replacement w/ pics

I used PL premium to hold the stringers in place. I tabbed them to the hull with mat and 18oz woven roving and covered the whole thing with mat. (csm)

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

Drewpster,

Did you seal your plywood decking? What type of plywood did you use?

And whereabout in TN are you located? I'm in the Memphis area, myself

 

[drewpster]

Re: My tri-hull transom replacement w/ pics

Sealed the bottom and the top of my deck. On the underside, I used poly resin and a light weight cloth. On top I tabbed it in place around the edges using mat and roving then covered the whole thing overlapping the edges. I built up the thickness of the fiberglass the same as the factory.
I used ACX plywood for my deck. I used marine ply for the stringers and deck but if I had it to do over I would use ACX for all of it.
(ACX $50- Marine $100) The only advantage I can see of using true marine plywood would be if I were building a wooden boat or if I needed a specific species of wood. I don?t see the advantage of marine ply as a fiberglass core. ACX is a good enough grade in my opinion.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

I know this may not apply to you, Drewpster, as it looks like you went all the way down to the fiberglass all over, but any suggestions on how to get the new deck to "mesh" with the sides? My sides look fine, so I only need to replace the floor. Should I fiberglass onto my old sides, or just resin the seam between the deck and the sides?

 

[drewpster]

Re: My tri-hull transom replacement w/ pics

I would tape or "tab" the seam between the new deck and the inside of the hull before coating the whole thing. It similar to taping seams in sheetrock work. You can cut strips to lap from the deck to the hull side. The double layer at the edges will strengthen the joint.
You can get CSM tapes or cut your own.
To make it look right tape the seam first then when you cover the complete deck only take the edge of the glass up to the seam. Or up the corner where the hull side rises from the deck edge. You can then clean up the rough edges with a grinder. Then it will soften the hump of the double layer. Avoid stacking the edges together like a stack of paper. Instead taper the edge of each layer by cutting each one back slightly.

tabbed seams

covered deck

Here is the seams at the hull side, you can barely see a hump here and this is four layers. The black lines in the resin are the cut lines I marked with a sharpie pen when I cut the glass. Notice they are not directly on top of eachother.

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

You've been a ton of help. This seems much more do-able now. What's your resin of choice? And did you use 6 oz cloth? I've heard I should use 8-10oz cloth for the new decking.

 

[drewpster]

Re: My tri-hull transom replacement w/ pics

Are you using epoxy or polyester resin?

 

[1970Thunderbird]

Re: My tri-hull transom replacement w/ pics

Open to either, but leaning towards epoxy.