Transom Rebuild

[Dukestor]

Well you guys got me motivated to tear into my soft/broken transom as a winter project. My 1989 Phantom had a crack in the splashwell which was opening up when I hammered the throttle. Got me a little nervous, so I decided to tackle the repair to be sure the XR4 stays on the back of the boat.

I took the path of cutting the splashwell out. Taking the whole cap off was way out of my ability, plus I plan to be fishing this spring. So the splashwell came off last week. First impression is that I was in no danger of the transom ever actually dropping the motor off the back. The fiberglass is unbelievably strong. Second impression is that I WAY underestimated how difficult it would be to get all the wood out of the old transom. There was no rot whatsoever, it was simply wet/spongy. So far, I've used a chainsaw, sawsall, rotozip, air grinder, and hammer and chisel. I've got about 15 hours in just getting the wood out.

My plan is to replace the transom and knee braces to at least as strong as it was originally built, repair the crack in the splashwell, and hopefully strengthen the area where the crack developed.

I need a little advice on materials to order. The original knee braces have a very heavy layer of at least 1/4" of fiberglass. It looks to me like they used some thick mat, covered with heavy 18oz cloth. I've been looking at the US Composites web site and they have a lot of choices. I think I probably need;

1/2 oz mat to go between the 3 layers of 1/2 plywood for the new transom

2 oz mat to build up the high strength areas

4 (or 6 or 7-1/2 or 8.5 or 8.9 or 10) oz cloth for covering the mat and used in tight corners (Which one?)

18oz cloth for the transom and top layer of the knee braces

Do I need the 4 or 6 or 8.9 oz S-glass for anything?

What about biaxial?

Appreciate any help from the experts.


Here are some pics of progress;














-Duke
1989 Phantom Panther
Merc 150 XR4

[ranger230v]

Hey Duke, Welcome to Hell...just kidding, if you got the time and the interrest then this type of work is actually a pretty cool. It's educational at the very least. I'm know expert on this stuff, so I'm a little hesitant to give advice.
I used all 45 deg biax on my rebuild. I was told it's stronger than reg cloth. You'll need about 3 lbs of wood flour for making glue and fillets. There's a good tutorial on boatbuildercentral for this type of work.

Good luck and keep us posted

[cart7]

Wow. Those are some serious cracks.

looking good so far. Keep the pictures coming as I've got a similar job to do on my Champ and can't decide which way to go with it.

[Dukestor]

Did you use 12 oz. or 17 oz. biaxial? Any idea how thick it was after layup? I want to get at least 1/4" on everything, but I'm not clear on how may layers of mat/cloth that will take.



Thanks,
-Duke


Modified by Dukestor at 10:01 AM 1/13/2009

[Dukestor]

Does anybody know the real story with Marine grade plywood? I can't find it anywhere in Nashville in 1/2". I did find 3/4" for about $125/sheet, but I need 1/2". I've also found 1/2" BCX for $23/sheet.

Next best option is to mail order some marine - for somewhere between $65 and $130/sheet depending on grade (plus shipping).

Can I get away with just using the BCX and not drilling holes in it?

-Duke

[ranger230v]

When you glass in the transom... you start with 12oz biaxial tape around the edges. 3 layers offset. Then you use 1708 biax across the whole thing. 4 layers of 1708 will be 1/4" thick. 1708 is 17oz biax with fiberglass mat stitched to one side. the first layer you cut is 3" over the second layer is 6" over and so on so that when your done, you have stairstepped out 12" onto the surrounding areas.

All you need for this type of work is marine grade Fir plywood. They don't sell it in home improvement stores usually. In my area they have a couple of large plywood/lumber yards that cater to contractors and cabinet makers. This is where you want to look.

[Dukestor]

Thanks Ranger. Is BCX Fir the same as Marine Fir? The Lumber yard has BCX fir.

Also - (Question for anyone) What can I use to 'paint' the new fiberglass black? Can I use black coloring agent mixed in some leftover epoxy and just 'paint' it over the work I've done? I believe I can also buy some black gel coat and do the same thing. Anyone have thoughts on this?

Thanks for everyone's help so far - I've almost got all the old wood dug out. I wound up pulling out the old decking under the fuel tank and batteries as well - it was also rotten - original builder had only put mat on the top - bottoms were exposed...

Getting stoked about putting something back in my presently demolished boat.

[BASSCAT7]

You can mix a coloring agent in with the resin you are using to make it black.

Something along this line. Click on the product info tab for the colors available.

http://www.jamestowndistributo...=2078

[ranger230v]

I think marine Fir comes in ACX and BCX. The salesman should be able to tell you if it's marine grade. The price tag should also tell you. Sorry I have the memory of a gnat, but I think mine was around 80 bucks for 3/4". It should also have at least 8 plys.

[northrivergeek]

Dont buy that garbage about needing marine grade for transoms , and stringers , you dont need marine grade, yes you can pay 100 a sheet for it if you want.

But marine grade wont keep rot from coming back, what will is sealing up all wood with glass and resin, and marine caulking any water water can get access to bare wood. All you need is A/C or B/C exterior grade plywood its about 30-40 a sheet .

Rot happens when water is trapped and gets no air to dry, no matter what wood you use, even pressure treated rots after enough time.

the wood in you boat your removing was not marine grade, nor do you need it now, Quality fiberglass work,and ventilation will keep you from doing this again for at least another 20 -40yrs


And if your support stringers are gone Id bet that all your wood needs replaced not just transom

[Dukestor]

Thanks,

I called two local marine repair shops last week to ask where they get their marine wood, and they said "Home Depot". Both said they use plain old exterior plywood, and just to be sure my new wood is sealed up good. I've found BCX locally for $25/sheet, so it looks like that's what I'll use.

So explain 'ventilation'. Are you saying I need to leave some of the wood exposed to 'dry'?


As for the rest of the boat being wet you're probably right, there were holes all over the place along the stringers where they'd screwed things together before laying the glass. But I'm not going any deeper than the knee braces other than maybe adding a couple layers to the rear parts of the stringers now that I have everything stripped bare. From what I can tell there isn't a lot of strength in the 'wood' anyway - It seems the wood's more a 'form' to shape the fiberglass into place than anything.

Now if I can only get my wife off my back for spending every free moment in the garage these days...

[northrivergeek]

DONT Use CDX get either A/C or C/D grade exterior ply CDX is not as strong, the inner cores can be any kind of wood, besides pine, unlike the other it is the same on all layers.

Ventilation - as in air flow vents the pull fresh air in and out as your going down the lake, and I also put 2 small vents on the wall near the live well / and storage boxes.

So that air circulates all over the inside of the boat, just make sure you dont cut into the live well, or boxes

[Skeet'r89]

Yes there is a difference in marine ply and regular cdx or what ever. Marine ply has no voids which make it stronger than regular ply. Marine ply should be used for transoms where the extra strenght would be needed. Regular ply can be used for floors and such where true structural strenght is not an issue. Yes both types will rot equally as fast. They are both laminated with the same types of glues and need to be sealed properly to prevent rot.

[Dukestor]

Decided to go ahead and rip as much of the old wood out as possible. Glass and epoxy arrived from US Composites this week. Also decided to go with with some A-C Fir I found locally.

Here's some pictures of the naked shell and the knee and cross-brace mock-up.

[DG]

Hey, I think that's what they build them Allison boats out of to make them so light . Looking good!

[22R]

Yep, but ya never hear of anyone rebuilding Transoms in Allisons built since the late 80's.
Looking good on the rebuild !

22R