plywood rotting in transom - grp boat

in my fibreglass catamaran 16 ft boat the ply in the transom has rotted away. It has a 1/4" glass then 3 x 3/4" ply glued together then 1/4" glass,(hope i explained that alright LOL) anyway the ply has rotted away at the two outer sides (of the transom).

i am not too bothered as i was going to change the drive of the boat from a small outboard at both port and starboard to one big one in the middle, so i was going to add a bit in the transom anyway to 'clean' the water away from swamping the engine in the middle, so it will be stronger if made in one piece.

I have to check with all you builders and designers before i get the angle grinder out and ask if there is anything i need to know before attempting this procedure. I have repaired wooden boats all my life - and i have also repaired fibreglass - only holes - , but this is a fast powerboat and the last thing I want to do is to knock the boat astern and look back to find no transom, LOL!

so any advice is welcomed

thanks

brian

 

I had the same problem several years ago but mine was a 19' Skeeter bass boat with a 150 hp merc outboard. It was a used boat only 8 years old but used extensively for tounaments. I had gotten several estmates after I hit a rock that never used to be
there cruising at a speed of about 35 mph. You could have imagined what kind of a shock that was to me and on the boat. let this also be a small testimonial to fiberglass construction. Surprisingly to me, My motor was still mounted, my prop was a mess and my lower unit was not damaged except for a sheared rip about 3'' long but still had forward, nuetral, and revese much to my amazement but I was able to drive the boat five mile to are campsite ( at low speed). To make a long story short... I inspected the damage once pulled out and found that the threw bolts had been pulled in , embedding themselves a good 1/2'' into the transom. At that point RED flags flew high
I suppose if it were not for a rotted transom I may have lost motor, Transom and quite possible injury or life.

THE FIX... the boat was'nt worth the $3500 dollars to have someone do it nor the deductible to have my rates rise so I did it myself. After starring at my boat for a week with head in hand, I went for my grinder! I cut the top cap or gunwale just behind the the rear platform at a stratigic location to achieve the straightest line
possible from port to starboard and once I cleared the interior fiberglass from the
transom I had no transom. It was literally mush. A 2'' putty knife and a shop vac
cleared my transom in about 1/2 hour time.I picked it out in handfulls.

Once clean and to the hull I made a pattern with card board of the entire transom.
Trim and check, trim and check, trim and check.I used (2) peices of 3/4 '' marine ply
a 1/4'' more than the original. Once fitted ,I glued and mechanically fastened,Screwed the two peices together and wrapped with glass . then glued and screwed into place
threw the hull and bottom of boat to acheive a full perimeter of good connections then to the finish layers on the inside I had plenty of areas to acheive overlaps from all directions then to the fairing on the exterior of plugging finishing and gel coat.

I enjoyed myself doing this project so much That I gained a new confidence and addicted myself to a new level of craftmanship. I still own the boat and that was five years ago. She runs outstanding,her hole shot improved and she does'nt chine as bad as she used to at high speeds. Just might have been the best rock I ever hit . I made the tournament the weekend she was finished . Oh! I forgot to tell you it cost me $600.00

Just do it! The grinder's waiting.
donjames

 

Ya, just do it. Use a respirator/googles and lot of clothing when grinding. Hose her out, toss the clothes in the washer by them selves and head to the shower. HeHe A good grinder helps. Do the work from the inside if you can. If rot is the only problem just put back what you take out, plus some for new loads you plan on adding. If it ain't sound fiberglass grind it out. I used treated ply for mine so the rot will take longer next time, and there are option to wood you could explore. The first transom only lasted 30 years.