Stringer and Transom Rebuild / Upgrade for 80s Ski Boat

Rebuilt and Modernized

This 1987 Malibu Sunsetter boat has been covered in other project categories as well.   The entire boat was reconstructed,  updated and modernized -- all of which started after rotten floors and stringers were discovered.  This project just focuses on the stringers, transom and floor.  

A decision had to be made once I discovered the stringers were bad.  I discovered wood rot in the stringers when I went to tighten a motor mount bolt, which screwed directly into the stringer, and just simply spun around without any grip.  From there I pulled up soft spots in the floor and continued searching for bad, rotten wood.  I found an awful lot.  These boats were ticking time bombs because they were simply resin over wood, very little fiberglass over wood floors, and then screwed and stapled together, which allowed water to penetrate the wood for over 20 years in this case. 

Malibu, and most others, did not start using composite (waterproof) stringers and floors until the early 1990s.  The Sunsetter is a phenominal boat that does everything well, and really helped Malibu get off the ground.  It was the first open bow Sunsetter and is a blast to drive on the open water.  But the cost to have a fiberglass shop gut and rebuild the boat exceeded the boats value -- so most boats like this get pushed to the side and left in a scrap yard somewhere.   That was simply not an option because we loved this boat.  We got to work and did the large majority of the work so that we could keep the boat, and improve it at the same time.

Phase 1: Removed the seats and strip the hull of all accessories
During this phase I found the seats were also made of wood, and also had rot.  They ended up getting rebuilt too, as outlined in the Wake Garage interior project (found here).

Phase 2: Removed the floor, the floor stringers and flotation foam
I used a skill saw and sawzall primarly to remove the floor and outer stringers.  It was an awful lot of work to say the least.  I also found loads of water sitting beneath the floor thanks to voids in the floatation foam.  20 years of slow leaks created a mess.   The outer stringers are primarily for floor support, unlike the center which provide primary hull integrity and the drivetrain stabilization.

Phase 3: Removed the engine and transmission
The motor and transmission were unbolted and removed from the boat.  The driveshaft, which was new, was left as it lay. From here all the extra floor and floor stringers and tabs were cut or ground out using hand tools and sanded.  This was messy and required air respirator filters.

Phase 4: Removed the structural stringers
Once you remove the main hull stringers you need to ensure the boat doesn't move or be removed from  its trailer.  The gel coat will crack as the hull will flex too much without the stringers present.  Even the dash, which was also held up by wood sides, had to be supported before we cut away the wood siding so it didn't fall and crack from the lack of support.  For this we used a 2x4 tower and strapped the dash to it so that it could hang without cracking.

Phase 5: Stringers and Transom Rebuilt / Modernized
We rebuilt the transom to be stronger and thicker to one day support a wedge.  The transom was again used out of wood and shaped based on the old transom's template, but was "doubled" in thickness. The structural stringers were also made from wood for its strength, and shaped to match the previous stringers exactly.  Both were wrapped and tied together with vinyl ester resin and heavy biaxial fiberglass materials.   Essentially we created a strong bond like a knuckle.  The strength from the new build far exceeded the original specs.  It was bomb proofed.  Additionally, a bulk head was added across the back, tying in the stringers and floor joist/stringers to totally seal the foam under the floor area once the floors were attached.

You can see my finger at the transom... notice how thick the material is and how the biaxial tape/glass connects the stringers to transom.  Even the floor joists were double layered for waterproofing and strength (ballast was gonna be added too).  I had Kevin McCarty (McCarty Marine) help with the fiberglassing expertise.

The final piece was the gelcoat, which was also added to the stringers and bilge.  Everthing went smooth from this place forward. 

Phase 6: Rebuilt the Floors using composite material and "plexus" epoxy
The floors were made from the same materials current Malibu boats use, "Space Age Materials" which is marketing mumbo jumbo for composite.  This stuff is 100% waterproof, strong and lightweight.  Instead of unprotected screws and staples from the original build, this time the floors were attached using plexus epoxy for a permanent bond without leaving holes in the floor.  

Phase 7: Floatation Foam was Added 
The foam was poured through holes in the floor and then sealed when it was done expanding.  This flotation foam sits between the floors and the bottom of the hull, this time completely filling all voids underneath.

Phase 8: The motor and transmission was reinstalled on the new stringers and re-alligned.   This time no bolt penetrated the double wrapped fiberglass wood, without being sealed in epoxy.

Phase 9: Reinstall new carpet and interior  (See interior project)

Phase 10: Complete assembly and enjoy a brand new boat

All in all, the boat came out even better than we'd hoped it would.  We wet sanded the gelcoat (another project here) and added new decals to tie in the shiny new hull and modern structure underneath.  

This was a large project but we love the results, and thankfully the boat went to MartinArcher who added surf gate, a Titan III tower and more!   Beautiful boat and I miss it for sure.