Stringer/motor mount repair

Replacing the stringers and motor mount supports due to soft/wet wood. Was some of the black rot in the starb side and bulkhead. The boat has a high self bailing deck and the stringers are stepped. The bottom is 1/2" thick at the through hull fitting. Unfortunately, there is no glass guys local to me so hoping to hear from individuals with some experience that can help me out. Haven't decided which is the best way to tackle this so open to ideas as well. Leaning toward making the taller step into a full height stringer in addition to the shorter one and box it in. Would help stiffen things up in the event the maintenance of an I/O got old and a pod with twins wanted to be added down the road. Only going to tackle from rear bulkhead to transom at this point so I don't lose the whole season. Was fortunate the transom was resin coated so it had no water intrusion. Was going to order up some marine grade 3/4 for the frame work. No idea what to get for cloth and resin. Inputs would be greatly appreciated.

Look up friscoboater on YouTube and watch his repair. Really comprehensive video log of a major repair similar to yours.

I did a small repair of a piece in our bilge and used cloth over plywood with west systems epoxy. Really easy to mix up and work with. Not cheap though.

1708 biaxial glass and epoxy, shop the net, west system, Jamestown total boat, MAS epoxies all good.

Thanks guys! Not sure about the shipping involved across the border with the epoxies so will probably just keep it simple and go with a local supplier. 1708 looks to be what I will be going with for the best part of it. Watched a bunch of the Frisco vids. Picked up quite a bit and they will come in handy going forward. Hoping others inputs will as well.
This whole project started with a simple but not so simple transom assembly rebuild. Needless to say, although that part of it is all stripped, painted and ready to go back together, I have to get this problem behind me first. A big "Hopefully" only 1 more boat buck before she's back on the water.
In the first pic I posted, there is a small piece of 3/4" plywood that was used as a spacer under the motor mounts. The mounts are mid way through their adjustments and I am planning to build up the bases enough to eliminate those spacers. Seems to just add to the complication of trying to seal it all up. Is there a reason for them (spacers) that I am missing? Just to the right of that spacer in the above pic, you can see where the engine mounting screws are anchored. Under the glass there was another piece of 3/4" plywood sitting on a piece of 2x6 laid flat. Wasn't really tied into anything other than the 3/4" vertical stringer and supported by foam underneath it. The 2x6 looks to be a hardwood. Any ideas as to what the best choice of wood would be for that? It was not resin coated. Would a composite material be a better choice? Have also been contemplating the idea of spacing the lower stringers out more and just glassing in a reinforced ear to mount the engine on. The extra 4" on either side of the engine down low would sure be nice.
Will attach a couple more pics of what I am dealing with to help you all get a better idea. Keep in mind this is a custom build by Sea Ray as I understand it. It has a one piece high deck with the fuel tank rising up underneath it. I do not want to chop up the deck at this point to fully remove the fuel tank. Going to try to slide it forward into the cabin enough this weekend to address the stringers ahead of the first bulkhead. It is a 100 gal L shaped tank with limited access. There is no indication of water in the cabin. It appears it has entered the hull behind the cabin below the rear deck. Have to love these old boats.
Appreciate all inputs. Want to get this done right but getting it back on the water in a timely manner is important. May have to address anything too much more that will limit that window next winter.

Well probably no surprise to anyone but the engine mounts were only the tip of the iceberg. Going to be going a lot deeper due to structural concerns than what I was initially hoping to. Anyway, it is a solid well performing hull and I would like it to be around for many more years. Was pretty disappointed with what I found with the finish work during it's build, but it is what it is. Will post a few of the big problems I found to enlighten others in the event they are looking at some of these older boats.
In the above pic (bulkhead removed) you can see where the main stringers were not tied (or capped) into the lower deck. It is the case for the full length of both stringers forward through the cabin and the joint is covered only with carpet.
The carpet in the cabin was laid before the rear cabin walls were put in and is actually sandwiched between them and the deck. Water seemed to have followed the rear cabin walls down to the lower deck and into the stringers. It all seemed to eventually work it's way to the bilge so little to nothing it trapped in the floatation.
There is a couple upper rear deck supports on either side of the fuel tank in the engine compartment. They look to be inline with the high step of the stringer except there is no stringer to support them. Just the plywood deck and floatation under that. (They will be added)
Under the fuel tank, the narrow piece of wood was not completely sealed either with a few open holes. It to is rotted and has water trapped under it. Ended up removing the tank so everything below it too can be replaced.
The tank is overall in great shape but it had two spots where there is some corrosion. The large one is actually just on the surface where the wood wasn't covered. It can be cleaned up with little effort. There is a smaller spot though where a screw was laying that had warn into the tank a bit. Going to try to find a local shop to build it up if possible. Not sure if that will add a stress point for a crack later or if there is some sort of cement that might be a better option? Anyone have experience with that?
Putting together a glass order. Another question about it. With 1708, I have the impression it is a heavier material. When covering the stringers and deck, is one layer enough or should I be ordering enough to do it twice? There does not seem to be a very thick layer on it now.
Thanks for any input.

Dug deeper on the weekend. Both inboard and outboard stringers (starb side) were pretty much all dry rot as well as a small section of the transom where all the mounting screws came through for the trim tab and it's cylinder anchor. Got it all cut out to sound wood and pulled up the floor under the fuel tank. Will open up the port side next. Not holding my breath but hoping it won't be as bad. My hats off to the glass guys. This is not the kind of thing I would want to be doing every day. Found a couple areas where the resin was light. Not sure what to do with it if anything. Light grind and a layer of resin maybe? Survived 38 years like this.

Getting closer. Was able to get the fuel tank welded. Talked to Rust-Oleum, and they recommended their 3800 as a better corrosion protection for this application. Kind of looks similar to what might be on there now. It, along with the glass and pour in floatation is on the way. Repaired the soft spot in the transom and roughed in the stringers and mounts. Changed the engine bed and mounts a bit. Doubled up the bed stringer and raised the mounts to eliminate the 3/4" spacers. Left the bottoms open so mounts could be thru bolted. Hopefully that doesn't turn out to be a mistake. Planning to fully glass in the engine bed/stringers and mounts. Just going to treat the hidden framework with resin and tab one side with glass.

Nice work. My first boat I owned end up having the same issue. I did the exact same thing as you. It was quite a bit of work. I don't envy you!

My son just bought a 1986 Marlin ski boat for $1,200. It's in great shape on the outside but has some stringers that will need to be attacked. The previous owner is a good friend of mine and he suggested aluminum instead of wood. That didn't seem like a good idea because the engine mounts might wear through those and I don't know how well the fiberglass would stick to the aluminum. I would LOVE to go all glass like the Sun Runner's did back in the 70's so there will never be an issue with rot.

Looks like my future so I'm watching carefully!

I was interested in looking at a 53 Navigator that came on the market in our marina. It 'looks' gorgeous and has had a fortune spent on it in cabin upgrades. I ran into one of the long term liveaboard tenants that knows of all the skeletons buried in the marina and he gave me some very interesting 411 on the boat. Turns out that it has been plagued with termite issues in the stringers and the only fix had been to kill the termites and squirt super penetrating epoxy into the stringers. Needless to say I lost all interest in looking at buying this boat! Its a shame but I couldn't imagine the scope of the job as there would be no alternative to gutting the entire boat and literally rebuilding it from the stringers up. Some poor sap will end up getting a "great deal" but it wont be me!
I admire your enthusiasm in keeping this old classic alive.
Carpe Diem

Nice progress you're making there, Thornton. These are always "bigger" than first appear, right!

Just an fyi... if you haven't already installed the tank, it's best not to use foam. Even though you are coating the tank, coatings can crack over time. With the foam against the tank, it will retain moisture, leading to corrosion. An aluminum tank is a good material - but it needs an air gap to "self protect" itself.

Thanks guys.
LD, although it may not look like it in the pics I posted, the tank wasn't originally foamed in. Probably the reason I was able to save it. The wood under it had not been completely glassed and was wet and starting to bulge a bit. Surface corrosion had just started where it was contacting the wet wood but was nothing more than surface. There was a spot a screw somehow got under it and was wearing it thin. Had a local welding shop build it back up for me.
The project is moving along a bit slow but still making some head way with it I guess. Tank is cleaned out and painted. A bit of a bad color choice but it is going under the floor anyway. Thought it was closer to original but turned to be a safety yellow. Have every thing in the bottom framed in and compartments sealed up. Applied a coat of unwaxed resin over it all to keep it that way. Hoping to start laying the 1708 within the week. Here's a few more pics. Sorry, they didn't seem to want to load in their correct orientation for some reason.

Started glassing and tabbing the motor mounts but having some problems with getting the 1708 to make the tighter outside bends. It does not want to stick to the inner edges of the motor mounts and bulkhead cap due to the tight folds. Does anyone know of any tricks with this stuff or possibly a better material to use in these areas? Hoping to get it all sealed in before the end of the month.

Make an epoxy peanut butter with cabosil and mold it into the hard 90 corners and joints. Once you have it setup, then lay your mat down. The mat will lay much better on a radius.

douglee25 said:

Make an epoxy peanut butter with cabosil and mold it into the hard 90 corners and joints. Once you have it setup, then lay your mat down. The mat will lay much better on a radius.

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Thanks for the reply. It is actually the other corners I was trying to refer to. Trying to wrap around the cut edges of the plywood on the mounts and the top of bulkhead. The corners are bevelled a somewhat. It just seems to keep lifting on me. May try using multiple layers of lighter fabric. Was wondering if anyone had any tricks to do it with the material I have now.

Lighter will work. Strand will also work better initially.

1708 can be tough to get it to stick on an outside edge when the radius is small. I'd make it at least a 1/4" radius - won't hurt anything at all to go larger, either. Then, you just have to stick with it while it starts to setup and keep pushing it down.

You could even try clamping the cloth to the vertical - to keep the cloth tight to the radius. Use a piece of wax paper then a length of wood to span the the vertical from left to right (to spread the load of the clamp and keep the tension even) and clamp on that length of wood.

Thanks guys. Will look to increase the radius on the mounts and try the wax paper, wood and clamps on the bulkhead. The rest seems to be laying out nice for me or at least was up until a liter of resin was tipped over.

Increased the radiuses on the corners and the 1708 seems to lay pretty good now. How many layers do you guys think should be used on the mounts? 3 layers with a 4th on the top be enough? They were built with doubled up 3/4 plywood glued and screwed.

3 - 4 should be more than enough.