Front motor mount stringer 1987 Larson 16ft

[Ted-2025]

The wood in the rear motor mount stringer has rotted. The front engine mounting bracket is resting on a rectangular piece of plywood under each foot. Don't know why these were put on top of the fiberglass cover that is over the wood stringer. The fiberglass does not appear to have compressed down and looks as if everything is ok until you reach underneath and find the wood has completely rotted under the bolts. Maybe they put the plywood pieces under the feet because the bolts were no longer holding? The motor mount stringer is simply a rectangular piece of wood, maybe 1 1/2 inches thick that covers an area over the bottom of the boat but does not reach all the way to the stringers that run fore and aft, that covered with fiberglass. The stringer is just wider than the feet and runs a little less than half the distance toward the back of the engine. It has to be cut out and replaced and fiber glassed. Does anyone know what the original design of the stringer was (thickness of board, type of board (?hard wood) and shaping involved before it is glassed over) and width and length. Strength to hold engine in place and at the proper height is important for alignment of engine and holding the engine in place while under way.

If anyone knows of any design charts of the boat that might be available that would be a great help in this task and the rest of replacement of stringers and flooring as well as placement and support for items like gas tank and battery.

Any help is greatly appreciated. Thanks, Ted A.

 

[bondo]

If anyone knows of any design charts of the boat

Ayuh,..... There's no such thing,.....
I'm guessing the plywood shims, are just that, shims to align the gimble bearing,....
The motor mounts should be lagged into the wood under the plywood shims,....
If you use hardwood to replace the rotten motor mounts, use a rot resistant species, like black locust, or boiled white oak,....
Other wise, most are laminated plywood,.... including the stringers,....

 

[Ted-2025]

Thanks bondo, stringers in the 1987 Larson appear to be solid wood although I do not know what kind. Unfortunately they did not completely cover them with cloth and resin, only 6 inches up. The uncovered part rotted and was continuing down. Motor support stringer was not covered on the bottom, thus rot. Any guess where I can find black locust (I guess 1 inch thick?)? Do I need to put some padding between the fiberglass and the motor support bracket feet?

 

[leaky]

Pictures would probably help.

Unfortunately a lot of boats just aren't built very well, things like this are common.

Coosa is a material which is basically a synthetic plywood (the 26 lb Bluewater version especially is made to replace plywood), which can be fiber glassed about the same, but will not rot, and will not soak up water to any appreciable degree, which makes a repair like this a lot easier. Some places sell half sheets, which may make it cost effective for a small project.

Also something to consider is, if the stringers are outboard of the engine, you can possibly mount something to the stringers to carry the engine, depending of course on if the stringers are any good for this, if the bracketry can be created. I know more about inboards, but with those it's very typical to mount something like a 4X4X1/2-inch piece of angle (or 4X6, 6X6, whatever works, sometimes in 3/4 thick), sometimes with a little welding, directly to the stringer by through bolting. Then the engine through bolts to the aluminum brackets.

 

[Ted-2025]

Leaky, will 26lb Bluewater Coosa hold Lag bolts? My current thinking is to make a 15in by 15in by 2in thick composite using epoxy and wood powder to hold the lag bolts and volcanic fibers for strength. Do you think this would work considering the vibration of the engine and the pull on engine thrust?

 

[Roadking57]

I hate to be the nay sayer here but my motor mounts in my 1988 regal sebring VBR were rotted. Further investigation and the transom was the same.
I got lucky and my stringers were okay. They were covered good. Even the seat wood was crumbling and the side covers around the bow where wood was used was all crumbling. This boat was kept inside its entire life in one of those 3 high stacked marinas. The seat vinyl was all in great shape.
I found an independent shop that replaced both the transom and motor mounts for around $2,500. He used marine grade plywood which will outlast me. That price was after I removed the engine and bellhousing/transom plates.

Figure out if the boat is worth it to you then let a professional repair it. They know all the materials needed and you will have a great boat once you are done. It will be way less expensive than purchasing a newer boat. Yes it will rob you of some time so lots to consider.

I've got about 5k in my boat not counting the time.

Good luck to you.