Transom/engine bay repairs

[HPwannabe]

Hi all,
I started this adventure with a thread on the Mercruiser repair section, but now I'm doing hull work so I thought I'd get a fresh start. I know there is a lot of information out there regarding transom/stringer repairs and the like, but I have a question about a specific aspect of that. I'm trying to do a "partial" transom rebuild - see the pictures. I've opened up a portion of the transom, and trying to remove material from the areas beyond the opening well enough to stitch in new material without having to gut the whole transom. The transom is in good shape from about the midway point up. But the rot goes all the way to both sides in the lower areas. I think I have a handle on this... I'm intentionally limiting the repair so I don't have to gut the whole cockpit. And, yes there is some rot in the stringers that I'm not going to be able to address. But overall, the stringers are not it that bad a condition, and this is an old boat that seems like it was overbuilt - the glass on the stringers is extremely thick, I'm not too worried about a structural issue there.
The little question I have at the moment is what to do with the area in the engine bay where there was an "inner bottom", which I've removed (see pics). There was a horizontal board fiberglassed in the bottom that created a small "sub-bilge" area below this false bottom. I've removed it up to the bulkhead separating the engine bay from the area forward of that which houses the fuel tank.
My question is, does this inner bottom need to even be replaced? Is there any real structural element provided by this board? Is there some reason I can't leave it open to the hull there? What are the pros and cons of replacing this board?
The first picture is prior to removing it, other photos are after.

 

[kcassells]

Restraint says I! from commenting. Im sure someone here will have an idea.

 

[Chris1956]

Gee, that board that bridged the bay looks to have 2 motor mounts on it. I am not sure of the function of the rest of the board. Sometimes they would mount a bilge pump on them. That keeps you from putting screws into the hull.

 

[Scott Danforth]

I recommend getting all the rot addressed. the bacteria that causes rot does not stop, and introducing new material simply gives it more food.

the side foam flotation boxes outboard of the motor are most likely full of wet foam and mildew 9have been on every boat I have opened up.

 

[HPwannabe]

Gee, that board that bridged the bay looks to have 2 motor mounts on it. I am not sure of the function of the rest of the board. Sometimes they would mount a bilge pump on them. That keeps you from putting screws into the hull.

Yes, it makes a nice flat surface for the bilge pump. The motor mount was a transverse 4x6 that I installed when we converted from a straight six to V8. The last 6" or so of it on each end was sitting on the hull, the part between that sat on the inner bottom board. I can re-engineer the engine mount system to be fully supported by the hull only. I'm just curious what other boats typically have in them, and whether this is in any way a structural thing.

 

[HPwannabe]

I recommend getting all the rot addressed. the bacteria that causes rot does not stop, and introducing new material simply gives it more food.

the side foam flotation boxes outboard of the motor are most likely full of wet foam and mildew 9have been on every boat I have opened up.

Thanks Scott. I have agonized over this for a long time. I've done the full tear-out and reconstruction on two previous boats. This boat is 54 years old. It's a family heirloom, but there is no one after me who would take it over. After I'm gone, this boat will wind up in a landfill somewhere. I want to give it another ten years of life. I am not into a restoration effort. I simply don't have the time or inclination to take on such a project right now. I'm pretty sure I can make the transom solid, and I have a plan to treat the stringers with something like CPES. To tell the truth, I'm not sure this boat even has flotation foam in it. I may do some exploratory drilling to see what I can find.

For reference it's a 1966 Slickcraft SS235. Pic below. A very solidly built boat. The amount of rot in the transom was actually quite small compared with what I've seen in boats half this age (it was garage kept for a long time, and after that has been stored in a covered lift, so it only got exposure to water when in use). But yes, it's there, and I know it spreads. I know it's "best" to remove all rot. But in this case, I'm going for a "good" result. Also, the boat never goes offshore, and rarely sees anything more than a light chop.

 

[HPwannabe]

A follow up on the issue of flotation. Drilled a hole in a stringer (where I drilled was rock solid) and sure enough it is empty. See pics. Should I pump foam into these spaces?