1976 170 replacing floor

[sfmudder]

I am starting the replacement of the floor in my '76 170. All indications show that it is all original and rather decayed! The port stringer has actually broken in two different places and no appearances of delamination, starbord stringer looks to be in excellent shape. At some point prviuos owner replaced the fuel tank and mounted starps in the tank coffin by putting 3" long screws through the side of coffin and through the stringers, and of course, upon inspecting the port stringer and removing foam the inboard wall of the stringer has 1/2" plywood which runs from just short of the casting deck back to about 12" behind the cross support to other stringer? I've not seen any mention in any of these threads. With that said, my plan is to:
                    finish removing the tops of stringers
                    remove the plywood
                    repair port stringer
                    Replace the tops of both stringers
                    Repor the foam
I appreciate any thoughts and history on the plywood inside of the stringers.

[RickK]

Hi SF,
I can only think that the plywood was added when they moved the fuel tank below deck and to give a place to secure straps for the fuel tank.  We have been seeing more posts about having wood inside the stringers. I didn't have wood in mine when I pulled them out, but my fuel tank was above deck inside the console.
I don't know if there was a solution later on for securing the straps, like thicker glass or ??
If the plywood is still sound and encapsulated in glass, I'd leave it. You can re-use the connection points for securing your fuel tank but through-bolt the straps. If the wood is compromised I would remove and I might think about re-using plywood for the same purpose. I'd resin coat it and stick to the inside where you need it. I'd slightly over-drill the holes and coat the inside of the holes with resin.  Then re-drill at the smaller, proper size. The new kind of foam (4 lb) will protect it also. If coated it should last longer than you.
Since we can't see what you are talking about, on the stringers, if there are cracks vertically in the stringers you can repair them. If you cut "most" the top the stringers off (if you leave some connections across the stringers you keep them in shape) you can grind the glass around the crack and lam 2 layers in increasing width of 1708 on them and they will be secure.
Next question is are you going to raise the sole.

[Capt. Bob]

upon inspecting the port stringer and removing foam the inboard wall of the stringer has 1/2" plywood which runs from just short of the casting deck back to about 12" behind the cross support to other stringer? I've not seen any mention in any of these threads.
I appreciate any thoughts and history on the plywood inside of the stringers.

We have seen (at least I have) several instances where a strip of plywood was enclosed within a stringer. This is on the older models but isn't consistent with any year or given model but does exist. Who really knows what went on during a late shift in Hialeah?

 I need to search some of the older rebuilds to find examples.

[sfmudder]

Thanks for the replies, good thought on leaving periodic strips on the top of the stringers, I will do that. The plywood is not in good shape and my plan is to remove and not put any back. I think I will strenthen theem up and refoam. i will glass the tank coffin in and probably foam the tank in place? I will clean it and seal it in coal tar epoxy. I do not plan to raise the sole.
Capt. Bob, i believe you about not knowing what goes on in Hialeah, the best I can tell the sole is al original and under the sole we have found period correct beer can!!! and numerous items from old fishing bobber to what looks like battery hold down straps- all VERY old, LOL. I will post some pics up when I can.

[Woodeneye]

Lots of people on here have pretty definite opinions on foaming tanks in. i.e. definitely don't do it. Moisture sits up against the exterior of the tank and it fizzes away considerably shortening its serviceable life. This method is the one a lot advocate. Good luck. http://www.yachtsurvey.com/fueltank.htm

[sfmudder]

Woodeneye, thanks, seems like very good info.

[wingtime]

I used the Pascoe method when I replaced the tank in my 200XF.

I have a good friend that is a marine welder who has repaired and built many many tanks. (Including mine). He said a bare tank that air can get to and flow around will last the longest. Anything that traps water against the tank such as foam will cause severe corrosion. He also believes coating the tank with epoxy or powder coating is counter productive as well. Remember the tanks are made from a marine alloy. It's okay if it gets wet. As long as it can dry out.