Hull construction

[BWB]

I have a general question concerning the hull construction of 1970's flatbottom hulls. I am repairing a stringer in a 1970 Wesco hull, the design with the intergral mid deck. The stringer had been cracked at the fastener for the rear brace of a Casale top loader v-drive. Along the base of the stringers I had noticed some cracking and delamination of the floor fiberglass over the plywood core. So, I figure that I will peel the fiberglass back to where it had a good bond to the plywood floor. I would let any moisture that got trapped in the plywood floor dry, apply penetrating epoxy to the plywood to keep it from delaminating and re-glass over everything. Two things surprised me: one, the plywood floors are covered with one layer of fiberglass mat and one layer of 10 OZ fiberglass cloth. I had expected at least a couple layers of glass cloth, and the mat I could see no reason to use at all. Second, the plywood floors go under the stringers. I had always thought the stringers attached to the glassed hull, then the floors were laid in, then everything was glassed over.
So what was the procedure in the 1970's and did the building procedures change later in the 1970's or 1980's??

[gfinishline]

Everyone has/had their own way of doing a "lay up schedule". Some want cheap, some light, and others strength. I personally have not seen any flatbottoms with wood in the bottom, NOT have the stringers ON TOP of the plywood. I question the "10 oz cloth" you mentioned, that is thick stuff. The mat used under the cloth helps the cloth stick and fill in uneven areas in the wood. If you think the lamination you cut out is thin, (inside) don't drill or cut thru the glass outside (under) the floor wood. It will be about 1/8" to 1/4" thick, and that would be standard on "mid/late" 70's flats. Now, race boats (like K's) will have more MEAT inside and out, but the "ski boats" (around 650 to 800 lbs) are built just that way. The deck is usually only about 10 to 14 oz's of lay up, (1/4" thick) with wood or core (mat/foam) added in the big flat areas, and around the gunnels. 30 to 50 lbs of wood, 250/275 lbs of resin, and 275/350 lbs of mat and cloth. The flat floor pieces were "glued in" (resin on a bed of mat) and most used 'car batteries' to weight down the wood to the hull bottom. Then the stringers were cut to fit the bottom "with no gaps", and a strip of mat was wetted, and the stringers were laid down with weight on them and a "bracket or brace" at both ends to keep them parallel. As the "bond strip" was setting up, the stringers were "tabbed in" down to the floor wood. Next day, it was all glassed over. Few days later, deck and hull were glassed together. Toe board installed. Sit in mold for a few more days, and then POP. Bow eye installed and then 'flow coat' sprayed on floors. (unless the cap rail was to be filled) That's pretty much what I know about the stringers and floors in flats.

[BWB]

Thank you very much. That is exactly the info I was looking for.
When balsa core is used, is that also laid across the entire bottom of the hull and the stringers are set on top?

[RiverRacer]

No, the Balsa is cosmetic and layed in after the stringers are put in!..

[gfinishline]

Later boats don't have wood in the center. This allows the propshaft, strut and turn fins to go thru glass only and avoid trying to seal the holes in the wood. Some boats have used balsa instead of plywood in the bottoms, most had fracture and "water rot" problems. Even though balsa is considered a "hard wood', it is very impact damaged and it just won't replace plywood as a "stressed member" of a hull bottom. It is correcly used as a "light weight lamination builder' and is great when used to make 1/2" of glass react like a thicker member. (sides and decks) Balsa (5/8") under a deck would react like a (1/2") plywood at less than half the weight.

[FC-Pilot]

Alright, I will add the very little bit I learned to add to what Art and George have shared. (This probably has no bearing to your boat, but just sharing it as info as to how "some" of the early circle boats were built). They had several thick layers of glass laid then put the stringers down. After the stringers were set they would lay the balsa in the floor and then go over it with mat and cloth. (This was in reference to some of the Biesemeyer boats laid up as light weight boats for racing).

Both George and Art have more knowledge and experience than I do in regards to this stuff. Heck they have more experience with anything to do with boats than I ever could. I love it when they post info because it means school is in session.:D

Paul

[hm66Howard]

Be careful with the penetrating epoxy! Wear a respirator and gloves. That shit does funny things with your head before you know it. :o I played that game before!

[Stickman]

Beware... polyester resin will not adhere to epoxy.

We used to use 8 oz cloth and 2oz mat for the bottom plywood and stringer overlays at Jones/Starfire. Overlay the stringer onto the wood then overlay the bottom wood. It makes for a smooth floor and a very strong encapsulation. There are 30 year old Starfires still racing without any stringer or floor delaminations. We kept our overlays clear so we could see any damage occurring.