The purpose of this post is mainly for the San Juan Users Group as I've owned and rehabed a couple San Juan 24's - up til this one - and as they are a great sailing vessel but aging. Many conjectures are forwarded as to whats underneath the gelcoat.
It is raining outside so I don't have the hull pictures to show. These are mostly cross section shots - sometimes fuzzy - to get and idea of the San Juan 24's internal construction.
Also here is the e-mail post to the group explaining - keep in mine that I am not an engineer and these are only my opions as a back yard boat fixerupper guy:
Yesterday I began sectioning the heavily delaminated 1972?4? SJ24 hull for disposal via sawz-all. Took about 4 hours for the deck -
being careful to cut around good used parts. I will take picture of
some cross section and post them on my blog page for those interested
in a more detailed view of the San Juan 24's internals.
Tearing away with the sawz-all did give me some opinions on the deck
construction. Keep in mind that this boat was riddled with deck
component add-ons that were not bedded or re-bedded in the recent
decade (or two); drilled holes through any core were not resin filled
and redrilled; virtually no backing plates were used except tiny
washers; the boat was laid up in a mid-atlantic state where it does
freeze at times in the winter:
1. The side decks are cored with a good grade of plywood - probably
marine grade as it was still solid, stable and harder to cut through
even while noticably wet. About 1/4 inch from the forward cabin to the
rear cabin bulkhead brace.
2. The main winch platform was 1/2 inch plywood and was found to be
dry and solid and hard to cut through.
3. The transom is un-cored thick and harder to cut through than the hull
4. The hull/deck joint is an over and under lap joint were about one
inch of the deck lip rests on top of an inward facing hull lip of
about an inch. They were glued and thru-bolted from the teak toe rail.
No apparent leaking could be seen at those few places where I cut
across it.
5. The transition from cored deck to deck joint has the two halves of
the laminate meeting about 1/2 inch before the step-up ridge to the
lip. I think this is the boat weakest area - everything on the deck is
hanging across this thin - about 1/8" + laminate. I believe a layer or
two of fiberglass mat and cloth along this thin area would firm up the
whole boat, but you would have to remove the toe rail and stantions -
not a pleasant job! And grind back the gelcoat to resin them in.
6. Almost every balsa cored area in the cabin top was wet and much of
it rotted, black and sometimes non-existent. Black rot-ooze could be
seen leaking out from the inside of the cabin at fastener holes. The
mast step area was crushed, but the mast compression post and lower
fiberglass base were intact. I bet the PO just kept tightening and
tightening the stays!
7. Even though the cabin top fiberglass laminate was some of the
thickest on the boat the sawz-all cut right through it - much easier
than the side deck.
8. Sectioned cored pieces were surprisingly heavy!
9. The entire deck was stress cracked. My best guess is once the
cabin core lost its bond with the inner and outer laminates it no
longer could support mast loads and tried to push the entire deck
downward. The bulkheads prevent most of this, but as the boat is
worked in a sea I imagine a rolling ripple effect working that thinner
hull/deck joint. Plus the winter freeze/thaw did the rest.
10. The main bulkheads were wet and slightly mushroomed at the top,
and looked ok until I took the cabin top off, then you could see the
laminates of the bulkhead spreading and becoming rotten. The port
bulkhead was also showing signs of wet separation at its base. So
their main job of support were also negated.
11. The chain plates have no elongated holes and look good and the
chain plate bolts are solidly in place. But as I worked a piece of
deck up a down over the chain plate slot my belief in the trampolining
deck started to take shape.
12. Overall I believe the SJ24 was built very well to good standards
that one would expect of its class and design. The deterioration of
this boat no way reflects this as no standard was held in attaching
deck hardware - anywhere. No boat of any design would hold up over 30
plus years of constant water intrusion and freeze thaw cycles.
I now have a new respect for resin filling of thru-deck holes and
using larger backing plates. BUT I will continue using balsa for
coring with this in mine as I've come to find out through a noted
marine surveyor that no foam coring material as yet will match it in
being able to withstand higher levels of heat and compression. That if
you properly bed and seal your hardware balsa will last indefinitely
