Re: Plywood 12-1/2 - Keel Construction
- It wouldn't be hard to attach a solid piece of wood on the
leading edge of the keel to cover and protect the plywood edges.
Something rot-resistant and hard, preferably, which could take an
occasional bump without significant damage.
Does the plywood 12-1/2 still have the horizontal keelbolts as shown
in Boat Design Quarterly and BWAOM? If so, I'd be very
concerned - this is one of the few new ideas from Mr. Bolger that I
think is really mistaken and likely to fail. (I'm a mechanical
engineer, so I have at least some background in this sort of thing).
Under stress, the horizontal keelbolts are likely to tear out of the
edges of the plywood. Although I havent worked out the math in
detail, I'd sincerely recommend using conventional vertical
keelbolts. Remember, the keelbolts have to be strong enough
to keep the keel on when the boat is on her beam ends, with a safety
factor of 2 or 3 at least; this is not a place to take chances.
I don't know of any full size plywood 12-1/2s, but I did see a
model that Dymnamite Payson had made, and was really impressed. It
isn't as pretty as the origninal Herreshoff, few boats are, but I
was really surprised how handsome it looked.
--- In firstname.lastname@example.org, "Mark & Marie-Claude" <hobie@c...> wrote:
> I'm building a model of Bolger's Plywood 12-1/2 (from BWAOM - a
plywood interpretation of Herreshoff's 12-1/2 ) before deciding to
build the full-size version. On paper I don't mind the chines, but
since even Bolger admits the chined version isn't quite as pretty as
the original, I want to take a look at a 3-D version before my final
> My question here though is regarding the keel/backbone construction
used by Bolger for this design. He's modified the construction
details slightly from the sketches in BWAOM and now has a solid
backbone/keel assembly made up from 6 layers of 1/2" plywood. I'd be
interested to hear any experiences (good or bad) that people have had
with this style of keel nstruction.
> My primary concern is all the plywood end-grain that is exposed on
the leading edge of the keel. My planned sailing area is fairly
rocky and I'm concerned that any substantial knocks may damage the
fiberglass/epoxy sheathing and allow the plywood to start 'wicking'
in water - with the inevitable rot that follows. Since it's going to
be on a mooring, the keel will only get a close inspection once a
year when the boat is pulled out for the winter. Because of this I'm
considering going with a traditional construction keel & backbone,
but maybe I'm being too conservative.
> Additionally, just out of curiosity - is anyone aware of any
completed Plywood 12-1/2's?
> Mark Oliver
> Does the plywood 12-1/2 still have the horizontal keelbolts asshown in Boat Design Quarterly and BWAOM?
I'm a little confused. My copy of BWAOM does not show any
construction detail for the 12 1/2 at all. I am beginning to get the
idea the PCB finally created a buildable plan which is shown in later
editions of BWAOM. True? False?
- Oops - I think the final plans were in Boat Design Quarterly. There
was considerable detail, and that's where I saw the alarming
keelbolts. I don't have BWAOM handy, but now that I think about it,
it doesn't show much.
-- In email@example.com, "Peter Vanderwaart" <pvanderw@o...> wrote:
> > Does the plywood 12-1/2 still have the horizontal keelbolts asthe
> shown in Boat Design Quarterly and BWAOM?
> I'm a little confused. My copy of BWAOM does not show any
> construction detail for the 12 1/2 at all. I am beginning to get
> idea the PCB finally created a buildable plan which is shown inlater
> editions of BWAOM. True? False?
I don't have my copy of BWAOM since I've lent it to a friend, so I
can't recall what detail was there. However, the plans have been
completed for 'experienced builders' (in PCB's words) and he has them
available for sale. I've got a copy and they have all the
information I think a builder would need. He has made some other
changes - the rig is now a Solent lug rig (the mainsail is about the
same shape as the jib-headed rig, but the top two-thirds fo the luff
hoists on a vertical yard)and the jib is a balanced-club type, self-
trimming in tacking and not hanked to a stay. Very pretty rig
Regarding the horizontal keelbolts - yes that is still in the plans.
The outer two layers of the keel/backbone assembly (6 layers of 1/2"
plywood total) overlap the lead by approximately 2 inches on the top
and back. The lead keel(750 lbs now) is attached by six 1/2"
horizontal keel bolts (3 on the top and 3 on the back)through the
outer two overlapping layers of plywood. Being a mechanical engineer
myself I was also a little suspect of this, but want to do some
calculations before I jump to conclusions. I was also considering
the vertical keelbolts, but looking at it, the vertical keelbolts
have the potential to start 'splitting' the plywood since some of the
forces will be 'cross-grain' between layers.
Whatever I do, you can be sure I'll have some more discussions on
this with PCB&F before proceeding with the full size boat. I've
almost completed the 1/6 scale model and am finding the shape quite
nice actually. Unfortunately, I've got to go back to work tomorrow
after a bit of time off and my schedule won't allow completion for a
couple of months. I'll put a picture of it in the files once it is
Additionally, regarding the earlier comment about the Haven 12-1/2.
I've looked at it and it is still quite a bit more complex even
though many amateurs have built it. While I do enjoy building - I
enjoy sailing even more. Additionally I prefer the fixed keel.