Parallax ) writes:
I did manage to find a design for a good nesting dinghy but its still
75-85 lbs. Then I looked at that Airolite boat site about
ultralightweight boats made from dacron skins on a lightweight frame.
His designs, especially his 8' dinghy are closer to what I have been
imagining. He also discusses Tyvek sails and putting the two together
is sorta fleshing out an idea.

I think Monfort cautions that the boats would not make good yacht tenders.
I expect they would not last long overturned on the deck with water coming
aboard. A traditional coracle would probably stand up better but not
really be strong enough. I designed a coracle made of one sheet of plywood
but a round boat would take up room on deck. Hmmm, maybe two nesting
semicircular sections lashed to the deck on edge, or four quarter
sections, ....


So, essentially, the dinghy problem for sailboat cruisers is that many
of us have mid-sized sail boats (mine is 28') with not enough room to
carry a dinghy of any size on deck. Even when we do carry such a
dinghy on deck (mine is a Nautilus 8), the thing is so heavy, we have
to use the jib halyard as a hoist to get it in and out of the water.
Even then, it can be exhausting to launch or retrieve. Even then, it
will not really carry my wife, myself and two kids and I have 3 kids.

Two adults at 150 lb and 3 kids at 100 lb is a 600 lb load. I don't know
how you'd get all that weight into a light dingy. Try two adults and a
dog, or substitue a couple bags of groceries for the dog.

So.........Instead of the Airolite concept where the geodesic-like
structure where the frame carries the load with the dacron simply
covering it, I envision a sort of tensile structure where the skin
hold the frame in tension like an inverted free standing tent with
internal poles.

plywwod works by getting strength in the skin from bending the
plywood into a curve.

...Flexible fibreglass batten like poles would run
lengthwise through tubes in the skin from a common point at the bow to
the edge of a stiff transom. Widthwise battens would be inserted
through loops and joined to the battens at the edges to form the hull
shape. Lightweight seats would help hold the shape. I am not yet
sure of how to fasten the widthwise battens to the lengthwise ones but
various things come to mind such as the fasteners used to secure
canvas to things. Ont he outside of the skin would be a keel of
lightweight fairly stiff closed cell foam (I have various types of
this stuff at work so have been looking at it).
Although Tyvek is permeable, I may experiment with it because of its
tear resistance and low cost. I am certain that some type of similar
material is available that is waterproof.
Any thoughts on this?

I tried making a crab claw sail out of fibreglass tent poles and found
them heavy, fragile, and flexible where I did not want them to flex.
(Look at the Bear Paw sail under Boats on my website.) I hear there are
flexible aluminum poles for dome tents which would be stonger. At least
they would distort rather than break.

Another approach would be removable side panels. Ancient boatbuliders made
a watertight dugout bottom which rode above the waterline, then to keep
waves from coming into the boat they added more height by tying boards or
whatever along the side. Maybe a plywood nesting dingy could be made with
removable side panels which would fit on like the cap on the back of a
pickup truck or the side panels on a flatbed truck. Perhaps in calm water
the panel could be left off. Or for watertight side panels they could be
made to fold down with watertight canvas or similar keeping the water out.
There is a folding boat somewhere on the Internet which shows how this is
done. That is a plywood boat which folds flat. You might consdier two
small dingys which fold flat instead of one large one.

One more technique for adding bouyancy is sponsons, like putting an
inflated innertube around the boat. I've had home made foam sponsons on
two small boats, the Blue Canoe and the Loonie on my website.


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