Ken,
I am using 6mm okume ply for the fuselage with 13/16x 1 1/2 longerons.
I have put one bulkhead in front of the steering assemble on other
similar boats. Its in the back of my mind . I just haven't got to it
yet. My first home made dirtboat was triangular shaped . It was a
conventional wingmast and sail. I had the sheeting in front of me in a
rumble seat configuration. As the boat loaded up you could see the
triangle shape flex to leeward. The torsional load your talking about.
On a funny note about 35 years ago my dad sailed his boat all weekend
without the runner plank nuts on. I guess the shrouds and whisker
stays kinda held her together. When we took apart the boat we were
wondering where all the runner plank nuts were. They where in the tool
box of course.
I was thinking of putting some floatation in the front of the boat
beyond the bulkhead.
Any ideas for flotation?
John










--- In wingboats@yahoogroups.com, "wind2nice" <wind2nice@...> wrote:
>
> John:
>
> I have most of the materials on hand to start my boat, as well. I
> looked through the plans, and cannot find a material list or plywood
> thicknesses for the hull. I am running some strength calcs, and
> believe 3mm ply with 3/4 x 2" longerons should be more than strong
> enough. There is a fairly high torsional load between the mast step
> and plank connection, and a diagonal piece of the longeron stock
> should carry that load, with either a bulkhead, wood, or metal knee to
> get the moment load from the top of the mast backing board to the
> diagonals. A bulkhead and center line stiffener seems prudent beneath
> the deck. Also, I much prefer scarfs in teh plywood rather than butt
> joints and backing plates.
>
> The torsional load comes from the mast step side force which must be
> transferred to the plank connection.
>
> It appears you used 4mm ply and smaller longerons and no mid-panel
> stiffeners, and no bulkheads. Please confirm. This "feels" a bit
> flimsy compared to the ice yachts I am familiar with. As a minimum, a
> bulkhead at the aft springboard connection point seems indicated.
> This additionally closes a volume and provides a flotation chamber for
> weak-ice (or weak-headed moments) with thin ice. Foam hip pads, seat,
> and foam fillers at the seat back corners also provide some flotation
> in those OH-SH** situations.
>
> Thanks for the reply,
>
> Ken
>