Note , if you are careful with the weight distribution in the ww hull
with batteries and water storage you can just bring it back the other
way, but it is still a bit tight for my liking,
Robert
--- In harryproa@yahoogroups.com.au, Mike Crawford <jmichael@g...>
wrote:
>
>
> That's about as good a masthead flotation system as one could
> imagine. Nice design, pretty aerodynamic, and it doesn't look like
the
> hobie "training wheel" bob at the top. The renderings are nicer
than
> the sketches I was anticipating.
>
> Two thoughts:
>
> a) It looks like it would be a better fit for a rigid stayed
mast
> where it wouldn't whip around up top.
>
> b) It would need to be able to rotate to allow for sail twist.
The
> higher you go, the further aft the apparent wind tends to move, so
a
> twisted sail becomes more efficient. This means the sail top will
> likely not be fully aligned with the mast at the masthead
>
> It seems like it could be a great idea, but I'm not sure if I'd
want
> to be the one to test it. I'd probably take the lazy approach and
wait
> for someone else to go through the trial and error.
>
> ---
>
> The big question is how much buoyancy you'll need.
>
> Let's say you take a 12m Harry that's on it's side, assume that
the
> windward hull weighs 1000kg with gear, water, and people, and
assume
> that the beams have slanted 10 degrees past vertical because the
masts
> aren't located directly on the leeward edge (or due to swells).
With 6m
> of beam above the water, that puts the center of the windward hull
1m
> horizontally past vertical, yielding 1000 kg-m of heeling moment.
>
> Assuming a 15m mast, and going with Robert's calculations of
160kg of
> flotation at a center of effort 5m up the mast, that's 800kg-m of
> righting moment, leaving another 200kg-m to be dealt with. That
means
> 13.33 kg of flotation at the mast head. Let's round up and call
that
> the equivalent of ten two-liter bottles of foam at the masthead.
>
> I do think it's possible to come up with that, given your
design. A
> bit bulky, but probably not that bad if distributed the way you
> suggest. It wouldn't be the same, though, if much of that volume
is on
> the sail top and the sails are reefed.
>
> Four to six square meters of 5mm foam would also probably be
enough,
> but only if the sails were all the way up.
>
> ---
>
> On a separate note, you'd likely need a lot more flotation for a
> catamaran or trimaran because both would have to tilt further
before the
> masthead float would become effective.
>
>
> - Mike
>
>
>
> Chris Ostlind wrote:
>
> > OK, Mike... and everybody else who may have an opinion on this.
> >
> > Located in the Files section is a folder titled End Plate Sail
where I
> > have put a collection of renderings of a concept device for
preventing
> > turtling, principally for multihulls. The idea here is pretty
straight
> > forward.
> > http://au.groups.yahoo.com/group/harryproa/files/End%20Plate%
20Sail/
> >
> > I'd been seeing a bunch of folks talking about adding foam panels
up
> > high on the sail to assist the sealed mast when capsized. It
occurred
> > to me that you could go all the way with this idea and just make
the
> > foam a specific shape to take advantage of an end plate effect at
the
> > head of the sail. If it were slotted to fit the sail chord up
high on
> > the head, it would help to contain the airflow that gets lost up
there
> > and contribute additional drive to the sail. I was going for the
same,
> > wingtip thing that you see on most modern airliners to enhance
wing lift.
> >
> > A matching form would be fit to the mast head as well so that the
flow
> > would be smooth and not abrupt. This piece, too, could be made to
> > provide buoyancy at the far end of the mast righting lever if
tipped
> > over. The two pieces would not be attached, so the sail can be
hoisted
> > and/or reefed like normal and the endplate float would move with
the sail.
> >
> > I haven't done any aerodynamic calcs, so I don't know if the
design
> > would make more drag than it could save. It will, hopefully,
provide
> > two tasks at once and might be worth it. I know for sure that
other
> > floaty stuff up on the mast like Hobie Bob's are not making any
> > additional power for their drag, so it might be a cool idea,
> > especially for cruising boats that don't have big worries about
total
> > performance like a racer would. They cold pick-up some lost power
from
> > their sails and gain some peace of mind at the same time.
> >
> > If anyone is an aeronautical engineer and can contribute to the
design
> > of the product, I'd be interested in hearing from you. There's
bunch
> > of prior art established and I have dropped the dime on the USPTO
for
> > the provisional patent thing, so I'd like to see where this could
> > go... if anywhere.
> >
> > So, have at it. Would it work?
> >
> > Chris Ostlind
> >
>
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