-In -http://groups.yahoo.com/group/kssboat/ there are a series of
well referenced posts on the problems of capsize after a post by
Derek Kelsal about a multihull designer being asked to be taken off
his boat for fear of imminent capsize.
So far most of this discussion on the Harryproa group has been about
wind assisted capsize, which most of the time can be prevented by
quickly dumping the sheet. Unless the sheet jams, then this seems a
much more useful method than having a panic string to pull for
inflating masthead bouyancy or dropping a shute in the water.
The idea of an endplate is a lovely idea but how will it behave on a
flexible mast and I can't see a great deal of volume. This, I think,
is worth investigating but who among us armchair sailors is prepared
to put in the time. I think a hydrostatic release for a flotation
device as on liferafts is worth considering. The technology is
already there for extreme marine conditions.
A problem of wing masts in extreme conditions is the tendency to hunt
when moored. At sea attached to a parachute anchor this same effect
can lead to disaster. I was wondering if the masts were rotated so
the front of the masts were pointing downwind, whether this would
relieve the problem ar make it worse. According to some research for
monohulls a drogue set on the bow can end up with the boat on the
beam from sailing up under bare poles, but from the stern the boats
in the test were prevented from capsisze. In summary, wind assisted
capsize is mainly prevented by good seamanship but we all can stuff
up sometimes so a litle extra belts and braces are reassuring. Mast
bouyancy is just enough to prevent complete capsize providing weight
is stowed correctly but wingmasts would add a little more security
and extra masthead bouyancy is a possibility. In severe conditions
the wingmasts might be a problem and the response to a bridled drogue
or sea anchor is not known.
To me the priorities are
1. Making sure the sheets can be dumped easily and every body on
board is trained to respond appropriately.
2.Making sure weight is stowed low. How much weight is in the rode?
Can it be taken to the bottom of the hull through a pipe? Is the
water storage either under the floor or, if in jerrycans, lashed
down? Not much can be done about the outboard or fuel as they are
stuck on the bridge deck. Loose people can also be a problem. Don't
think you are allowed to put them in irons down below ;-)
3. Is the drogue or sea anchor set up appropriately? The response to
the bridle can be ascertained to a large extent by observing the
motion at anchor in strong winds as can the response of the masts.
I am pretty confident that the boat can handle more than most boats
when it comes to being hauled through a breaking wave by a sea anchor
but it would be good to know the best position to set the bridle and
how to minimise hunting. I have read the most effective drogue and
anchor was the set up with lots of little drogues in series on a long
line with weight on the end.
Only then is it time to look at the next level of options
4.Extra mast bouyancy and an under deck gantry with sea bucket.
5.Upside down comfort and safety
6 Re-righting methods
Regards,
Robert.
- In harryproa@yahoogroups.com.au, "Chris Ostlind" <Chris@W...> 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
>
>
> ----- Original Message -----
> From: Mike Crawford
>
>
> <<what if a mast head flotation system could be built that
actually enhanced the anti-capsize function while having a positive
gain on aerodynamics? Would that get your interest?>>
>
> Well, only a fool would say "no" to that question. :-)
>
> If I were to try to design such a system, I'd ponder the
following:
>
> - Minimal impact in huge gusts. If one were to get caught in
a 60-knot squall (and the sails are reefed), the resistance of
anything at the masthead could represent some additional heeling
moment, as well as additional stress on the tops of those flexible
masts.
>
> - Minimal heeling moment due to weight at the masthead.
>
> - Compatibility with the flexible unstayed masts.
>
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