Ben,
There has been much discussion on Blind Date's steering and
luffing. For a full recounting, the best thing to do would be to
search for Rudolf's posts in the past. He's better than most in
terms of being concise.
As a general summary: Blind Date is a shallow draft boat. Extra
shallow. As a result, there's not as much foil area beneath the
water as there could be. The boat was non-optimal in its original
design, with the rudders on the lw hull, and when the rudders were
switched to the beams (closer together, further from the lw hull),
steerage was reduced and luffing tendency increased.
There is an argument that deeper foils would solve the problem by
providing the ideal amount of underwater surface area, but going
deeper is not an option.
A daggerboard could be a solution, but in a shallow-draft boat,
probably not the best idea. Even if there's a crash box, and the
boat doesn't sink, who wants to repair the damage? It could be an
expensive proposition just to build it in the first place, at least
in terms of finding an ideal design that works in both directions,
doesn't get unstable or ventilate, and somehow manages to gracefully
handle a grounding.
A leeboard might work, but there's still the issue of designing it
to be strong, efficient, stable in both directions, and able to kick
up.
Rudders with more lift probably won't do the trick with the
steering issue, which really depends upon having a larger moment arm
(rudders further apart) to generate turning force. And if the
rudders are losing their laminar flow with the current design,
higher-lift versions are likely to lose that laminar flow even
sooner.
A partial solution was a bi-directional tandem keel, which
provides most of the lift of a deeper keel, but without the depth.
Since it doesn't have to be lifted or flipped on each shunt, the
keel is a plus when taking blind sailors out for a day with a
limited sighted crew. This has helped the problem, but not fully
resolved it.
Rudolf definitely knows what he's talking about; he and Arrtu have
more time on the larger Harryproas than anyone, I believe.
There are many suggestions about what to try next, but the budget
for modifications is limited. And since I haven't sent a check to
Zeilen met Visie ( http://www.zeilenmetvisie.nl/EN/index.html ) to
fund my personal theories, I can't complain.
- Mike
bjarthur123 wrote:
rudolf: have you thought about replacing the rudders with ones that can generate more lift, either by using a different NACA section and/or by lengthening them?
relatedly, with the existing rudders and "keels" (dagger boards you mean?), how much leeway do you make? if the leeway is not too much, then you're right-- would be better to move the rudders further towards the end of the boat. but if it is too much, then making them generate more lift would fix both the leeway and the luffing tendency simultaneously.
ben
weta #358
and thinking hard about a big harryproa