Rob Denney & Bucket List

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Rob Zabukovec
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Rob Denney & Bucket List

Postby Rob Zabukovec » 19 Oct 2014, 04:28

All,

Our old friend Dave Culp forwarded this to me today......The entire concept, not just the boat is absolutely fascinating!!!!

http://harryproa.com/index.php/design/2 ... ucket-list

Mind you, doing a hard Sydney Hobart or Fastnet race in one (I've done both) would test anyone's endurance: Like sitting on a bidet in a wind tunnel blowing full blast with buckets of freezing water thrown in for 24 hours.....It really will feel great when it is all over!!

Cheers

Rob
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Skip
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Re: Rob Denney & Bucket List

Postby Skip » 19 Oct 2014, 14:22

Rob Zabukovec wrote:Like sitting on a bidet in a wind tunnel blowing full blast with buckets of freezing water thrown in for 24 hours.....It really will feel great when it is all over!!


All the more reason to finish quickly :)

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Rob Zabukovec
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Re: Rob Denney & Bucket List

Postby Rob Zabukovec » 19 Oct 2014, 20:34

.....Except that it will be more like 48 hours, strapped in all the way....Any "rest" below will be in the same wet clothes, strapped into a in a wet bunk to stop being airborne one second and crashing down the next and the noise will sound like someone is on the outside continually bashing the hull with a baseball bat.....Extremely character forming!!!!

Actually, the way to sail it in bad (most) weather would be to have the canopy up, hatch open and steer from inside the ama sitting on a (chart?) table cantilevering out from the weather topside so that your arms and elbows are above the deck.......

Rob
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Re: Rob Denney & Bucket List

Postby red cedar » 22 Oct 2014, 21:04

25' beam is a long lever-arm.
what are the implications of that long lever-arm ?
i guess that lever-arm is necessary to generate the RM to counter 600sq.' of sail high on a 60' mast.
but doesn't a longer lever-arm also lever an increase to the windward drag of the ama ?
especially a fat and heavy weight-to-windward ama ?
isn't that why most proas prefer vaka CL to ama CL as short as possible, and amas as slippery as possible ?
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Re: Rob Denney & Bucket List

Postby Rob Zabukovec » 22 Oct 2014, 21:51

The answer to all your questions is yes......theoretically.

If anyone has has experience of short fat heavy amas to windward with all their theoretical problems, it has to be Rob Denney, but he persists with them and sells them, so they can't be that bad???
"Bucket List" is an extreme proa for racing, its only intentions are to be fast "unbreakable" and cheap, that doesn't mean necessarily that it will be well mannered or easy to sail. It certainly will be tough on the crew off shore for starters. And "self righting" after a capsize when the crew is 25 ft up in the air could be interesting.....

But where else can you get a brand new 40 ft racing multihull (or any kind of new 20ft plus race boat for that matter) for $50,000???? I can see some being bought, and then if they live up expectations, a lot more will be on water PDQ.....Could even have an international one design proa class!!!

Denney does offer a cruising option with a longer ama, more accommodation and shorter cross beams.....

Rob
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Re: Rob Denney & Bucket List

Postby tdem » 25 Oct 2014, 05:55

A thought I just had on the "heavy ama".

In slow sailing conditions, a relatively short fat shape probably has less drag. As the wind increases, the effective weight of the ama decreases, which means it is no longer short and heavy, just short, and will get into planing speeds faster than a longer ama (assuming it planes or has a similar high speed effect).
The most important thing is to keep the most important thing the most important thing.- Donald Coduto
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Rob Zabukovec
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Re: Rob Denney & Bucket List

Postby Rob Zabukovec » 25 Oct 2014, 08:30

tdem wrote:
In slow sailing conditions, a relatively short fat shape probably has less drag. As the wind increases, the effective weight of the ama decreases, which means it is no longer short and heavy, just short, and will get into planing speeds faster than a longer ama (assuming it planes or has a similar high speed effect).


Short and fat means less WSA in slow sailing conditions, short and fat is good for skimming or planing as well....... Your average Harry proa windward hull is too fat and heavy to do this, but "Bucket List's" ama is light enough and flat bottomed enough to do exactly what you say.......According to Denney (via Michlet software), anything over 5 knots boat speed, flat bottoms are better than semi circular sections. It doesn't take a lot of wind to get to 5 knots in a 40 ft proa........

Cheers,

Rob
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Re: Rob Denney & Bucket List

Postby tdem » 26 Oct 2014, 00:16

Rob Zabukovec wrote:
tdem wrote:Your average Harry proa windward hull is too fat and heavy to do this


The only difference a hull that is "too heavy" would have is it would require more wind to get the same effect. Eventually the displacement of the ama will still effectively go to zero, assuming there is enough sail area, right?
The most important thing is to keep the most important thing the most important thing.- Donald Coduto
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Rob Zabukovec
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Re: Rob Denney & Bucket List

Postby Rob Zabukovec » 26 Oct 2014, 01:08

Correct...the average Harryproa hasn't enough sail area to lift the ama sufficiently.....Bucket List has.....
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Re: Rob Denney & Bucket List

Postby Manik » 26 Oct 2014, 14:13

I think ultra-wide proas seem like a good way to significantly increase the amount of RM per unit of displacement. 7.5m beam on a 12m proa is definitely a bit on the high side, compared to an offshore trimaran for instance. I think the danger with them though is that you can get very bad boat handling / behaviour in waves. The waves will hit the ama way before they hit the vaka, and with all that beam, the extra drag at the ama at that point in time will cause the boat to yaw significantly (or require a lot of rudder to prevent them from pointing to windward). That requires a very active helmsman and causes a significant increase in average rudder drag.

With the large amount of weight in the ama in a harry proa, I think you could really get quite a pronounced spike in ama drag when you come down into the trough between the waves (you've got less wind in that moment too). Looking at the top view of the boat, if you can keep the heading angle at something close to 25°, then that wouldn't be an issue (ama and vaka would hit the wave at the same time then), but 25° off the true wind seems like pointing pretty high, for strong winds and a bad seastate. A narrower proa, or a trimaran won't have this issue to the same extent, since the hulls are closer together (the windward hull on the tri is way up in the air anyway) and thus the time between the waves hitting the hulls is smaller, or the course angle at which they hit at the same time, is larger. You sacrifice RM per unit of displacement then though.

In the end, who knows, maybe this would work out fine, even in a significant sea-state regardless, so I at least am definitely looking forward to seeing it out on the water! :)

Cheers,
Marco

P.S. - I've been thinking a bit about the possiblity of getting weight up and to windward of the ama, like moth-style wings with a buoyant water ballast tank on the end or something, to increase RM per unit of displacement significantly, but that too is pretty risky, if the water ballast tank is submerged in the wave, on account of the waves just being really steep, then I think you'd probably have a tendency to broach which is much worse than Bucket List might have.
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