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Reply | Forward Message #1640 of 6721 |
Re: [harryproa] Re: mast bouyancy

<<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.


  I like the compressed gas system because it represents no aerodynamic profile or drag, but you could argue that it's a complex system that might fail.  A fixed system that just works without any kind of trigger mechanism would likely be more reliable.  And assuming you only need it in extreme emergencies, that's a good time for something to be reliable.

  Assuming the masts rotate freely, you could probably put something up top that works like a foil to create some lift with little drag additional drag, kind of like a fixed sail top.  Is that what you're thinking?

       - Mike



Chris Ostlind wrote:
So, Mike, 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?
 
Chris
----- Original Message -----
 
I've had conversations with three racer/cruiser open deck catamaran manufacturers about masthead flotation systems.  All three chose to avoid them because the extra windage that high is pretty significant, and also because they wanted to avoid weight at the masthead.

  One manufacturer decided to avoid righting systems altogether, one went with a compressed-gas system that will inflate a bag at the masthead, and one has yet to unveil its new righting system.

  A schooner rig with wing masts would likely offer enough flotation.  I'd still consider a compressed-gas system as well.  Either that or I'd keep an inflatable dinghy ready, as well as a spare halyard, and make sure I had a system to hoist it up the masts when the boat is on its side.


Tue Feb 7, 2006 11:20 pm

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Did some rough calculations on the Harryproas stability at 90 degrees. Empty, a Harry is stable on its side but not by a large margin. Probably the resistance...
Robert
cateran1949
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Feb 7, 2006
12:06 am

Hi Rob I do not have experience with the bouy at the top mast but I wonder how much a cleated sail in the water acts as a fulcrum to force the mast to go under...
carlos Solanilla
carlosproaca...
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Feb 7, 2006
12:44 am

Hi Carlos, My own experience with lots of capsizes in small boats and windsurfers is that the sail damps the initial rotation and then if you don't uncleat you...
Robert
cateran1949
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Feb 7, 2006
2:02 am

... Brian Phipps does it successfully with Darts, AFAIK. But a standard Dart will not normally turtle immediately anyway. ... Don't forget that in strong winds...
Dave Howorth
Dave_Howorth
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Feb 7, 2006
7:37 pm

I agree. Beyond the lower righting moment when reefed, buoyant sails would also be less useful once you uncleat the sheet in order to right the boat, allowing...
Mike Crawford
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Feb 7, 2006
8:01 pm

So, Mike, what if a mast head flotation system could be built that actually enhanced the anti-capsize function while having a positive gain on aerodynamics?...
Chris Ostlind
wedgesail
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Feb 7, 2006
10:51 pm

What about preventing the capsize with a device attached to the ama? Let's say a parachute hung on the side of the ama in a bottomless square box in such a...
carlos Solanilla
carlosproaca...
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Feb 7, 2006
11:18 pm

<<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...
Mike Crawford
jmichaelcraw...
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Feb 7, 2006
11:20 pm

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...
Chris Ostlind
wedgesail
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Feb 7, 2006
11:53 pm

-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...
Robert
cateran1949
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Feb 8, 2006
1:57 am

... He doesn't seem to have deployed anywhere near enough parachute with anything like the right amount of tether line. It sounds like some pretty skilled...
proaconstrictor
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Feb 10, 2006
9:43 pm

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"...
Mike Crawford
jmichaelcraw...
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Feb 9, 2006
1:11 am

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...
Robert
cateran1949
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Feb 9, 2006
6:03 am

Oh, I forgot... The full treatment to the sail also includes a boom like you would see on the really spendy, mega-yachts where there is a decided wingish,...
Chris Ostlind
wedgesail
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Feb 7, 2006
11:59 pm

An interesting idea, alltogether. Bouyant panels and endpieces. I will discuss this with a sailmaker. I´ll relay his opiinion. Thanks, Peter ... like you...
petermirow
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Feb 8, 2006
1:32 am

G'day, Agree with your comments except for the mast angle. I suspect it will be pretty close to 90 as the lee hull will be partially in the water. As long...
Rob Denney
proaharry
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Feb 9, 2006
9:22 am

-my calculations are in the order of 3-5 degrees and have tried to imagine the circumstances where the wind wave would work together. It would be coming off...
Robert
cateran1949
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Feb 9, 2006
12:33 pm

... degrees. ... stop ... situation ... big ... the ... I just don't see the point. The HP is the most stable multihull design in existence relative to the...
proaconstrictor
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Feb 10, 2006
9:20 pm

One of the big reasons I started looking at passive, functional flotation at the mast head was the complexity factor of anything with moving parts such as an...
Chris Ostlind
wedgesail
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Feb 10, 2006
10:34 pm

Very solid arguments for fixed masthead buoyancy. The potential failure of an active system, and the problems of re-arming it in nasty seas, are tough to...
Mike Crawford
jmichaelcraw...
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Feb 11, 2006
12:26 am

... My guess is that mast buoyancy or leepod are only good to deal with errors of judgement in moderate conditions. If you flip a cruising multihull by...
robertbiegler
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Feb 12, 2006
11:11 am

<<My guess is that mast buoyancy or leepod are only good to deal with errors of judgment in moderate conditions.>> I agree. I'm not sure that anyone here...
Mike Crawford
jmichaelcraw...
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Feb 12, 2006
7:24 pm

A fully flooded Harry lw hull will have in the order of 300-450kg bouyancy and you would need to move ~9 tonnes of water to fill the hull. It would be easier...
Robert
cateran1949
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Feb 12, 2006
11:48 pm

<<It would be easier to lift the 350kg weight of the hull... This is only 700-900kg off a 3m gantry.>> Good point. Not unimagineable once the weather has...
Mike Crawford
jmichaelcraw...
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Feb 13, 2006
7:33 pm

-If I had the drogue set up I would be wanting to avoid being side on, lying ahull. I feel surface area is too great to withstand such a hit of white water....
Robert
cateran1949
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Feb 14, 2006
6:46 am

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