Subject: [harryproa] Re: mast bouyancy
From: Mike Crawford
Date: 2/13/2006, 2:32 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 calmed down to swells.  If those masts are sealed, you can add another 150-400kg flotation, depending upon the rig, making it a bit easier for that gantry to work.

<<the recommendation is that the drogue is to go over the stern>>

  And which end of a harryproa would that be?    ;-)

  I know, you answered the question.  Fortunately the proas work in both directions, so as long as the boat is stabilized windward, as as how you've suggested, there's no need to worry about it being unseaworthy in one direction versus another.

  I must correct something I wrote the other day.  The goal was to have some sort of anchor to windward, be it a para anchor or jordan-type drogues, along with a minimal break, such as a good length of bare chain, off the leeward end to help resist surfing after the wave passes.  I shouldn't have used the term drogue for the leeward break.  Towing drogues while being dragged behind a sea anchor could get quite weird.


  Another option would be to keep the windward hull to windward, lying ahull to the weather, and fastening the drogue bridle off of each end.  That would provide a similar effect to tying the drogues to the the stern of a monohull, thereby using its flotation to keep it with the wave surface instead of trying to crash through the wave the way the bow would. 

  Since the proa is so stable in that direction, and the boat is so light, you wouldn't need extreme forces to keep the boat from going over.  Because of the 6m beam, even bare poles would enable the boat to weathercock into the right position without additional help.

  Lying ahull would also be useful with preventing the surfing speeds that a fast boat can have once it crests the wave.  As long as there aren't any keels on either hull, there won't be anything to catch under the water and spill the boat as it slides sideways.  That would eliminate the need for a leeward break, which some argue is not a good idea.

       - Mike

Robert wrote:
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 to lift the 350kg weight of the hull (add
another 100kg or so for masts and rudders), especially encouraged by
mast bouyancy. This is only 700-900kg off a 3m gantry. You only have
to work a distance of 4m or so. This is no more than I have done
hauling vehicles up a slippery slope. With the right winch,
exhausting but doable- or maybe you could fly a kite ;-)

I've been reading the Jordan series drogue website and the
recommendation is that the drogue is to go over the stern as it gives
the windage and the under water resistance such that the boat doesn't
tack up on the rode to end up side on. On a Harry, slight rudder down
on the end where the waves are coming from and a tiny bit of rag on
the opposite end mast would similarly stabilise the boat I think the
reports on the website well worth a read 


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