Subject: RE: [harryproa] Rudder Designs, was Re: Anyone there ?
From: "Jim Baltaxe" <>
Date: 1/16/2008, 5:53 AM

Hi Mark &al
Thanks for the clarification. If I understand you correctly, the problem with that old design is that they lose the ability to shunt in a shoal condition, which is obvious now that you point it out. They have to go through a "fully extended" position during a shunt. Try that in Pelorus Sound at low tide - Ouch!


Jim Baltaxe

They said, get a life. I looked on TradeMe but I couldn't find one.

From: [] On Behalf Of Mark Stephens
Sent: Wednesday, 16 January 2008 7:50 p.m.
Subject: Re: [harryproa] Rudder Designs, was Re: Anyone there ?

Good to see others are thinking about rudder designs. Jim we have four criteria for the rudders/daggerboards. They must turn at least 240 degs, they must pivot or break away in a collision, they must balance and they must retract for shallow  draft. . Your rudders do the first  three but  dont retract. They must score 4 out of 4.


Jim Baltaxe wrote:

Hi All, Rob, Mark especially
I just remembered that my first correspondence with Rob had to do with rudder design. His early plans for Harry had two side-hung rudders in cases that pivoted vertically on their bottom corners with their top corners held in place in/on a semi-circular slot or track in the hull. My original note asked which was intended since the sketches were, well, sketchy.
Mark's comments made me think that perhaps that old idea might be worthy of reconsideration. I just added an old sketch I sent to Rob at the time to the Files section of Harryproa group (labelled Rudder, naturally). The idea is that the rudder is free to pivot around the stock as one would imagine but the entire stock assembly would pivot on a pin through the hull and its angle could be determined by yet another line to a car or flange riding on a semi-circular section of track bonded to the hull. That line, in turn, could be fixed via a clutch or jam cleat which could be rigged to slip under a strong enough load. Resetting after an "incident" could be quick and easy.
This strikes me as too good to be true, so could the engineers in the group please tell me what I've missed?

Jim Baltaxe

They said, get a life. I looked on TradeMe but I couldn't find one.

From: [] On Behalf Of Mark Stephens
Sent: Tuesday, 15 January 2008 11:20 p.m.
Subject: Re: [harryproa] Re: Anyone there ?

The biggest negative about the hull hung rudders, well the mk 2 version, is they would be difficult to replace once the shear pins broke. At the moment they are designed to 'break away' in the event of a collision. You would then have to retrieve them from the end of the attachment line and refit them with new shear pins. This may seem like a big disadvantage but it will only happen in a catastrophic event which would render any catamaran with a stuck and broken daggerboard at best and a split hull and bent rudder shaft at worst.


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