Subject: Re: [harryproa] Rudder Designs, was Re: Anyone there ?
From: "Rob Denney" <>
Date: 1/16/2008, 12:29 AM


The side hung rudders (very similar to yours, except the shaft went
all the way through the hull) failed because the two way foils stalled
at very low angles of attack when luffing on the aft rudder/bearing
away on the front one. This was because of their shape and would not
be a problem if they were only used for leeway prevention. There were
also some issues with altering the angle after each shunt (does not
happen automatically so is another job to do while shunting) and not
getting enough turning angle.

Thought I had some pictures, but can't find them. Will post them when
they turn up.



On Jan 16, 2008 11:35 AM, 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?
> Enjoy
> 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.
> To:
> 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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