Subject: Re: [harryproa] Leeboards?
From: "Gardner Pomper" <gardner@networknow.org>
Date: 11/4/2008, 10:16 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

Mike,


Thanks for finding those posts. I remember reading them (I believe they were responses to other posts I started <blush> ) but I couldnt find them. At the time, I don't think I understood the answers well enough. The key statement (for me) was:

"Mostly though, a proa needs lots of steering control at low speeds
after a shunt. Big rudders provide this, daggerboards don't"

After reading the Dave Gerr section on rudders, I understand this a bit better and can see the advantage of larger rudders, making the leeboard unnecessary.

Have you run across the underwater dimensions of the rudder on Rare Bird or Blind Date? I would like to pop those into the rules of thumb from the Dave Gerr book on monohulls and see how they compare.

- Gardner

On Mon, Nov 3, 2008 at 9:10 PM, Mike Crawford <jmichael@gwi.net> wrote:

Gardner,

  U, the predecessor to the current harry design, had a leeboard and rudders, but Rob has since changed his design.  A partial description is here:

    http://au.groups.yahoo.com/group/harryproa/message/3899


  A comment on symmetric (non-rotating) foils can be found here:

    http://au.groups.yahoo.com/group/harryproa/message/3194


  There was another post at one time (at least I think), but I can't find it.  I believe it had two main comments:

  - It's tough to make a foil that is stable at speed in both directions.

  - You need a lot of steering surface in any case.  So, if you already need large rudders, why increase drag by putting a third foil in the water?

  I apologize to whomever made the original post if I've gotten it wrong.


  I personally don't have any experience in fluid mechanics, and can't tell you why a vertical symmetric foil won't be stable.  I'd personally love to see two rudders that don't have to flip 180 degrees in order to shunt; not just for convenience, but also for the ease of integrating an autopilot.

  What's nice is that your quick-and-dirty boat should end up being the perfect test bed.  You won't have to worry about ruining a $10,000 awlgrip job each time you want to experiment with a new system.

  There's also a lengthy discussion of rudders starting in early January 2008 that you might find interesting.  Lots of back-and-forth about how different people would improve things.

       - Mike




Gardner Pomper wrote:
Well, I plan on having Rob do the design for me too, but one of the things I really like about this forum is how people explore different options. All designs are tradeoffs, and I am not yet convinced that a very complicated all in one rudder solution is actually simpler that simple rudders and leeboard, which is why I am looking for feedback.
 
Are there other reasons, besides building the case, that you don't like the idea of leeboards?
 
- Gardner

On Mon, Nov 3, 2008 at 6:21 PM, George Kuck <chesapeake410@yahoo.com> wrote:

Hello 
 
I am not realy keen on the idea of a leeboard but if I did want one I would think of it more as a supplement to the oversized rudders which might be slightly downsized but still capable of working as originally planned.  The leeboard would not be the traditional type but a daggerboard case leeboard. The case would pivot but the daggerboard could be set at whatever depth was needed for the conditions and depth of water, or it may be a short board used to supplement daggerboard rudders when they are set for shallow water.  The leeboard may also give you some redundancy if one rudder should fail, you may be able to continue sailing on one rudder and leeboard.   
 
My main problem with the addition of a leeboard is the added complexity, cost, building time and it is just one more thing to have to deal with when sailing.  If the Harryproa works as Rob designs it why make more work.  One of the main attractions of the Harryproa is the Easy Rig.  Keep it easy and do not make it more complicated even it it may give you a extra 1/10 th knot.
 
When I am ready to build I will just pay Rob for the plans and trust his design.  That's why you pay him, why try to redesign it.  If it does not work then you can blame him but it appears that the Harryproa concept does work.  I expect that the design can be refined over time but I would not make radical changes to it. 
 
Happy sailing,
George Kuck
Chestertown,MD 
 
      

--- On Mon, 11/3/08, Rudolf vd Berg <rpvdb@freeler.nl> wrote:
From: Rudolf vd Berg <rpvdb@freeler.nl>
Subject: Re: [harryproa] Leeboards? Date: Monday, November 3, 2008, 4:32 PM

Hi,
 
I' ve been thinking about using a leeboard on a HP too.
We have a lot of boats with leeboards here in the Netherlands, and I have some experience with them.
You would have to use a fore and aft symmetric profile which is not perfect. Also I am not sure how they work at higher speed. 
The attachment to the hull would be right next to the mast where it strong already.
 
My reason for taking leeboards into account was the same as yours: have simpler and less vulnerable rudders.
On BD sailing with both rudders down the front rudder is hanging loose in it's casing.
The aft rudder is highly loaded. So I figured having a leeboard with some length and pull it aft to to balance the boat and steer with a rudder as small as possible.
But where to put those small rudders?
 
Rudolf
 
 
 
 
 
----- Original Message -----
Sent: Monday, November 03, 2008 3:23 PM
Subject: [harryproa] Leeboards?

Hi,

I have been wondering about the use of a leeboard on a harryproa. I
know that Rob tried it on one of the small prototypes and had
problems. I was wondering if he (or someone else) could elaborate on
what the issue was, and if they think it was a design/construction
issue, or if there is a fundamental problem with using a leeboard on a
harryproa.

If you will forgive me for belaboring the obvious, the reason I am
considering it is that it seems it would make the rudders much simpler
and more reliable. They could be smaller, and would no longer have to
lift up to provide extra draft. It seems that 2 kick up rudders and a
single asymmetrical lifting (and kick up) leeboard would be simpler and
(possibly) more reliable (although less attractive).

I was just going through David Carr's "Nature of Boats" and his
description of leeboards seemed to indicate their practicality. I wish
there was a similar book that spent more time with multihulls.

- Gardner
York, PA




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