The rudders on BD can be disconnected. When they are linked together they work in opposite direction, if the front goes left the aft goes right thus the boat turns a tight circle.

The front rudder does work as a huge break when turned more then a couple degrees so should be used only at low speed.

When the rudders are turned parallel they pull the boat sideways.

 

Rudolf

----- Original Message -----

From: Gardner Pomper

To: harryproa@...

Sent: Wednesday, November 05, 2008 5:20 PM

Subject: Re: [harryproa] Leeboards?

Another rudder question.. do the fore and aft rudders turn together, or in opposite directions? By this I mean, are the rudder blades always parallel to each other, or when the aft one turns to port, does the forward one turn to starboard?

Thanks,

- Gardner

On Wed, Nov 5, 2008 at 7:30 AM, Rob Denney <harryproa@...> wrote:

G'day,

Great threads, guys. Everytime I have something to say, someone beats
me to it!

Rare Birds rudders are 1.6m/64" deep x 500mm/20" wide. This is 1.8 sq
of total immersed area which is 2.5% of the sail area. On future
boats it is a smaller percentage as the boats steer so well and have
comparatively little windage.

regards,

Rob

On Wed, Nov 5, 2008 at 12:16 AM, Gardner Pomper <gardner@...> wrote:
> 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@...> 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@...>
>> 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@...> wrote:
>>>
>>> From: Rudolf vd Berg <rpvdb@...>
>>> Subject: Re: [harryproa] Leeboards?
>>> To: harryproa@...
>>> 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 -----
>>> From: gardner paper
>>> To: harryproa@yahoogrou ps.com.au
>>> 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
>>>
>>>
>>
>
>