Subject: Re: [harryproa] Re: BD sailing
From: "Rudolf vd Brug" <rpvdb@freeler.nl>
Date: 10/18/2009, 12:18 PM
To:
Reply-to:
harryproa@yahoogroups.com.au

 

Hi,
 
I don't claim to have all the answers, but it seems that from a standstill the rear rudder does most work to get the boat to bear away.  With just 2 rudders the aft rudder has to move the entire midsection of the boat across the water against the pressure of the sails. At this stage the forward rudder is somewhere near or at the pivot around which the boat is turning. So it doesn't steer the boat much.  
The leeboard compensates the sideways load and provides a pivot
to turn the boat with the aft rudder.
 
regards,
Rudolf
 
 
----- Original Message -----
From: rob
To: harryproa@yahoogroups.com.au
Sent: Sunday, October 18, 2009 1:08 PM
Subject: [harryproa] Re: BD sailing

 

On further thinking:
I can't get an integrated understanding of all these points. Why further apart rudders allow the boat to sheet in and sail away as does a leeboard. I can't see why having the rudders further apart can make such a difference to simply angling the rig to a fairly fine angle, getting a lift and driving the boat providing there is enough rudder area. The only difference I can see is the distance to lw of the COE being a smaller prop0rtion of lever arm when using the wider apart rudders or the leeboard,
regards,
Robert
--- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@...> wrote:
>
> Hi,
>
> As I see it things seem to be pointing in one direction.
> This is how I feel it works on bigger boats like BD.
>
> Rudders closer to the mast loose steering effect. Shunting is getting more difficult.
> Rare Bird's and the old BD set up seems the minimum distance from the mast to steer well and sail
> with acceptable rudder angle. Arttu's boat shunts easily with rudders further apart(5.3m)
> The old set up didn't allow us to sheet in and sail away.
> The leeboard we tried indicates that a central(ish) leeway preventer improves steering and shunting.
> All this seems to lead to the conclusion the best solution is to have normal size rudders as far to the ends as possible with a leeboard or 'luffboard' next to the mast. Rudders have to be kick up and the front one lifted out of the water always. As they have to be near the ends I would prefer in hull rudders. I am working on those, it seems possible.
>
> regards,
> Rudolf
>

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