I am waiting to see how Rob's rudders go before I decide on the final design for mine. The spacing looks like being 4.5m from the centre on a 14.95m lee hull. This is to give sufficient distance from the masts set on the outside of the main beam bulkheads. I believe this is marginally further out than the original rudders on Blind Date.
I am not sure how much wave interference this configuration will give but as the boat is aimed at somewhere between Aroha and Blind Date in weight, with the length of Blind Date, I am extrapolating it should be OK. I will be going with a leeboard on your experience which,though adding to complexity, should reduce rudder loads. I am not sure on overall drag but am hoping for an overall reduction. If nothing else, it will give an extra safety margin in case of damage to a foil.
--- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@...> wrote:
>
> Yes this must be confusing.
> This is the original message I posted October 8 last year.
> Someone sailing BD contacted Rob Denney about the rudders.
> We considered this should be on the chat group so Rob put it on again.
>
> On the topic of jib induced luffing, I think it is because the bow is being pushed down by the extra power
> causing the centre of lateral area to move forward to a degree the (aft) rudder can't correct.
>
> Adding the leeboard helped, and the keel. A large rudder angle is still necessary to keep it going in the
> right direction. We tried sailing with an old rudder, lifted the new ones, and rudder angle was negligible.
> This was with keel fitted.
> regards,
>
> Rudolf
>
>
>
>
> ----- Original Message -----
> From: robert
> To: harryproa@yahoogroups.com.au
> Sent: Tuesday, June 01, 2010 1:54 AM
> Subject: [harryproa] Re: BD sailing
>
>
>
> I am confused. I can understand the front rudder inducing luffing. I don't understand the jib inducing luffing.
> All I can suggest is trying with tillers to get full control of the rudder angles and go from there. Is this with the small keel added?
> I thought it worked with the rough leeboard arrangement.
> Commiserations,
> Robert
>
> --- In harryproa@yahoogroups.com.au, "proaharry" <harryproa@> wrote:
> >
> >
> >
> > --- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@> wrote:
> > >
> > > Hi,
> > >
> > > Yesterday we have been out sailing BD with the new rudder set up.
> > > Wind about 16 knts. After hoisting the sails we pulled the sheet and the boat luffed.
> > > Pulled the other sheet to get the right bow pointing downwind and sheeted in again, the boat luffed.
> > > After a few attempts I descided to take the jib down, and we got her going.
> > > Rudder angle was about 10 deg. so no high speeds.We tried shunting and we had to get BD going really downwind to be able to build up enough speed to keep her from luffing straight into the wind.
> > > After some time we set the jib while sailing on a close reach. Once the jib started pulling the boat luffed into the wind the rudder only putting the brakes on.
> > > We took the jib down and proceeded without it. The front rudder has to be pulled up at least half way to keep the rudder angle 'down' to the 10 degres I mentioned. Front rudder all the way down makes it hard to keep the boat from luffing into the wind.
> > > We also tried the front rudder tilted out of the water entirely which made made for very nervous steering behaviour.
> > > Returning to the marina we were very disapointed.
> > >
> > > As we brought BD to the marina after the launch we had to negotiate some bridges and a lock all less than
> > > 1 metre wider than the boat. I noticed that steering was less precise compared to the old set up. Reaction is slower and seems more abrupt, probably because the late reaction causes one to turn the rudder further than usual.
> > > Reactions please,
> > > Regards,
> > >
> > > Rudolf
> > >
> > From someone who sailed on the boat with the new rudders:
> >
> > The problems are:
> > 1. the construction with a toothed bar fails when the rudders are turned the wrong way around.
> > 2. for the helmsman the position of the rudder blade is not clear. Most of the time the rudder blade is under water.
> > 3. the construction has a lot of friction and a lot of play.
> >
> > The result of 2 and 3 is that the rudders cause a lot of water resistance.
> > For optimal performance even one degree difference in the angle of attack of the rudder makes a lot of difference in lift and drag.
> > I estimate the punctuality of the present construction somewhere around 15 degrees.
> >
> > Even if the present construction is improved the disadvantages are:
> > - indirect contact between the steering wheel and the rudder blade
> > - no 360 degree turn of the rudder
> > - end of the toothed bar is difficult to see for the helmsman
> > - vulnerability: I do not know what will happen and how long repair will take when a rudder hits the ground and a braking pin brakes.
> > - many wheels where ropes can be derailed or too much friction when the steering ropes are tight end quote
> >
> > Looks like the connection between the rudders and the wheels is the first problem to be sorted, then look at the rudder location, size and whether additional leeway resistance is required. Apparently, they are going to try it with tillers and see how it goes.
> >
> > rob
> >
>