Subject: [harryproa] Re: BD sailing
From: "cateran1949" <cateran1949@yahoo.co.uk>
Date: 10/10/2009, 11:08 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Induced drag from the rudder applies a greater luffing torque the further it is from the lee hull, especially when it has to work hard. Look at the extreme case of the rudder on the ww edge of the lee hull.

--- In harryproa@yahoogroups.com.au, "Peter Southwood" <peter.southwood@...> wrote:
>
> I dont know that the distance from the lee hull is particularly relevant. I think the loading is the main factor, and that means area. Aspect ratio may affect the stall angle and suddenness of stall. Fore and aft position of the boards and rudders is also important as it will affect the load sharing.
> Cheers,
> Peter
> ----- Original Message -----
> From: cateran1949
> To: harryproa@yahoogroups.com.au
> Sent: Saturday, October 10, 2009 8:48 AM
> Subject: [harryproa] Re: BD sailing
>
>
> This is a bit of a relief.
> How much of it is more area and how much being closer to the lw hull. I suppose the obvious is to try an ogive leeboard or daggerboard pivoted as high as possible just below the mast and constrained by a rail. This would allow the blade to be pivoted back far enough to copy the results for the daggerboard
> It also suggests that a larger rudder blade as close as possible to the lw hull would work.
>
>
> --- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@> wrote:
> >
> > Hi,
> >
> > Today we went out again, this time with an obsolete rudder blade strapped to the lw hull walkway ( so ww side).
> > Straps everywhere to keep it in place, only one in the water around lw side of the lw hull to take the side load.
> > Because BD has a central walkway 1.8m wide,leading from the cockpit to the mast it was not possible to have it in the middle next to the mast. Also the blade is a naca section (more or less ;) so it was going backwards in one direction. In this direction it was aft of the mast.
> > This appeared not surprisingly to be the tack that benefited most of the daggerboard. There was a bit too much wind to be at ease with this contraption, about 16 knots. We had one reef in the main no jib.
> > After hoisting the main we pulled in the sheet gently and we just sailed away with no fuss.( dagger aft)
> > This was even better than with the old rudder set up! But when we were at speed rudder angle was still about 10 deg. When I didn't pay attention to the rudder and lost speed by pointing too high the boat kept going when bearing away. We stopped the boat to refasten something that had come loose and drifted downwind slowly with mast and sail to leeward. Once ready we sheeted in and again sailed on with no fuss.
> > Then we shunted, at least we tried. Three times, the boat kept turning straight in to the wind when pulling the sheet.( dagger forward of the mast) We then got her on a downwind course by pulling the opposite sheet and when we gained some speed we could sheet in. Steering on this tack was unpleasant as the boat wanted to go everywhere and it seemed we were oversteering all the time.
> > The boat was clearly moving straighter through the water than without the daggerboard, far less leeway and more speed. Forgot the GPS but we did come close to 10 knots I would say, without the dagger we didn't get it over 8 knots by GPS.
> > The dagger may have been between 1.5m and 1.8m deep.
> > We had both rudders down all the way all the time.
> >
> > regards,
> > Rudolf
> >
> >
> > ----- Original Message -----
> > From: Peter Southwood
> > To: harryproa@yahoogroups.com.au
> > Sent: Friday, October 09, 2009 7:28 AM
> > Subject: Re: [harryproa] Re: BD sailing
> >
> >
> >
> > If your lateral resistance was insufficient the boat may have been on the verge of stalling, and the extra sail area may have pushed it over the edge. One would expect the high aspect ratio rudders to stall more suddenly than the low aspect ratio bow/hull, so the centre of effort would shift forward rapidly, and the stern would skid out to leeward, resulting in a hard and uncontrollable luff. Loading on the forward rudder is consistent with this scenario. More rudder area or a centreboard should help.
> > Cheers,
> > Peter
> >
> > ----- Original Message -----
> > From: Rudolf vd Brug
> > To: harryproa@yahoogroups.com.au
> > Sent: Thursday, October 08, 2009 11:35 PM
> > Subject: Re: [harryproa] Re: BD sailing
> >
> >
> >
> >
> > Hi,
> >
> >
> > The second time we raised the jib I purposely kept sailing the same course -close reaching- and didn't change the sheeting angle.
> > Speed was something like 8 knots. The jib was hoisted while sailing. The power and speed increase was noticeable, and along with it the boat went out of control.
> > I think power of the sail will always push the bow down causing the bow to be the deepest part of the hull.
> > Maybe the bow acts as a pivot in that situation and causes the boat to turn upwind without lots of leverage at the other end?
> > Another thing I noticed was that the front rudder had load on. In the old set up the front rudder was hanging loosely in it's casing. We were able to lift it at speed which I remember well as I was surprised by that.
> >
> > regards,
> > Rudolf
> >
> > ----- Original Message -----
> > From: heinrich_meurer
> > To: harryproa@yahoogroups.com.au
> > Sent: Thursday, October 08, 2009 10:35 PM
> > Subject: [harryproa] Re: BD sailing
> >
> >
> >
> >
> >
> > I was wondering why the problem increased with the jib put up. One would expect the opposite. So what you are saying is that when you put up the jib the bow gets more depressed while sheeting in moving the lateral trim of the hull forward? Would the cure then possibly be to sheet in very slowly to keep the bow up? Did the luffing become more managable once you were up at speed?
> > Heinrich
> >
> > --- In harryproa@yahoogroups.com.au, "Rudolf vd Brug" <rpvdb@> wrote:
> > >
> > > Hi,
> > >
> > > The things that changed are :
> > > Distance rudders from centre was 4600MM, now 3800MM. Also they moved sideways 800MM to ww.
> > > Fitted the electric drive with batteries weight max. 120kgs.(probably less)
> > >
> > > Rudders are smaller but the other setup worked also with blades partially raised.
> > > Also we sailed with only two of us, with the old set up there was no problem sailing with six persons sitting in the cockpit, so well to ww.
> > >
> > > Thanks Robert, yes I was thinking just that. I am going to try to temporarily fix an old rudder blade in the middle as a dagger board. I think the bow down attitude of the boat with full sail up might be the cause.
> > >
> > > regards,
> > > Rudolf
> > >
> > >
> > > ----- Original Message -----
> > > From: Rob Denney
> > > To: harryproa@yahoogroups.com.au
> > > Sent: Thursday, October 08, 2009 11:08 AM
> > > Subject: Re: [harryproa] BD sailing
> > >
> > >
> > > G'day,
> > >
> > > Very disappointing. Could you make a list of the things that have changed, please, so we can try to figure out the problem. eg, sails, rudder location, rudder size, weight in ww hull, differences in water drag, etc etc.
> > >
> > > Ta.
> > >
> > > regards,
> > >
> > > Rob
> > >
> > >
> > >
> > > On Thu, Oct 8, 2009 at 3:14 PM, 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
> > >
> >
> >
> >
> >
> >
> >
> > ----------------------------------------------------------
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> >
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> >
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