Many thanks. First time I have seen these photos. My fault, not yours. What is the second to last photo in the sequence? What were your reasons for choosing the split keel?
I still do not understand how the keel makes a difference to the weather/lee helm. I do not think having the rudder further to windward makes a big
difference. If it did, throwing a tied on bucket off the windward hull would cause a violent luff, and it doesn't. The drag on a well faired rudder is not high, if it is
pretty much fore and aft. If the boat luffs while sailing with the aft rudder only then adding more underwater area ahead of the coe will not help. If it did, the front rudder would be even better than the keel. I do agree that if the rudders are turned significantly, the bows will go down and the drag and the pitching will add weather helm. There also appears to be too little rudder area (from memory, this was based on El), but this should not make a huge difference, particularly if the steering is still difficult with a reef, or with just the main.
Do you think that deeper rudders on the beams would work (apart from the draft increase), or is it a bigger problem? If so, what?
How much of the Ijsellmeer is less than 2m deep? Pretty sure this was the limit set in the early design stage, with the ability to go less occasionally.
Is the "balance thing" with the old rudders the effect of raising them and requiring more force to turn them? Apart from this, would you be ok going back to them?
No idea the effect of the shafts being immersed. It was not a great photo and not possible to see how deep the bubble went. It was one of a few things that needed correcting before I was prepared to throw away the beam mounted rudders.
I appreciate your openness. Very much. Will make it a lot easier dealing with the BD committee. I am still confused about why either or both the beam rudders work on El, the rudders work on RB but the lightest of them all is having problems. Hopefully we can keep discussing it and find some answers. Also hopefully, I will be over there next summer and can see it for myself. Do you know what they are planning to change/do before the boat goes back in the water?
rob
Rob,We added the keel after trying an extra board strapped in place behind the mast. There are photos of that in the photo section.The addition of the extra board lead to a leeboard experiment. The leeboard showed improved control by the rudders,we could sail off by just pulling the sheet. (more or less)Also sailing close winded was possible, which without the leeboard was absolutely impossible. (anything higher that reaching was)After the leeboard(testpiece) broke and the owner saw the extra handling it would need it was decided to add the keel.A drawing of that is also in the photo section (Blind Date - new rudders). Dimensions keel are: 0.6m deep, two fins each 0.5mwide at the base about 0.4m at the tip, 0.5m apart.The old rudders were 0.5 m wide and 2m deep. The new ones are 0.47m wide ( not .4 as mentioned yesterday) and 1.5m deep.We sailing with the old rudders partially retracted several times, no problem apart from the balance thing. Don't know if we tried all the way up to 0.7 draft, but we never lost control.If the rudder shaft is making spray would it be of such impact that the boat gets out of control and just turns upwind?We couldn't gain speed for the rudder angle needed to keep course. Ventilation occurs at speed as far as I know.(and experienced)It was obvious the nose went down quit a bit, which isn't strange as the brakes were on with rudders at that angle.Nose down leads to shifting of the CLA forward which isn't helping.On a small boat you compensate trim without thinking, you just react.All this information (at least most of it) I have written here after we did the testing.Hopefully experience shared - positive and negative- will lead to improvement by discussion and perceverance, as we shouldn't expect to reach perfection ;) How's that for a motto?I have never been wanting to be secretive about what we do or what we experience working on BD or whatever boat.If that impression occurred it was not my intention.Rudolf----- Original Message -----From: Rob DenneySent: Friday, March 04, 2011 12:47 AMSubject: Re: [harryproa] Beam mounts and tillersGreat to have the information. Thanks.
Couple more things, if you don't mind. How does the immersed area of the two compare? Were the tests before or after the keel was added? What are the keel dimensions? How difficult is it to steer with the old rudders with the board raised to 700mm draft? Peculiar that the shaft on the aft rudder was below the water in the pictures I saw. Probably a wave, but do you have any other suggestions?
I am not sure you can compare the two either, this was one of the unknowns when we decided to try the beam mounted rudders. I still can't see any reasons why it would be a problem, though. Until it is fresh and downwind, I sit pretty much in the middle of El.
rob
On Thu, Mar 3, 2011 at 10:32 PM, Rudolf vd Brug <rpvdb@freeler.nl> wrote:
Rob,Current problems weren't around when we tested the new rudders.The rudders themselves are straightforward 40cm wide and 1.5m deep, NACA section.The rudder shaft is 70mm square and is not faired above the blade to be able to pull it upall the way to the tube with the rudder bearings. That does produce some spray but the fairedpart is piercing the water surface at rest.The rudders draw .7m minimum, pulled up all the way.This shallow draft ability is important to the owner. They sail a non tidal water with well charted shallows.We tried sailing BD with one 'old' rudder as an extra. We pulled the new one out and used the old one instead,steered with a tiller. That worked well. We steered with the aft rudder.I'm not sure if you can compare small boats like El. with bigger boats one - one.Lengthwise trim might have something to do with this too.RudolfG'day,Honest answer is, no idea. I have not seen any pictures or reasonable descriptions of the rudders, the keel or the steering set up. The pictures of the boat I have seen have shown the jib sheeted to the mast and the rudder shafts kicking up a shower of spray and destroying the flow over the rudders. There are 5 people on the committee running BD, and they have 5 different ways of shunting and 5 opinions of what is wrong and how it should be fixed. I have made numerous suggestions to improve the steering, but have had no feedback on whether they were tried, or worked. It is heartbreaking for me as BD is the epitome of how a hp cruiser should be.
I do know the beam mounted rudders work well on El, even with comparatively more weight in the ww hul than BD. I am putting a similar set up on my boat and the second one we are building. It is also going on the two 20m/66'ters.
I also know the original rudders work on Rare Bird and consider this a far better option than keels, rudders on the ends etc. The problem is not shallow draft steering. This can be done with the original set up. The problem is if the boat is sailed at high speed in shallow water, when the rudders become unbalanced and steering loads get high. I think this is unseamanlike so the unbalance on the raised rudders will force the boat to slow down, which is a good thing.
I am happy to discuss this further, but until I have all the information, and the current problems are corrected, I will not be much help.
rob