A really interesting thread of comments has developed about rudders and other movable appendages on the French aluminum expedition yacht from Boréal.
The Offshore Voyaging Reference Site
A really interesting thread of comments has developed about rudders and other movable appendages on the French aluminum expedition yacht from Boréal.
The mini-daggers are quite an intriguing idea. Yes, it’s two more things to deal with when changing course, but I imagine you’d just leave them alone if you’re tacking in tight quarters. From a hydrodynamics standpoint, I think it’s quite a clever trick, although it would clearly take a fair bit of design experience to work out the exact angles, cambers and areas to make it work.
How big are the mini-daggers, compared to the boat’s other appendages (or total lateral plane)- ie. how much of a turning moment do they actually produce compared to the rudder?
This is all very fascinating. How many ways there are to solve the age old problem. Of course one solution may be better on one particular boat than another. But clearly Boreal seems to lead the pack of boat designers at the moment. This is the high tech field of modern cruising sailboat design. Previously the high tech designs came from the racing boats.
Here is another very interesting expedition sailboat, Glory of the Sea, http://sailboat-for-sale.periple.com/aluminium-boat-index.php . Twin rudders, saber daggerboards, double hull, inside steering. Definitely designed for the expedition minded sailor.
I would never have off center appendages on an ocean cruiser. Exposure to damage from semi-floating debris, extra first time cost, extra maintenance cost, extra weight, all in all an elegant solution to a non-existent problem. For me the number one consideration for a rudder is its suitability for control by a transom mounted servo-pendulum windvane, that means an inboard spade rudder with maximum area and balance and a simple tiller. Now that’s Attainable Adventure Cruising.
Hi Matt,
Good question. Perhaps Boreal will answer it.
Hi Victor,
Took a look at Glory of the Sea. An interesting boat, although she does look more complicated than I would like. Not sure about the double hull either. I think I would prefer putting the weight into thicker plate. Finally, the Danforth style anchors do not work well in the high latitudes, at least in my experience.
Hi Robert,
I would agree with you if the offset appendages were mission critical. For example, I’m no fan of twin rudders for just the reasons you state. But in the case of the Boreal where the dagger-boards are not, as I understand it, required to safely sail the boat, I think they may be a very good idea. If they are as effective in improving tracking as Boreal claim, they would really help a self steering vane out. I’m also thinking that should the main rudder be damaged, the combination of the dagger boards and the paddle of the self steering vane as an emergency rudder might easily get one home.
One thing I would want to be sure of is that in the event of a collision the dagger-board would shear off without damaging the casing and potentially starting a leak.
A lot of comments, with a lot of questions and remarks.
Thank you !
Matt,
Jean-François Delvoye’s son is a hydrodynamic engineer working for a big company in that field of expertise. That made it possible for us to do a lot of research which usually is not done for this kind of boat. We are happy to show to visitors to our yard the method we applied and the results… But I’m sure you understand it is something different to put all the results of hours and hours of research on the internet…
Victor,
I saw Glory of the Sea some years ago in Ushuaia when Jacques Peignon was sailing her. I cannot agree more with what John says about her. This point of view was confirmed to us last week, when the skipper who did the last delivery of the boat came along to visit us.
Robert, John,
The daggerboards are of wood and are meant to shear off without damaging their casings (moreover there is a watertight bulkhead in front of the casings and the ruddershaft).
We too did not want twin rudders for the same reason as yours (see also my previous comments). The daggerboards really help the pilot, so they would help a windvane as effectively…
Like Matt says it is indeed one more thing to trim but the trim has a real and immediate impact you can feel when steering yourself.
A very big thank you to Colin for a really excellent review. I wonder, if the Boreal 47 had existed before we commenced what turned out to be a three year refit on Morgan’s Cloud, what we would have done…
Also, a special thank you to Jean-François(s) for their very open attitude, even when their brain child was criticized, and the clear way in which they have answered all of our questions.
The Alden design office used an extra centerboard located on the centerline aft in several of its big centerboard designs. The reasoning being that a rudder large enough to suit them was not possible with shallow draft. The aft board was lowered to help steering control offwind, and helm balance in high winds.
Steve Dashew comments. http://setsail.com/twin-center-boards/
As I recall the Garcia 45 Passion which my friends Bernard & Monique sailed from Bear Island (N of Spitsbergen) to Cape Horn about 20 years ago had a retractable centerline daggerboard ahead of the rudder. They used it running downwind in heavy conditions to provide directional stability. Raised the center keel entirely leaving a flat bottom. Also, the boat was built with 12mm plate to the turn of the bilge- no worries about letting her dry out!
We have a Garcia Passoa 47, similar to the boat described by Richard.
The after daggerboard can be put down to about 2.4 m draft, and reduces weather helm when pressed hard on the wind.
We also pull the main centerboard all the way up when the wind is any more than about 20 degrees aft of the beam, with the daggerboard all the way down. Steers finger and thumb on the wheel in 45 knots plus.
More importantly, I do not think we can broach.
I understand the Boreals have a VERY shallow keel, so will not be quite to resistant to broaching, but will still be much safer downwind than a deep keel boat.
Neil,
The Boreals have a keel box or foot that has two functions as I see it.
1) It provides a wider flat bottom for the boat to sit on when beached
2) it serves as a housing for the keel when in the “up” position.
A third possibility is that serves as a mini keel for directional stability when going downwind. This would have to be verified by either of the two Jean-François of Boreal. Obviously they know much more about it than I.
I do believe though the possibility of broaching a Boreal is slim especially with a daggerboard down. Hopefully Jean-François Eeman will weigh in on this topic again.
We have no dagger boards or other appendages on our Meta Dalu 47. We do however have a fiberglass deep rudder in the rudder cassette than extends another 2 feet or so below the hallow alloy rudder. In addition because the rudder is transom hung the the effect on steerage is remarkable i.e. a little turn makes a big difference.
If we’re going to keep hitting kelp (and occasionally rocks) with our rudders there would seem to be a case for transom-hung rudders that kick up for clearing and maintenance. Saves donning diving gear and jumping into cold water. And if we’re going to hang them off the transom, why not have two like so many current racers deploy? By motoring or sailing cautiously we would even have a rudder for steering while attending to the other.
Dual rudders? Boy would I dearly miss the possibility to use the propwash across a central blade…
Hi Paul,
Yes, there are benefits to transom hung. We were going to go that way with the A40. That said, I would not want twin rudders. Just way too vulnerable to debris and rocks. Also see Ernest’s point.