Rudders to a Sharpie-proa?
I would like to thank all those who took the trouble to comment on my postings. It is this courtesy and helpfulness that characterises this forum and makes it so useful. If I might summarise, the responses have been generally encouraging but with the warning that a ‘lift/lower’ steering approach, even if it could be made smooth-running, may not respond rapidly enough to cope with gusty conditions, traffic, narrow channels and when running downwind.
As far as I can tell, there would be no reason not to adapt my proposal to accommodate a Brown/Newick dagger-rudder - but I haven’t worked out what would happen to the steering linkage(s) during a kick-up. Presumably it is expected that the front dagger is raised (either fully or at least above the level of the rear one) during sailing and so the impact will always be on the skeg part of the rear dagger-rudder.
Perhaps the solution would be to combine the Hughes/Johnson ‘bendy end’ design with the Dierking cassette mounted at bow and stern with a coverplate to fair the slot. That way the dagger board(s) can kick-up without disrupting the steering mechanism. The dagger board would be constrained by its downhaul and the coverplate and should re-seat OK. Only the dagger board would be at hazard – the steering gear should not be damaged in the event of a kick-up. The whole shebang can still be built as two identical units each bolted to an end of the vaka.
Add the Hielkema idea of ‘lift/lower + ogival foils’ for leeway control and a bit of trimming then we can spread the kudos/blame as widely as possible….. :o)
thanks again to all
Peter
End rudders on a proa. Kick ups.
Hi Alex,
Thanks for a tantalizing post.
How well did they work ?
Do you have constructional details ?
What were the pitfalls in construction, deployment and operation which should be watched for ?
They appear from the photographs to have undergone evolution - do you have details of this ?
A French proa that crossed the Atlantic. I’m guessing that the red rudder was first and then had a cassette added to vary depth.
I like that it can kick up easily,as held in place by rope.
Found it as a link on the proa petrel site - French version- proa armada.
Iam sure this will not work properly. Perhaps you can steer a proa on the open sea using the forces of CLR and CE of sails, but as soon as you have to avoid a crash with another boat or entering a tight habour you will see, that this system responds by far not fast enough to change direction.
The next thing is that you have to realize that the centers of efford on a boat are not fixed, they are moving a little. If a puff hits the boat, the boat speeds up and the sail is deforming under the pressure of the wind, both effects change the centers. Imagine a hard puff lifts the ama and the boat wants to go into the wind, but you want to steer off the wind to bring the ama down to the surface to avoid a capsize.If you want to steer straight ahead, you will constantly trim both centers ... I cannot imagine that this is comfortable and/or effective to steer. Or think of steering it in big short waves. And last you have to have a buttersoft sliding of the “dagger” in its case up and down against the side pressure of the water ... no easy engeneering.
I love a poster who is sure of himself. 😉 In this case, though we’ve never met and I mean no offense, I’m fairly sure you are mistaken; not outright wrong, but mistaken in the details and the magnitude of the issue.
This is not a new concept (few are) and has been extensively discussed over many years. I have seen precisely this scheme built at full size and I have myself built several boats with analogous steering schemes; in my case with kiteboats. Rather than raising and lowering boards under a more or less fixed rig, we attached the kite’s lines to a block on a fore and aft track, at the leeward deck edge, then mounted a single, fixed daggerboard amidships. Moving this block fore and aft is analogous—though not identical—to raising and lowering the daggerboards in this example.
Works a treat. It’s very easy to maintain a fixed course—to the wind—and relatively very easy to change course—even quickly, even at high speed. You actually have two options; which can be used together for very (very!) quick course alteration; raising/lowering the board(s) and as Mel pointed out, sheeting the mainsl in or out. When I say very fast course changes are possible, I mean fast enough to throw you out of the boat; and I mean the skipper, not some inattentive non-sailor passenger. First-hand experience…
What is difficult is to steer when there is no way on the boat—and/or there is no sail force (steering requires a force couple, in other words). Therefore the scheme is useless for in harbors and of only limited value as the wind goes light. It is also no good for “shooting” marks or docks—as soon as the sail goes slack the boat’s on rails, completely out of control.
Regarding your statements about migrating CLE, these are technically accurate, but one of the very reasons daggerboards exist is in order to limit such migration—rather than the CLE moving X% of the hull length (often as much as 20-30%), with one or more daggerboards you get migrations of CLE on the order of 10-20% of the board’s chord, which is very much less than with a non-daggerboard hull.
So yes, like most every boat the steering system requires some input to maintain perfect balance and optimal course-holding, but as this system can be made aggressively self-steering, and if one can put up with a small amount of “hunt” in one’s course, this concept remains a winner.
Cheers,
Dave Culp
Here is my take on proa rudders
might be better suited to larger proas
inbuilt steerable retrtactable proa rudders that kick-up on grounding
http://www.tacking-outrigger.com/proa_rudder.html
n peter evans - Melbourne, Australia
I plan to use the Dierking cassette rudders on my 6m proa. To me, they are the only style of rudders that can survive hard groundings in any direction without damaging the rudder blade.
Kickup rudders that need to go into a slot in the hull to kick up will jam at some point, because the trailing edge of the foil enters the slot first. However if the tiller is off center, the trailing edge will find the hull, not the slot. I suppose if the blade is designed so that the hinged portion can lay flat under the hull when the foil swings up, then the only negative is that the steering system will be forced to the 90 degree position if the rudder grounds hard.
I thought about using the cassette rudders at the ends of the hull. However, I plan to leave both rudders fully down all the time, since there is no other centerboard or leeboard. So if the forward board hits shallow water, there needs to be enough room for the rudder blade to swing under the cassette housing. But the bow is there, and my boat doesn’t have enough rocker to make room for the rudder blade. So, I’ll use quarter rudders. If the bottom is the cassettes is slightly above the water line, then there will be enough room for the rudder blade during groundings.
At least, that’s the plan…
I plan to use the Dierking cassette rudders on my 6m proa. To me, they are the only style of rudders that can survive hard groundings in any direction without damaging the rudder blade.
Kickup rudders that need to go into a slot in the hull to kick up will jam at some point, because the trailing edge of the foil enters the slot first. However if the tiller is off center, the trailing edge will find the hull, not the slot. I suppose if the blade is designed so that the hinged portion can lay flat under the hull when the foil swings up, then the only negative is that the steering system will be forced to the 90 degree position if the rudder grounds hard.
I thought about using the cassette rudders at the ends of the hull. However, I plan to leave both rudders fully down all the time, since there is no other centerboard or leeboard. So if the forward board hits shallow water, there needs to be enough room for the rudder blade to swing under the cassette housing. But the bow is there, and my boat doesn’t have enough rocker to make room for the rudder blade. So, I’ll use quarter rudders. If the bottom is the cassettes is slightly above the water line, then there will be enough room for the rudder blade during groundings.
At least, that’s the plan…
If the sails are arranged so that the resulting forces acting to leeward are applied aft of center (i.e. towards the stern) then the aft dagger-board will have to sit deeper than the fore dagger-board. So the first dagger-board to kick-up will be the aft one - the lack of clearance for the fore dagger-board under the bow will not be an issue. Neither will the problem of hitting the rudder, whether set over or not, rather than the skeg.
If the sails are arranged so that the resulting forces acting to leeward are applied aft of center (i.e. towards the stern) then the aft dagger-board will have to sit deeper than the fore dagger-board. So the first dagger-board to kick-up will be the aft one - the lack of clearance for the fore dagger-board under the bow will not be an issue. Neither will the problem of hitting the rudder, whether set over or not, rather than the skeg.
I plan to use a schooner rig, so I think you are right in theory about needing more lateral resistance at the stern than at the bow, but if the weather helm is not excessive, I may leave the leading rudder fully down anyway. I could compensate by adjusting its angle of attack when I lash its tiller down.
Maybe I wasn’t clear about my design - I have no dagger boards and no skeg, only two large rudders, which will resist most of the lateral force. I’d like to experiment with asymmetrical rudder profiles, and if I’m unsuccessful, I can just make two new rudder blades with NACA profiles.
I still think having rudders at the end of the hull is a problem if I hit a shoal at 10 knots. I will have less than a second to raise the bow board after the stern rudder hits. This is the best case. The worst case is the shoal has a steep side and the bow rudder hits and the bow rides up and over the blade. Something will probably break - most likely the blade. But maybe that’s not so bad. It may save the bow from damage.
It’s interesting to think through these things. Thanks!
As far as I can tell, there would be no reason not to adapt my proposal to accommodate a Brown/Newick dagger-rudder - but I haven’t worked out what would happen to the steering linkage(s) during a kick-up. Presumably it is expected that the front dagger is raised (either fully or at least above the level of the rear one) during sailing and so the impact will always be on the skeg part of the rear dagger-rudder.
Perhaps the solution would be to combine the Hughes/Johnson ‘bendy end’ design with the Dierking cassette mounted at bow and stern with a coverplate to fair the slot. That way the dagger board(s) can kick-up without disrupting the steering mechanism. The dagger board would be constrained by its downhaul and the coverplate
I have been thinking some on the kick-up stem and stern mounted cassette - Newick/Brown rudders, and this is what i came up with.
A simple daggerboard-rudder with a diagonal turnable rudder-part. It should be easy to control with wires or dyneema-cord running inside the daggerboard-part.
I hope the pictures shows my idea better than i manage to describe it with words.
Cheers,
Johannes
Above is only the rudder part.
I borrow a picture from post 5 by pr1066. This is what i mean by stern/stem-cassette-rudders.
When testing the simple model i have a very good control of the rudderblade. Its easy to turn the rudder even though i hold my fingers in the way, resisting the blade.
Cheers,
Johannes
I think there must be some development on the The Epic Track Master Steering which moves the entire stern of the kayak.
In AYRS No 68 (1969) detailed a proa called Kia Kia, by Chris Hughes, which had moving sections at each bow. The bow section had a hinge mounted on the leeward side of the vaka, it could therefore be moved away from the ama. The bow would be locked and the stern would be used to steer. In the report it says the rudder was trimmed about 10degrees and further steering done by weight. The system was reported as highly satisfactory. The picture shows a break in the hull of a couple of inches so I can’t image the drag it may have caused.
My fear with such systems is locking the bow rudder, I can see it breaking free and suddenly swinging over to one side and getting over stressed. The Newick/Brown rudders obviously lock when raised.
On a side issue kayaks have remote retracting and deployment down to an fine art.
Tink