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Old 26-11-2008, 07:21   #1
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Aft Mast Ketch Rig

Brian Eiland designed a very interesting aft mast ketch rig Sail Propulsion - Revisiting a Mast-Aft Sailing Rig
This rig offers a boomless ketch rig with one mast only (saves weight).
All sails roller furled for easy single handling. On top the mast offers
a good top space for radar, antennas and or windgenerator in the aft top section being out of the way avoiding the ugly radar arch and stern loads.
Theoretical it sounds quite well that I'm asking why its so seldom used.
Does anybody has experiene with this type of rig?
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Old 26-11-2008, 08:26   #2
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Mr. Eiland's ideas have been discussed ad-nauseum here and in many other forums. His is a life-long dream that is based on inaccurate premises. In reality, the engineering challenges of building a structure to support a cantilever mast are enormous. The tension required to keep two long luffs straight (a mandate for roller furling) is easily calculated and is orders of magnitude higher than the forces required for a vertical mast. The load on the structure that supports the mast increases the same way. To picture this, compare the neck of a harp with the neck of a violin. That raises the question "Why bother?" His answer is that the mast in front of a main sail spoils the aerodynamics and reduces the efficiency of the sail. In truth, that is not always so. In fact, a rotating foil-shaped mast increases the power of the main over a wire supported Genoa. It is a three dimensional foil, providing a greater pressure differential that a two-sided sail can. He also suggests that it is far easier to furl a wire or rod supported sail using roller furling, which is true. But if you are reefing because the winds have kicked up, you want to lower the center of pressure, not move it forward.

My Grandfather was a farmer. we pulled stumps to clear a field for plowing. We rigged an A frame and used a come-along from the top of the A frame to another stump. If we couldn't raise the stump on the first try, we canted the A frame away from the stump and tried again. This worked every time. In this case, the stump is the back stay chain plate, and the fore stay on Eiland's designs is the come-along. The more the mast leans forward, the greater the mechanical advantage in the part you most want to stay taut. end of rant.

I do think there is a lot to be said for an A frame mast. A main sail with a boom cound provide its own aerodynamic balance, making it possible to control with much lower forces.
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Old 26-11-2008, 11:42   #3
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Quote:
Originally Posted by tallboy View Post
Brian Eiland designed a very interesting aft mast ketch rig Sail Propulsion - Revisiting a Mast-Aft Sailing Rig
...
Theoretical it sounds quite well that I'm asking why its so seldom used.
Does anybody has experiene with this type of rig?
As noted, it's been discussed before here. Sandy is quite adamant there is little to no value in the rig; I believe it's novel, nice looking and might be some or all of what it's claimed to be. The designer, who incidentally posted to the thread, obviously likes it.

But it's relatively untested and there deserving of critical review.

I personally think the way to get a definitive answer is through finite element analysis. But this is an expensive process and not all that many designers (or their clients) want to do that.

Anyway, let me refer you to the ketch rigged Cat
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Old 26-11-2008, 13:39   #4
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Maren is accurate, and I've been adamant. But my point is not that it won't work, but that to make it work requires a foolish waste of money, engineering, and exotic materials to achieve no improvement over something you can enjoy today, or build tomorrow for a fraction of the heartache.

Finite element analysis is overkill, freshman Engineering Dynamics will at least resolve the loads. You can build a boat to support three times the load at the mast base and 8 times the load at the back-stays, and still have too much sag in the fore and jack-stays to furl the sails, but it will cost many times as much as an elegantly simple and light weight cat that won't get laughed at.

Rube Goldberg's mouse trap is a case in point. Are you out to amuse yourself with a hilarious collection of long-cuts for the bragging rights alone, to cherish the elegance of the absurd, or did you just want to catch a mouse?
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Old 26-11-2008, 13:45   #5
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Why is it called a ketch rig? I thought ketch rigs were two-masted with the aft mast being the shortest. Am I wrong?
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Old 26-11-2008, 13:51   #6
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The original thread wandered a bit. It started as a discussion of the apparent absence of ketch rigs in general. IMHO they have a place on cruising sailboats; cat. tri or monomaran.
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Old 27-11-2008, 12:37   #7
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Aloha Sandy,
Oh, sorry. I guess I do know what a ketch rig is. Had one for many years. Great for cruising but kind of unhandy for day sailing.
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Old 27-11-2008, 12:49   #8
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Quote:
Originally Posted by sandy daugherty View Post
Maren is accurate, and I've been adamant. But my point is not that it won't work, but that to make it work requires a foolish waste of money, engineering, and exotic materials to achieve no improvement over something you can enjoy today, or build tomorrow for a fraction of the heartache.
Mmmm, maybe. Except for that fellow Barefoot who actually put one on a tri.

Quote:
Finite element analysis is overkill, freshman Engineering Dynamics will at least resolve the loads. You can build a boat to support three times the load at the mast base and 8 times the load at the back-stays, and still have too much sag in the fore and jack-stays to furl the sails, but it will cost many times as much as an elegantly simple and light weight cat that won't get laughed at.

Rube Goldberg's mouse trap is a case in point. Are you out to amuse yourself with a hilarious collection of long-cuts for the bragging rights alone, to cherish the elegance of the absurd, or did you just want to catch a mouse?
To be fair, it really isn't like a Rube Goldberg device. You aren't going to crank in on the winch handle which will activate the gas solenoid which causes the anchor to drop which ... you get the point. In fact it's a lot more like stay inside the cockpit and raise or lower all your sails. That seems a lot safer than going to the mast in heavy weather for most cats.

You know, ever since the Amaryllis was designed by Herreschoff people have had bad things to say about catamaran. They didn't really catch on until our lifetime. And, many laugh at proas. I don't think people laughing at thinking something is dumb necessarily invalidates it. But I work in a field with the attitude of 'if it's dumb but it works, it ain't dumb.'

My point is: The jury is (at least for me) still out since it has had limited implementation which was seemingly shown to work but no rigorous testing.

SkiprJohn: Well, the aft-mast rig is called just that. But I think Brian Eiland's view that his rig is a ketch or ketch-like in that its more keeping with a traditional rig. That is a jib, a main sail, and (to address your point) a smaller second 'mast' in front of the rudder post.

Now, if memory serves, I was expecting the thread to go into loads and how the dolphin striker has to convert a vertical load to a horizontal one, often causing the low bridgedeck clearance. So I thought a second one ... well, I leave that as an exercise for the reader.

I do think the other thread is worth reading as there were several good exchanges, and the links were good.
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Old 02-12-2008, 11:22   #9
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Maren: I've satisfied my need to save the world from dead-ends, and will gladly apologize to everyone when someone builds a successful Eiland design. However:
The trimaran you cited proved my points, and reverted to a conventional mast at great expense when things broke. It was not engineered to begin with, and the choice of hull was ill-advised, so it does not completely invalidate the concept, but it does underline my objections.
It is easy to take all sail controls aft to the cockpit on virtually any sailing vessel. Not doing so is a simple matter of choice. Many stock cat rigs (such as my own) can be completely controlled from the cockpit. This has nothing to do with building a structure strong enough to keep the luffs taut. So my question remains; why bother? Is there any concrete evidence at all that such a rig would be so much more efficient, or safer, or easier to handle that it would be worth the extra expense? If so, why hasn't anyone done it?
If you say its because the people who can afford such an experiment are too cautious, You are right. That might be how they got to be that rich. But since there are still enough wealthy non-conformists out there to try anything, there might be another reason. Like "the jury is in, its just not worth it." Lets go back and rerun that Smithsonian film of the grand (failed) experiments in flying machines, where the skeptics were right. Some wild and crazy ideas are just that.
Please don't picture me as a staunch Luddite opposed to innovative thought. I've been a avid member of AYRS for many years, and would love to see more of those efforts bear fruit. But I'm also a retired accident investigator; I can't express how I felt about the results of some of the wild and crazy things I've had to investigate. One case still stands out in my mind, where a paraplegic adventurer became a quadriplegic in someone else's lifetime dream, an ultralight aircraft that became dynamically unstable and uncontrollable in a mild crosswind. I've lost track of the designer. He was neither an aerodynamicist or an engineer, or he would have been able to see the potential for what actually happened.
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Old 02-12-2008, 15:29   #10
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Ok, I concede. I didn't realize there were two masts.
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Old 02-12-2008, 16:13   #11
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Originally Posted by sandy daugherty View Post
Maren: I've satisfied my need to save the world from dead-ends, and will gladly apologize to everyone when someone builds a successful Eiland design. However...
Sandy,

I think you have outlined some good points, as any good skeptic should. Youíve given me no reason to think you are luddite and Iíve never thought that about you. Iím skeptical from the opposite side in this case. However, considering this and that Iíve recently purchased a similar boat that could conceivably have the rotating mast replaced with an aft-mast, the obvious question is why not?

My answer is that while I like new technologies this simply doesnít meet the standard of proof. Weíre in agreement no concrete proof has been offered and I think anyone who reads the other thread will be able to draw the same conclusion. Iíve seen no unquestionably successful implementation, even though it seems Windwalkerís failure was likely to be metallurgical quality control. In the absence of that, Mr Eiland hasnít met, proactively, what I consider to be the gold standard of engineering modeling. So, Iím sticking with a rotating mast or might purchase a conventional rig if I know the situation will be a net cash gain. Iíll decide in February.

You mention the cost of convenience, which I think is a really fair point. For a center cockpit cruising trimaran, I see little benefit over a rig where the mast is located in cockpit. For a rotating mast, I think this is even more true as I can turn the mast into aerodynamic dis-alignment which is effectively a first reef point and is accomplished at not risk to crew or myself. But I leave the possibility of benefit for other boats open. For me the aft-mast is an interesting novelty rig thatís, to my eye, attractive. Put another way, the artist is suitably happy, the skeptic is not; the financier wonít consider anything until both are in agreement.
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Old 03-12-2008, 09:22   #12
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A searunner 34 center cockpit! Lovely! With a rotating mast? More Lovely!
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Old 03-12-2008, 09:48   #13
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While I could easily take issue with a number of the posts on here, I will confine myself to the aft mast concept and its lack of proof.

I would suggest that this concept has been alive and well for the last 40 plus years, and fitted to well over 500 boats.

This rig is basically the same as that fitted to Prout catamarans.

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Old 03-12-2008, 11:19   #14
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While I could easily take issue with a number of the posts on here, I will confine myself to the aft mast concept and its lack of proof.

I would suggest that this concept has been alive and well for the last 40 plus years, and fitted to well over 500 boats.

This rig is basically the same as that fitted to Prout catamarans.

I've seen this one before and Mr. Eiland cites it as an example. Overall, it strikes me as an issue of degree. This rig is more aft but not as much as the aft-mast rig. I'm not sure of what benefit either is over a conventional rig but I hold out the possibility there is some.

As for the taking issue with a number of posts, I think you should. As long as our discussion is based on the issues and not something that ends up getting the thread locked, I'm up for considered discussion on all the points.
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Old 03-12-2008, 11:48   #15
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The convenience of this rig is that reefing can be done from the cockpit. big wind = reef the genoa anyway.

Downwind, dont worry about the main, stick that big genoa out.

The mast is better supported because it is in a position that allows a substantial load spread, rather than perched on top of an unsupported part of the main roof.
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