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Old 22-12-2007, 19:42   #1
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Rotating Rigs on Cruising boats?

I'm after input from people who have experience. Is there much advantage with using a rotating rig? Not a wingmast, just a normal section set up to be able to rotate.

Like anything, there are bound to be pro's and con's. The ones I am aware of are:

Pro -
improved sail efficiency - possibly by around 5%
The possibility of being able to reef or lower the mainsail when running downhill - without having to round up.

Con -
I have heard that rigging failure might be more likely, but not sure.
Masthead navigation lights become more complicated
where do you mount the windvane or wind instrument transducer?

Anyone who has used a rotating rig care to comment?
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Old 23-12-2007, 00:49   #2
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My experience with rotating rigs is with small daysailors and racing dinghys. They are usually fractional rigs and the mast would usually have a more teardrop shape than a standard rig or even a football shape(American football) In theory it improves the airflow across the mainsail but I could not quantify by how much. Three stays, a headstay and a swept back port and starboard side stay attach to the same place on the front side of the mast. A stay attached a several feet below the masthead running to a spreader and down to a spot the same distance above the mast step on each side(a diamond stay?) keep the mast in column side to side. On a larger mast there may be additional spreaders and stays. The teardrop or wing shape of the mast gives it enough stiffness to keep it in column fore and aft. As you can see this is actually a simpler rig less prone to failure in my mind. There is less compression load on the mast so the whole thing is under less stress.
The problem I see with your idea is using a normal mast section. How do you get the fore and aft stiffness? You can't use stays because the mast needs to rotate. It has to come from the shape of the mast section. The three stays that hold the mast up all attach to a central point on the front of the mast so that's all they do, hold the mast up. So you need a special mast section and a fractional sloop rig or a cat ketch type rig. A book by Chris White titled The Cruising Multihull has chapter on rotating rigs.
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Old 23-12-2007, 02:39   #3
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I had a Corsair 36 for a while... the rotating rig is the first reef point, since it depowers quite a bit when the laminar flow goes away. That's kind of handy.

A downside is that it makes masthead tricolors a real pain.

Cheers,
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Old 23-12-2007, 02:41   #4
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I met a chap in France who had one of these rotating masts ,this wasnt his first one but certainly his biggest the yacht 13.5 m ,he said the extra efficency resulting in speed on all points were remarkable, i to asked about strength issues he laughed and said that on many passage racing and ocean crossings no problems yet,though he certainly wouldnt rule out the possability
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Old 23-12-2007, 08:37   #5
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I think Eric Lerouge cruises with a rotating mast aboard his multi. Don't know any others.

lerouge-yachts.com design@lerouge-yachts.com
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Old 23-12-2007, 16:35   #6
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Thanks for the replies. I'm particularly interested to know if rotating rigs really do allow the main to come down without rounding the boat up. Intuitively it seems unlikely, but that's purely based on years of using a non-rotating rig.

Steve, there is no problem keeping a normal section in column - using triangular spreaders and 3 sets of diamond stays - in line with the shrouds and down the front of the mast.

Really a rotating rig on a multi is pretty much the same as a fixed rig - except for the mast being mounted on a ball and socket, and having a spanner.

Mounting masthead nav lights is a problem. Also wind instrument transducers. The question is - do the advantages outweigh the disadvantages?
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Old 23-12-2007, 16:41   #7
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On my tri, the wind instrument issue was settled with a dedicated compass sensor on the mast-angle control arm, with a little processor that integrated that with the main ship compass to feed the Nexus system.

I joked about using this signal to drive a servo-controlled platform for a tricolor, but in practice I just had standard bow and stern lights in addition to an all-around aloft.

In sum, I liked it a lot. Geeky and practical!

Cheers,
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Old 23-12-2007, 16:59   #8
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I've heard about that being done, and also people using twin wind transducers mounted on the targa - you select the windward one after tacking. It's extra complication and expense though, either way. I could also set up twin port/starboard mast lights, selectable on tacking. Again, more hassle and expense. Is it worth it?

Would you say the benefits outweigh this?
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Old 23-12-2007, 18:42   #9
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Well, in my opinion, yes - if you are performance-oriented. I'm not, really; my new boat is much more sedate than a Corsair 36, and I'm happy to have a stout rig with plenty of redundancy in the standing rigging.

But the racers I know sure do love 'em, and it certainly does feel like a turbo charger kicking in when you rotate the spar in a good breeze and get rid of that big aerodynamically sloppy leading edge. Things go all quiet... and the boat is noticeably smoother and faster.

I'm sure there are other trade-offs. The rotating rig felt a lot more fragile to me (just a simple triangle staying base), and of course an insulated backstay was not an option.

Steve
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Old 23-12-2007, 19:01   #10
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Although it seems to be the most comon practice I don't believe you have to have your navlights mounted at the masthead. You could mount them at deck or cabin height like a powerboat. Be easier to change the bulbs too. Are you converting an existing rig or are you in the planning stages of rigging your boat? I cannot see how it could be worth the hassle and expense to convert functioning existing rig. A mast designed for a rotating rig whether teardrop or wing shape is more aerodynamicaly efficient than a standard mast and thus gets maximum benefit from being able to rotate into the wind. Taking your standard oval mast shape which is not all that efficient aerodynamicaly and rotating it into the wind may result in a slight improvement but is it worth it? My gut feeling says no but I don't have any evidence to support that.

I would like to hear from "microship" steve as to whether the mast on his Corsair 36 was a standard oval shape or something more teardrop shape specifically designed for a rotating rig. That may provide you with some insight into the problem.
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Old 23-12-2007, 19:19   #11
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Foiled again

Ah, good point, Steve - and yes, it was a foil. You're right; doing that with an oval stick would not make a lot of sense.

You can get a good idea of the shape in the photos below... and other details are visible over yonder.

Looking at those photos now kinda makes me chuckle; my current ship is exactly the opposite! Still love multihulls, though...

Cheers,
Steve
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Old 23-12-2007, 19:39   #12
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I'm sure there are other trade-offs. The rotating rig felt a lot more fragile to me (just a simple triangle staying base), and of course an insulated backstay was not an option.

Steve
Why not an insulated cap shroud? I've been thinking of doing that with my Dragonfly.

BTW, nice photos of your new boat!
As a member of NWMA I hope to run into you one of these days somewhere at anchor.

Steve B.
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Old 23-12-2007, 20:37   #13
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Steve B....

Hey Neighbor (Camano Island here) - hope to see you on the water! I'll probably be spending a fair bit o' time in the mighty Saratoga Passage this coming season; I have to vacate the yacht club guest dock when it gets busy. Should be on the hook here and there...

I contemplated the cap shroud idea - on my folding tri it was awkward: longer feedline through the aka-folding system and unfortunate tuner location in the relatively harsh enivoronment of an ama. But probably quite do-able with more thought!

Speaking of NWMA, I fly the burgee even on the new boat, and I still have the Microship in my lab... them's my roots!

Fair winds,
Steve
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Old 24-12-2007, 07:24   #14
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I'm particularly interested to know if rotating rigs really do allow the main to come down without rounding the boat up.
Although I haven't done it in really strong winds, my bat cars permit lowering the main for reefing on a non-rotating spar. I've never tried to fully lower the main downwind, but I imagine it would work the same way - with the possible complication of having it flake preferentially to one side of the bag (but this would also be the case on a rotating rig). Except for the battens fouling the lazy jacks, raising the main from fully lowered can also be accomplished. Once the battens are above the lazy jacks - as in shaking out a reef - raising the main downwind is easy. Again, the stronger the wind, the harder this would be.

I recall that the early Dophins had rotating rigs - or at least an option for them. Don't know what became of this.

Dave
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Old 24-12-2007, 10:33   #15
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At least on the C36, the rotating rig was actively controlled by lines attached to a control arm, so keeping it under control was easy... just center it, slap down a rope clutch, and treat it as normal.

Cheers,
Steve
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