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rotating masts

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jonh View Drop Down
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Post Options Post Options   Quote jonh Quote  Post ReplyReply Direct Link To This Post Topic: rotating masts
    Posted: 28 Apr 15 at 10:42am
If rotating masts, as used on the Tasar are reckoned to be more efficient,faster etc,why have other classes not adopted them?Why did classes which had them in the past,I think Fireflies and Grads did at one point, decide to abandon them? Are they just an unnecessary expense and complication?


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boatshed View Drop Down
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Post Options Post Options   Quote boatshed Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 11:07am
Good question.   As I see it, they were very efficient on the Tasar because 1. The mast is very carefully and properly shaped.  2.  The shroud bases can be slid forward to get the boom out nearly square. 3.  The mast can be over rotated independent of the boom angle.

The main benefit in the Tasar was upwind due to the ability to rotate the leading edge of the mast to windward which made significant improvements to the mainsail shape, in particular the upper leech.

I think the cost, the emergence of carbon spars and big asymmetric kites pretty much did for rotating masts.   But for non kite boats, I believe it is definitely an advantage to have the Tasar type rotating mast.   Tasars are still deceptively quick boats today, especially upwind!

There is a lot in the Bethwaite book about this.

I believe Mike Lyons, who used to post here, initially toyed with rotating masts on the Icon as that has it's roots in the Tasar.    I would have liked to have seen an aero foil shaped, rotating carbon mast with sliding shroud bases on the Icon.  Maybe with carbon mast building improving all the time, we may see this but right now the cost vs performance is probably not worth it.

By the way, the old rotating masts on the Grad and Firefly rotated due to the boom angle and a fixed goose neck, so, didn't have the advantageous Tasar ability to over rotate.


Edited by boatshed - 28 Apr 15 at 11:10am
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 12:14pm
I've played with them a bit and I still think there's unfinished business there, but I see three main factors.

Firstly that the aerodynamic disadvantage of a pole mast has turned out to be far less than earlier simplistic theorising would have it.

Secondly that dynamic bend and gust response has turned out to be far more important than we ever dreamed of, and at the moment pole masts have far better characteristics.

Thirdly they are complete b**tards to design, set up and tune, and most of the experiments with them were doomed before they started.
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Post Options Post Options   Quote MerlinMags Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 1:19pm
Don't lots of catamarans use rotating masts? They have a little lever on the bottom.

You'll also find them in vintage Merlins. See this article (note the April Fool section is preceded by historical fact!)
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tickel View Drop Down
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Post Options Post Options   Quote tickel Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 1:30pm
Looking up when up wind in a Tasar you can see it working. Even when pointing very high there is no dead patch behind mast. Tasar did contemplate a carbon copy but expense ruled it out. I never knew grads had them. Were they wooden?
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boatshed View Drop Down
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Post Options Post Options   Quote boatshed Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 1:32pm
Originally posted by JimC



Thirdly they are complete b**tards to design, set up and tune, and most of the experiments with them were doomed before they started.


They are probably better on single or two sail plan boats.   I imagine adding a kite would be a nightmare.

I sailed Tasar for a bit and it was  well sorted and worked.  It was more grief to shift the shrouds and jib cars when turning downwind and that was before putting up the jib stick.  

I've always wondered if an IC would be a good platform for a proper over rotating mast.  No doubt it has been tried....


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tickel View Drop Down
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Post Options Post Options   Quote tickel Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 2:24pm
Originally posted by boatshed


Originally posted by JimC


Thirdly they are complete b**tards to design, set up and tune, and most of the experiments with them were doomed before they started.
They are probably better on single or two sail plan boats.   I imagine adding a kite would be a nightmare.I sailed Tasar for a bit and it was  well sorted and worked.  It was more grief to shift the shrouds and jib cars when turning downwind and that was before putting up the jib stick.   I've always wondered if an IC would be a good platform for a proper over rotating mast.  No doubt it has been tried....


It is true, Taser keeps the crew busy bearing in min
d a 2 sail boat!
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 2:32pm
A roughly hounds height kite is no problem at all on a wing mast. A masthead kite is a bit of a pain to stay, but it has been done.
Yes, loads of catamaran classes have them, one of life's mysteries really although I suspect the huge roll inertia is something to do with it, and I wouldn't be surprised if catamarans were less sensitive to weight in the rig, what with it being to windward of centre of buoyancy.
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Post Options Post Options   Quote Roger Quote  Post ReplyReply Direct Link To This Post Posted: 28 Apr 15 at 2:39pm
Originally posted by tickel

I never knew grads had them. Were they wooden?


Yes my first ever boat was a Grad with a wooden rotating mast, zero gust response from the mast, but if you over rotated it then it appeared quite efficient upwind, at least by the standards of the last century.


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Post Options Post Options   Quote timeonthewater Quote  Post ReplyReply Direct Link To This Post Posted: 01 May 15 at 6:49pm
As Jim says, there is unfinished business regarding wing masts. I have used a carbon one and seen the benefits, but the benefits not as significant as the theory suggests. The time taken to get the right blend of the bend characteristics, pitching moment, longevity, robustness, and especially cost is substantial.  Even the cheque book classes where they are allowed have had little success.

Perhaps with high modulus becoming less exotic some years into the future, there may be a skinny wing mast that reaps all the advantages without costing megabucks.  I'm thinking something organically grown.


Too many toys..not enough time
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