Rotating mast - worthwhile performance gains?
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Posted: Nov 16, 2018 - 04:49 AM
For your average less than 20 foot beach cat with an aluminum spar, just how much of a performance gain do you get from having a mast that rotates? No doubt for a wing mast it's critical, but since most aluminum extrusions are very nearly round and not primarily designed to be rotated anyways, is it worth the additional complexity? -
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Posted: Nov 16, 2018 - 05:48 AM
There’s a reason why Hobie put a rotating mast on the Hobie 14 fifty years ago and virtually every beach cat since has had a rotating mast - better performance.
I really can’t see any reason not to use one. I think you would have just as much difficulty designing a mast step that prevents the mast from rotating as one that allows it to rotate.
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Posted: Nov 16, 2018 - 05:50 AM
There’s a reason why Hobie put a rotating mast on the Hobie 14 fifty years ago and virtually every beach cat since has had a rotating mast - better performance.
I really can’t see any reason not to use one. I think you would have just as much difficulty designing a mast step that prevents the mast from rotating as one that allows it to rotate.
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Posted: Nov 16, 2018 - 10:15 AM
It makes all the difference in the world on my boat. The new sq top really rotates the mast. I can tell the difference if the mast hasn't rotated after a tack and then rotates.
Edited by gahamby on Nov 16, 2018 - 11:16 AM.
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'82 Super Cat 15
Hull #315
Virginia
Previously owned: '70 H14, '79 H16, '68 Sailmaster 26, '85 H14T
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Posted: Nov 16, 2018 - 10:23 AM
+1 to gahamby.
In light air I often have to manually rotate the mast. There is a significant and instant increase in power once rotated into correct position.
Brad in Jax
Stiletto 27 on a 2 year repair plan. -
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Posted: Nov 16, 2018 - 10:05 PM
I had a rotator arm on my Nacra 5.7, which allowed one to lock, limit, or force rotate the mast to any desired position.
You could destroy the power in the sail by not allowing it to rotate between tacks.
The masts, even on legacy beach cats, are nowhere near circular, & if not pointed into the relative wind, (or some reasonable angle of attack), the telltales will be anywhere but streamlined, with a resulting loss of power.
Edited by Edchris177 on Nov 16, 2018 - 10:06 PM.
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Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
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Posted: Nov 17, 2018 - 02:45 AM
It just does...
I'm no physics major or anything, but think of the mainsail as a wing that is vertical or standing up. The mast on a Hobie is a bit "teardrop" shaped and rotates in order to make it one with the shape of the sail, so as to be like the leading edge of the "wing" . Common sense tells me that the smoother the airflow across the "wing" means more pressure/power or lift, in this case it is a vertical wing instead of horizontal, therefore the mast becomes a part of that wing or mainsail so it rotates to keep the same angle that the mainsail is experiencing. That's my take on it anyway, hope this helped. Correct me if I am wrong, but all I
know is that it works!!!
How exactly is a rainbow made? How exactly does the sun set? How exactly does the posi-trac rear end on a Plymouth work?
It just does...
Edited by martyr on Nov 17, 2018 - 03:12 AM.
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Marty
1984 Hobie 16 Redline Yellow Nationals, "Yellow Fever"
Opelika, Al / Lake Martin
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Posted: Nov 19, 2018 - 01:15 AM
wing mast writeup by tom speer
http://www.tspeer.com/Wingmasts/teardropPaper.pdf
Edited by ziper1221 on Nov 19, 2018 - 02:16 AM. -
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Posted: Nov 19, 2018 - 01:35 AM
Interesting (and long) thread on rotating masts at the Yacht Design forum: https://www.boatdesign.net/threads/rotating-wing-mast-%E2%80%93-theoretical-discussion.14714/ -
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Posted: Jan 20, 2019 - 08:29 PM
It's interesting that no one has mentioned the fact that a rotating mast is used to help shape the the mainsail. The cross section of the mast being teardrop shaped will allow the mast to bend more when allowed to rotate more. When the mast bends it pulls a big section of the main forward flattening the sail.
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Jan 20, 2019 - 10:24 PM
I’ve seen the flow tests that show a tear drop basically does jack crap at keeping attached flow behind the mast regardless of how it’s rotated. The shape of the sail and how you rotate to optimize that accounts for way more drag reduction.
Thus the thinner wing mast was invented that can actually keep flow attached.
