Mast vibration.

Boat handling, ideas, questions...
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seadago
Posts: 123
Joined: Sun Jun 03, 2012 8:42 am
Location: Lowestoft, England

Mast vibration.

Post by seadago »

I'm having some good vibrations... :mrgreen:
Just spent the night, and half of yesterday, and the rest of today judging by the anemometer at dawn, at anchor, in winds around 25 knots, gusting to 40. Clocked 42 at two o'clock this morning.
But this isn't the weather report.
Point is, at about 22 or 23 knots, the main mast starts vibrating (mizzen too, but less), and it stops at wind speed about 28 and above. I can see it shaking in the middle. The vibration transmits, so the whole boat shivers. Strong enough to wake me up from deep sleep.
This is clearly some harmonics effect, maybe caused by the tension on the topping lift or some other tight line attached to the mast top. I'll figure which. I just wanted to know if this is a common phenomenon to all F30s, or simply my boat's quirk.
Rafael
s/v Nausikaa
SSR 30570, sail GBR 4619L
F30 CK (Hoyt), wishbones, centreboard, G10 rig. Built by Fairways Marine, Humble, UK, '82
Beta 16 hp with two-blade prop

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Castaway
Posts: 246
Joined: Sat Dec 13, 2008 8:40 pm
Location: Lerwick, Shetland Isles

Re: Mast vibration.

Post by Castaway »

Hi, Rafael.

I've had some frightening mast shaking when dropping a sail in strong wind with the sheet completely slack; putting some tension on that , or getting the sail right down fixed it promptly.I've just once noticed vibration with sail dropped and strong wind. Moving the boom, and hence topping lift away from the centre line of the boat stopped that, perhaps because the topping lift was not in line with the masts, more likely because of the change in tension on the lift. Certainly some tension, and thus bend, stabilises the very flexible carbon fibre mast, which is otherwise free to waggle about. It doesn't appear to happen when the sails and booms are not attached to the mast, like when the boat is laid up, even in very windy conditions. Castaway has stood out, masts up, in winds gusting over 100mph in our Northern winters!

Hope your journey South is going well!

Best wishes,

Gerald
Gerald Freshwater,
s/y 'Castaway', (UK F35 cat ketch, centreboard, 1987)
Lerwick Boating Club
Shetland Isles, Scotland

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seadago
Posts: 123
Joined: Sun Jun 03, 2012 8:42 am
Location: Lowestoft, England

Re: Mast vibration.

Post by seadago »

Thanks Gerald! Yep, I think -especulate- that it may be a similar effect. The simile is a bow in tension. When you loose, the vibration of the string transmits to the limbs of the bow and it shakes, so it's the topping lift that vibrates harmonically with the wind, not the mast. I have ss wire topping lifts, with the last meter or so with dyaneema braid for adjusting. Neither very stretchy.
I haven't noticed bad vibrations when dropping the sail, but I always face the wind when doing that. And in strongish winds, I'm probably too focused on the manouver to pay attention! 😂
Passage going well, but slow, like Nausikaa. In Baiona today. Hitting the coast of Portugal tomorrow. Overnight passage to Leixoes. With a bit of luck, 18 hours. The north coast of Spain and Galicia have been a delight to cruise. Really a gorgeous part of the world, and some navigational challenges. All in all, fantastic!!
Rafa
Rafael
s/v Nausikaa
SSR 30570, sail GBR 4619L
F30 CK (Hoyt), wishbones, centreboard, G10 rig. Built by Fairways Marine, Humble, UK, '82
Beta 16 hp with two-blade prop

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