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  #1  
Old 03-16-2010
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Climb the mast on small boat

I working on a Pearson 26, 5,400lbs disp, 2,200lbs fixed iron ballast. I've climbed 27' but I'm wondering what the lightest boat a 200lb guy can climb and not have the boat tip over?
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Old 03-17-2010
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you will be fine on that boat, you might be able to get 10 degrees of heel just sitting there. my boat has 3300 lb shoal keel ( total weight about 8k ) with a height of 40 over the water anf i can get about 5 degrees of heel if i lean out.

as for lightest, i have no clue
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Old 03-17-2010
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Lets say you want no more than 15 degrees heel, sin 15=~0.26, so 0.26*30*200= 1560 ft lbs of moment. What boats develop 1560 foot pounds of righting moment at 15 degrees heel?

You would need to know the center of mass, center of bouyancy and displacement, then you could figure it out.

I would think at 15 degrees heel the distance athwartships between the CM and CB would be something like 6 inches at most, so a 3120 lb boat? That seems realistic. I guess. It depends on the shape of the boat, the displacement, how tall the mast is, and where the center of mass is.

One way to find out would be to try it. Worst case scenario you break the mast and yourself.
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Old 03-17-2010
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David,

You could also do a rough a "no heel" approach and you see if the center of gravity can counteract your weight at the top with no heeling (benefits from hull shape) needed for righting moment.

If the center of gravity is 1 foot below the center of buoyancy, you can climb up to a height of H before you'll get any heeling:
5,400 lbs x 1 ft = 200 lbs x H ft

H = 27 feet
You could always lose a few pounds. Just sayin'.... Leave your heavy tool belt at the deck. Take you shoes off. Don't eat a big meal before hand. Shave. Skip the big belt buckle.

Saving 15 pounds looks like this:
5,400 lbs x 1 ft = 185 lbs x H ft

H = 29 ft
Just remember that you'll be suspended from a halyard at the top. So even if you go part way up, if the boat heels, you'll be dangling from the top. You have to use the full height in you calculations, even if you see your center of gravity staying a couple feet from the top or many feet from the top. (Picture this: if you don't have a loop around the mast as you climb, then when the boat heels, you'll be out over the water creating more heeling force than if you were against the mast.)

Anyway, that's my method for doing a rough calculation. Anything more and you have to look at the righting characteristics at angles of heel. (How the center of buoyancy gets farther from the center of gravity as the boat heels.)

Use a loop around the mast and climb slowly?

I'm a guy with a calculator, not a rigger. Take the above with a hefty grain of salt.

Regards,
Brad
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Old 03-17-2010
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I climbed the mast on a twenty foot sloop. Only as far as the spreaders, but I weighed over 200 even then. The boat had an 800 lb keel.
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Old 03-17-2010
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Since righting moment due to ballast varies with the sine of the angle of heel, at small angles, most boats' form stability probably dominates over ballast stability. Still, it sure is fun to play Archimedes

Brad's "no heeling" approach is mathematically interesting, but, imho, unrealistic. We've all experienced how every little movement made by you and your crew members below causes the boat to pitch and roll like a bucking bronco
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Old 03-17-2010
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If your up a J24 mast 35' 900# keel 4' draft

DONT be doing much moving as a 200# pound person will fully heel the boat
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Old 03-17-2010
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Quote:
Originally Posted by AdamLein View Post
Since righting moment due to ballast varies with the sine of the angle of heel, at small angles, most boats' form stability probably dominates over ballast stability. Still, it sure is fun to play Archimedes

Brad's "no heeling" approach is mathematically interesting, but, imho, unrealistic. We've all experienced how every little movement made by you and your crew members below causes the boat to pitch and roll like a bucking bronco
Adam,

As you know, stability is different than a lack of momentary pitching and rolling. That said, if you see the boat listing significantly when crew members change seats, it's a good indication that the math will say "don't climb".

The sine of the heel angle that you mention is the same rate at which David's weight is causing heeling when he's at the top of the mast, or when he's got a strap around the mast on the way up. That's what allows the rough approximation. For boats with a heavy, ballasted keel, the form stability for small amounts of heel isn't changing the COB-to-COG distance that much. And for larger amounts of heel, the form stability usually gives you more stability as the COB-to-COG distance increases. It's a useful approach.

Put another way, the approach I mentioned makes it so you don't have to factor-in form stability, which would usually give you more stability that the "no heel" approach.

That said, I'm a guy with a calculator and a physics book. Wouldn't be all that surprised if I'm missing something.

Regards,
Brad
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Old 03-17-2010
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Suspended from a Halyard?

Quote:
Originally Posted by Bene505 View Post
David,

Just remember that you'll be suspended from a halyard at the top. So even if you go part way up, if the boat heels, you'll be dangling from the top. You have to use the full height in you calculations, even if you see your center of gravity staying a couple feet from the top or many feet from the top. (Picture this: if you don't have a loop around the mast as you climb, then when the boat heels, you'll be out over the water creating more heeling force than if you were against the mast.)

Use a loop around the mast and climb slowly?

I'm a guy with a calculator, not a rigger. Take the above with a hefty grain of salt.

Regards,
Brad
Huh....??? I think I'll take the hefty grain of salt!
This guy is going to be suspended by the halyard????
OK, on a 26' boat there cannot be much more than 200 sq. ft. of mainsail so how strong a halyard pulley is needed to hoist this sail? How is the pulley attached to the top of the mast, two rivets, four rivets, a few screws, will it support a 200lbs person? What if that halyard pulley broke loose just as you reach the top...???
Does the marina have a scafolding dock where you tie up to the dock and climb the ladders on the scafolding to access the mast top? We have one at the marina I slip at and that is what I would use.
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Old 03-17-2010
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Quote:
Originally Posted by scottyt View Post
you will be fine on that boat, you might be able to get 10 degrees of heel just sitting there. my boat has 3300 lb shoal keel ( total weight about 8k ) with a height of 40 over the water anf i can get about 5 degrees of heel if i lean out.

as for lightest, i have no clue
I'm not so sure. Your boat is over 50% heavier. I suspect that would make a lot of difference
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