| Re: trap line....
[Re: Tornado_ALIVE]
#54152 08/01/05 06:43 AM 08/01/05 06:43 AM |
Joined: Jun 2001 Posts: 1,911 South Florida & the Keys arbo06
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Posts: 1,911 South Florida & the Keys | My guess would be that there would not be any advantage to using the trap line. The point at which the righting line touches the hull and leads to the sailor is the limiting factor. If the line could go directly from the mast hound to the sailor with out touching the hull, there may be an advantage.(?)
Eric Arbogast ARC 2101 Miami Yacht Club | | | Re: trap line....
[Re: arbo06]
#54153 08/01/05 08:41 AM 08/01/05 08:41 AM |
Joined: Jun 2001 Posts: 12,310 South Carolina Jake
Carpal Tunnel
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Carpal Tunnel
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Posts: 12,310 South Carolina | No - no mechanical advantage from where the line originates. Just more or less loading on the line or boat parts. You can safely eliminate the line from the equation because, in a sense, nothing is moving and the sailor, the righting line, and the boat can be treated as one solid unit. You are simply looking at a balance equation with the mast on one end and the sailors on the other pivoting around the hull in the water. Placing the sailor's body weight further away from the boat and the closer to the water will result in more righting moment.
Jake Kohl | | | Re: trap line....
[Re: Jake]
#54154 08/01/05 09:45 AM 08/01/05 09:45 AM |
Joined: Aug 2004 Posts: 145 Cheshire, UK Simon
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Posts: 145 Cheshire, UK | So Jake, how far out on your F18 dagger board would you stand to get the most leverage? Do you think it is strong enough to take the weight of helm & crew if you stand at the end of the board?
Simon
Simon Shadow 067 | | | Re: trap line....
[Re: Simon]
#54155 08/01/05 10:47 AM 08/01/05 10:47 AM |
Joined: Jun 2001 Posts: 12,310 South Carolina Jake
Carpal Tunnel
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Carpal Tunnel
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Posts: 12,310 South Carolina | The boards are pretty heafty. I usually go to the tip of the board - I've righted my F18 boat three times by myself by standing on the tip (twice with the crew still on the dry hull). It does not give me any indication of being overloaded when I do so (I weigh about 170lbs). However, putting both of us on the end of the board would probably be a bit much but we've never needed to do that.
Jake Kohl | | | Re: trap line....
[Re: Rolf_Nilsen]
#54157 08/01/05 11:37 AM 08/01/05 11:37 AM |
Joined: Oct 2002 Posts: 1,226 Atlanta bvining
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Posts: 1,226 Atlanta | Rolf, You bring up a good point, are the forces the same or greater?
I've never used daggerboards to right an HT, I assumed they would break, and I wouldnt think of using my daggerboards to right my A cat, but I just went down stairs and leaned on my A cat boards, and they didnt move. I just assumed that a 1.85kg hollow carbon board wouldnt hold my weight, but would it?
Any engineers out there care to comment? If it doesnt break during sailing, does it mean you can stand on it to right the boat? Or are the loads different?
Are the forces more fore and aft as opposed to sideways?
Bill | | | Re: trap line....
[Re: Jake]
#54158 08/01/05 01:52 PM 08/01/05 01:52 PM |
Joined: Jun 2004 Posts: 141 Panama City Beach, FL steveh
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Posts: 141 Panama City Beach, FL | Jake, how does being closer to the water help? If you have a playground see-saw and hang under the seat instead of sitting on top of it, you don't gain any mechanical advantage.
Rolf, the dagger doesn't counteract the heeling moment, it counteracts the leeward force generated by the sail. In fact, the windward lift force acting on the dagger increases the heeling moment. However, the dagger has a smaller moment arm than the sail, so its contribution is proportionally smaller.
As for the magnitude of the force, assume a 15 knot cat with a 3 ft long dagger (exposed below the hull) with a chord width of 16in with a lift coefficient of about 0.15 at a 2 degree angle of attack.
L = 1/2* CL * density * speed^2 * area L = 1/2 * 0.15 * 1.99 * (1.69 *15)^2 * 4 L = 384 lbs
That force will act roughly 1/3 the distance from the hull to the tip giving a 384 ft-lb moment. For an equivalent moment, you could have a 128 lb person stand on the very tip. Factoring in structural safety factors, a higher design speed, etc, etc, etc, it looks to me like the dagger would be plenty strong enough to stand on. | | | Re: trap line....
[Re: steveh]
#54159 08/01/05 02:04 PM 08/01/05 02:04 PM |
Joined: Jun 2001 Posts: 12,310 South Carolina Jake
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Posts: 12,310 South Carolina | Jake, how does being closer to the water help? If you have a playground see-saw and hang under the seat instead of sitting on top of it, you don't gain any mechanical advantage. Just like proper trapeze form, getting yourself more parallel to the water surface moves your center of gravity out as far as it can go to achieve maximum leverage.
Jake Kohl | | | Re: trap line....
[Re: steveh]
#54160 08/01/05 02:07 PM 08/01/05 02:07 PM |
Joined: Jun 2001 Posts: 12,310 South Carolina Jake
Carpal Tunnel
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Posts: 12,310 South Carolina | That force will act roughly 1/3 the distance from the hull to the tip giving a 384 ft-lb moment. For an equivalent moment, you could have a 128 lb person stand on the very tip. Factoring in structural safety factors, a higher design speed, etc, etc, etc, it looks to me like the dagger would be plenty strong enough to stand on. Steve, why 1/3 the distance? Most boards are straight section and not tapered. After seeing the hell my boards were going through at Performance Race Week last year (boat leaping clear into the air in 4' waves and coming back into the water sideways) I didn't feel to worried about putting my full weight on the tip! Most boards are designed with a pretty big factor of safety.
Jake Kohl | | |
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