Damn your logic, Spock!
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| Getaway double trapeze http://www.hobie.com/forums/viewtopic.php?f=23&t=14577 |
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| Author: | McGyver [ Fri Mar 01, 2013 6:03 pm ] |
| Post subject: | Re: Getaway double trapeze |
mmiller wrote: Quote: - On the Getaway, the tang is attached to the comp-tip, not to the aluminum part of the mast (unlike on the 16), which may be more fragile (???) - There is no dolphin striker, so more wight on the outside can put more pressure on the the crossbar Correct on both counts. Trapeze loads are compression on the mast and crossbar. Since the tang is in the CompTip... we don't recommend the extra loads there or on the forward beam. Example: The trapeze loads are why a striker was added to the Hobie 14 when we went Turbo (Jib and Trapeze) on that model. Matt, I have to agree with gzmovala on this. I don't have the math to put this in formulas, so bear with me. Let's assume that four people on the rack equal two people on the trapeze. Now, the compression forces on the beam would be stronger with four people on the rack, since the shroud is closer to the mast than the two trapeze wires. To prove it by the absurd, if we had a long enough rack, even a small kid could keep the boat upright, while the compression forces on the beam would be minimal. To take to an extreme, with an infinite long rack, an infinitely small weight will will keep the Getaway upright, while exerting an infinitely small compression force on the beam. Resuming: the farther away from the mast you apply a righting force, the less compression there will be on the beam. |
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| Author: | Roy [ Sat Mar 02, 2013 6:40 pm ] |
| Post subject: | Re: Getaway double trapeze |
You can sit as many people as you want on the wing as that does not increase the down load on the mast, but would increase the righting moment of the boat. It makes sense if you hang 200lbs from the top of the mast it has to increase the down loading on the mast...but then you should be able to (under the exact right conditions) remove the existing side stay as you are effectively replacing the side stay load by your weight on the trap line holding the mast up. Under higher wind conditions you would not have enough pull to hold the mast up against the wind pressure and then any additional load caused by the crew weight on the trap would be added to the existing downward pressure on the mast. At the end of the day Hobie engineers have worked all that out and to be safe you should stay within the boundaries set by Hobie. It would really ruin your day if the front cross bar failed 3 miles off shore in a 20kpm + wind.. |
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| Author: | McGyver [ Tue Mar 05, 2013 12:34 pm ] |
| Post subject: | Re: Getaway double trapeze |
Roy, I'm afraid I disagree. You say: "You can sit as many people as you want on the wing as that does not increase the down load on the mast, but would increase the righting moment of the boat." Sitting more people on the wing DOES increase the down load on the mast, BECAUSE it increases the righting moment of the boat. The reason why less people on the trap vs more people on the wing REDUCES the load on the mast (and therefore on the cross-bar) is because the heeling force can be seen as perpendicular (90°) to the mast, pointing to leeward, so the more the righting force (shrouds or traps) approaches 90° to windward, the more the forces would compensate each other, reducing compression on the mast. Imagine a very tall wing, so tall that the crew is trapezing at a 90° angle from the center of the heeling force of the sails on the mast. The compression forces on the cross bar would be not more than the weight of the mast. |
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| Author: | mmiller [ Wed Mar 06, 2013 9:08 am ] |
| Post subject: | Re: Getaway double trapeze |
It's less the beam I'd be concerned about and more the Tang connection being in fiberglass and the CompTip joint crushing into the Aluminum section.. |
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| Author: | McGyver [ Wed Mar 06, 2013 11:27 am ] |
| Post subject: | Re: Getaway double trapeze |
Thanks, Matt, I didn't think of that. |
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| Author: | Roy [ Wed Mar 06, 2013 6:49 pm ] |
| Post subject: | Re: Getaway double trapeze |
mmiller wrote: It's less the beam I'd be concerned about and more the Tang connection being in fiberglass and the CompTip joint crushing into the Aluminum section.. Well if that's the case why can't we just rivet a new tang just below the com tip joint and use it only for the hiking wires? |
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| Author: | hobie17li [ Sat Apr 06, 2013 10:50 am ] |
| Post subject: | Re: Getaway double trapeze |
if you need two people on trapezes on a Getaway, I'd suggest that you are over powered and may wish to roll the jib. If you already have done that you may wish to head back in. I have sailed with one on a Trapeze and one on the wing and found it satisfactory.Get as far back as possible and have crew trap outboard of skipper and as far back. And if you do double trap and break the comp-tip let me know, I have a brand new one still in wrapper, I'd be happy to sell, Doug |
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| Author: | McGyver [ Sat Apr 06, 2013 3:00 pm ] |
| Post subject: | Re: Getaway double trapeze |
Damn your logic, Spock!
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