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Old 26-11-2009, 21:35   #1
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Calculating Rigging to Survive 360

I am interested in possibly replacing my 1/8" stainless wire with 3/8" spectra. This would give a 10x increase in strength yet be lighter weight.

The real question is, how strong does it need to be to survive a 360 or pitchpole without losing the mast?
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Old 26-11-2009, 22:23   #2
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Depend if you have the sails up or down, with the main up ! a 360 roll probably break the mast in pieces, remember that the sail act like a break and the hull try to reach a upright position, the loads in the right are impresive.
A pitchpole is a diferent history, is a good idea to have the stronger material in the rigging, you have better chances to save the mast in the 360 scenario, but dont forget tangs, chainplates , etc... are the same structural things onboard to keep the pole upright.
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Old 26-11-2009, 22:49   #3
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One bonus with going to 3/8" is that the large increase in drag will make your 360 slower so less damage to the boats occupants hopefully.

You sure you've done your numbers right? By my calcs you won't save any weight or next to none with a distinct possibility you actually add some, you will increase the drag a lot and you'll be paying a tidy amount to do so. I think I would do a double check before going shopping.
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Old 26-11-2009, 23:12   #4
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If I remember correctly, in most cases where capsizing caused a failure of the rig, it was the mast that failed, and not the rigging.

Because of the rigging, the compression loads on the mast are pretty high, and latteral loads will cause it to destabilze and fail, leaving the rigging wire intact.

I remember seeing a racing boat come back into the yacht basin in Hong Kong after broaching with a poled spinaker. They lost a 10' section of the mast from about 1' off of the deck to above where the pole was attached, and the rest of the mast came tumbling down.

Apparently when the boat rolled over, the sail caught the water, and all of the breaking force caught in the sail was transfered up the spinaker pole directly as latteral force to the mast. This bowed the mast at the pole attachment point, and the compression forces from the rigging caused the mast to shear off above and below the bowed area.
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Old 27-11-2009, 01:57   #5
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Quote:
Originally Posted by geckosenator View Post
I am interested in possibly replacing my 1/8" stainless wire with 3/8" spectra. This would give a 10x increase in strength yet be lighter weight.

The real question is, how strong does it need to be to survive a 360 or pitchpole without losing the mast?
Actually the real question is: will you be increasing the strength of all your fittings x 10? It's not the wire that usually lets go, but the associated hardware.
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Old 27-11-2009, 11:36   #6
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I think that for my purposes, I am only considering a standing rig, or a possibly a storm jib (attached to inner fore stay, so opportunity for a mechanical fuse exists)

I believe my mast is overbuilt and very strong, but I can see how having a spinnaker would put much more force in the wrong places of the mast causing it to break.

My question then is, does stainless steel cable stretch (I'm pretty sure it does) which means if it does too much on the wrong conditions, it would allow the mast to bend too much possibly weakening it. If the stays are stiff enough and have the strength, then maybe the mast is safer too? Any comments on this appreciated. Anyone know how to calculate it directly?
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Old 27-11-2009, 16:21   #7
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No matter how strong the mast is, it cannot compare to the force of the water pushing against the surface of even a reefed mainsail or storm trysail.

Unless you had wires rigged specifically to make the mast rigid, it will flex. These wires can be done, Hunter boats use a similar concept. but it incrases the weight aloft and the drag through the water.
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Old 27-11-2009, 16:50   #8
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One problem I have with the idea of spectra (or any non-wire) for standing rigging is chafe or accidental cutting.

The inner forestay has the genoa pulled around it every tack and the lazy sheet can rub on it 24/7 if not slacked right off.
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Old 27-11-2009, 17:39   #9
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Technically the stability of the mast is increased with additional spreaders and stays. Increasing the strength of the stays may help but the mast will fail between stays (stabilizing points) when the load capacity of the mast between stays is exceeded.

Also, given enough load eventually something will break. Increase the stay strength? Then increase the fitting strength. Increase the fitting strength? Then increase the chainplate strength. Eventually all these loads are transferred into the boat structure. I personally would rather the rig failed before pulling a hunk of the deck out of the boat.

Cable will stretch initially but then it will stabilize.

Also 1/8th inch wire seems awefully light. What kind of boat are we talking about and how is the mast configured?
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Old 28-11-2009, 14:35   #10
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Turns out the wire is 3/16 (i had eyeballed it)

I want to know how strong it needs to be to not lose the mast in a 360, then I will know if it is realistic or not.

Anyway, maybe it would just break where it is connected to the hull or mast instead. I wonder if a mast which were structural (like a tower) designed to bend, and have minimal water resistance would be able to reliably 360 and pitchpole. and work better. There is a boat from the USSR anchored here which has a boom that looks like a bridge structure.
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Old 01-12-2009, 11:17   #11
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What kind of boat is it? What kind of sailing do you do with the boat?
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