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Old 20-05-2013, 19:55   #1
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Rips in Sailboat

Hi guys, I'm doing a physics project regarding rips in sails. What will affect the velocity and overall integrity of the boat more, one large rip, or a bunch of tiny rips?

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Old 20-05-2013, 20:20   #2
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Re: Rips in sailboat

Small rips have a tendency to grow into big rips. If there is enough wind, an untended for rip will enlarge to a point where the sail may blow out completely.

That said, any rip is going to interfere with the flow of air on both surfaces of the sail. A sail is an air foil just like the wing on an airplane, and generally speaking, the presence of rips will reduce the ability of the sail to create lift and direct the airflow over both surfaces aft, thus decreasing generated thrust.

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Old 20-05-2013, 20:24   #3
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Re: Rips in sailboat

Okay so the larger rip would be more likely to blow out faster but the smaller rips would just grow to larger rips fast enough that sailing would be unfeasable anyway. Lets say you has to pick one of the two to sail with though, which would you pick?
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Old 20-05-2013, 20:42   #4
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Re: Rips in sailboat

I would guess one large rip would effect the performance of the boat more. Maybe you get your hands on some model yacht sails, a force balance, craft knife and fan.

The tear spreading depends on the cloth used.
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Old 20-05-2013, 22:11   #5
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Re: Rips in Sailboat

Let's assume both conditions allowed for the same loss of pressure of the wind upon the sail. So, the volume of air passing through the large rip was the same as the sum of all the small rips. In this case I would expect the sail with the small rips to perform better than the sail with the one large rip. The many small rips would still leave the sail with the shape of a functioning airfoil, while the large rip would deform the shape of the sail.
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Old 20-05-2013, 22:27   #6
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Re: Rips in Sailboat

With small rips, the sail might still be able to retain its shape as an airfoil. With large rips, the airfoil would distort, and performance will suffer considerably.

Much of this depends on the sail. Spinnakers are not supported by their luffs; at a certain point a spinnaker with a large rip will no longer fly. A lot depends, as well, on the type of sail. A panel-cut sail with a sizable rip turns into a rag pretty quickly, but I've seen a ripped tri-radial main finish a race without much loss of performance.

I would think that the location of the rip would also be of prime importance. I've had the clews rip out of two sails, both a main and a jib, and it was game over for each sail even though the rip covered a relatively small area.
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Old 21-05-2013, 05:36   #7
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Re: Rips in Sailboat

Sounds like an interesting project. Keen to hear what you come up with. FWIW regarding the possible benefits of rips I can only think of these odd examples.

There was some fad in the 18th century or so for square rigger sails with carefully placed holes in them to increase the lift. It didn't seem to take off as an idea, but certainly the horizontal slots between the square sails help to increase the drive. Choke them up to much and you kill the speed, much like closing the slot on the jib on a modern sloop.

The Chinese junks had slotted rudders with lots of small diamond shapes deliberately cut into them to prevent stalling, or so it's said, and the sails were said to be made from a porous weave of bamboo to leak air for the same reason, and often where riddled with holes.

Somewhere I also think I remember reading something about deliberately putting holes into Bermudan sails to do the same thing, maybe the AYRS, or something by Czeslaw Marchaj?
Both are worth a look at if you are interested in sail dynamics.

Me? I like my sails in one piece and without any rips! Most rips seem to start at the leach and tear towards the luff. Thats certainly one big advantage of radial cut (or traditional vertical cut) sails, the seams can act as a ripstop preventing catastrophic failure. A strong leach cord can also hold the lot together long enough to get the sail down.

Full length battens and Reef bands can also act as a ripstop with a vertical split, very handy if your sail is radial cut.
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Old 24-05-2013, 21:33   #8
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Re: Rips in Sailboat

We've sailed with both small rips and large rips in various sails. Small rips, as mentioned, don't immediately affect the integrity of the entire sail or the work it's doing aerodynamically. They can be patched with tape to postpone the development of larger tears. We did this once for small rips in our genoa and it worked for most of the upwind leg of a race, until we ran out of tape. The sail was essentially unusable by the end of the leg. We also once had a tear in a seam of one of our mainsails. We did not notice the flapping until the tear grew large, and the flapping noise reached almost gunshot proportions: we were beating in about 30 knots of wind and rain, in the dark, on an overcast night with no moon. The small rip took about fifteen minutes to stretch across about 8' of seam by the top batten of our sail. It was obviously not an efficient airfoil, but it got us 34 miles to windward, and 34 miles back that night. Our light-air main would have been ruined in those conditions. We had the heavy main repaired.
I've also had the top blow off a spinnaker from having it fill suddenly after we'd surfed down a wave and had the top of the mast swing it out into the full force of the breeze.
It is quite disappointing to have that happen, to say nothing of having to get the scrap of cloth and the halyard down from the masthead. People tape their rigging carefully, trying to avoid any chance for rips to start. Got to do that this weekend.

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