Triple trapezing - pyramid style

[Tom Peterson]

One windy day a couple of years ago, we got the idea to pull one of the trap wires to the other side of the boat to make three. We put Doug, our heaviest guy, up front, and convinced Charlie to climb out on our shoulders. We hooked up kind of high because I was afraid with that much weight we would end up dragging in the water, but the wind cooperated and we zoomed right past our pontoon boat where Peggy was waiting with the camera. Charlie even spread his arms for the photo but his fun ended when Doug and I started to spread out. We have also pulled water skiers with this boat but have no photo proof. Maybe next year...

[Bill Roberts]

Hi Tom,
There is something you should consider. The boat is designed for two persons on the trapeze, max righting moment, with a safety factor of a little over two. That max crew righting moment would be something like: Ri Mo = 2 x (8ft+3ft) x 160 lbs = 3520 ft lbs. When you add another person standing on the shoulders of the two persons already on the wire, that person's Ri Mo = 1 x (8ft + 5.5ft + 3ft) x 160 lbs = 2460 ft lbs or a 75% increase in crew righting moment. The basic platform righting moment is: Ri Mo = 325 lbs x 4ft = 1300 ft lbs. To fly a hull with this much crew righting moment means that the total righting moment on the boat is up by (3520 + 2460 + 1300)/(3520 + 1300) - 1 = .51 or about 50% over the normal boat design righting moment. When you hit a wave and put a jerk into the system, the instantaneous load could exceed the max capacity of the boat and "POW" down comes the mast.
So Tom, the botom line is you could easily break your boat and someone might get hurt. Be careful and understand what you are doing.
Good Sailing,
Bill

[DanBerger]

Bill,

For grins and giggles, I was considering tripple-trapezing my SC19. I wouln't have 3 big guys on the wire, but maybe a total of about 500lbs. I would think that having a third guy on the others shoulders would add a lot more weight than just having him standing on the deck. I mean, 500lbs is like two pretty big guys on the wire and that seems like a reasonable amound of weight!!

[Bill Roberts]

Hello Grins,
There is one very important and overlooked factor about taking extra heavy loads, extra passangers, out sailing on a beach cat. There is no problem taking large numbers of people sailing at the same time in light winds. No overload possible. The problem comes on a windy day. On a windy day the water is rough; there are big waves. Sailing over and through these waves the boat pounds and jerks. During these jerks, the sailors experience 2 to 3 G's. This means that for an instant they weigh 2 to 3 times what they weigh on the bathroom scales. This extra load shoots right up the trapeze wires and comes down the mast as extra compression load. The mast is a tall slender column and is prone to "buckling failure". Two people, 160 pound people, on the wire pulling two g's in rough water is the same jerk load as four people on the wire in smooth water, no pounding, no jerks. Now if we put three people on the wire and go sailing on a windy day with rough water, which is normal water on a windy day, they can put loads into the rigging and mast equal to six people on the wires during the jerks. This is an overload condition! The boat was not designed for this! Something is going to break and that something is likely to be the mast.
Good Sailing,
Bill

[Tom Peterson]

Well, I guess ignorance was bliss, and we got lucky for a day... We took the Hobie 16 out one day in winds and waves so strong they canceled the race were trying to sail in. We didn't think we could stay in the traps so we had three guys all hiking out. We hit a big wave and bang, the windward shroud broke. I always wondered if we had at least one guy in the trapeze whether that guy's weight on the wire would have taken enough load off the shroud to prevent it from snapping. But, maybe then something else would have popped. I have lost a mast three different times but never had one break - I think that would be scary.

[klipps]

Interesting reading and detail. Thank you. As a beginner sailing a 17, knowing these details helps make sure I am learning the right way...

[DanBerger]

You know, Bill, I remember a long time ago my mother telling me not to jump my skateboard over the makeshift ramp I made in my driveway. Did I listen to Her?? NOoooooo. My wrist still hurts to this day.

OK, so maybe tripple trapping the rig is not a good idea...bummer.

[Peter Kirschhoffer]

OK, this brings up a related question about shroud tension. I have a SuperCat 15 that I have sailed on & off since I got it new in 88. It is my understanding that the tension should be loose in light air to allow the mast to rotate more easily. But in stronger wind conditions the shrouds should be set a little tighter. My thought are that the stronger wind force will be able to rotate the mast sufficiently under tighter tesion. But, is this also to keep the rig, with or without someone on the wire, from bouncing around as much preventing an early shroud failure?

Peter

[Bill Roberts]

Peter,
The reason for low shroud tension in light air is because as the mast rotates it runs into the leeward shroud. If this shroud is tight, it will stop the mast from rotating to the proper position. If the leeward shroud is slack, the mast is free push the shroud out of the way and rotate to the proper position. In light air the leeward shroud can be made slack in one of two ways. One, you can set the mast up with little to no shroud tension . On any point of sail the slack will always go to the leeward shroud, so the mast will push the leeward shroud out of the way and rotate to the proper position. Two, if you have put the mast up with a tight rig and while sailing you see that the mast is not rotating as far as it should, like in downwind sailing, you can open the leeward shroud lever. This puts a couple of inches of slack into the leeward shroud and the mast pushes the slack shroud out of the way and rotates to the proper position, like parallel to the main beam. This is a "go fast" device that only SC and ARC products have. Don't forget to tighten the leeward shroud lever before jibing into the other tack.
Bill

[Peter Kirschhoffer]

Thanks Bill for the tip. My boat has been set with a loose rig, so the light air rotation hasn't been a problem. But, when the wind gets extremely light or dies, everything bangs arround annoyingly when large power boat wake passes under my hulls. Setting the rig a little tighter and opening the leward lever could make the wait for a puff of air less frustrating. Perhaps, I may have had it set too loose all along. Is there a way of determining what is too tight or too loose for conditions?

Peter

[Bill Roberts]

Peter,
Since your boat has shroud levers, there is an easy for me to tell you how tight to set your rig. When you are closing the last shroud lever, you should be taking all of the slack out of the rig as the shroud lever handle approaches level, horrizontal. As you close the shroud lever from 3:00 o'clock to 6"00 o'clock, it should take some effort to close the lever. This will set the rig snug and you can still make it slack by opening the leeward lever while sailing downwind.
In strong winds it is not necessary to open the shroud lever to put slack into the leeward shroud. In medium and strong winds the mast bends and the hounds is slightly closer to the deck, the mast gets shorter because it is bent, not straight, and this puts slack into the leeward shroud. The mast will rotate to a position parallel to the main beam while sailing downwind automatically, no problem.
Bill