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Old 29-12-2010, 21:02   #1
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Traveler Position Challenge

I am finishing a complete restoration of a SANTANA 39. My plans are to integrate a full enclosed cockpit (using a custom arch and canvas). In order to do so, I will have to relocate the traveler of the main sail to a different location.



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Now: The Main sail traveler is located (longitudinal) 3/5 of the boom right in the cockpit (seat level). The sheets, traveling from the traveler to the boom are right in the way and prevent any "encapsulation" of the cockpit.

Solution 1: Position the Main Sail traveler on the roof portion of the boat (move 4 feet forward) which would then be approximately 1/4 of the boom length. (attach-point on the boom being relocated accordingly)

Solution 2:I am building an arch that will be positioned in the rear of the cockpit. I could integrate material and additional structure support to accommodate the Main Sail traveler. The position of the traveler would then be located a little behind the boom (attach-point on the boom being relocated accordingly)

Question A: Although I would prefer to go with option#2, I have serious concerns about the effect of elevating the traveler (which is a fixed component) vs being low (originally)? Would the boat be less steady / performent sailing to weather?

Question B: On solution 1, considering the lever effect of the boom (attach point being moved forward), Is it a bad idea to add such stress on the roof, or would it acceptable considering proper reinforcement of the boat in that area?

Thoughts and ideas are welcome! Thanks
email: mbrault <at> konsultech <dot> com
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Old 29-12-2010, 21:24   #2
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Moving the boom attachment point forward will require some professional engineering help from a spar builder. And a much stouter boom.

In Option #2, moving the sheet attachment to an arch, or anywhere for that matter, does not change the sailing dynamics for a given sail trim. Moving it up close to the boom does affect how the traveller position controls the boom and leech. But moving the traveller closer to the boom should improve sail control (that's my initial guess anyway).

Again, mainsheet loads are substantial. I'd recommend getting some design help or copying from a successful boat.
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Old 29-12-2010, 21:32   #3
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Thanks Daddle

Just thinking purposes... The fact that the traveler is a fixed components and it is being located to higher grounds, you do not think it would act as a lever on the boat as it is being pulled by the main sail, making it more sensitive to cross wind (tilting the boat)?
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Old 29-12-2010, 21:38   #4
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My opinions are about like Daddle's.

1. Moving the traveler to the front 1/4 of the boom concerns me. That is putting a lot of load on the end 3/4 and would probably require replacing the existing boom with a much heavier, stronger section.

2. Setting the traveler on top of the aft end of the cockpit enclosure should still allow the same if not greater level of control of the boom. The heeling forces will be from the wind pressure on the sail and mast. Location of the traveler higher or lower would have an insignificant effect on heeling, as long as the boom and sail are at the same height as before.
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Old 30-12-2010, 03:12   #5
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Moving the traveller forward may require more mainsheet purchase as well. from a leverage perspecive you get much more power when sheeted aft on the boom and less as you go forward.

Others have mentioned the obvious deck strength issues, so its probably a moot point. But I would certainly have a pro look at that option.

I think the idea of flying the traveller is the best at this point. But I would also have a pro look at the coamings or whatever area youre planning to mount the targa. Due to the close proximity of the traveller to the boom, in this case, you may want to have it shaped into the arc of the boom.

Cheers
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Old 30-12-2010, 17:30   #6
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Changing the point of contact on the boom greatly changes the loading on the boom. Make sure structurally the boom will support the change. Moving the mainsheet to the end of the boom means that more unsupported loading is in the center of then boom. That could lead to boom failure.
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Old 30-12-2010, 17:49   #7
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Moving the mainsheet to the end of the boom means that more unsupported loading is in the center of then boom. That could lead to boom failure.
That's right and, almost counter-intuitively, the danger for a boom thus rigged increases when you reef because the greatest unsupported load moves further forrard and away from the supported end. I've seen a couple of booms bustes in those circumstances - and one of them was mine.
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Old 30-12-2010, 18:12   #8
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That's right and, almost counter-intuitively, the danger for a boom thus rigged increases when you reef because the greatest unsupported load moves further forrard and away from the supported end. I've seen a couple of booms bustes in those circumstances - and one of them was mine.
Yup,

This problem is still overlooked by designers - witness the booms breaking in the last volvo race. They broke when reefed.

But I still prefer the end of boom arrangement because the cabin top arrangement looks like it will create a greater leaver arm along the boom (and hence much more load), for more of the time (i.e. when not reefed).

And there is the forces on the cabin top to consider. FYI - my boat is designed for the traveler to be in this location. Even so, the cabin top distorts by about 75mm (1.5 inches) when the main is sheeted hard. It's a lot of load at that point - you will have much less load at the end of the boom.
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Old 30-12-2010, 18:13   #9
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I'm not certain why you fear reduced performance using the traveler arch. Consider the fact that you'll be shortening the mainsheet significantly under this option, where there will only be a few inches of sheet when you're close-hauled.

One thing to consider with the traveler arch option, is that you really should go with a rigid boom vang at that point. You'll want to set it so that it's physically impossible for the boom to descend lower than the traveler track.
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Old 30-12-2010, 18:25   #10
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Yup, This problem is still overlooked by designers - witness the booms breaking in the last volvo race. They broke when reefed. But I still prefer the end of boom arrangement because the cabin top arrangement looks like it will create a greater leaver arm along the boom (and hence much more load), for more of the time (i.e. when not reefed). And there is the forces on the cabin top to consider. FYI - my boat is designed for the traveler to be in this location. Even so, the cabin top distorts by about 75mm (1.5 inches) when the main is sheeted hard. It's a lot of load at that point - you will have much less load at the end of the boom.
And for the reasons you've mentioned, I also prefer the end of boom rig. But a snapping boom is kinda unpleasant, so I've added mid boom fitting to allow me to provide extra support from the cabin-top when reefed. A bit agricultural and haven't given it a real tryout yet but...any other ideas?
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Old 30-12-2010, 18:31   #11
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Sorry guys... if its got a kicker/vang whatever you want to call it I cannot see any reason it'll matter if moved aft to the end of the boom.... I've sailed many such boats and its down to the integrity of the boom... surely those booms aren't more fragile than other booms.. I've moved a main sheet traveler from the front of the companionway... real pitb... to aft of the tiller/helm... worked a treat
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Old 30-12-2010, 18:50   #12
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Sorry guys... if its got a kicker/vang whatever you want to call it I cannot see any reason it'll matter if moved aft to the end of the boom.... I've sailed many such boats and its down to the integrity of the boom... surely those booms aren't more fragile than other booms.. I've moved a main sheet traveler from the front of the companionway... real pitb... to aft of the tiller/helm... worked a treat
But Boatman, I don't see that a boom vang can stop the lateral bending of a boom, and that's the force that breaks it.

I think your comment that "it's down to the integrity of the boom" is on the money. But if a particular boom is engineered/designed for a mid-boom takeoff, wouldn't a change in takeoff position sharply alter the original design parameters and thus bring the "integrity" of the boom into question.

Or maybe the boom that you successfully re-rigged was over-engineered in the first place?
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Old 30-12-2010, 19:48   #13
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Quote:
Originally Posted by At sea View Post
But Boatman, I don't see that a boom vang can stop the lateral bending of a boom, and that's the force that breaks it.

I think your comment that "it's down to the integrity of the boom" is on the money. But if a particular boom is engineered/designed for a mid-boom takeoff, wouldn't a change in takeoff position sharply alter the original design parameters and thus bring the "integrity" of the boom into question.

Or maybe the boom that you successfully re-rigged was over-engineered in the first place?
No... my sorry chicken scaredy ass brain can't get round anyone letting the loads get that high anyway without being in storm rig down to 3rd reef... and heaved to..
I know you guys don't get sails like that over there... I've had to request the 3rd reef added as only 2 seems standard.
So I take it a centre sheeted boom is of inferior quality to the other... hmmm.. still not sure I buy it
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Old 30-12-2010, 20:07   #14
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G'DAy all,

Seems to me that the horizontal loads on a boom arise from the clew/outhaul fitting, not much from the slugs along the boom. Nowadays, many mains are loose footed, and in them, there are NO horizontal (or vertical for that matter) loads anywhere along the boom. It is very hard for me to see that moving the sheet attachment to the end of the boom can do anything but reduce bending loads. When reefed the clew moves forward, and does then put loads in more forward positions... but these loads, at least in our boat, don't seem to affect the boom visibly. One should also remember that by moving the attachment to the end the magnitude of the sheet load is reduced by the geometric ratio of old:new distance from the gooseneck.

In short, I don't believe that moving the attachment to the end of the boom will cause a problem .

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Old 30-12-2010, 21:39   #15
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G'DAy all,

Seems to me that the horizontal loads on a boom arise from the clew/outhaul fitting, not much from the slugs along the boom.
That's the key issue

It's the distance from where the load in the sail enters the boom (clew) to where it leaves the boom (mainsheet). You will have to put much more force into a mid-boom sheeted main than a end-boom sheeted main.

Next time you're out sailing, grab the boom end and pull it to windward. Then try doing that half way down the boom.
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