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Old 7th October 2009, 12:34 PM   #1
PH68
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Default Technique for popping cams

Hi

I am having trouble with cam rotation after transitions on my race sails and usually have to resort to 'kicking' the cams. Strangely, it is more of an issue in strong winds when I am overpoered and a bit slow to sheet in after a tack or gybe.

I have found that if I am 'hanging off' the boom (maybe because that is bending the mast) after the tack or gybe I can get them to pop better.

I have also noticed that some guys can flip a sail on the beach and get the cams to pop which I have never been able to do.

Is there a 'technique' to sheeting in that gets the cams to rotate properly?

Cheers!
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Old 8th October 2009, 03:17 AM   #2
Ken
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PH68,

Be sure that you have the sail rigged correctly (proper downhaul and outhaul). Variations from the recommended settings can make it more difficult to rotate the cams. Also if the battens are too tight, that can be a problem too. If the sail is rigged on a mast other than the recommended brand, this can also be a problem (mast diameters vary slightly).

I have found that "sticky" cams will rotate better with more wind. After a gybe or tack, you must snap/pull the boom in. With more wind, it adds more force against the sail, helping to push the cams around.

Popping cams on the beach works best with some wind, same as on the water.

I doubt that hanging on the boom and "bending the mast" helps.

There have been some sails manufactured that must have a "kick" or "punch" to rotate the cams even when everything is rigged as specified and on the correct mast. No solution here except to kick and punch.

One thing that can help if all else fails is a product called "Mclube Sailkote". Spray or rub it on your mast where the cams make contact with the mast. Avoid the area where you attach the boom. Do it before you insert the mast in the sail.

Hope this helps.
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Old 8th October 2009, 12:11 PM   #3
Roger
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Hi PH68,
Thanks Ken, good suggestions!
First, can you tell us which race sails you are using, and do they have roller cams?
As Ken suggests, the correct downhaul and outhaul are very important to cam rotation.
Too little downhaul and the mast does not bend the correct amount and some of your cams will be underloaded, others overloaded. With the correct downhaul, the seam down the front of the sail should bear at pretty much the same angle in front of each cam.
If you see that the upper and lower cams are about right, and the middle cams are under rotated (the seam is less far around the mast) then you need more downhaul to bend the mast more in the middle.
So, check the angles of the seam/crease (from the center of the mast measured around from the front of the mast). It may be on your masts you need some additional downhaul to get the angles all the same.
Also when your sail is rigged, check the tension of the luff sleeve adjacent to each camber. You can "flick it" with your finger and the sound should be about the same for all of your cams. If it's too tight it will sound loud/sharp, and if you don't have enough tension the sound will be softer/duller.
If you have roller cams, check for proper rotation of the rollers.
Also check if there are shims between the convex saddles on the front of the batten adapter and the concave saddles in the back of the cam.
The McLube Sail Kote that Ken suggests can be very helpful, but also check your mast is the areas the cambers ride to ensure that it's smooth to help with easy cam rotation.
Outhaul is also important, since if you run negative outhaul, there is no clew tension until you load things up.
Also do you give a quick snap with both hands when trying to get the cams to rotate?
Can you send me a photo of your sail (s) the way you rig them and perhaps a photo of one of the cambers and the front of the batten adapter?
You sometimes have to sacrifice a little performance (if you are not racing) and file the back of the cambers to loosen them up a little.
The also need to fit the radius of the mast almost perfectly. If the cams are too big, you don't get good rotation due to point loading, and if the cams are too small in radius you get lots of drag on the points of that are supposed to be tangent to the side of the mast.
Could be lots of little tuning things with each cam, and sometimes you have to fit and file a bit to get the best rotation with good performance.
The luff sleeve cannot be really loose (not enough cam tension or not enough mast bend) but conversely they cannot be too tight.
Larger sailors/racers normally run the tension in their luff sleeve/cambers pretty tight, but they have the brawn to snap them over.
Smaller sailors (like me) tend to run the luff tension/cambers a little looser by either tuning the cams individually or backing off a little on the batten tension.
Hope this helps,
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Old 8th October 2009, 09:42 PM   #4
PH68
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Hi Guys

Thanks for taking the time to reply to my post.
The camber that is causing me the most grief is the 2nd from bottom on my 11m CR
R2 when I rig it exactly to spec.

I am using no spacers on any of the cams but have quite a bit of tension on the bottom two battens. Having said that it does not seem to me that the batten tension makes much difference to the pressure on the cam.If I put about 1.5 cm extra d'haul (over spec) then I get reasonably good rotation but I only like to use this setup when the wind is consistently over 15 kts.
In lighter winds I rig 'to spec' or at most 1cm over which does not really improve the rotation noticeably.

Roger, can you explain what you mean by the 'cams being under rotated' and 'the angle of the seam'?
Which seam are you talking about exactly?

Thanks again for your time.
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Old 8th October 2009, 10:27 PM   #5
Ken
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Roger is great with the details - try some of his suggestions.

"Rigging to specifications" may not result in a perfectly rigged sail. New sails normally can't be rigged to the recommended downhaul until they "break in" and stretch some. Old sails may need to be over downhauled as they wear and streatch.

If you have to under downhaul to gain power in the sail, resulting in a sticky cam, then the solution is to either rig a bigger sail or get used to punching / kicking the cam. Try the Mclube on the sticky cam and you may be able to get by with under downhauling. Back off on the batten tension too unless you get too many wrinkles.
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Old 9th October 2009, 12:30 PM   #6
Roger
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Hi again PH68,
I'm not sure what brand your 11.0 m2 CR R2 sail is.
I'd like to see the specs and see how it rigs on the sailmakers website.
As far as the "seam" I'm referring to, down the front of many 2 piece luff sleeves the material is sewn together right down the front of the sail, making it stronger and helping
the designer get just the right luff curve.
On sails with a one piece luff sleeve that is only sewn at the back where it connects to the other panels in the sail, a crease develops when the sail is rolled up for shipping and when you roll it up after a session for storage in the sail bag.
Regardless of whether you sail has a one piece luff sleeve with a crease, or a 2 piece luff sleeve with a seam, there is almost always some indication (seam or crease) as to where the exact front of the sail is when it's laying on a flat surface.
When you push your mast in the crease/seam remain flat except at the very top and bottom of the luff sleeve, until you begin to add some downhaul.
Then the crease/seam will pull back against the mast curve as the mast bends to the luff curve.
Sailmakers use "broad seaming" to put lots of shape into the luff curve to make it compatible with the mast bend.
As you add more and more downhaul, the crease/seam at the front of the sail will pull back, and then begin to rotate around the front of the mast.
If you don't use enough downhaul, the perimeter tension (around the outside edges of the sail) and the panel tension will be too low and the front of your battens will tend to kink or knuckle due to the back end of the cam being rotated too far out to the side on the leeward (convex) side of your sail.
As you add downhaul, the cams will rotate futher until the luff sleeve profile is exactly what the designer intended.
This will give you the optimum draft for power and at the same time give you the correct amount of twist up on the higher parts of the leech so your sail handles well and is responsive to gusts by having the upper leech "open up" slightly.
So, by looking at the seam/crease, you can tell pretty well whether you have the correct amount of downhaul to optimize the power and handling.
Not enough downhaul lowers the tension throughout the sail and results in cambers that are "under rotated".
Too much (well beyound the additional 1.5 cm you are adding I would think) downhaul will cause the cams to rotate further around the mast (rear of the cam moves in toward the centerline of the sail) due to too much tension throughout the sail.
This can also occur if you use too much outhaul tension as both too much downhaul and too much outhaul can draw your sail out too flat, reduce it's draft and power and make it feel heavy and gutless.
Since even the mfg's "best" suggested mast can vary slightly due to manufacturing tolerances, you need to really pay attention to when the sail is loaded uniformly throughout and the cams are rotated to the designers specifications.
This means on some sails you have to stay under the designers recommendations for downhaul as your mast is a little too soft, and conversely if your mast is a little too stiff you will need to add more downhaul to "spread" the tension and get the battens and cams rotated optimally.
Hope this helps,
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Old 25th October 2009, 01:52 PM   #7
ZegeVele73
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Default Technique for popping cams

CAMS offer better sail set for more power and more control. Additional weight sometimes a problem with water starting if air is marginal for power needed.
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