Modifying Cams on Severne race sails

Some of my race sails that I rig on older non-tapered masts, used to have poor rotation, until I modified the cams.

You can test the cam pressure, by trying to push the cam off the mast using your fingers by pushing it away from the mast while it lying on the ground.

Steps

Scribe a line, like this (this was damaged cam). Use a set of calipers to measure and be precise.


grab one of these 80 grit or similar

Undo the two screws at the back and sand back each side at the back end of the cam and put a little bevel on it, like this. You can now use spacers if you change masts or you overdo it.



I only needed to do one or sometimes two cams out of the four, etc. I could then also reduce the spacers on the rest.

Hope this helps someone else.

It looks like something that I have sometimes had to do too.
It is the opposite of adding shims, i.e. when even zero shims are still too much pressure on the cams, one can make the cam shorter by remove some material in the front.

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Roy1000 said..
Im confused.
Are you able to explain it in more depth?
I use a rsx mast 520 (2imcs too soft) for the HGO 9m.
My cams dont pop atall i have to kick and push them to get them to rotate.

The length of the cam is chosen to match the outside diameter of the mast and how much the luff curve of the sail differs from the natural bend of the mast. (e.g. if want to use an RDM you would need an even longer cam). In my case I am using an older Severne mast that should have a similar curve but has a wider outside diameter, than a newer SDM from severne which would be narrower in the midsection (i am told this is to increase strength) .

What ever the exact reason was is some sails have had excessive cam pressure on 1 or 2 cams (mainly 1). You can try an release some of that pressure by putting spacers on other cams, but that is probably not a good idea anyway. Keep in mind that top cam probably don't want as much pressure as the bottom ones.

If you going to modify the cams make sure you got excessive cam pressure in the first place.


If you overdue it you can put a spacer back in. You can even use a spacer to measure amount you want to remove (that is what I did) that way you can use a spacer to get back to same spot if you choose.

hope that make sense?

If you have a friend who has the correct mast, measure the outside diameter at cam attaches and compare.

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Roy1000 said..
Im confused.
Are you able to explain it in more depth?
I use a rsx mast 520 (2imcs too soft) for the HGO 9m.
My cams dont pop atall i have to kick and push them to get them to rotate.

As an aside, the HGs don't take a lot of batten pressure. If you have them cranked down, back off a bit. Don't back off too much because it's possible to create a bit of slack in the batten pocket when pumping and the string holding the tensioner will pop off and you'll loose the tensioner.

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SurferKris said..

Paducah said..
Don't back off too much because it's possible to create a bit of slack in the batten pocket when pumping and the string holding the tensioner will pop off and you'll loose the tensioner.

The tension of the batten pocket and the camber pressure against the mast are unrelated. Reducing camber pressure will (or at least shouldn't) affect the tension of the batten in its batten pocket.

I don't think that is strictly true. When you have excessive cam pressure it will move the front of the body of the sail. It may crinkle slightly shortening the batten pocket where it is hidden by the luff sleeve. Or stretch it somewhere else. The former happened for me. For more normal amounts of cam pressure I would tend to agree, that they are not related. But it easy enough to readjust which I think is wise.

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SurferKris said..

Paducah said..
Don't back off too much because it's possible to create a bit of slack in the batten pocket when pumping and the string holding the tensioner will pop off and you'll loose the tensioner.

The tension of the batten pocket and the camber pressure against the mast are unrelated. Reducing camber pressure will (or at least shouldn't) affect the tension of the batten in its batten pocket.

Yet, it works and was recommended to me by HG sailors here. With a lot of batten tension, the sail wants to remain curved and resists changing shape to the other side. It's the same way that some non-cam sails e.g. Ezzys have static shape. ymmv.

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Paducah said..
Yet, it works and was recommended to me by HG sailors here. With a lot of batten tension, the sail wants to remain curved and resists changing shape to the other side. It's the same way that some non-cam sails e.g. Ezzys have static shape. ymmv.

I don't know anything about foiling, but for windsurfing with fins you do want to have some shape in the boom area. The battens can therefore be tightened a little more in this area compared to the top ones. The battens in the top part of the sail should not give the sail any shape.

I would recommend to tighten the battens with the sail laying flat, not rigged on the mast. Tighten until the wrinkles are removed, but ignore sections where the batten changes size/shape (here there will always be a few wrinkles that cannot/should not be tightened out).

Then rig on the recommended mast and check the pressure of the cams onto the mast. There should be a little wiggle room here, i.e. with sail lying on the ground (boom on) and you push downwards on the batten at the end of the cams they should leave a little gap towards the mast. This "gap" is tuned with the spacers, and the goal is to have profile that doesn't change in the wind gusts while sailing. After that the rotation is what it is, a sail with the modern longer cams will rotate better than the older shorter ones, the mast and cam can be lubricated with McLube etc. But one should not try to tune the cam rotation with the batten tension....