Monday, April 28, 2014

Cam Rotation

In this message I will discuss the problem of cam rotation and hopefully, provide some solutions.  In the previous post I mentioned Martin Cross and the problems he experienced with his new Overdrive.  He has just upgraded his Turbo for an Overdrive and where the Turbo rotated beautifully, the Overdrive sticks on the top two cams.

To save a lot of writing here is a copy of the e-mail I sent Martin:

Hi Martin

You are right about this being a common problem and I need to write a post covering this aspect of camber induced sail rigging.  My experience in this area has taught me to follow these steps to effect proper rotation of sticky cams. (Please forgive the rambling explanation):

 1. Ensure that if the inducer is an asymmetrical one, that it has been installed the right way up.         Sometimes the factory gets this wrong.  Just look at  how the cam sits on the mast.  If it is being pulled unnaturally, try rotating it and see how that works.  If the inducer is symmetrical - no problem.

 2. Give a bit more downhaul and see if this improves things. 

 3. Ensure that the cams are not getting snagged on loose protective tape (which Severne used on older masts).  This tape is quite soft and can distort and  bunch up where the cams make contact.  If the tape is snagging things - cut loose bits off and sand the area down. 

If the above measures fail, you are going to need to file the curved section of the cam down slightly.  This is the section which comes into contact with the batten pocket (NOT THE MAST!).  You will need a circular cross sectioned file (we call them rat-tail files).  Make a mark about 1mil from the existing curve edge and file the opening down until you reach your mark.  You are aiming to bring the cam away from the mast by enlarging this space.  The concave form runs the width of the cam of course so make an identical felt tip pen mark on either side of the cam and file down carefully until you reach both marks.  This can be a fairly long process as you shave the surface down, rig the sail and test the rotation. Repeat until the cam rotates nicely.  If you get one cam working properly it may just pull the other one round as it rotates but if not, then you need to repeat the process with the other cam.

The photo attachment indicates the cam surface I am talking about.  This is what you need to file down.

Please let me know how you get on

Here is the picture I attached to the mail:

Martin says that he is not that keen to start hacking away at his pristine new sail and I have to say that I understand this.  Cam filing should only be done as a last resort.

In a follow up e-mail, Martin mentioned something which caused my ears to prick up.  He said that he noticed when he de-rigged, that the bottom of one of the cams had gouged the mast (obviously as it rotated).  This opens up a really important further measure which I had not mentioned.  When you do your final downhaul after snapping the cams onto the mast, it is possible for the upward movement of the mast and downward movement of the sail to result in one or more cams being pulled out of alignment.  When this happens it compromises the cam's performance - the rollers do not sit squarely and so cannot do their job.  This can have two effects - firstly the cam in question does not rotate, secondly the adjacent cam can be prevented from rotating because it's mate is locked.  You then assume that both cams are faulty.  Wrong diagnosis!  Further, if one of your cams does settle in a missaligned position and you then force it round by kicking, head butting or punching (we've all been there), then what you get is a weakening and stretching at the cam/batten interface.  This can cause the cam to default to the incorrect position every time you rig and you can be left labeling your sail as "that damn thing which doesn't rotate".

The upshot of all this is - please ensure that all of your cams sit squarely on the mast before you hit the water.  This is really important for new sails.  You may just need to pull the cam slightly into the correct alignment to free it up.  This is crucial if you have one of the older red Enigma masts.  The protective tape on these masts is quite tacky and can easily snag your cams.

I hope that this post is useful.
Good winds


  1. I use MauiSails TR cambered sails and have had similiar issues. People made suggestions on the MS forum. What worked for me was loosening the batten that is just above the boom and applying McLube water resistant lubricant. After about 10 outings all issues disappeared. I now call this "breaking in the sail". Too bad about the mast scuff that happened to Martin @#$%^&*

  2. Thanks for this JW.
    The more knowledge we can share around this issue, the better.