Brian Kerslake wrote:
I fancy cambered, but there are some questions:
Hello Brian,
Welcome to the website, and thanks for putting Paradox on the map - I wish more people would. One question - you've put her into HM Prison on Portland!! have you taken up residence there as well? She just needs dragging northwards a bit into the marina.
Thanks for posting all these interesting questions. Where do I start?
On all junk rigs, the yard is trying to rotate so as to lower the peak and push the throat forward, tending to crease the panels diagonally. This is true in the upper panels of a flat, Hasler sail, but it is easily remedied with tension on the luff parrel. It is equally true on a sail with cambered panels, but it shows up more if it is not remedied. It shows up more further down the sail, because each panel does not have the diagonal stability of a flat panel. The problem gets worse, the higher-peaked the design of the sail - a Van Loan sail is easy to deal with, since applying a little luff tension will readily pull down the throat. A very high-peaked sail cannot be controlled by luff tension, since luff tension has little effect on controlling the rotation of the yard.
The essential thing is to have a yard parrel and upper luff parrel that effectively work together to peak up the yard. If the yard parrel is attached to the yard, not at the halyard attachment point, but further up, as near to the masthead as possible; and if the end of the upper luff parrel is attached, not to a batten, but to the heel of the yard, then you are getting the best possible control over the angle of the yard.
I have never liked Hong Kong parrels. You can only get them absolutely right for one set of circumstances, and they are at best a compromise at other times. I much prefer to use a second luff parrel to control the middle of the sail. It pulls the sail down, into the mast and aft all at the same time, and after some experimentation in how to rig it, can provide effective control over diagonal creasing in the middle panels. I go further, and say that a lower batten parrel, to the lowest battens, is similarly effective. With three batten parrels, you have lines that can act as downhauls for all battens, as well as acting as sail shaping aids.
To give an example: I made cambered panel sails for Badger in 2006, but left to go voyaging before they were rigged. A week ago, I visited Alan and Gloria Parsons, who told me that Badger's performance was greatly improved compared with that obtained with the old flat sails, and that using upper and middle luff parrels did allow them to shape the sail effectively without diagonal creases; but that they had to work a little more at achieving a good result than they did with flat sails.
High or low aspect ratio won't have a great deal of influence - it's the control over the yard angle that matters more.
A mast that bends unduly is what throws the fixed Hong Kong parrels out of kilter most, and there's no answer, except to use an adjustable system - luff parrels.
Gravity doesn't have much effect on the tubular battens you'll be using, they're too light. The answer? a set of luff parrels.
All the problems in setting cambered panels well increase with the amount of camber built in. For this reason, I advise those not looking for the ultimate performance not to get too carried away when putting in the camber. 6% is enough to get good performance, without looking excessively droopy when the wind doesn't blow.
I met a Freedom 39 in Stornaway, years ago, and thought it a nice-looking vessel, but the owner was complaining of lack of windward performance. I suspect that it was because of the large carbon masts in front of the bermudan sails destroying their effectiveness. I don't think you'll notice much loss of performance compared with your present rig if you go for a good cambered panel rig. You'll do a little more string-pulling than with a flat sail, but not much more. You might actually get to enjoy the feeling of going to windward well!