View Full Version : Canoe mast design question
11-20-2006, 05:02 PM
Rigging my 15' Bob Special canoe for sail, I'm about to cut the dumb sheave (for the halyard) in the top of the mast for a 35sq ft. lateen. Should this slot be cut in the mast aligned with keel line or perpendicular to it? I don't recall seeing this particular detail illustrated. Does it matter? Hoping maybe Todd or other canoe sailors will weigh in on this. Thanks.
11-20-2006, 06:45 PM
Crosswise to the keel for a lateen.
11-20-2006, 08:10 PM
...and crosswise to the grain too.
11-22-2006, 09:18 PM
Just think of what the halyard for any rig does as the sail moves from fully eased on one side to fully eased on the other.
ie opposite gybes. The exit for the halyard should be at the midpoint of these two positions.
11-23-2006, 01:23 PM
Hey, Arthur, when you're ready to launch come down Austin way and I'll advertise an instant messabout at Lake Bastrop or somewhere close and we'll all gather to wish you well and admire your creation.
Steve Lansdowne (A Wee Rob 'sailor' of sorts.)
11-24-2006, 09:05 AM
I run a lateen of 44 sq ft alot and I hoist it to a mast which does not rotate. I have a bamboo sleeve that fits atop the mast (carbon fibre spar); to it is affixed a small length of hardwood dowel to which is affixed a sheave/pulley which rotates about the mast on a brass fitting (a la Rob LaVertue).
I have seen other sailors mount a litte tab or flange to the top of the mast (through which the sheave runs in a 90 degree orientation with a similiar litte tab to that part of the yard that gets hoisted to the mast. I guess the idea is to bring the yard snug up to the mast. Sorry I have no image.
IIRC, the mast roatates on many canoes set up this way.
11-24-2006, 01:51 PM
On a lateen, it really doesn't matter whether the mast or halyard fitting up top rotates or not. The sheave is placed crosswise primarily to make a straighter pull for the halyard when raising or lowering sail. Since the gooseneck slides on the mast and the only thing providing downhaul tension is mainsheet tension, if the mast doesn't rotate, as you switch from tack to tack, the entire sail, it's yard and it's boom may climb or decend the mast 1/2" or so. This has no effect on sailshape or luff tension it just raises or lowers the C.E. a fraction of an inch.
Small sails where rotating masts can be helpful are sails where the halyard or snotter are pulling against something fixed, not a floating gooseneck. A spritsail, for example, gets much of it's sailshape from tension on the snotter, forcing the sprit and peak corner upward and creating tension along the sail's head. This tension prevents the head edge from sagging and putting excessive draft in the top third or more of the sail. As the sail swings from one tack or jibe, through the eye of the wind ond out on the other side of the boat for the next tack or jibe, a fixed (non-rotating) mast will exhibit a broader variation in snotter tension than one that can rotate as the sail does. This in turn can cause variations in both upper sail draft (and on some sail types, luff tension) from tack to tack as well as within the same tack (depending upon how far you have eased the sail out). It doesn't take a lot of tension increase or decrease along the luff or head to make a fairly substantial sailshape difference. So it's a good thing in these cases to encourage the mast to rotate as you tack back and forth, keeping the snotter tension and sail draft similar on both tacks.
Since lateens are immune to this problem, rotation or not just isn't a big deal for them.
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