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Discussion in 'Canoe Sailing' started by Treewater, Mar 22, 2021.
This is a 14 ft Chestnut Chum
I decided to make it a sailing canoe. I put an Old Town mast shoe and Old Town cross piece, cut down, to hold the mast. Positioning the mast was the question. The lee board position is fixed by the center thwart. I made that lee board bracket myself and it works fine on another boat, means that I only have one board as you see. With the lee board fixed by location the only that is moveable is the mast. I choose the forward seat location. The rudder is a problem and I made this arrangement because I have only one stern mounting for the Old Town rudders I have. Also, I dislike the rope and pulley arrangement. What I observe is this: when the wind is upwind of the spar on the mast the rudder displaces one way. When the wind is downwind the spar and mast it displaces the other way. This means the center of "lift" (aviation term) is shifting on the sail depending on what side of the mast it is one. Someone tell me if I am correct so far.
I'm sure some other people will respond to this but I will try. I think you may have to research some of your sailing terms to fully describe what is going on, but I think I know generally what you are saying, though my response will be in more laymen's terms than others. Basically, depending on where the mast/sail is mounted and the leeboard is placed, it will impact how your rudder will work. Look up "lee helm" and "weather helm" to learn more.
Since you have a fixed point for your lee board and the sail, you may be stuck in this configuration.
You can adjust a little by moving the little gooseneck hook on your boom forward or back to change the sail position, and where you tie the halyard. This will slightly shift your center of effort. When sailing a sunfish, you can adjust the gooseneck in the same way and that can "balance the helm".
See this video:
" I think you may have to research some of your sailing terms to fully describe what is going on"
Yes, it's difficult to figure out the question at this point. If we are talking about where the mast needs to be positioned. then there is a pretty simple design suggestion to follow. We want the center of effort of the sail pretty much directly above the leeboard for starters. If the leeboard position is fixed, then the adjustment is made by either moving the mast, or in the case of certain sail types, moving the spot where the sail and its support spars (yard and boom) intersect the mast. Whatever it takes to get the sail's center of effort over the leeboard.
Pinpointing the center of effort on any three-sided sail is pretty easy. You just draw a couple of lines from two of the corners to the halfway points on the opposite sides. The spot where these lines cross is the Center of Effort. If desired, make a little pencil mark at the CE on the sail for reference while you are adjusting things. Fine tuning can then be done to some extent by adjusting the leeboard's angle a bit.
Good video and good picture. Thanks both. Perhaps something is wrong with what I'm doing but I learned to sail with a sloop rig. The lateen rig is different in one major way, it has an upper spar, gaff, that by necessity is one side or the other of the mast. Todd, I have your book out as I write. You mention that there is a change in center of effort when the spar is leeward vs windward. As you say, it is seldom noticed. In my case, my real struggle is the rudder and the change in center of effort became noticeable. Anyway, thanks Floyd, I'll watch the video several more times. And thanks Todd, I got the answer from you and my real problem is the rudder. Thanks again.
Better worded: the center of effort changes depending on if the upper spar, gaff, is windward or leeward. The sail section forward of the mast has become unusable when the gaff is windward. This changing the sail area and center of effort.
Things will be much easier if you simply use an adjustable leeboard bracket. See https://www.wcha.org/forums/index.php?threads/10672/ for some examples. Good luck,
"the center of effort changes depending on if the upper spar, gaff, is windward or leeward. The sail section forward of the mast has become unusable when the gaff is windward. This changing the sail area and center of effort."
Not that I remember, as all of these statements are false. Theoretically, the sail's performance may change a bit due to the mast interfering with the airflow over the sail on one side, but the Center Of Effort is just a measurement used for estimating fore and aft positioning of the sail in relation to the hull. It is strictly related to the sail's perimeter shape and always stays the same. It is used to fine tune helm balance.
As to whether or not having the mast on one side of the sail actually makes much difference in performance, in most cases it doesn't seem to be a big deal at all. If in doubt, you can always set the boat up with the mast on the port side of a lateen sail, balanced lug or other sail where the yard or boom cross the mast. That way, even if your performance was hindered slightly by the mast, you would at least have the starboard tack right-of-way in your favor.
Ever see a cross section of a Dragonfly's wing? It's a thin membrane with a couple of rigid internal spars. Look familiar? They seem to "sail" pretty nicely.
The fixed dagger board came because of a 12 portage trip in as many lakes. I had enough gear to carry without the extra dagger board and crosspiece. I'm satisfied with the arrangement. The shape of the sail I will have to photograph next time I am out. All of this is in anticipation of repeating my Canadian multi lake journeys.
Forgive me for being a biologist here, but a dragonfly wing is something radically different from a sail, and much more complex than a thin membrane with a couple of igid spars built in. The physics of dragonfly flight is remains actively studied because it is so complex. That said, the canoe sailing discussion here is great.
The point was simply that the shape created by a mast up against a sail is not the kiss of death for that airfoil to perform well and create lift, as some people seem to think it must be.
One of the things I've always found interesting about canoe sailing rigs is that the vast majority of them are basically hacked together by amateurs, no insult intended. They tend to be a lot more creative and a lot less stuffy than your typical sailing crowd. That being said, there are still some critical factors at play in order to get things to work properly, many of which can't be ignored by either the yacht clubber or the canoe sailor with his home-made rig.
The design and construction of most canoe or dinghy sails or sailing rigs isn't terrible difficult, but there are a lot of little tedious factors which need to be juggled and accounted for in the process to do it well.
I would encourage you to practice with this rig before setting out on an extended trip and to think carefully about the types of wind direction and speed where you intend to use it. You may be able to eliminate the leeboard completely if you only intend to sail down wind for example. Sailing canoes generally don't perform very well when heading upwind, even with fully optimized rigs. A different sail which is more balanced over your fixed leeboard may give better upwind performance, if you need that.
I have some experience with the issues related to a fixed and badly located center of resistance. My 1927 sailing canoe came with a very large set of spars and the fixed centerboard is unusually far forward. This is shown at http://www.wcha.org/forums/index.php?attachments/46941/ after the restoration. You don't need any complex calculations to see that the sail is not well aligned over the centerboard. This is great fun in light winds but terrible upwind. The smaller sail and spars shown at http://www.wcha.org/forums/index.php?attachments/46942/ actually makes it faster (and more fun) upwind especially at higher wind speeds. You may also find that a 14 foot long canoe might be a bit small for an extended camping trip. Everything is a compromise. Good luck,
Thank you Benson. Those are impressive pictures. Also obvious, that large sail doesn't fit and maybe the factory sent out a different sail. Of course, practice is what I am doing. Fourteen ft too small? Not really, and it sails very well loaded down. The issue here is the portage. If I can't carry it there is no portage and I'm confined to sharing the lake with powerboats. Only one portage gets you away from power boats, generally. A fourteen or fifteen ft canoe I can portage. Ten years ago I portaged a 17 footer with sponsons. Not any more. In anticipation of turning eighty and eighty five I've a twelve footer waiting for new canvas. The number of portages figures into the number of things you can carry but not necessarily the total weight. Those daggerboards and rudders are awkward and that's why I developed the simplified system I use. I like to keep it down to three trips. Beyond three trips a one mile portage is too time consuming. By the way, the lateen sail makes a great wind and rain shelter in camp. Quick to set up as well.
This was a no portage trip but the boat is a 15 ft UFO I've portaged once or twice on a trip with this amount of gear but not more and not long portages.
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