Leeboard dimensions

Pernicious Atavist

Canoe Sailing Publisher
I'm getting ready to rig a ~54' sprits'l on my 16' White-style canoe. I need a shallow board--I often run in less than 3' of water. With twin boards I run each half-way down when called for in shoals.

At 10-15% of the sail size, I figure the each board needs to be between 5.5' and 8' square. Wow. This would call for boards that seem too long for my conditions. I like leaf-style boards but am concerned with drag.

Input?
 
Just bore a hole through the top ends of a couple 4x8 sheets of plywood and use them. You'll be fine.....

Those percentage figures are not the area of the boards themselves, but the area of the hull's entire underwater profile. On a 16' canoe, you draw maybe 3", so you'll have up to around 4 square feet of profile from the hull alone. Add another square foot or foot-and-a-half for the rudder blade and you are up to the 5 sq. ft. or more neighborhood before you even add the leeboards to make up the rest of the required profile area. Sound a little more practical?

Keep in mind though that all the formulas we use, like this one as well as the CLP/CE relationship guidelines are design tools and not physical laws. There is a rather large fudge-factor involved, especially on a boat where the movable ballast (the sailor) has such a huge impact on such things as heel angle and fore and aft trim - both of which can make a big difference in what portions of the underwater profile are providing resistance to slipping sideways and which portions are not contributing much.
 
Thanks, Todd. I seem to forget I need to consider the hull, etc. So--what thickness should that plywood be? Do I need to work it into a NACA foil? Should it be hung short or long side down?:D
 
I suppose it would depend on the plywood and how stiff or strong it is, but I don't think I would go thinner than 3/4". If you make foils (and especially their leading edges) too thin in the interest of reduced drag, etc., they often don't really behave very well and can tend to want to wander side-to-side, rather than just cutting through the water and being done with it (how's that for a scientific explanation?).

In general though, I pretty much detest everything about plywood leeboards (and rudder blades). Only about half of their wood fibers are pointing in the direction you want for strength and stiffness, the rest are mainly just along for the ride. Vulnerability to water intrusion (and eventual damage from it) is greater than on a regular wooden slab if the leading edge or tip get dinged-up from rocks because you have exposed end grain on all sides and I don't think they look as nice as real wood. I'd much rather get a couple nice hunks of 5/4 mahogany or other nice wood and spend a little time with the spokeshave rounding the leading edge and tapering the trailing edge. There are just some things that look rather cheap in plywood and rather elegant in varnished wood and I think leeboards and rudder blades are among them - plus they usually work better. Option #3 would be laminating front-to-back with smaller slabs, which can also make a nice board.

You can spend as much time as you feel you want to devote to making them a good airfoil shape, but in the grand scheme of things, the rewards for doing this may be fairly small and take a GPS or knotmeter to really see. Thousands of boats (like Sunfish and similar production designs) have sailed a lot of fun, successful miles with foils that were nothing more than wooden slabs with rounded leading edges and tapered trailing edges.
 
Uh, Todd, I was jerking your chain about the plywood....

I'm inclined to agree with you about foils. I taper and round the leading edge a bit and taper the trailing, but never to a knife edge. As much as I like the Dutch style boards, I know they'll give more drag than long boards, but again, how much more? The slower the wind, the less board is in the water, anyway. I often pull my boards and leave just an couple inches dragging to provide a little bit of CLR. In stiff winds, more board--good!
 
Dutch style lee boards

My experience with Dutch style lee boards on my canoe is that they are excellent for shallow water, but you need to have some speed when you turn, or you may slow too much. Also, be careful of them angling their bottoms towards the bow, or you may be in for swim...

Mike H.
 
I have several vintage leeboards that could be used for templates. Some with short draft.

Robert P. Ross
Ross Bros.
PO Box 60277
Florence, MA 01062
413.320.2306
 
Well! I guess I should have said something earlier. I'm about 2/3-way through building my new boards and folding bracket. Need sanding, adding lead ballast and varnishing.

Thanks for your offer, though!

Now, if I may encourage you, would you be willing to let me share your leeboard photos and any info you have on them with my readers at Canoe Sailing Magazine? Boards are something we all need and I'm sure others would enjoy seeing yours.

Thanks in advance, and thanks for offering to share yours with me!

Ed
 
Dear Ed,

I'll try to get some photos up over the weekend.

Robert P. Ross
Ross Bros.
PO Box 60277
Florence, MA 01062
413.320.2306
 
Sorry I didn't get to those photos yet. Here are some Ted Shea ones to hold you over.

Robert P. Ross
 

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Very nice! Thank you! No hurry.

I'm slowly working on my new board. It'll be too windy to sail the next day or so anyway....80mph is a bit stiff!:cool:
 
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