Lee-board Sailboats

Leeboards, like everything else have good and bad points about them. Terry, fixed bilge appendages are bilge keels and commonly seen in areas where there are large tidal ranges, such as Great Britain.

Leeboards are the most efficient retractable appendage for their deployed depth. This is because they are effective lateral area from the LWL down, where as all other retractable appendages begin to be effective lateral area at the hull bottom. Leeboards can use less draft and have the same effective lateral area for this very reason. Tumble home or flare isn't that much of a consideration, though it would seem to be. The mount and pivot arrangement are key to success with this type of board. First it has to be surprisingly strong and second it has to permit the board to hang straight down, regardless of the hull shape. Most employ a wedge shaped element for this. If allowed to cant outward they offer even more efficiency.

On the down side they have to be placed at the widest portion of the hull, which in modern hull forms is further aft then desirable for the bulk of your lateral area. The type of hull that seems to work best with leeboards is those that have a relatively flat portion (in plan view) around midship. So, Gonzo, you can see why your canoe worked well with a leeboard, it's shape is just about what you want. On a more modern hull, where the entry is fine and displacement is carried further aft for sail carrying and bearing area, the boards will be too far aft if mounted on the widest portion of beam. If placed where they need to be on the hull to balance the sail plan, then the hull over laps the flow "shadow" on the trailing edge side of the board, effectively turning the flow, so you'll have a heavy "leeing" effect. Progressively more so the harder you push her.

Couple these things, with the way a big 'ol board can clutter up the sweeping curves, on the side of a yacht and it's pretty easy to see why they aren't that common. In small craft they can solve a lot more then they create, but you better have a good grip on where they need to live on the side of the boat and have a set of waterlines that will tolerate their optimum placement.

 

Just out of curiosity-would you guys consider the foils on the sides of this boat leeboards?

 

Unique and appear to be the only appendages other then rudder(s). They're not really bilge keels, maybe "wing keels".

 

interesting design Doug..I was just thinking that little craft looks like one of those delta-shaped experimental aircraft from the early NACA and NASA days...delta shapes are obviously proven winners in aerodynamics...at the speeds those test bodies flew the air might as well have been fluid ...then I saw your Cocoa Beach address...any connection?

 

Thanks-no connection-except in my dreams! The boat was an experiment and worked fairly well. For lack of a better description I always called the foils
"fixed asymetrical leeboards"....

 

A factor influencing the leeboard attachment problem is the extra length down to the water compared with a daggerboard, giving a longer moment arm.

Doug: interesting boat indeed. I assume it is heeled deliberately to raise one or other foil and give the other more bite.

 

Tantra

-------------------
Thanks-you're right. Upwind the boat could match a US1-and it had a relatively high aspect ratio centerboard. That was pretty good because the US 1 and this boat sailed with the same rig during initial testing-and the Tantra was quite a bit heavier than a US 1(Windmill rip-off/derivative). The "fixed leeboards" were toed in a few degrees and had replaceable tips.

 

The foils look to be asymmetrical as well as toed-in, something I am planning to use in a new project.

 

GrantJones

Years ago I designed and built a 28 ft leeboard sloop. It worked very well. It was fun to run up on the beach and tie off to a tree or skim over the thin water areas of Puget Sound. After my own experiences with a leeboarder, I feel the only use for a deep keel is if the boat is large and rarely comes into sight of land. The theoretical and practical advantages have been discussed at length on this forum. I have just started construction on a 40ft leeboard motor sailer with a staysail schooner rig.

 

I'm strangely fascinated with this design (as I am with most of your work). One might call your work brave, as all your designs incorporate multiple features and radical deviations from established practice. Perhaps brave is not right, and maybe defiant is a better label.

You remind me of the one raccoon who unlike the others who scurry to the side of the highway, raises one defiant middle finger in response to approaching trailer trucks, standing unflinching and firm in the center of the road. This seems to apply to both your designs and your personality.

This is not the easiest route to surviving long enough to achieve market success for the imaginative featurefests you seem to favor, but it is interesting in a cruel real-world "Coyote versus Roadrunner" kind of way. Most of us who build products for a living have to concede to customer's wishes, even if their wishes are in conflict with our own preferences. You must have one hell of a support network to give you the confidence to stand by your ideals.

What was the original design brief for the Tantra? Who was it going to be sold to? What were the original performance goals? Was there more than one built?

--
Bill S.

 

Short videos of traditional Dutch coastal sailing ships with a lee boards in action:

http://www.tjalk.org/bontekoe-race2009/admin/2009/
http://www.youtube.com/results?search_query=bontekoe race&search_type=&aq=f
http://www.youtube.com/results?search_query=klipper race&search_type=&aq=f
http://www.youtube.com/watch?v=9AL11xA6I5Q

 

Several sources have averred that setting some incidence angle into a lee board is a no no. Inevitable leeway induces A of A into any board so what is the problem with initial angle? The claim that one half to one degree of angle is the limit. How about gybing centerboards.? Manfred Curry experimented with that idea way back in the day. He claimed that it worked quite well.

About ventilation. I recall a catamaran, maybe an Aussie design, that was called "Dingo". It had a single daggerboard extending down from the center of the tramp. The crew could see the swirling cavity at the water surface /board intersection. You could also hear the sucking sound. The little cat was aptly named. A dingo is a particular kind of dog. How come I do not see or hear any problems from my outboard rudder then? Maybe the dingo board was running in the convergent, perhaps turbulent, bow waves of the twin hulls and my rudders have not suffered from that condition.

 

Seriously, what do we use as a benchmark to compare sailors and their ability to handle change?

Even when I was a kid, offshore racing yachts were regularly outmoded after one season; I think they got age allowance after 3 years around here.

In what other popular sport does an item of gear that can cost as much as a house become obsolete so quickly? Hell, IIRC something like air racing still uses 60 year old gear!

If people prefer old gear, maybe it's because it's better for the use, or because it's cheaper - and really, who is going to throw away an incredibly expensive toy just to finish faster?

I, for one, still sail an old cruiser that rolls downwind, simply because I have better uses for my money than worrying about whether I roll about or no. Rolling can be a hassle, or it can be like leaning a bike into a fast curve; that is, it can be one of the sensations that makes for a wonderful sport.

Maybe - just maybe - your fellow sailors are not conservative congenital idiots, but often highly intelligent people who make the right choice for their leisure pursuits?


PS MEssabout, I don't think the Dingo was an Australian design, but some popular early Aussie cats (Quickcats, maybe Yvonnes IIRC) used centreboards that hung down from the centre of the tramp. AFAIK, they were less efficient hydrodynamically, but more efficient cost wise and for amateur building. Those classes were replaced by boats that were more efficient hydrodynamically, but normally less popular.....

 

Nice boat. Would you mind sharing a few more boat details and pictures?

 

Great thread...it really resonates with me as I sail open canoes predominantly, with a single leeboard mounted robustly to pivot about a fixed thwart.

I sail much in the way of lakes and shallower estuaries and bays.
Any thoughts about Atkin's Gretchen, 18' leeboard gaff headed sloop.
Has some nice tumblehome and not terribly beamy for it's length.
Draws 1'4", per designer, fully laden.

Are there some similar knockabout minimalist cruiser designs out there that I may be overlooking?

All insights appreciated.

Best,
David