In praise of leeboards

For a long time now, I’ve been rebelling against the modern “plastic fantastic” sailboat in favour of traditional design in wood.  This goes as much for the hull as for the rig.

And though they’re efficient into the wind, offwind they lose out every time.  For cruising, there is much to be said for the traditional well-found, seaworthy craft with gaff rig.  We’ve looked at hulls and rigs in other posts but today I’d like to look at leeboards.

Look at what?

OK, bitta theory.  If you look at the pic below, you’ll see CE [centre of effort] and CLR [centre of lateral resistance].  Ideally and simplistically [as it's not precisely so], you want CE of the sails to be over the CLR of the hull, thus giving neutral “helm” as it’s called – or the tendency of the boat to sail “true”.

In a modern sailboat, where the sails are precisely designed, the CE is placed directly over the CLR, allowing a long, thin board [centreboard or dagger board] to be lowered below the keel in that vertical line. This has the effect of highly efficient manoeuverability and in racing boats is ideal.

Like everything in sail boat design though, there are costs and trade-offs:

While looking side-on at the boat [as in the diagram above], this works well … but if you look bow-on [from the front] or stern-on [from behind], when the boat leans over [heels], that centreboard [or keel] is angled back towards the windward side down at the tip.

So in the pic below, the boat wants to go forward but is being pushed left, downwind or leeward.  The keel is angled back up to windward.  This is not good.

To illustrate the effect, take a bread board and hold it upright in the bath.  Drag it [still vertical] towards you.  Now angle the board with the lower tip away from you and drag it towards you – much easier, isn’t it?  It begins to skip through the water.  Well, the same happens at sea – a heeled boat loses much efficiency in the board and if the boat is wide and flat [as modern keelboats are], then that board needs to be duplicated either side, both angled outwards, which doubles the wetted area and the drag.

Two boards is increasingly taking on.

The way round it is to build retractables and have one down but if you do that, you need boxes built into the keel and quite apart from eating up cabin space, they almost always inevitably leak.  Acceptable if a racing boat is to be taken in after every race but unsuitable for a cruising boat, which is my concern.  In fact, any hole in the keel is not a good thing if you can avoid it on long journeys, epoxy or no epoxy.

You know what I’m going to suggest but before doing so, let me make this point that Man, in his quest to design ever more efficient machines, often loses sight of all the things he loses.  For example, a Bermudan rig is hopeless downwind and thus a spinnaker is needed, which adds complexity and danger.  If they’d used a gaff or lug rig in the first place [as in the photo above], the problem wouldn’t have arisen.

My only concession to “modern” and even then it is South Pacific, is the catamaran.  Frankly, for cruising, it can’t be beaten.   Separately, the best rig for cruising is the ketch or yawl, with three sails [on average]:

Cruising people will tell you that the rear sail [the mizzen] is a godsend in harbour and when wanting to trim at sea, the jib[s] at the front are easily furled or maybe the middle sail can be dropped and you can go on the foresail and aft sail – they’ll steer by themselves without rudder. The ketch/yawl is the rig of choice.

Unfortunately, a catamaran doesn’t lend itself to the rig because cats tend to drive the bows down and a mast too far forward will cause fore and aft rocking or pitchpoling. That’s why you’ll see one mast stepped amidships and only triangular foresails ahead of that.

However, there are ways round it and one is to make the bows fuller, putting less rocker into the lines, running a second mast further back and various other little tricks.   Everything’s a compromise but it does let you get your ketch rig onboard.

There’s one more thing with the ketch – that if you reef [reduce sail], it depends where you do it, as you can seriously unbalance CE over CLR, unless you have a long, shallow keel, in which case you still have the heeling problem plus the increased drag.  One of the main pluses with cats is their “beachability”, their ability to go right into the beach.


The leeboard, especially if the bolt holding it can slide fore and aft. That makes the CLR variable and means you can drop this sail or that almost at will and it’s no problem for the helm – simply move the leeboard pivot [hub] fore or aft.

DOWNSIDE: There is one – perception of style.   Some people think they’re ugly, entirely unsuited to modern, slick sailing and you need two of them, one for either side.   However, if you’re on a cat, you need two boards anyway so why not use leeboards?

There is a reason you wouldn’t use them on a racing cat and that is that the water is forced along the convex [near to the hull] side and gets squeezed between board and hull.  This is not good at high speed.  For a cruising cat though, it’s fine.

ADVANTAGES: There are many and I’ll quote from various articles below.

Imagine a regular double sided centreboard, cut in half through the section. You end up with a flat side and a curved, times two.   You’d not actually do this, as the resultant boards would be too thin – you need to purpose make them.  This is vastly more efficient though than a doublesided centreboard, as it creates far more lift and incidentally, less drag.

The streamlined convex sides are placed against the hull. The straight (cut) side is on the outside of the leeside. Leeboards never became popular on the North American continent, mainly because their working is not properly understood. A plank against the leeside of a hull does not make a leeboard.

Leeside, by the way, means the downwind side, the other being the windward.

They are up to 20 percent more effective than a centerboard. It allows for shorter boards. They never jam. They are easier to maintain and to repair in case of damage. Just take them off. Their main advantages are that they eliminate the need for a centerboard box, which in 90 percent of the cases is the cause of leaks, and leave a roomy, uncluttered cockpit.

The disadvantages are two extra ropes to handle when tacking, and you have to be (more) careful when docking.

They’re only effective when angled slightly outwards from the hull, so that when it heels, they are vertical:

And with less area and shorter boards, there is less drag again.  Win-win.

Should your leeboard hit ground, unlike a centerboard, where your boat will come to a dead stop, the hull of the boat will do a spin around the leeboard when you ground it. Then it’s a simple matter of pulling the leeboard up to be on your way.

This doesn’t tell it all.  The leeboard can be easily rigged so that strong shockcord holds it down and then when it hits an obstruction, it just comes up, to be held up there by a line.  With its rounded shape too, it is easier to extract from sand and is far less easily damaged.

EF Knight’s Small Boat Sailing [1901] is a classic many sailors have on their bookshelves.  He writes:

If expense is a consideration, the novice cannot do better than fit his first little boat with leeboards. We will suppose that he has purchased a secondhand craft for a few pounds. To fit a centerboard into her would be a costly bit of work, only to be undertaken by a skilled boatbuilder.

But any boy who has even a very small experience of the use of carpenter’s tools can construct a leeboard and fit it to his boat. The author once placed leeboards on an old P. and O. lifeboat, and sailed with her from Hammersmith to Copenhagen and back, cruising round the Zuider Zee, coasting up the Frisian islands, winding in and out among the many pleasant fjords.

He mentions a “first little boat” and yet leeboards are equally used on large boats in Holland and on Thames barges – they suit any craft.  If you like traditional designs and are comfortable with not having a plastic fantastic costing hundreds of thousands of pounds, then leeboards can very well be part of your solution – they’re simply better in a cruising situation.

More shots:

I mentioned a moving pivot but that’s if you use one board only each side.  What if you go crazy and run two leeboards on each side?   Then you can lower or raise each to precisely match the state of how you have the rig at any time and there’s no need to slide the pivot.  Critics would point out the expense [true] but there’s no more wetted area with the two boards because you’d only have part of each down at any time, unless preventing leeway was everything, in which case you sacrifice with drag and prevent sideslipping.

The reason you don’t see double leeboards is that with a slow craft, it’s not all that necessary.  With a cat, it might be more critical and it might be necessary to mount them a little further out from the hull for that squeezed water to get through.  So we’re talking 15 knots on a reach max and cruising around 10 knots.

Who said they can’t be modern looking?

4 Responses to “In praise of leeboards”

  1. Mark in Mayenne July 16, 2012 at 15:57 Permalink

    I love sailboats, but prefer windsurfing. To my mind, the critical advantage of a sailboard is that the stronger the wind, the faster it goes. I can’t cope emotionally with the physics of something wind-powered that goes slower, the more wind there is.

    (Does that apply to cats too? I like cats)

  2. James Higham July 16, 2012 at 23:24 Permalink

    How about tris?

  3. Mark in Mayenne July 17, 2012 at 06:34 Permalink

    Fair comment.

  4. Chuckles July 17, 2012 at 09:09 Permalink

    So leeboards help with floaty and leewardy bottoms, but what does it do to the zug?

Leave a Reply

Please copy the string RWakDV to the field below: