Catamarans have earned a reputation as poor performers when it comes to sailing to wind.
But it doesn’t have to be that way.
There is nothing mystical about cats that make them inherently poor performers when it comes to going to wind. In fact, the opposite is true, cats have qualities that make them inherently better than a keel yacht when it comes to windward performance. Not leaning over is one of them.
The daggerboard seems to be one of the most misunderstood pieces of equipment on a multihull. They were a mystery to me too when I built my boat. But after the first year in the water, I set out to demystify and get to know more about these devices. That took so much time to make and took up so much valuable room inside my boat.
I built a 40ft catamaran called “Tokyo Express” back in the 1990’s. In my first year of sailing and living aboard, I too was disappointed in its windward performance. The boat’s design was a cruiser/racer and it was light and fast. But beating to wind was disheartening; I covered a lot of ground fast but progress toward my destination was poor.
So I took a lot of measurements, recording GPS data, wind & water speeds and making diagrams. I read many books, in particular, a book on the “Aero-hydrodynamics of sailing” I found at the library and did a lot of number crunching. I looked at the sail areas and compared keels and board sizes of many multihulls and keel yachts.
Finally, I came to a conclusion. Catamarans don’t have enough keel area, simple as that. The boards on most cats are too small. I also believe that their short chords work against them not for them.
Cats only seem to get given a small daggerboard.
Maybe the reasoning is that because they move fast, they require less area than the equivalent keel yacht. In any case, these small boards or even worse mini keels are expected to counter the force of the large rigs placed on top. A keel yacht in comparison with a similar size rig has one big keel with a lot of chord and thickness. These large keels anchor them in the water.
When a yacht sails hard to wind most of the force generated by the sail is pushing the boat sideways. Only a small proportion of that force acts to drive the boat forwards. This forward acting force is proportional to the reaction force generated by the keel or daggerboard.
The sail needs something to resist it, something to push against. The power of the rig depends on the power of the daggerboard that opposes it. You can spend all the money you want on a big rig. But unless you have an equally powerful daggerboard or keel to oppose it, it’s a waste of money.
When you overload the board it stalls and the boat get’s pushed sideways creating a lot of drag from the stalled or semi-stalled board(s). The first thing you notice is that the rudders load up and it’s more difficult to steer. High side loads and bearing friction cause the rudders to become more difficult to turn. They are doing what they are not designed to do, go sideways through the water.
To remedy the situation you ease off the wind picking up speed. With the extra speed the boards generate more lift and finally, equilibrium is reached. Now you are zooming along fast, but you aren’t going to wind, or not at a good angle. It’s a no-win situation. You have to move fast to get the boards to work. At the same time you aren’t going anywhere, except backwards and forwards across the wind (more or less).
A daggerboard is often long and slender, to give it a higher aspect ratio.
But chasing a high aspect ratio doesn’t always mean positive results. High aspect ratio is not the be all and end all. Slender foils with a short chord also have negative qualities. They have a lower stall angle, less area and less “grip” on the water.
I designed and built a single large daggerboard that replaced the two original boards in my cat. It was roughly 150% larger than the 2 original boards combined. It transformed the boat, it went to wind like it had never done before, and fast…
I had sailed many times up and down the east coast of Australia, between Sydney and beyond Cairns to the north in the early days. More than half of my sailing was against the wind. (it seemed like all of it..) On one occasion I’d even woken up after sailing all night to see the same landmark as the day before. If there was any current against me sometimes I didn’t move far at all toward my destination. The new board changed that, completely.
The daggerboard is the heart of a multihull.
It is literally your engine. You can have the slipperiest of hulls, lightest of boats and most expensive rig out there, but if you don’t have this part of the boat right none of the above is going to make you go to wind. Whether racing or going places on a cruising yacht, the ability to go to wind makes or breaks a boat.
There is a video on the building of the daggerboard on Tokyo Express and my experience with it – on YouTube.
I hope this information is helpful.
PS – I have just released my 2nd book, “Building Tokyo Express“. The story of how I created the boat in this post. It explains every aspect of the build with many ideas to save money by making things yourself. It’s also a story of the ups and downs of life during these 3 years and the twists and turns beforehand that started with the purchasing of plans for a keel yacht and why I ended up building a catamaran.