Sailing Catamarans - Open Transoms

production Strider 24
plywood Romany 34
lightweight 14ft Zeta mainhull
Strike 15 trimaran at speed
28ft Skoota in British Columbia
10ft 2 sheet ply Duo dinghy
24ft Strider sailing fast
36ft Mirage open deck catamaran

One of the modern multihull fashions is to fit vertical or ram bows - which I write about elsewhere. Another is to have open transoms with big transom steps, often with a big cut out in the inner hull side.

Clearly the idea is to make it easier to board from a dinghy and to use as a swim platform. That maybe OK on a charter boat, but not one used for serious sailing. Open transoms are also used on racing monohulls to save weight and reduce windage, more important, they make the cockpit properly self draining.

Now, I like transom steps, they do indeed make boarding easier, and not being able to fit them is a major drawback to canoe sterned boats. However I only draw small steps and I always like a completely surrounded cockpit, even if it makes access harder. Boats are for sailing - they aren't swimming platforms!

So it's the big steps I object to on ocean going boats. There are several reasons why open transoms are not a good idea

It's very easy to slip and fall backwards out of the cockpit, especially as a catamaran has a deceptive motion. Just because it sails flat doesn't mean you don't need to hold on, as the boat will bounce around - just like when walking down the aisle on a bus or tubetrain. Many catamarans built for charter have very big cockpits with few handholds.And it's not just worries about the crew, "stuff" can roll out, even pet dogs.

Of course, the worst place to fall overboard is at the stern, because you are immediately a boatlength behind the boat and have no chance of catching anything to save yourself.

Long raked transoms also shorten the useful deck area, making a smaller boat. The same is true inside of course, the accommodation has to start further forward. Marinas charge by length, not interior volume. Often so do cruising permits when travelling abroad, and regulation changes are usually based on length.

There are possible structural problems on a boat with big open steps as there is no real boat behind the cockpit to hold the hulls together

The aft sections lack buoyancy (especially true if the inner hull side has been cut away). A cut out on the inner hull side might be OK in flat water, but as soon as there are any waves (or as soon as the boat is pushed hard when the lee hull begins to bury) the sea washes over the lower cutout step. In other words, there is then no boat there. So no reserve buoyancy to help stop pitching, and no added waterline length to increase speed. It cannot be fast!

See this photo for what I mean - no buoyancy on this Crowther cat extension!

Most serious, there is nothing stopping the boat from being pooped. Pooping happens either because the boat is driven backwards when it sailed up/into a big wave, or because a breaking wave comes in from aft when running downwind. It seems this is one of the causes of a recent abandonment of a new catamaran. At any rate, it had big open transoms and was pushed backwards by a big wave.

The rudder stocks have to be short so there are more loads on the hull and a tiller bar is hard to fit. That makes emergency steering difficult and means relying on continuous cables (which can be very long, making it hard to get the right tension) or hydraulic steering, which is usually horrible on a proper sailing boat.

So what many builders have done to solve those problems is fit the rudders forward, and the engines behind them. True that gets the noise and smell out of the accommodation, but makes for very scary steering in reverse, when the prop thrust goes onto the back, not front of the rudder. it's then very difficult to stop it overbalancing. And of course engine maintenance is harder than even with an outboard - there's no room to work and you're stuck at the back of the boat, head down in an outside locker

Also of course makes it much easier for unwanted "guests" to board the boat - whether with 4 feet or 2.