Seaworthiness

The most important feature of any boat, its seaworthiness, is the most difficult one to assess. Seaworthiness is simply the capability of a boat to afford the crew safety and comfort in any condition. But it can take time before the seaworthiness of a new type of craft is fully understood even by designers and sailors. Especially so, since there are infinite possible combinations of wind, sea and hazard that a boat might be exposed to by any crew, in any state, attempting to execute any plan.

In the late 1950s when the pioneer catamaran designer, builder and sailor, James Wharram, was sailing catamarans across the oceans, very little was known about the seaworthiness of these craft. In the 60s and 70s offshore catamaran sailing and racing went up a steep learning curve with many "bleeding edge" multihulls crashing out spectacularly. This confirmed suspicions voiced at the time, that multihulls were unsafe. In the same period much more sturdy and secure designs were built and began safely to clock up ocean miles. However, without today's design know-how, many lacked performance. This confirmed suspicions that multihulls do not sail well to windward.

Now, thirty years on, multihull design has matured through the prolonged exposure of thousands of different craft to a generation of world-wide sailing experience. Safety records over the years are second to none and consequently, catamarans and trimarans have earned their place in the mainstream of the boat market. Even so they are still viewed with distrust by many of the seafaring community. However, there is no reason to doubt that the glowing safety record of multihulls will not continue to grow, and that misgivings will diminish with more time.

So far it can be said with total confidence that a multihull, as a type of vessel, is at least as safe in any condition as a monohull. Possibly multihulls are safer. Naturally, they have different strengths and weaknesses than monohulls in their "capability to afford comfort and safety in any conditions." No boat is ever 100% seaworthy.

In this section you can see what makes a multihull so safe.

Multihulls in motion

The restless and relentless motion of a boat can invoke the comforting rocking of the womb, or the rising nausea of an eternal rollercoaster ride. Which it is to be will depend on the mood of the wind and sea, the sensitivity of the crew and quite a few aspects of the boat's design. The movement of the boat will also change with the course and boat speed.

A more seaworthy boat will have less movement in a seaway and conserve the energy and wellbeing of the crew. Besides barring enjoyment of a sailing trip, seasickness commonly contributes to the cause of accidents. As too does crew exhaustion from long exposure to being thrown around in bad weather.

In very bad weather conditions, or when pressed too hard, the behaviour of a boat becomes critical to its survival. It could be it moves too much, for instance rolling over on a steep wave, or burying a bow when carrying too much sail. It could be that it does not move enough, for instance not rising over big seas and taking excessive water on to the decks and into the cockpit. 

Every design of boat has its individual character at sea as even subtle differences in hull form, weight distribution and rig have an influence on the six directions of motion: roll, pitch, yaw; heave, surge and sway. However, characteristically there are some typical minor differences between catamarans and trimarans and major differences between multihulls and monohulls.

Rolling

The classic image of multihull comfort is the glass of wine that remains un-spilled on the saloon table while the skipper does a mid Atlantic watch. Multihulls don't roll much. They do not have gimballed galley stoves. They rest astride on the water with their immense stability, but they do move, albeit with a different motion than a monohull. Multihulls are light, and have low roll inertia - in technical jargon the tendency to roll is very highly damped. This means they stick faithfully to the moving contours of the sea. This sounds like it might not be good news, but the resulting roll is less pronounced than a heavier displacement, less damped single hull - though quicker. A monohull has less resistance to rolling and more momentum in the keel once it starts moving, so it tends to roll further. The slow pronounced roll of some monohulls when sailing downwind is found unpleasant by many prone to seasickness.

Pitching

... more to come here