October 23, 2011

Multihull vs. monohull

SO MUCH HAS BEEN WRITTEN about the virtues of multihulls that it might be a little out of order even to ask why there aren't more multihulls than monohulls. Whereas a heavy displacement monohull's normal maximum speed is limited to 1.34 times the square root of her waterline length (in knots and feet), a catamaran can often reach speeds twice or three times those of a monohull of the same waterline length. And who in his right mind would rather sail at 5 knots than 15? Well, most people, as it happens. Certainly most cruising people.

A trimaran or a proa has a main hull shaped more like that of a monohull, a broader, roomier hull, and, like a catamaran, it gains the extra stability afforded by an outrigger or amas. This extra stability allows a multihull to spread a greater area of sail. That means more horsepower per ton of weight, and thus, along with more slippery hull shapes, greater speed.

But (and there's always a but where sailboats are concerned) cruising multihulls, especially catamarans, mostly fail to come up to their owners' expectations of speed because their theoretical potential is more severely curtailed by extra displacement than is a monohull's.

Most cruisers are notorious for cramming aboard all the stuff they were trying to get away from on shore, and carting it around with them everywhere they go. Their waterlines climb up the side of the boat inch by inch as the years go by, and nobody cares much because on a monohull this results in very little damage to the boat's average speed and may even improve the handling and stability of some boats.

A multihull, on the other hand, suffers quite badly from overloading, and often becomes more  difficult to handle at sea, being less responsive to the helm. If you have sacrificed comforts such living space and stowage for the thrill of speed, as you might with a catamaran, you might be rather more than disappointed to find that you have inadvertently sacrificed speed as well when you go cruising.

There are also other reasons for the preponderance of monohull cruisers, such as the problem of finding moorage for a multihull in today's congested marinas, and the fact that a multihull is as stable upside down as it is the right way up. There's no doubt that multihulls have many virtues, especially in areas where the water is shallow, or where you might want to dry out on the sand. Charter companies in the Caribbean use catamarans extensively, too, so there's obviously a demand for them.

But on the whole, most sailors, deep-sea and coastal, prefer monohulls — and have trained themselves to grin and bear it when a multihull comes tearing past them.

Today's Thought
Nothing is more vulgar than haste.
— Emerson, Conduct of Life: Behavior.

“I have five noses, six mouths and seven ears. What am I?”
“Quite ugly.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)


Bill said...

John -
The reason I'm not in the market for a multi-hull was summed up by one of my sailing instructors:

"You get two boats for, well, the price of two boats."

You can buy a HELL of a lot of monohull for the cost of a much smaller catamaran.

Anonymous said...

You hit the nail on the head. We call those Condo Cats, great at anchor or motoring with their twin saildrive. And what I've see they sail like slugs.

You need a different mindset on a cat, i.e. all that shore side stuff behind. Check out "Cookin Fat" to see all that's needed:)

But then 99% of the "cruising" boats I've seen on the east coast are motoring also.

Still the great thing about sailboating is the diversity. Just because I love to cruise in a Tiki doesn't mean I can't appreciate Pacific Seacraft 37 or Cobo Rico 38. So please let's not start a war of mine is better than yours.