M is for Multihull

We’ve already discussed hull types (displacement, planing, etc) but up to now I haven’t spoken much about the multi-hulls, specifically catamarans and trimarans. Simply put, catamarans have two hulls and trimarans have three. The advantage of multiple hulls is when you distribute the weight of the boat amongst multiple hulls there is less draft, there’s less boat in the water of any one hull. Also when you spread the hull out there is great stability, enabling the designer to put a lot of sail area on the rig. The combination of large sail area and great stability gives great speed. There is a disadvantage to that though, for a multi-hull craft has maximum stability when she is either right side up or upside down. If you ever flip one, they can be challenging to get back up on their feet. This isn’t so hard when it’s just a small Hobie Cat, but when an ocean going trimaran turns turtle, that’s not so good. There are open ocean sailors that install hatches in the hulls of their boats on the bottom for just that eventuality.

When I hear the word catamaran, the first image that comes to mind is of Hobie Cats.

a to z - hobie cat

I’ve sailed them, mostly on large lakes. They’re a lot of fun and, and a friend of mine who raced them said, ‘Even when you lose you’re going fast as hell.” In the photo above you’ll notice a bulb at the top of the mast. That’s for flotation if you capsize the boat so she won’t go all the way over with the mast sticking straight down into the water. Makes it easier to put back up on her feet.

There are, of course, all different sizes of multi-hull sailing vessels, right up to Oracle, the America’s Cup racing catamaran.

a to z - oracle

Oracle is huge. She’s 113 feet over all and her mast is 180 feet high. So she’s more than a third of a football field long and her mast is higher than an 18 story building. You can get a gut feel for her size from the photo above. If you look at it closely you can see crew clinging to the windward side of the boat and along the beam connecting the main hull to the ama (the outer hulls). Also if you look carefully, you’ll see hanging down from the ama a thing that looks like a curved blade. That is a hydrofoil. When Oracle gets up to speed she actually lifts all three of her hulls out of the water up onto hydrofoils, which drops her wetted surface area to virtually nothing (as compared to the size of her hulls) and then she really flies. In testing prior to the America’s Cup, she was clocked at going a little more than three times the speed of the wind, over 30 mph in a 10 mph wind. Now that’s cooking.

The older more truly traditional multi hull vessel is from the South Seas and is called a Proa.

a to z - proa

The photo above is a slightly modernized version but if you look closely you’ll see that there is a rudder at both ends of the boat. When a proa is sailing into the wind you don’t ‘come about’, turning the boat from a starboard tack to a port tack and so on (a starboard tack is when the wind is coming in on the starboard side of the boat, the port tack is the reverse). Rather than doing that, a proa just trades ends, i.e. the sail is switched to the other side, one rudder is lowered and the other is raised and presto, the boat is sailing in the other direction. The out hull is always kept to the same side for ballast. Don’t ask me for specific details on how the sail shifts around because I’ve never sailed one but this is just the coolest thing. The Polynesians were master mariners.

More cool stuff next time.

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4 thoughts on “M is for Multihull

  1. I can see my husband in one of those cats. He has a thing for speed. In his younger days, he pushed his Datsun 180Y to the limits on dirt country roads in Tasmania. That was well before I met him and he was driving an Austen Healy Sprite as well as becoming a motivational speaker of sorts to the computers at work. They also seemed to know when he was on holidays and went on strike.

    • If he has a thing for speed he should definitely find a friend who has one. You can fly a hull up out of the water even on a Hobie and if the boat is rigged with trapezes you can hang out way out over the hull and watch the water fly by beneath you. As a younger friend of mine says ‘just wayy cool.’

      • My goodness! That sounds thrilling but a bit like a ballerina up on point…something I’ve never achieved. That said, he is more adventurous than I…especially when it comes to speed and that would be legal!

  2. This is definitely cool! I’ve never sailed a cat but would love to try it. I WAS glued to the TV during the America’s Cup, but miss the days of the longer races with the monohulls. I’m really enjoying your posts!

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