What's required to make an ocean-going Catermaran?

Hi,

As the subject really. Is it an equipment requirement primarily? If the boaat itself is well-built, this on its own shouldn't be sufficient to limit it should it?

I'm in the UK/EU, if that makes a difference.

Best regards,
Robin.

 

The boat must be well-built, yes. It must also have a hull shape that is stable in really really big waves, and doesn't tend to stuff the bow into a wave or take a dumping from behind. Equipment needs to be more durable than for an inshore vessel, there's more emergency gear to carry, the list goes on....
The features that make a good ocean cruiser could be the subject of hundreds of pages of discussion here. Many say it helps to know ocean cruising, before trying to learn ocean cruising boats.

 

Hi,

I'll certainly remember this.

Thanks for the info!

Best regards,
Robin.

 

Bridge-deck clearance is a major factor seperating the inshore catamarans from the off-shore catamarans. Anything less than 3' of clearance from the bottom of the deck to the water between the hulls would not be well-suited for off-shore use. More would be better.

"Tall" bows. The most dangerous point is once the forward crossbeam smacks a wave. It produces a profound "braking" effect, tripping the front of the boat up, shifting all the momentum and all the weight to the front of the boat- the begining stages of a pitchpole. The bows must be tall enough to keep the beam clear, and bouyant enough in case the beam does hit a wave.

Notice the bows in the picture below:


Width. It should be around half as wide as it is long. Some are above this ratio, some are below. You don't want it so wide that the leeward hull cannot support the pressure before the windward hull becomes airborn. Otherwise the leeward bow will plow under and pinwheel the craft. Unlike a racing cat, it would be better to lose the rig than flip the boat. The design should note the boats maximum righting moment. It's your call on wether the rig is set up to withstand more or less than this figure. Typically, the rigs are strong enough to stay put and the skipper is wary and experienced enough not to push the boat over the edge. Up-side-down cruising cats are usually the result of a pitchpole.

 

Size is an issue, since stability goes up rapidly as the boat gets bigger.

Many designers are of the opinion that 40 feet is a reasonable minimum. On the other hand, look at the designs of Thomas Firth Jones. He circled the Atlantic Basin a couple of times on designs under 30 feet. One of his cat designs, Brineshrimp, is 23' overall, I believe, and he says it's suitable for ocean crossing with no more than two aboard.

Bigger is safer, in multihulls, but I wonder how small is unsafe.

 

Hi,

Thanks for the info regarding the bows etc.. !

I'll keep in mind the (shall I say) general consensus on minimum ocean-going hull lengths; this is something that I've been wondering about.

Best regards,
AstroTux.

 

Two years or more past, I researched the same question. At that time, 14 meters was general answer I found.

If you are going to live-aboard, then it becomes difficult to fit in enough full-time living space for two with a wl less than this. That is providing you are keeping weight out of the ends and a small bwl:lwl ratio.

Well that is my amature comments.

 

I suppose this is dependent on how much luxury you require (or can afford.) Referring again to Thomas Firth Jones (I like his work, as you can probably tell) none of his multihull designs are over 30 feet. None of them have standing headroom either, but he and his wife did voyage pretty far in those little boats.

On the other hand, Jones cheerfully admits that he sees sailing as a delightful break in a shore-based life. On some of his voyages, he and his wife lived aboard for many months, but it was never their intention to become full-time liveaboards. As he said, the decks of a multihull are wide, but the decks of his house are wider still.

If I were a designer, I'm sure I'd encourage clients to build ocean-going multihulls bigger than 40 feet, for several reasons. For one thing, the design fee would be bigger. For another, the stability of a 40 footer is much much higher than a 30 footer, so my clients would be less likely to capsize their boats and sue me.

Anyway, I admire Jones for being brave enough (or foolhardy enough) to tell people, and to demonstrate, that oceans can be crossed in small multihulls. Not everyone can afford a big one.

Ray

 

Basic needs

Having built only one multi out of dozens on mono's.....
I found the most necessary need was a little T. L. C.



which when explained further........means "Truck Load of Cash"

Believe me, you are building 3 boats.
Good choice though, I do like sailing on them

 

Johnsailer, thats hitting the nail right on the head, I reckon in terms of square metres of construction, fairing-painting, doubleing of propulsion & rudders etc & all fitout a 40' cats a lot like a maxi mono & you need plenty to afford one of those, I still want one though. TLC I like it!!! Jeff.