Catamaran vs Trimaran

Doug, above graph from http://www.john-shuttleworth.com/Articles/NESTalk.html who has articles on the subject also.
the tri's beam is wider tho and not toutching all the cats merrits i'd say a tri is and behaves different than a cat in many ways.

 

A trimaran may also be faster in drift (<5 knots) conditions as the boat is healed slightly allowing the sails to fall into a nicely aerodynamic and twisted shape. These days with heavily battoned sails it may not be such an issue.

Dave

 

Cat vs Tri

I think, as time goes by, the most important criterion for high speed multies will be : what is the best configuration to maximize the use of hydrofoils? And I believe the trimaran probably wins that hands down.

 

looking out the window here i'm thinking hydrofoils for cars, what a summer, its pooring! orange blosom road winibago time? hell, i can be like this there too! yes, think your rite, cats are great, tri's even harder/higher on foils

 

Re: Racing cat or tri.

An issue that seems to be forgotten is the stress on the crossbeams.

Given: - that the mast is being driven through the center of the main
crossbeam of a cat and this beam is also trying to hold the boat together.
It follows: - that said beam has to be pretty substantial.
So: - if you were to have as wide a boat as a tri - your crossbeam
will need to be HUGE.......and heavy.
Where as: - the centre hull on a tri absorbs the downward force of the
mast(s) much more easily - with less weight.

Also as a tri's main hull - is in line with the forestay loads - it is proberly
resisting these loads better than a cat's crossbeam does. So are we not also going to get a tighter forestay on the tri? A factor in windward performance.

 

weight, weight, weight

Weight is a very important factor in the speed of a multihull and a catamaran can be made lighter than a trimaran and the structure is much more simple to design and to optimize

However, with the use of more expensive building technology and better FEA simulation, a trimaran can be made almost as light as a catamaran and it will be faster in many conditions.

Open 40 is a interesting example because there was a 1800kg minimum weight and the class was dominated by catamaran at first because they were able to meet the minimum weight requirement. With the improvement in the building techniques, the trimaran were also able to meet the minimum weight requirement and they started to dominate.

As far as the new giant multihull, again, the class is dominated by the catamaran because they are simpler to design and are cheaper to build. There is one competitive trimaran however, it doesn't have the latest advances from the Open60 series like foils, canting rigs and amas steering capability.

 

Re: Cat or Tri ? Part II

Yes, CLEBLANC, the Formula 40 results were interesting.

- And yes, the three most important design considerations for designing
multi - hulls is weight, weight and weight!

However: I think it is an open question as to which is lighter.

I keep going back to the crossbeams - that are INHERENTLY less
stressed with a tri.
( Except - perhaps - when brave people insist on flying 2 of their 3 hulls.)

- If, LORSAIL, you made a cat as wide as a tri, the weight of the crossbeams
will start to enter the zone of diminishing returns.
For if, lets say, you DO have a weight advantage in your cat - the extra
weight incurred as the beams grow outward - will eventualy bring you
up somewhat even.
( Remember the loads increase, at least, as a square root multiplier.)
A lot of effort too get to the same place as the tri - but now you have
even worse light air performance than you had before you grew wider.

- Frankly, this is an discussion that has gone on for years - and I dont see the debate ending - anytime soon.

- Suffice to say: I have witnessed catastrophic failure of the
hull / crossbeam connections on a cat. A sobering sight !
Luckily, I was close to shore, at the time.
- Also, I'm aware of this happening, historicaly - with other vessels.

- Help me out here, sailors with long memories,re:
- A list of the Structual Failure of cats Offshore.

I hasten to state:
I wont suggest that trimarans haven't had there share of troubles.
( Witness the sad legacy of Mr. Piver)

However, before you build that super - wide cat......let's see what our
informal survey says.

 

I have to largely agree with Cormeran on his thoughts about going much wider than 2 to1 on the cat. The loading increase on crossbeams is already well known and more strength plus more length equals a lot more weight. Heavily loaded cat hulls are slow!
Further, manouverability of a very wide cat would be worse (especially tacking) than a regular width cat which is already worse than a tri.
This is not an opinion that cats or tris are generally better, although I personally like the aesthetic and design solutions afforded by tris.

 

Thank you FROSH,

for your support - re: racing multi - hulls.

Like you, I lean towards trimarans. Almost to prejudical level.
However, outside of ocean racing - they tend to be a hard sell.

All that wonderfull beam we've been talking about - becomes a decided
negative - when you are trying to find a slip in a crowded marina.
Or selling a your concept - Super Tri Cruiser - to an Investment Banker........

 

i have this long narrow mono hull im currently working on as a working boat...though in order to keep the design it may need to become a trimirian
and iv always liked trimirans...so perhaps if people regularly see a tri as a working ship instead of just a racer ,specialty pleasure craft, they will start gettng around...and perhaps a open mooring spot is better and cheaper.

 

Turning a monohull into a tri

To Redsky:

As a WORKING boat - are you refering to - a SAIL or POWER boat ?

If we are talking power only - my research indicates - that your options
are more flexible than you might realize.

We have done a lot of work, specificaly, in respect to commercial
Tri - Hulls. So we can be of practical assistance.

Send us an E - Mail with a bit more information and we will see how we
can help you.

Cheers !

 

Thoughts from Dick Newick

Dick Newick is one of this country's foremost multihull designers, with specialty in trimaran design. He's mostly retired now and living in California, but I thought his opinion, printed in the March 1988 issue of SAILING WORLD, is worthwhile and to the point: I quote:

"I've predicted all along that a good trimaran will beat a good catamaran almost every time. For an all-around multihull racer-cruiser, I would suggest that tris have the following advantages: They have more stability because they are wider for a given length. They have more maneuverability because when they turn, they are dragging two long slender hulls cross-ways around an imaginary point in the middle--they have one long slender hull pivoting around the same point with the amas largely out of the water. They have an easier motion at sea; they don't have a quick jerky motion; they don't pitch anywehre near as much going to windward. With a smaller-size cruising boat you can get more useful accommodation without excessive freeboard since it's down in the hull instead of on a platform several feet above the water. And, because of the trimaran's easier motion, it is much easier on its, rig, so it doesn't need a heavy one. Lastly, you are stepping your mast in a hull, instead of someplace out over the blue water, and therefore your engineering problems are fewer.

"In really light weather the trimaran has a very big advantage in less wetted surface. When you can't fly a hull in a catamaran, you're just stuck in the water. As soon as you're sailing practically, you're flying the weather hull on a trimaran. Other than that I think catamarans are fine."

Eric

 

Newick is a great designer, and many of his points are valid.

However, in my opinion, catamarans are superior as cruising boats.

Trimarans are generally faster over the usual range of conditions, the engineering problems are easier in terms of rigging, you have accomodations in a central hull that can be more open and well-integrated in function, the boat is more maneuverable, and so on.

But one great advantage of the cat is that unlike the tri, it does not heel appreciably. You have to expoerience this advantage over the length of a cruise for the wonderfulness of it to truly sink in. You can set your drink down on the deck, go below and check the chart, come back on deck, and your drink will still be right where you put it. I know, it doesn't sound like a big deal, but it really is. It's much safer, for one thing. The leading cause of death at sea is man overboard. Your crew is much less likely to fall off a flat stable deck. It's also much less tiring than sailing on a slant and you will be better rested and better able to make good judgements.

The other huge advantage of a cat (or at least an open deck cat) is the vast acreage of deck. Most folks, when cruising, spend the majority of their time at anchor. With a nice awning and some deck chairs, a folding table, a chaise lounge or two, you have a space aboard that can't really be duplicated on a monohull or trimaran. It's like a terrace on the water-- ultimately luxurious.

Ray

 

Newick is - with no question - an authority on Trimarans.

Also he is quoted or paraphased all the time by myself - and others to
our prospective clients:

" YOU CAN HAVE A FAST BOAT, SIR .............
YOU CAN HAVE A LUXURIOUS BOAT.............
YOU CAN HAVE A CHEAP BOAT....................
......... BUT YOU CAN NOT HAVE ALL THREE !"

 

Gosh, Ray, doesn't all that substantiation of the cruising cat-over-tri argument, really depend upon the design details of the tri?

For example, if the tri amas are designed to just kiss the water surface at design load, there is very little heeling going on when the sails are engaged and the ama is pressed to equilibrium. Any gusts beyond the norm would cause both boats to experience a degree of enhanced heel and that comfy notion that a martini will sit still in a seaway goes right out the door.

There are other scenarios where the supposed advantages in cruising are not what they seem, but I won't address them now.

What really sets the cat apart as a cruising machine is the aircraft carrier style deck space that can be utilized aong with huge, below decks stowage. That kind of room is just not up to luxury cruising standards on a tri until you get to the 40'+ LOA designs and really throw down some serious money. (assuming all appointment levels are nearly equal)

It is really hard to compete with one of the performance oriented cruising cats like the Gunboat, for example, if you want speed, accomodations and pure stroke on the waterfront.