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Old 19-08-2007, 16:02   #1
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Catamarans versus Trimarans

I grew up in the 60s when Catamarans were beach cats and cruising multihulls were trimarans.
Now racing multihulls are trimarans and cruising multihulls are catamarans.
Why?

I have some opinions of my own but I like to hear what the forum has to say.
The focus should be on suitability for Cruising (not racing)
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Old 19-08-2007, 19:58   #2
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Beau,

Basically I think it boils down to:

- Living space
- Accessibility
- Simplicity (both for the builder and for the owner faced with managing all the "systems" on a modern cruising boat)

Each of these favors a cat.
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Old 20-08-2007, 01:45   #3
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Catamarans under 40 ft are two long narrow tubes with a bridgedeck that is either too low to the water or lacks sufficient headroom
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Old 20-08-2007, 02:14   #4
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I'm guessing it also has to do with advances in materials techology, manufacturing and computer aided design.

For cruisers, you can build really stiff, light cats with less material which makes them (somewhat) more affordable. A cat is a natural configuration for a pleasure boat: Lots of space, stable, reasonably quick.

For racers, a featherweight tri is has less windage and the ability to point like a monohull whilst carrying the speeds of a beach cat. What tri's lack is space due to the narrow beam of the hull: They're fast, small and relatively expensive.

You used to see a lot of bridgedeck style tri's back in the 60's & 70's. I suspect that configuration resulted from materials and design limitations of that era. Fibreglass hulls used to be quite beefy until material technology & computers made the design of superlight but strong composites possible.
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Old 20-08-2007, 15:01   #5
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I suspect the tri's of the 60's and 70's were mainly home built and built from plywood and later glassed over.
Bridgedeck Trimarans would be too expensive to build re moulds etc for production. Which is why I believe catamarans are now more popular in cruising multihulls.
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Old 20-08-2007, 15:26   #6
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huh?

Quote:
Originally Posted by beau
Catamarans under 40 ft are two long narrow tubes with a bridgedeck that is either too low to the water or lacks sufficient headroom
Your very specialized trimaran notwithstanding, I would submit that most tris under 40 ft are one narrow tube without sufficient headroom, berth room, galley space (including ref/freezer) or storage space with two narrower tubes (one on each side) attached.

Yes, many cats suffer from a bridgedeck that is too low and many of the ones that do are under 40 ft, but builders have to also keep their target customer and build costs in mind or they will never get a boat in the water.
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Old 20-08-2007, 16:26   #7
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The short answer to your question is that this is the platform that the charter companies support and consequently, it is the platform that manufacturers provide (or maybe it's the other way around).

Your observation that "Catamarans under 40 ft are two long narrow tubes with a bridgedeck that is either too low to the water or lacks sufficient headroom" has merit, but they still provide adequate accommodations for 4 couples of average height for a 1 week charter. This has little to do with the typical single couple cruiser. But, at least in the Caribbean this style of boat revolutionized the charter industry in the mid 90s. As a result they now dominate the market; they are proven designs; they represent what is available from reputable manufacturers; and they are what cruisers are willing to spend significant $$$ to buy.
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Old 20-08-2007, 17:54   #8
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Many reasons for the trend toward cats for cruising but you hit one right on with the economic issue. From a production standpoint the cat is more efficient to build, fewer hulls, molds, and connective structure, etc. Another reason is that cruisers are demanding more luxury and wanting "to take it all with them". A cat with it's larger interior has the room for all these goodies. There is a penalty in performance for this but many see the tradeoff as acceptable. I don't think there is a big differance in seaworthiness and I doubt that it plays much of a role in the decision process. The motion is differant between the two with the tri heeling a bit more and the cat having a little quicker pitching motion fore and aft. Reguardless they are both more comfortable for most people than a monohull. Cats are better under power and have a great place to store the dink.

One thing I have not seen discussed is the cockpit. You spend so much of your time outside and the cat with it's large cockpit for socializing is hard to beat. My Searunner with it's large center cockpit has never lacked for room either but not all tris have this.

The cruising tri has plenty of space for good accommadations but people seem to want more, more, more. What the tri has going for it is better performance and handling, it actually feels like you are sailing a boat and not "driving a bus."Don't mean to start an argument here. Asthetics is a personal issue but I like the low sleeker look of the trimaran over the boxy high sided cat.

For chartering and cruising with a family, cats are hard to beat but for just a couple I think the interiors can be an inefficient use of the space. The hull form does not lend itself to much real variation like a monohull or trimaran.

There are some trimarans out there like the Cross 46 and 50, and some of the larger Horstman designs that use the amas for living space and these easliy rival a cat for accommadations but they are not that common so I will leave it at that.
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Old 04-09-2007, 17:31   #9
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Well--my trimaran is just over forty feet and has berths in the wing decks which free up a lot of space in the admittedly narrow hull when compared to a forty foot mono--except perhaps some of the designs built for speed rather than cruising comfort.

The trimaran stops a lot of wind when at anchor compared to a mono--and if I have a criticism of this one, it is the slender entry of the hulls which tend to limit the weight which needs to be carried forward--such as a decent sized anchor and chain and a windlass to retrieve it all.

The strongest wind I have encountered with a lee shore was forty five knots with gusts to sixty, and by taking them on the quarter was able to forge my way out to deeper water well away from the reefs. I will not say I was afraid--just concerned to the max--green water over the port ama dorade box forward ventillator is not something I wish to see a lot of the time--fortunately the thing worked well and we only shipped a little water.

The good thing about a trimaran--and a cat too for that matter--is the stable platform it has when at anchor. The Loadstar does have full head room in the saloon and sitting headroom if the front and aft cabins. Heavily loaded with water and fuel she does about half windspeed, but the best she has done with a cruising load of stores, water and fuel is about ten knots--which many monohulls would also do in the sixteen to twenty knots of breeze it likes best.

If I were to change anything, I would prefer a more complex bow which would give a fine entry for the normal seas one encounters, but with a little more flare for more bouyancy. Pitchpoling can be a real problem with trimarans. I have considered fitting inflatable bouyancy around deck shelf outer beltings, just to lift the bows more quickly should they ever dig in. Any thoughts on this welcome.

My tri is underpowered by most standards. It rigged as a cutter but I hardly ever use other than the main and genoa, which gets her up to eight knots or so.

Trimarans are superb coastal cruisers--that is a fact. For offshore work in severe conditions--I am less enthusiastic. I have been in rough seas--but not for days on end. The need to watch constantly for extra big waves would be very tiresome indeed. A trimaran or a cat sheds little wind compared to a monohull which can roll away from the wind and present higher sides of the hull to weather--trimarans get wet in such conditions and reefing early saves broken gear or worse.

Then there have been cases when whales have attacked trimarans--

The amas on the Loadstar could each easily be made into 2 single cabins. One might retain some of the storeage by putting it under the bunks, where the bunk is the lid of a stores bin. The main thing is not to overload the amas--and since they are only likely to be occupied when at anchor or beached--they are certainly useable. In rough weather the hatches need to stay closed. I may explore this option later.
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Old 04-09-2007, 18:23   #10
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Quote:
Originally Posted by beau View Post
Catamarans under 40 ft are two long narrow tubes with a bridgedeck that is either too low to the water or lacks sufficient headroom
Nope. Maybe under around 35 feet, but certainly there are cats under 40 feet with reasonable room, and decent bridgedeck clearance, or decent room/reasonable clearance - i.e. Tasman 35, Seawind 1000, Oram 38, Schionning 1100, the Easy series......

I don't really agree that racing is all about tri's either - Orange 2 holds many records, and it's a cat, Playstation beat quite a few tri's in it's day, etc etc....
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Old 04-09-2007, 22:13   #11
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Hi Mike
I think alot of the issues you have with your Piver were addressed to some degree in later designs. The hull and ama shapes and center of bouyancy were fine tuned by those that followed to lessen pitching and improve sailing performance. Norm Cross had some modifications to the rudders and keels for the Pivers that helped but there is not much you can do about the basic hull and ama shape. This is not meant as a diss of your Piver as someone had to be first and it is only natural that those that followed improved the concept. If you compare the lines plans of a Piver, a Searunner, and a Cross you will see an evolution in hull and ama shape.
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Old 05-09-2007, 02:16   #12
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Thanks Steve--

This one has been fitted with Cross modifications which has improved the windward performance. She does not hobby-horse much at all--it is just that if things get a bit hectic out there it is a good idea to move as much ballast aft as one can.

Regards--

Mike
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Old 17-10-2007, 19:39   #13
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Hi Guys
I'm new to the forum this is my 1st ever post.Mike you mentioned extra bouyancy in the bows of you boat tostop pitch polling. Alain Colas did just that with his tri 'Manureva' . He went on to set a new solo round the world time so it obviously worked for him. Check out his book 'Around the world alone' its agood read and there are lots of good ideas to pinch.
I myself have a Cirro-Stratus 33 tri ,and she has a fine entry but then the bows flare out to give lots of reserve bouyancy and it also give a good working bow area. In the previous post a few people have said a trimaran is to narrow to be livable should check out tri's with wing aka's , this type of design is alot more roomy as the are no box section and bulkheads to duck under . In my boat I have full head room from bow to stern a double aft cabin and agood size gally and head. The only draw back is the double cockpit configuration, which are set off centre of the main hull. Anyway I've rambbled on enough for my 1st post. See ya
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Old 19-10-2007, 17:42   #14
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Extra bouyancy

Thanks Luski--I will certainly have a shufti.

I had intended the inflatable collar to be a temporary fixture. In an emergency it would be quick to fix in position and inflate--and it could be removed when not essential. For a more permanent solution I had intended to modify the bow and extend the amas.

Probably much cheaper though to sell the boat and purchase another without the problems.

I do like the comfort of a trimaran. The name Lodestar is a bit of a misnomer though--none of them like to be loaded any more than does any other sailing vessel, and although one CAN load them up they seriously lose performance at those loads. Still--I like to cruise at about six knots--so it does not bother me too much.

The extra strong for'ard box girder that most trimarans have is a bugger to crawl under. I think Horstman also designed full headroom as well as access to the amas from inside the centre hull by leaving space below the extended topdeck which goes completely over the amas--another useful idea. A fifty foot Horstman would have to be one of the ultimate cruising trimarans. Another is the Simpson Liahona--always wanted one of them--

The main problems big Trimarans have is getting them insured. Many companies hate them--as much as some hate ferro--and the premiums are high when one does manage to get one insured. Much easier to insure a big cat.
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Old 19-10-2007, 18:44   #15
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insurance for tri's. Look no further than Nautilus Marine ,they have offices in Queensland and melbourne . They gave me a good deal, much better than anythink over here in the uk
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