Super economical wave piercing catamaran cruisers

Discussion in 'Boat Design' started by Greenseas2, Feb 4, 2008.

  1. Greenseas2
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    Greenseas2 Senior Member

    In St Thomas there is a fleet of passenger carrying wave piercing catamarans that are owned by Dohm's Water taxi and built by Gold Coast Yachts of St. Croix. The outboard powered work horses are definitely fast with their elongated bows and are inexpensive to operate. The long narrow low friction hulls slice through the waves with ease. The deckhouses on the larger boats are quite spacious and elevated well above the hulls. It doesn't appear that deck space has been sacrificed by the design and the superstructure is only moderately streamlined.

    It would appear that the wave piercing catamarans of this particular design would be ideal for long distance live aboard cruisers whose primary focus is on fuel economy. A large version of the wave piercing design may be seen in Key West. It's used for taking passengers out to the Dry Tortugas and is inherently stable. One really great aspect of the design is that it leaves almost no wake at full throttle when operating in what could be considered past-hull-speed in monohulls.

    The construction of the boats is composite wood/epoxy and should be well within the building ability of dedicated amateurs. Other than a very futuristic look, I can find no faults with the design and feel that there is a good future use for it with private as well as commercial applications.
     
  2. rwatson
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    rwatson Senior Member

    I have had the experience of riding in "wave piercing" commercial catamarans - (developed by Incat in Australia), and one design fault became obvious - the ride motion in fairly calm water at high speed.
    I have expressed my opinion in a several threads on boat comfort over the last few months, but in brief they developed the name of "Spew Cats", and lasted only two seasons as ferries in open seas off southern australia.
    I and most other passengers got queasy riding them in calm seas because the narrow hulls resulted in lots of 'dipping' as they did indeed slice through long smooth swells. It was like being in the back seat of a car where the suspension is way too soft.
    In calmish waters, the ride on conventional hulls with stabilisers is much more agreeable.
    I guess in rough seas, everyone gets sick no matter what type of boat, but to get queasy in fine weather is not a great feature.
     
  3. Manie B
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    Manie B Senior Member

  4. tom28571
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    tom28571 Senior Member

    The ride in sea swells in a big cat at speed can make passengers run for their barf bags. I did not get sick on two recent 130 mile trips across the English Channel on the "vomit comet" but some did. These do not have wave piercer bows. They seem to handle waves much better than the long period swells. The Key West cats are far smaller and might actually be easier on the passengers.
     
  5. SeaSpark
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    SeaSpark -

    A super economical boat will never go really fast, does anyone have experience on a wave piercing cat at lower speeds, say lower than or only a bit above the hull speed of a displacement boat at the same length?
     
  6. Fanie
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    Fanie Fanie

    Reading Rwatson's post on this I can only agree with him. If the hull's don't move right with the water then you are going to get seasick, that's a given.

    Super piercing hulls go through waves, often with the oposite motion (or not obvious or predicted motion). Me, I'll just stick to something that moves right. Besides, what's the fun going to be when there's no motion ? Aint that called 'land' ?
     
  7. rwatson
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    rwatson Senior Member

    "does anyone have experience on a wave piercing cat at lower speeds"

    I can tell you about wave piercing hull performance at moderate speeds, based on a 20 ft trimaran.
    I built the centre hull with a really fine entry, and when powered by a 6hp outboard, it was a real joy at around 10 knots. The wave piercing meant that in short uncomfortable chops, the boat wasnt knocked around like traditional runabouts. It stayed wonderfully level and comfortable. Being a trimaran, fishing was great, as the small swells didnt make the boat rock badly at anchor, which had been the bane of many fishermen in the 'standard' fishing boat.
     
    Last edited: Feb 5, 2008
  8. Greenseas2
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    Greenseas2 Senior Member

    Ive ridden both the Key West wave piercer in rough weather and the Dohm's boat in St. Thomas and didn't experience adverse motion on either. I also had an opportunity to discuss economy of operation with the crews and found out that fuel consumption was less than half of an equivalent monohull. The drift of the thread is more toward speed and economical cruising in relatively protected waters. Of course, we can all introduce extremes that could make seasoned mariners heave their cookies. The economy of operation of a wave piercer would make it an ideal long distance cruiser on the ICW. It also has good load carrying capability.
     
  9. rwatson
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    rwatson Senior Member

    Do note however, I was complaining about SMOOTH weather operations.
    My observations were that under autopilot, the small course corrections (say every 3 -5 minutes) were done by increasing pressure from one or other of the twin waterjets. This caused the accellerated hull to dip - giving the very uncomfortable feeling of being in a car whose driver was accellerating and turning the wheel every 3 minutes - most puke provoking.
    They would have done better to have some sort of small rudder/trim tab to do the small course corrections I think.
    In rough weather, all boats are the pits!
     
  10. SaltOntheBrain
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    SaltOntheBrain Senior Member

    Hey Geenseas,
    When I lived down there, one of those water taxi's hit a big wave on the south shore of St. John. It blew the windows out and scattered debris all over the place.

    Here's my opinion: Those boats are fantastic for what they were designed for, which is a smooth ride in confused chop up to three or four foot wave height, but that bridge deck is an un-aero-hydro-dynamic wall not meant to meet big waves head-on.

    Guys, when he called them fast, he's only talking about 20 knots or so, which is a lot higher than displacement speed, and is a pretty good rate of travel in the chop we saw most days down there.

    I grew up fishing the Texas Coast, and when I moved down there, I never could figure how to time the waves in my little boat, I was always getting beat up and tired. Then I watched the water from a plane one day and notices a cross-hatch wave pattern. Waves came from two directions. From the SE (Caribbean) and from the NE( Atlantic). It was brutal in a small monohull, but those Gold Coast cats ate it up.

    I just don't think they'd make a good cruising boat in the open ocean.

    Lance.
     
  11. kengrome
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    kengrome Senior Member

    I was curious about the appearance of these boats and no one posted any pix so I did a google search and came up with these:

    [​IMG]

    [​IMG]


    There are bigger pictures here: http://www.watertaxi-vi.com

    I'm not sure what you mean by "really fast" SeaSpark, but according to Malcolm Tennant displacement catamarans can be as fast as planing boats. Tennant claims that as size increases the cost to make the boat plane becomes prohibitive, so he says larger displacement catamarans can be as fast as a planing hulls, but a lot less costly to reach these speeds. This is probably an over-simplification so I point you to the article he wrote since it explains better than I can:

    http://www.catamarans.com/news/2006/04/CatComparison.asp

    I'm thinking the same thing. I am hoping to take a trip on the ICW and do the Great Loop in a few years, in my own boat that I have built in my my little shop in the Philippines, and I'm interested in these boats because of their cruising economy ... and their spaciousness.

    Boats like these might actually serve as decent ferries for shuttling people in between islands in the Philippines, although the typical Philippine 'banca ferry' seems to be relatively efficient at this task already. Here's a picture of one that appears to be enclosed, or perhaps only semi-enclosed:

    [​IMG]

    But bancas are not "high-tech" enough for the rest of the world, whereas the super-efficient catamarans used by Dohm's Water Taxi just might be.

    For me, 20 knots or so is plenty fast enough for most everything I would ever want or need in a cruising boat.
     
  12. masalai
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    masalai masalai

    Ken, I am still researching, but have a look in my gallery. There is several pictures of a 10 metre Robin Chamberlin design which had 2 x 50 hp kubuto engines and did 16 knots for a 12 knot cruise getting near 1 litre/mile.

    John is building a 12 m version in Brisbane now. I hope to see it before it goes to the buyer... should be ready in a couple of months....

    Robin now lives in Tasmania (I think??)
     
  13. kengrome
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    kengrome Senior Member

    Hi Malasai,

    The Chamberlain boat certainly looks efficient with those very slim hulls!

    There's a new design I'm interested in investigating further, it is called "Derby Gravel Truck" (DGT) and it's from a little known designer by the name of Jeff Gilbert, a Kiwi who lives and works in Australia. Jeff's boat is smaller, and although it is designed for efficiency he has also given it a very desirable safety feature:

    Derby Gravel Truck is a genuine SELF-RIGHTING catamaran!

    I guess he figured that if he could design a self-righting cruising power catamaran he will have accomplished something no one else in the world has managed to do. He gets his efficiency from the catamaran design of course, but it could be said that the proper classification for this boat is a motor sailer since he also specifies twin "downwind sails" to help with efficiency whenever the boat is moving in the right direction, which theoreticlaly should be at least half the time, right?

    Here's a preliminary sketch, which as you can see is particularly 'rustic' in terms of its appearance. Personally I very much enjoy seeing boats designed to look like real old fashioned working boats, rather than the high-tech 'space ships' that so many designers are producing these days:

    [​IMG]

    Note that Jeff has nothing more than the premininary sketches of this boat at the moment. The plans are probably a year off or more since he is finishing his last year of "real employment" this year, after which he intends to devote full time to his boat design work.

    Fortunately Jeff is very proficient at designing with the actual materials in mind. What I mean by this is that he considers every piece that goes into the boat and tries to design for the efficient and economical use of materials -- to keep the actual building costs as low as possible so that "less than wealthy" retirees can afford his boats.

    Here are the rest of his sketches:

    [​IMG]

    [​IMG]

    [​IMG]

    That's the grand total of all the images he has made public at this point in time. I have them in my gallery in case anyone wants to see larger views. Sorry for going off-topic here, I'll stop now so the conversation can continue on wave-piercing hulls ... :)
     
  14. masalai
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    masalai masalai

    It is still "wave piercing"... Thanks for the other offer too...
     

  15. kengrome
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    kengrome Senior Member

    I guess my idea of piercing is when the entire forward section of the hull gets completely immersed in water. I would call Jeff's boat (and most other catamaran hulls) wave slicing rather than wave piercing. Then again, I guess it's just an issue of the size of the waves that determine whether or not a hull is piercing or slicing them at any particular time ...
     
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