The project fast lightweight power catamarans - is possible?

Discussion in 'Boat Design' started by romanewas, Jan 6, 2017.

  1. Stumble
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    Stumble Senior Member

    Passengers are probably the least dense cargo any ship can be designed to carry, I wouldn't worry about a SWATH used for passenger transport being overloaded, even if it handled primarily Americans. Any vessel designed for the purpose would be more than capable of carrying 20-30 people easily. It would probably have as much variable weight in fuel loading as people.

    Tansl,

    As I mentioned I have zero SWATH experience, but from what I have read they are generally designed so the Waterline on the struts is 1/2 way between the hull and the top of the torpedo. So to operate in 2m seas would require a 4m strut and something like a 3m draft.

    One of the things I haven't found is how SWATHs handle waves higher than their design height. I am not sure if they then handle like catamarans, more like a barge, or have a ride quality all their own. Do you know of any studies or industry data that discusses it?
     
  2. Stumble
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    Stumble Senior Member

    Off hand that ship looks to be in pretty rough shape, if i had to guess it has outlived its service life, which is why it lost its certification... I would only buy it if you had a scrap yard willing to take it from you, and you can accept a full loss on the purchase price.


    I am not sure what your budget is, but my first suggestion would be to contact Kurt Hughes and ask about his 60' Catamaran Ferry design. He will have a far better feel for the operational parameters of his design than I possibly could. I know there are a number of them, so a trip to Hawaii or S. America to ride one of them in the sea state you are planning to operate in might be in order.

    Then do the same with Incat, and a small SWATH Ferry design firm. As Tansl mentioned the designers will be the ones that really know or be able to predict, how their boats will handle a given wave height within the ISO standards for human comfort.
     
  3. kilocharlie2
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    kilocharlie2 Junior Member

    I think I mentioned it before, that there is a 65 foot by 26 foot, 75 to 90 passenger power catamaran called Speed Twin operating out of CISCO Sportfishing in Oxnard California. It might pay off for Roman to go take a ride on it, or one like it, before committing a bazillion Euros on the project. Call me if you decide to go, I'll go fishing with you.

    www.channelislandssportfishing.com/speed-twin-sportfishing

    Scroll down to the bottom and take the video tour of the boat. I just watched several youtube videos of them fishing, unfortunately nothing in 6 foot seas, not much underway footage.

    Stumble - From very limited experience, a big wave hitting the upper hull makes it much more like a normal ship ride, but usually more intermittent. The deck pitches and rolls only on the waves that hit the upper hull. In extreme wave activity, almost all design advantages are lost, except for speed. Both catamarans and SWATH can run down swell a lot faster than a mono hull. With skill, a pilot can climb or run down the back of a swell at the right speed and remove a lot of the wave-related accelerations.

    When the waves are routinely breaking over the bow or even the bridge, you are gonna need seasick pills and a friendly relationship with God. I've been in 20 foot swell on a 58 foot Alaska Limit seiner (mono hull). It's not fun.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I doubt there is any peculiarity of conditions in the operating area, or particular delicacy of tourists to the place, that would demand a solution different to that adopted almost universally elsewhere, which is a catamaran, it is just a case of comparing what is available in existing designs. And I suspect the operating economics of a SWATH would be bad for business.
     
  5. Stumble
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    Stumble Senior Member

    One study I found from the USN (in 1975 I think, so the data may be suspect) indicated SWATH operating costs could run as much as 80% more than a monohull (no comparison to a cat was made).
     
  6. TANSL
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    TANSL Senior Member

    It is true that the SWATH is not a type of boat that we can consider as abundant in nature, but I do not know why. Of course, if this type is applicable to some particular traffic it is in passage.
    It would be interesting to know the breakdown of these operating costs because, without further data, I can not find reason to be higher in a boat that needs less power to go at the same speed. But, honestly, I wish I could get out of my mistake.
     
  7. kilocharlie2
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    kilocharlie2 Junior Member

    At some point, Roman is going to pull the trigger and build or obtain a boat. I'm nearly certain that a SWATH will meet his performance criteria.

    Should he find that his customers' needs are met by a power cat, he'll likely go with it. It seems like it's time for him to go ride some boats, look at budgets, certification standards compliance, and keep a very sharp eye on operating costs.

    One possible reason the overall costs are so high for SWATH design boats is that most seem to have been built for military. That should skew even the cost of a drain plug, and the $400.00 hammer to install and remove it, not to mention the training manual and the special school to teach you how to use the hammer.
     
  8. TANSL
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    TANSL Senior Member

    Overal costs is a totally different thing to the costs of operation. My answer was in relation to the costs mentioned by Stumble.
    If we agree that the operating costs are, say, similar to those of a catamaran, he will simply try to make a SWATH, not for military uses but for civil uses, of low cost, which is one of the first premises indicated by Roman.
     
  9. kilocharlie2
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    kilocharlie2 Junior Member

    Curious about why operating costs are considered so high? Does the crew have a lot of extra work to do? Is it a case of scrubbing the pontoons of growth fairly often? Is it twin control surfaces?

    With a bit better performance on less power, one would think it should be lower cost to operate. What am I not seeing?
     
  10. TANSL
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    TANSL Senior Member

    Kilocharlie2, in my opinion you are absolutely right. I also do not understand why the operating costs have to be high in a SWATH that, as I say in my previous post, will need less power than any other type of boat. Other operating costs, unless somebody proves otherwise, do not depend on the type of boat either.
     
  11. Stumble
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    Stumble Senior Member

    That's the thing, they don't get better performance on less power. SWATHs operate at relatively high resistance for their Fn until the Fn excedes .65. So at low speed the extra surface area is deadly, and the gains don't happen until the ship is traveling at speeds in excess of what is commercially reasonable.

    Now to go those speeds requires a lot of HP, generally beyond the ability of the thin hulls to contain so you either need a complicated transmission with a shaft that's taller than the struts (4m in this case), or hydrolic with all its associated issues, or diesel electric with its conversion losses. You also have to carry a lot of fuel to power the big engines which means more weight for an already weight sensitive boat.

    Strut design is aparently a serious issue, and in high speed craft you almost have to go to four struts in order to keep wave making drag down, which further adds to complexity. In a vessel designed to operate in 2m seas you need >4m struts, which means the lever arm is very long, and even minor forces get magnified a lot but because the ride is so comfortable the skipper may not be aware he is stressing the hull very much. This has led to major problems, like the USN first SWATH designs having to be decommissioned due to dangerous cracking in the plate steel. Modern designs have hull strain gauges and computer outputs to measure the strain placed on the hull and predict this cracking, but that's an expense as well.

    There is also the issue that as strut length gets longer to tolerate hire waves, the vessel needs more and more width to keep acceptable traverse stability. Leading to very high cross beam loads. With a L/B of about half that of catamarans of the same length. It also increases wavemaking resistance, thus slowing them down further.

    For more
    https://www.witpress.com/Secure/elibrary/papers/NEVA93/NEVA93019FU.pdf
    http://www.sname.org/HigherLogic/Sy...tFileKey=0d07bf2d-c035-4ef8-abc5-6b3e797b69f4
    https://bib.irb.hr/datoteka/405051.Kos_S._Brcic_Francic.pdf

    Btw I don't have any issue with SWATH vessels. In the right application they may be the only vessel capable of handeling the sea states, but I just don't think that's true here. Think about where they are common, in the North Sea as wind farm/oil support vessels, bringing harbor pilots out to massive ships in the North Sea, scientific research vessels, and ferries in Scandinavia. To my knowledge that's pretty much it, everywhere else commercial operators have chosen hydrofoils, monohulls, or cats. There must be a reason for that beyond commercial dislike of them.


    Frankly we are at or beyond my technical knowledge so I am going to bow out at this point. But I would be very interested if someone can show me where I am wrong.
     
  12. romanewas
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    romanewas Junior Member

    Stumble, that's what you wrote above sheds new light on this issue. I will probably withdraw from the idea of a ship type SWATH. In the meantime, I spoke with the designer catamarans which you told me (KURT HUGHES).
    He sent me answer one of the helmsmen of my question. Here it is:
    "The bigger it is, the better Holo handles. The high volume in the bows do tend to make it bob a bit (I would, if it were mine, reduce the rocker if I were to build a second holo. Not by much. I'd keep the entry the same but flatten out the stern by 6-10".

    That said, in 6-8' crap, no one near her size can keep up. I've had her in 10-12' @7-9sec period with a large (3-8') long period swell underneath. I've had her off napali with a 2-3' chop and 30'@18sec swell with the rebound coming off the cliffs and she did well.

    I've only buried the bow once to the cross beam and one other captain did it to the front cabin. Mind you both of us did this nearing Lehua, with a 1-2kt counter current and a wrapping trade swell 8'+ from the NE and the SE. Every once in awhile under those conditions you'll get a hole. AND the best way to avoid it is slow at the top before you start surfing hard and accelerating hard right before the bottom.

    I drive a tug now, as well as a 62' power cat (I think it's a shuttleworth design). I have yet to be on a boat and feel as comfy or if it was really nasty, SAFE on a boat as I did on Holo.

    Like I said, there's some things I change (like stern rocker, another 1-2' beam, chamfer panels, step hulls (double inboard and single outboard) etc. But mind you, I put over 240,000nm on that boat and I had a lot of time to think. lol
    Chat Conversation End
    Type a message..."

    In conclusion I can be understood that such a catamaran: http://www.multihulldesigns.com/designs_other/61ferry.htm
    It is able to meet my needs?
     
  13. Stumble
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    Stumble Senior Member

    Only you can decide if a specific design is suitable, but if I were in your situation it would be on my list to consider. But if the major concern is how it handles passengers in waves, I would fly to Hawaii and go out on it, and see how the passengers react to being out in waves on it, or ask Kurt Hughes if there are any of them operating closer to home you can take a ride on.

    The other stuff like classification and the like I can't advise you on, but if the design was rated by the USCG for 60 passengers then as drawn it will likely do the same in Europe.

    I also wouldn't get tied to this one design, what he drew is a nice boat in my estimation, but there are other passenger ferry catamarans operating and it would be instructive to get a ride on as many as possible, particularly in weather similar to what you expect to operate in.
     
  14. romanewas
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    romanewas Junior Member

    Of course I've seen a lot of catamarans. Two weeks ago, some of them eg in Dubai. However, the sea state was quite different and that changes things. Therefore, I am very interested in a boat that floats in difficult conditions. These are definitely in Hawaii.
     

  15. kilocharlie2
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    kilocharlie2 Junior Member

    Still the right time of year (Winter) for rough seas in Hawai'i, though this is perhaps the last month (February) of the big stuff. Still, 2m seas can happen there any time of year. Wish I was over there to tag along :)

    Greg - Thanks for the specifics. I've just peeked at the first of your links, and It IS AN EXCELLENT READ. Unfortunately, I'm falling asleep and will have to get back to it next week, as the heaviest rain of the Winter just started a few minutes ago. Pray for the dam on Lake Oroville to not fail, and the evacuees who flee for safety. I have friends up there.
     
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