The project fast lightweight power catamarans - is possible?

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

  1. Stumble
    Joined: Oct 2008
    Posts: 1,913
    Likes: 73, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    I would agree that if the only design parameter is comfort then a SWATH is likely the best option. But initial cost and operating cost have also been mentioned, and in those SWATH's are far worse than a big cat. Like everything in design there are tradeoffs but SWATH's do one thing exceptionally well, handle rough water, and everything else poorly.

    If you budget $X for vessel acquisition, and half of that is eaten up in design because there isn't an off the shelf solution for the SWATH, compared to the Cat. You get a whole lot less boat than buying a cat for the same money. Worse SWATH designs are only good relative to their size, so while a 40' SWATH may be ideal for this application, if you could buy a 80' cat for the same amount the ride is likely to be similar.

    But on the back end if you need to liquidate selling a 80' passenger cat is easy, finding a buyer for a 40' passenger SWATH could be a major headache.


    Finally on passenger comfort, a 70-80 cat ferry will be fine in 6' waves. Maybe you have to slow down to 15kn instead of 20 but the ride isn't that big of an issue. And those 6' waves are the top of the operational window not the predicted daily. Which is why you do see a lot of SWATH vessels in the North Atlantic and in other places where 10m waves are common, they are the only good option short of going to a massive vessel.


    I should point out that I am not terribly familure with SWATH's and there are some members here who really are. So my pronouncements are just moderately informed opinions, not facts.
     
  2. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Stumble, yes, we both have "moderately informed opinions". The difference is that I have participated in the design of a swath ship and that I have tried to defend my opinion with some technical reasoning.
    In several of the things you say we could agree but do not forget that Romanewas wants not only to sail with 6' waves but to do so at 20 knots with maximum comfort for passengers. I do not know if that is feasible or not, because I have not done the project and there are many calculations and complicated to know how the ship is going to behave, but what I dare say is that a SWATH will be much closer of achieving the objectives of the Romanewas than a catamaran.
    Why the project and the construction of a SWATH, like the one that would need the OP, is much more expensive than a catamaran? There I would appreciate (maybe the others too), that you justify your statement.
    I'm just trying to clarify issues for Romanewas to make a correct choice. There comes a time when incorrect opinions could greatly undermine the choice.
     
  3. Stumble
    Joined: Oct 2008
    Posts: 1,913
    Likes: 73, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    Tansl,

    All of the predicted construction cost data I found from industry data, builders, and the military indicated construction costs for a SWATH are much higher than for a cat of the same capacity. But if you have direct experience of them and this is not correct I will hapily concede to your direct knowledge.

    But the design elements I have doubt of. Right now you can call up Incat and order their 24m pax-ro cat, 30 passenger 2 vehicles, with a operation speed of 25kn, and a operational wave height of 6'. There is no design process required because they have already done it, its litterly an off the shelf solution that can go to build as soon as the yard has a slot. And if you want you can go take a ride on one of the completed ships to experience the ride for yourself for the cost of a plane ticket and a hotel stay.

    Maybe I am wrong, but are there any similar SWATH vessels right now, or would the op need to have one designed? If they don't exist how close are existing designs to what would be required? I know there are some sub 25m swath's operating in the N Europe oil fields and as wind farm service vessels, but what is their operational window compared to a large displacement cat?


    I really am not trying to disparage SWATH vessels they really do have amazing capability, and when they are the right answer nothing else can do the job. I just don't see 6' waves and 20kn as all that exceptional an operating environment to mandate going this route.
     
  4. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I think it is important to re-read what I have written above. I say that, for the service that the OP wants to give, a SWATH is the most suitable boat. I also say that for the ship he's going to need, the most appropriate type is SWATH. Romanewas wants to take around 30 passengers to have a walk of 2 or 3 hours. That is, the ballast-arrival to port condition will differ by no more than 3000 kg from the full-load port exit. If the ship had to carry a car or two, I would not talk about this type of ship. Nor in that case I would think that boat could go at 20 knots with 2m waves. Since the OP wants maximum simplicity in the construction, the floats can be simple cylinders finished in individual cones at their ends; the "legs", hydrodynamic but very simple. Therefore, why is it going to be more expensive to build that boat than a catamaran?
    I suppose a boat for walks between islands can not be compared to a ro-pax. But this is just my opinion.
    I do not think there are second-hand boats that fulfill the desired service because SOR is totally exceptional. Let's not lose sight of what Ramanewas intends to achieve with his ship. What we should not tell him is to change his expectations according to existing second-hand boats.
    Many people immediately consider purchasing an existing boat as the most practical option. But that, in many cases is not what the OP has said it is looking for and greatly limits the options available. A designer will always try to ensure that the customer's needs are met to the maximum possible, even with a second-hand boat, but would justify his advice with compelling reasons.
    I do not have data from builders or ship owners, even from the small-vessel passenger traffic in the world, but I fear that what Romewas wants is not normal, so it will not be easy to find something already built that will suit him.
     
  5. Stumble
    Joined: Oct 2008
    Posts: 1,913
    Likes: 73, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    Tansl,

    I guess my larger point is I don't think the SOR is all that uncommon or exceptional. There are inter island fast ferries operating today with that SOR. Kurt Hughes has an entire class of 61' Catamaran ferries in operation, including one doing service in Hawaii. If anything it's passenger and speed are in excess of the SOR here (USCG certified for 65pax and a top speed of 28kn). I don't have average wave height data for the Cannaries vs Hawaii but I doubt they are all that dissimilar. http://www.multihulldesigns.com/designs_other/61ferry.htm

    Now if the SOR was for 5-6m not 5-6 feet service then it's a completely different issue. But 6' waves just aren't that big.
     
  6. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Here is the key to our discrepancies.
     
  7. romanewas
    Joined: Jan 2017
    Posts: 45
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Gdańsk

    romanewas Junior Member

    Here's the current state of the sea on the route between the islands.[​IMG]
     
  8. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Stumble, I want to tell you something even though as you're a big boat fan, you probably already know. When it is said that a boat will reach a speed of XXX knots, you will understand that it is in calm waters. Therefore, to achieve a velocity of 20 knots, with waves of 2 m, and with certain limits of the acceleration experienced by the passage, it is a SOR totally "uncommon and exceptional" and very difficult to guarantee for a designer.
     
  9. Stumble
    Joined: Oct 2008
    Posts: 1,913
    Likes: 73, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    Tansl,

    I had something long typed out then the website ate it... /sigh

    Anyway, I was thinking about this last night and I think what we have failed to discuss is not wave height, but wave period. 6' rollers 12 seconds apart are a substantially different issue than 6' waves at a 6 second interval. I routinely run my 24' fishing boat at 30kn in 6' rollers offshore, and can comfortably walk around without any issue, but those same 6' stacked waves in the lake at a 6 second interval will knock your teeth out at 10kn.

    So I went looking for wave data on the Cannaries to see what the data says.

    The mean wave height is 1.63m (5.34 feet) so smaller than we have been discussing. Of course the big question is what is the period at that height, and unfortunately that data is presented as a table, but as a scattershot graph. So it depends on how you read it, but as I look at it the period for a 2m swell (6.5') looks to be about 10-12 seconds.

    So you have moderate wave action, with long periods through most of the year. Which to me does not justify a SWATH vessel.

    On the other hand if the wave period was shorter, or the wave height was higher, then it could be a much bigger issue.


    So looking at the wave predictions posted above, only at the first day at 1pm would I have any concern about running a ferry. But frankly running almost anything in 12' waves on a 7 second period is getting dangerous. That's a lot of big steep waves coming by. Perhaps a large SWATH could do it but otherwise even a 100' vessel could be in trouble.


    More wave data here https://www.researchgate.net/profil...ment-of-wave-energy-in-the-Canary-Islands.pdf
     
  10. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Stumble,
    You have collected a meritorious collection of data. In order to arrive at more adequate results, it is worth noting that it is more interesting to take into account the wavelength (not the frequency), compared to the length of the boat.
    I am not going to do the dynamic study of that ship, among other things because I do not know how to do it. What I do know is that what Romanewas is asking for is totally out of the ordinary. Once accepted this, we will agree that it is a very complicated study that, at least I, I am not able to do (I do not know if you are able). And of course, I would be foolhardy if I told Romanewas that any catamaran is capable of getting what he wants.
    Let the experts talk and not the fans. The problem is very serious and bad advice can ruin a business.
     
  11. romanewas
    Joined: Jan 2017
    Posts: 45
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Gdańsk

    romanewas Junior Member

  12. romanewas
    Joined: Jan 2017
    Posts: 45
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Gdańsk

    romanewas Junior Member

    Maybe at the beginning I can buy used catamaran that will be able to operate only with a smaller waves (ie, up to 50-60% of the days in a year). However, allow me to start quickly and thoroughly examine the market and conditions for shipping. What do you think about this? I can buy at a very good price that ship eg:
    http://www.ships.pl/new/index.php/pl/pokaz/14/228/
    It is a ship for 50 people, however, do not have a valid class. The question is whether the shape of the hull will be suitable for waves of 1.5 meters? The next year, I would build a target ship type SWATH.
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,033, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    SWATH only suits a more or less constant loading, load the thing up and it will sink down with a massive increase in wetted area. ANd then not be a SWATH !
     
  14. romanewas
    Joined: Jan 2017
    Posts: 45
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Gdańsk

    romanewas Junior Member

    I'm not going to overload the ship.
     

  15. TANSL
    Joined: Sep 2011
    Posts: 6,946
    Likes: 542, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Let's talk about the data of a real ship:
    Overall Length .... 16,000 m
    Breadth ............... 6,400 m
    Displazement, no passengers ...... 35 tones

    The SWATH that could meet the OP criteria would also have:
    Passage (30 people) ............ 2.7 tons (8% of total weight)
    Tons per cm of immersion .... 0.14 t / cm

    Which means that the difference of draft between the ship with passage and the ship without passage (this is the only possible "overload") would be 20 cm. The height of the "legs" of the boat, since it has to sail with waves of 2 m, would be around 3 m. It does not therefore seem that "overloading" the ship is a problem.
    As can be understood, the above calculations are only an approximation to the problem. Any correction to my mistakes will be welcome.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.