Ramform vs SWATH for seakeeping?

Discussion in 'Stability' started by crasch, Jun 8, 2017.

  1. crasch
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    crasch Junior Member

    I don't personally know any houseboats that are 59 m LOA. The largest SWATH yacht that I know of is the Silver Cloud, which is about 41 m LOA.

    Yacht Silver Cloud SWATH Home http://www.yachtsilvercloud.com/

    Andrew Langton at Abeking and Rasmussen has designed one that is 60 m in length, but I don't know if it has been built.

    Are Swath platforms the ideal superyacht design? http://www.boatinternational.com/yachts/yacht-design/are-swath-platforms-the-ideal-superyacht-design--715

    I'm aware that there are tradeoffs between, among other things, cost and size. You seemed to be saying that a SWATH with a low draft could not be longer than 13-15 m without losing its seakeeping ability. So, I was trying to understand your reasoning.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Well, what is a SWATH?...as the acronym says, small waterplane area, so where is the buoyancy...yup..well below the waterline. The buoyancy needs to be far enough below the thin strut (that has the small waterplane area) so it is not influenced by the passing waves. Thus the result is...yup..a deeper draft than a conventional boat. So this limits the size of swath because of your max limit of just 1.20m (4'). A swath with that draft...is not big!! This also does not take into account that you will be running in shallow waters, and as such you most likely wont get over the Froude depth resistance hump, so the power requirements for such a swath will be approximately 20-25% higher than if running in deep water merely because you are in shallow water.

    Yes the A&R boat has been built. The worlds largest is the Radisson Diamond:
    Cruise Ships - Radisson Diamond http://www.cruise-ships.com/radisson-seven-seas-cruises/sold/radisson-diamond/
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Hmmmm...editing and adding bits to existing post is not easy in this new crappy format.

    So...here is a typical cat:
    A SWATH_Page_1.jpg

    With just half of the waterplane area, you need a deeper draft. A swath has roughly 1/4 of the WPA of an equivalent hull.

    So you end up with something roughly like so...:

    A SWATH_Page_2.jpg

    Hence a much deeper draft.

    So this limits the size of your Swath given a limited draft.
     
  4. TANSL
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    TANSL Senior Member

    It is possible that you could get enough buoyancy reserve in the submerged hulls to keep the entire structure afloat with a much lower draft than normal. You can not say or deny anything until you know the full weight of the ship at full load. In the latter case, a SWANTH type ship (SWA not tween hull) like that of Figure 1 would be the solution.
    The problem, among others, will be that, with waves of somewhat lesser height than the draft, the submerged hull may be out of water and resistance due to wave formation, or the pitching motion of the boat due to the waves will be similar to that of a Monohull boat See figure 2

    SWANTH.jpg
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    TANSL
    you clearly have no concept of understanding of swath hydrodynamics. It is not a 5min job - takes more than a one liner and child-like sketches.
    I'm not even going to attempt to try to explain to you why it is nonsense - as your reply will be yet more fantasy. I think you need to go to Disney land with Mr E..as that's all you're able to come up with - fantasy, yet bleat at those that do understand. To paraphrase - quit while you're behind!

    If you really wish to know and learn..read some books and research on SWATH hydrodynamics - then come back.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

  7. TANSL
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    TANSL Senior Member

    @Ad Hoc, LOL:) what a joker you are, how nice!
    With you neither I nor anyone else will learn anything about naval architecture but I have learned to forget what is not worth considering. Thank you.
     
    Last edited: Jun 16, 2017
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    If Ad Hoc enrols at Charm School, I will go to Disneyland ! ;)
     
  9. crasch
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    crasch Junior Member

    Thanks, Ad Hoc, I appreciate the time you took the time to explain your thinking.

    @TANSL, thanks for the design idea. As I'm interpreting it, instead of pontoons, you're proposing a relatively slender buoyancy chamber that extends across the full width of the hull, with a legs extending up to support a platform above the water. Is that correct?
     
  10. TANSL
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    TANSL Senior Member

    Yes, more or less I propose what you say but what I wanted to show you is that too small a draft is likely to make all the advantages of the swath ship disappear. That thing I propose, with waves, is as uncomfortable as a mono-hull.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    but wait...

    Oh dear, just nonsense then ...QED......about as helpful as a fart in a space suit! :rolleyes:o_O

    Why do you persist to post on subject matters you know nothing about....yet get all pugnacious when called out as such....
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    It is not my thinking, per se, it is basic swath hydrodynamics/naval architecture facts!
     
  13. TANSL
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    TANSL Senior Member

    @crasch, if you think I can help you with anything, do not hesitate to ask. My "ignorance" or my knowledge, are at your disposal. Only you can judge if my advice is useful, whatever my "swath hydrodynamics / naval architecture facts". Even if I do not use words to stun you, it may help.
    @Ad Hoc, thanks again for your clever humor, you're a joker.
     
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  14. Rurudyne
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    Rurudyne Senior Member

    This is really important.

    The pontoons, no matter the size of the boat, need to be deep enough to be themselves out of the swells at the surface while the accommodations need to be high enough not to be caught up in same. SWATHs are not ordinary catamarans or trimarans with immediately available reserve buoyancy to help avoid slamming.

    Moreover, I would say that a small SWATH sufficiently deep/tall to function as a SWATH may well be tippy unless you make its base wider than its top.
     
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  15. Rurudyne
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    Rurudyne Senior Member

    crasch, have you considered a good size sailing scow with a ballasted centerboard (correct term?)? In rough weather you can hoist weight from your mast(s) to help alter the period of motion vs the size of motion. Scows offer the best accommodations for length, have lots of capacity, aren't unattractive (they can actually be pretty if done right), and don't require sometimes hard to get, or so I'm told, dock space at the end of the dock (or a longer slip to get the width) as a ramform might.
     
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