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SWATH versus Monhull

May 10, 2010

An awesome comparison in high seas. Which ship would you rather sail on (the SWATH vessel is in the background)?

H/T to Think Defence.

17 Comments leave one →
  1. September 23, 2014 12:16 pm

    excellent points altogether, you just won a logo new reader.
    What would you recommend in regards to your post
    that you just made a few days ago? Any positive?

  2. Bill permalink
    May 11, 2010 2:32 pm

    This silly statement: “(I figure that I had to put that last comment in here since I am merely a guest here at the altar of street fighter that is maintained by this site).” shows only that you continue to completely miss the relevant points: Sea Fighter is built, its operating, it has certain usefull capbilities…. and it is under-utilized. IT is an existing asset that currently does little of nothing. It’s really that simple. If there were other vessels lying about that were similarly situated and capable, I’m sure that there would be proponents come out for using those to fill gaps too.

    But there are not any such others. About the closest ‘cousin’ I know of that languishes in similar fashion is ONR’s SLICE demonstrator..but the capabilities of that for any meaningnful OPV role are quite limited by comparison.

  3. Bill permalink
    May 11, 2010 2:27 pm

    The active stabilization on SWATHs does far more than deal with the divergent Munk-monent instability, although that is important, for sure. The active systems impart a high degree of roll and pitch stability at all speeds, making an otherwise tender and very sensitive platformm (highly sensitve to wind and weight distribution) very ‘stiff’ in effect. The active systems completely remove nearly all of the otherwise still-significant transient pitch, roll and heave motions that an untababilized SWATH will still exhibit.

  4. B.Smitty permalink
    May 11, 2010 9:21 am

    Cloud X hits 27kts.

  5. Anonymous permalink
    May 11, 2010 9:18 am

    Bill says… “On the speed in sea state question…there are plenty of 20+ knot SWATHS out there..SWATHs that will keep making 20 knots in conditions where much larger monohulls will have to slow down, alter course or seek shelter; possibly all three.”

    This needs to be clarified… there may be plenty of 20+ knot SWATHs out there… but they are BARELY 20+ knots. SWATHs have fantastic seakeeping capabilities that make them excellent candidates for certain missions, and active RCS will prevent them from bow diving near the Munk speed; which is around 20+ knots for most SWATHs in the lengths used for the pilot and windfarm support vessels being built, but like every other platform they have their advantages and disadvantages, and are not the holy grail, like street fighter. (I figure that I had to put that last comment in here since I am merely a guest here at the altar of street fighter that is maintained by this site).

  6. Distiller permalink
    May 11, 2010 5:42 am

    The monohull certainly looks cooler here :-)

    A more serious angle, and adding to what was said about survivability: Multihulls in ice are a no-no as far as I can tell. So as much as I love the multihull approach, its limitations are not to be forgotten.

  7. Mike Burleson permalink*
    May 11, 2010 4:36 am

    Scathsealgaire-War is a messy business!

  8. Scathsealgaire permalink
    May 10, 2010 9:26 pm

    I’ll take the monohull. I have always enjoyed the rollercoaster ride that is Beaufort 9+ seas (though this video seems to be about a 6-7). I especially enjoyed watching my shipmates puke their guts out while I held down the watch.

    So I’m sadistic about it. So what. You’ve got to have small pleasures at work.

  9. Bill permalink
    May 10, 2010 5:10 pm

    “Asymmetric flooding is a VERY REAL issue with SWATH designs”

    To be fair though, its is NOT a big issue with the designs that are favored in the last couple of all those built by SWATH Ocean Systems, for example. They developed a modified ‘V-cat’ upper hull shape and hence very short struts, to mitigate cross-deck slams in heavy seas and, equally importantly, to have a means of quickly picking up reserve bouyancy in the event of asymmetric flooding. Very few SWATH are built anywhere nowadays using the original Creed configuration (like ‘Kaimalino was), though they still pop up here and there.

    It’s certainly true you can’t get much down in to the struts and hulls. In fact, I’m getting old enough that I’m not sure how much longer I’ll be able to get ME down in them any more. Lost track of how many SWATHs I’ve commissioned..but regardless, the trip to the forward hull void to work on stabilizer hardwares was always challenging on every single one of them.

  10. Scott B. permalink
    May 10, 2010 4:57 pm

    leesea said : “I think you may be wrong about SWATH survivability?”

    Asymmetric flooding is a VERY REAL issue with SWATH designs.

    A somewhat related issue is the draft sensitivity to weight changes, which might require solid ballast (to preserve growth margins) and/or liquid ballast (to compensate for fuel being used).

    In addition, the SWATH configuration makes it hard to locate critical components (e.g. weapon magazines) below the waterline, which may not ideal for a warship from a survivability standpoint.

  11. Bill permalink
    May 10, 2010 3:30 pm

    ‘Semi-Swath’ means that the forebody (varying amounts of it depending on whose design) is small waterplane but the afterbody is not..or much less so anyway. Yes, the AMD hull (Type 022, therefore) is ‘sort of’ a semi-swath, but less so than Sea Fighter or the Stena HSS, for example. THE AMD is more like Austal’s hulls..and I see those referred to as ‘semi-SWATH’ types all the time. It’s not a hard and fast definition. In fact, its suitably vague enough to have brought out some pretty nasty lawsuits over the years.

    Sea Fighter, like that SWATH in that video, must be moving to gain the stabiility you see in that video. Both just wallow around in higher seas when operating below the speed at which the active stabilization becomes effective. For a true SWATH, however, the speed at which the stabilization becomes effective is typically very low; not so on Sea Fighter.

  12. Mike Burleson permalink*
    May 10, 2010 3:02 pm

    Lee wrote “if WT is lost in one hull the ship merely submerges to its hull waterline but does NOT sink.”

    That’s great! I’m sold. Also concerning SWATH speed, isn’t much of the complaint about LCS is you don’t need such high speeds for littoral work, especially if a helo is onboard? As DK Brown says, leave the high speed to the aircraft.

    The deep draft is a problem for littoral work. Semi-SWATH the way to go? Wonder how much of the stability is lost in the compromise. Bill, have you heard any complaints about the Sea Fighter stability?

    I wonder if the Type 022 might be semi-SWATH.They do 36 knots apparently.

  13. Bill permalink
    May 10, 2010 2:53 pm

    On the speed in sea state question…there are plenty of 20+ knot SWATHS out there..SWATHs that will keep making 20 knots in conditions where much larger monohulls will have to slow down, alter course or seek shelter; possibly all three.

    That active stabilization on a SWATH is impressive too, eh? It wouldn’t look near that good if it was not full stabilized.

    The ‘down side’ of having that kind of incredible sea keeping capability is that SWATHs can be (and have been) driven in to conditions so bad they find themselves ‘suddenly’ overmatched…the usual warnings (slams, green seas on deck, gross motions in general) that indicate limit conditions are near, are not present as they are for more conventional hull forms. Takes a keen eye for the sea and a good feel for the vessel to stay out of trouble.

  14. leesea permalink
    May 10, 2010 2:47 pm

    @TD I think you may be wrong about SWATH survivability? I have seen damaged stability studies which show that if WT is lost in one hull the ship merely submerges to its hull waterline but does NOT sink.

    I think that much higher installed HP is needed to propul a SWATH to HSV speeds?

    The two real problems I saw from my brief stint on T-AGOS 19 were these: SWATH are by definition deeper draft vessels, and they have a specific payload range so can not easily peform in a logistics ship role which demands large changes in payload.

    The SeaFighter is a semi-SWATH hull kind of a hybrid between catamaran and SWATH.

    As always I will defer to Bill the expert in HPMVs.

  15. May 10, 2010 2:07 pm

    Its horses for courses isn’t it

    If you want stability in a high sea state, in a compact design with a large work platform area then SWATH makes a lot of sense. If you want speed then there are other designs available.

    The design is slightly less survivable because a hit on one of the sponsons will badly affect stability and they are slightly more expensive but one would imagine cost savings are obtained in other areas.

    It is the stability that makes them attractive for pilot boats, mine warfare, offshore windwill tenders and similar applications. The Estonian Navy have recently ordered a few

    If you want to see a mothership concept that uses SWATH hulls have a look at the German pilots in the Bight, they use a pilot station ship and a number of smaller pilot transfer ships, all SWATH design

  16. MatR permalink
    May 10, 2010 1:27 pm

    If you look closely, you can see the SWATH is actually glued to the conning tower of a massive submarine. Nice try, Mr. Burleson…

  17. Anonymous permalink
    May 10, 2010 12:24 pm

    I’d want the monohull because…

    – It has higher speed and can get me to where I go faster / get me out of trouble faster.

    – Has its machinery in an accessible location for easier maintenance.

    But fundamentally, your question is defective… you need to restate it as “which would you rather have for [insert the particular operation/mission you have in mind here]”.

    If I was loitering for long periods of time I would want the SWATH. If I needed to insert SEALs I’d want the monohull.

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