SWATH concept design - Feedback wanted

Discussion in 'Boat Design' started by whataboutyou, Aug 18, 2016.

  1. whataboutyou
    Joined: Aug 2016
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    whataboutyou Junior Member

    Basic concept for a SWATH hull based on the Nekton Pilot.

    I guess this would be the Beta for this design, but I'm looking to get some feedback before I move onto a final design.

    (more on S.W.A.T.H. http://www.solarnavigator.net/s_w_a_t_h.htm)

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. Rurudyne
    Joined: Mar 2014
    Posts: 1,138
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    SWATH: IIRC neither fast nor shallow draught but great sea keeping.

    As for your shown design I'm guessing in the 30+' range? To get enough bridge deck clearance you've obviously pushed up the accommodations quite a bit and I'm guessing maybe 10+' or so in beam, so not a small boat (just not huge).

    As I understand them, which isn't necessarily saying a lot, to work you probably need to keep the pontoons out of surface wave action so it looks like you've more allowance for the wave crests than for wave troughs. Are you intending some form of adjustable (water) ballast too?
     
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    The drawings of a swath..by that I mean, the pretty pictures you show, is the easy part. It is just a strut and a buoyant tube underneath. The real hard part is the actual design. And by that I mean, design! Thus you need to establish the weight of the vessel, very very carefully. A swath is extremely weight sensitive in the design condition....why...because a swath is a fixed draft vessel.

    Thus if the time to draw your pretty picture is say 2 hours, the 'design' part would be about 20-40 times those hours as a minimum.
     
  4. Rurudyne
    Joined: Mar 2014
    Posts: 1,138
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    I wonder what the vulnerability to loading means on a smaller vessel where any passengers are moving about? In a relatively big ship, and the one referenced at the link is maybe 100' long, a few folks shuffling port or starboard won't matter much. A small boat though?

    Maybe for a small boat that other kind that I seem to recall seeing pretty pictures of, one submersed hull but with widely spaced amas of more typical amas design, might be better? There would be some reserve buoyancy port/starboard for people shuffling about.
     
  5. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Define small?...it is all relative.

    Swaths are sensitive and depending upon the type of swath i.e. the actual value of the WPA v displacement ratio...it can be either tender or very sensitive indeed. On small swaths this is exacerbated because the weight of 1 person, as a %'age of the full load displacement is greater, thus = more movement.
     
  6. Rurudyne
    Joined: Mar 2014
    Posts: 1,138
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    Well, we're looking at a 40' LOA max SWATH here and I weigh 300# ... me walking to one side may be a big deal. Otherwise, two people walking to one side.;)

    Edit: silly person that I'm, I'm now thinking of the Monty Python skit about Free Masons and the building that will be okay so long as tenants are relatively sedentary and of light build. :)
     
  7. whataboutyou
    Joined: Aug 2016
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    whataboutyou Junior Member

    It's 35', the other boat in the picture was 40ft for reference. Sea keeping was the factor that drew me to SWATH... Speed isn't much of a concern, I was looking at what type of boat I'd want if I'd be on the ocean for a while.

    One thing that I did scale down was the pontoons / submarines from the original size, maybe that was a mistake? I went from 6'x4' to 2'x4', once I started costing out the foam, that I was thinking of using for the structure of the pontoon.

    The vessel is about 9ft between the legs right now, would changing that to say 12 ft, be a lot more stable for people moving around? I think you have to know the secret hand shake to really figure out engineering (going back to the stone mason monty python skit).

    Yes, ballasts would be in order for this design- and more trough allowance - I lost it while trying to make the design more compact.


    [​IMG]

    The different colors of foam show different strengths, based on foam from:
    http://www.uscomposites.com/foam.html
    Red/brown: 16lb density - tensile 450 psi, shear 230 psi
    Black: 8lb - 225, 130
    Grey: 4lb - 110, 70
    Yellow: 2lb - 30, 50


    I'm glad you like the picture. I've probably put those hours into this concept, or more. But hours don't mean anything this reply has taken me more than 2 hrs.


    Anyway, I don't want to derail the thread but since it factors into the design (or may) I'm also consider alternative energy design, for example having a wind turbine on top, running an air compressor, to power pneumatic turbine. The compressor would be between 20 - 30 ft up. Judging by the other turbine, the blades barely clear the cabin.




    [​IMG]

    http://windcompressor.com/html/compressors.html
    - an 18 ft wind turbine will give 10 hp, 16ft will give 5.

    Having ballasts and working with air compressors seemed to go together. The same company sells water pumps that will pump 17.5 GPM @ 75 PSI that run on air.

    And this company: http://quasiturbine.promci.qc.ca/EProductQT75SCPneumatic.htm
    Sells an interesting motor.
     
  8. Rurudyne
    Joined: Mar 2014
    Posts: 1,138
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    About the beam: based on what I've read motion comfort can be had with small motions that are quick or large motions that are slow but not with both quick and large.

    In a normal boat with reserve buoyancy set out far from the centerline, like a catamaran or trimaran, the movements tend to be quick which means it's not necessarily a good thing to have accommodations high up ... one of the reasons that trimarans tend to be more comfortable than a cat with accommodations above the bridge deck.

    With a SWATH the accommodations are quite high up, but there is no reserve buoyancy (or very little of it) in the legs so I cannot really guess if widening the stance will dramatically affect the quickness of motion.

    Someone here might be able to tell you, but I would still encourage you to investigate this with one or more models, using an accelerometer to test the quickness of motion. You may be able to profitably use a swimming pool, dropping recoverable heavy/bulky things to literally make waves, rather than deal with a lack of repeatability on some lake or bay.

    Likewise I cannot guess how sub-hulls longer than the accommodation hull might affect things when it comes to shifting weight fore/aft.

    As for keeping your balance: if you can pump water ballast left/right and front/back, maybe under Adruino control using sensors to detect level, you may have more success ... just at the expense of simplicity. You might also try air bladders in otherwise flooded chambers as that would remove a lot of plumbing.

    You may want to consider posting signs to not run around no matter what.

    One thing more: this is a smaller boat and isn't going to ride over large waves like a big SWATH might, so maybe you should consider having more reserve floatation along either side, lower on the legs, still above the largest waves you except to see, as this will prevent slamming and may also give you greater safety if a sub-hull should be damaged.
     
  9. sharpii2
    Joined: May 2004
    Posts: 1,860
    Likes: 86, Points: 48, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    I'm thinking your SWATH will weigh in at around 34 mt, about the displacement of a commercial fishing boat of 40 ft in Length. This is assuming the submerged cylinders are 4 ft in diameter and the hulls are 2 ft across and 30 ft long.

    Since both hulls and cylinders will only be 'pointed' at their ends, I assume a cP of around 0.8. I also assume the hulls will be one cylinder diameter deep. The PPI of each hull would be just under 250 lbs.

    So, if you and nine of your 300 lb pals all walked over to the Port rail, your SWATH would heel about 12 inches, or one foot to port.

    Assuming the bottom of the super structure is just one cylinder diameter above the DWL, the port side of your superstructure would still clear the water by 3 ft.

    Now if you and your nine friends all went to the extreme forward railing, that might be a problem. Your SWATH would then trim down by the bow by around 8 inches.
     
  10. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    You're going to need a lot more hours than that actually 'deisgning' it, judging by your comments:

    So a sensitive Swath with a high VCG turbine...:!:

    Since the swath has a low pitch stiffness, owing to its low WPA, with the thrust being so high up any disturbance will create a constant pitching moment.

    Less drawing pretty pictures, more 'designing' required :rolleyes:
     
  11. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Aaahhh....you mean you only want whippiee....jump up and down full of joy comments that support your pretty picture as being the best thing since sliced bread and what a jolly good idea.

    Oh silly me, I thought you were after some actual guidance to make you think and do some leg work rather than post pictures. My bad! :eek:

    POST SCRIPT
    I see the derogatory comments above in post #11 (not there) have been removed.....so those in my post above...will appear odd as the post by whataboutyou is no longer there!
     
  12. Rurudyne
    Joined: Mar 2014
    Posts: 1,138
    Likes: 33, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    One small point, as the cylinders are already entirely submerged wouldn't the PPI then relate to flotation introduced by submerging one leg deeper than the other (as it heels) rather than by the pontoon?

    The displacement potential in the legs is somewhat less than in the pontoons.

    This, of course, brings up the benefit of some sort of dynamic stabilization system.

    Unrelated to your post: I'm somewhat curious why SWATH designs seem to have their pontoons directly below them rather than spread out a bit, like Prince George being taught to stand heroically while speaking.

    Edit: okay, maybe not THAT spread out....
     
  13. Ad Hoc
    Joined: Oct 2008
    Posts: 5,943
    Likes: 319, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    What do you mean by ...spread out?
     
  14. sharpii2
    Joined: May 2004
    Posts: 1,860
    Likes: 86, Points: 48, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    I tried to distinguish between the 'Hulls" and the 'Cylinders'. The Hulls are attached to the top of the submerged Cylinders, and its their PPI I am quoting. The Hulls are assumed to be 30 ft long, 2 ft wide and about 8 ft tall.

    The submerged Cylinders are 4 ft in diameter and 40 ft long.

    These numbers were picked for work ability. The hulls have to be wide enough to provide passage for an average size man down to the Cylinders.

    The Cylinders are cylinders to minimize whetted area, without a great deal in complexity in design. Their 4 ft diameter is to provide a minimal space for an average man to work on machinery in them.

    I imagine a 100 hp diesel in each Cylinder, plus a ballast tank on each end.
     

  15. kerosene
    Joined: Jul 2006
    Posts: 1,024
    Likes: 58, Points: 48, Legacy Rep: 358
    Location: finland

    kerosene Senior Member

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.