SWATH concept design - Feedback wanted

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

  1. whataboutyou
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    whataboutyou Junior Member

    Thanks kerosene for the ship design spiral... I'd say I'm proportions and preliminary powering. :)

    I"m looking at around 5 - 15 hp, not 200... This was about as small as I thought a SWATH could go, and still be useful, without just being a submarine, or a boat - my concern with power isn't how fast it'll go, but just that it'll go.

    The low HP is factored into being able to be sustained at sea for extended periords, which is why I wanted the superior seakeeping of a SWATH.

    I'll post the dimensions of the hulls. I couldn't show the width of them but they are about 20" thick, 10' long for the front and 8' for the back and 8 tall.

    The cone front and back of the pontoons haven't been finished because I haven't settled on the 4x2 proportions yet.

    [​IMG]

    The legs, or hulls aren't required to have a person go into them, just compressed air tanks, and ballast tanks. But otherwise filled mostly with structural foam, like the pontoons.

    To compress the air, I'm looking at a combinations of steam (through a steam turbine), and wind turbine - and possibly a bit of electric power from solar panels, but the electric power, would more be for habitation, navigation, mostly non-mechanical things.

    The compressed air tubes will run down through the legs to the turbines which are mounted direct drive to the propellers which are at the end of the pontoons. The pnumatic motors would be accessed (in theory) by removing a compartment, bringing the compartment out of the water, and then accessing the motor.

    (Of which I haven't mocked up)
     
  2. FAST FRED
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    FAST FRED Senior Member

    "I"m looking at around 5 - 15 hp, not 200.."

    At low speeds surface area is the key resistance you need fuel and HP to pay for.

    No small boat is going to be comfortable in heavy seas , stopped or in slow motion.

    To go with little power, a conventional monohull is usually the ONLY choice.

    Hull shape can decide sea kindlyness , but usually not sea worthyness.
     
  3. Rurudyne
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    Rurudyne Senior Member

    Not a Blackadder fan?

    Anyway: a splayed stance where the legs at the base are somewhat wider athwartship than at the top. That way as the SWATH heels the leg of the pontoon being thrust down does not immediately assume an angle that looks, um, trippy.
     
  4. Rurudyne
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    Rurudyne Senior Member

    Round about reminds me of comments I've read made in favor of light boats that ride over the waves rather then plough through them.

    I would guess the basis for such comments, observations and experience of the commentators aside, is that a small boat riding over the waves at worst has the same duration of movements as the waves themselves no matter the size of the waves while a relatively heavily ballasted boat resists some sizes of waves some wave sizes in a less than ideal fashion.

    Of course, all things being relative, all hulls probably have some sizes or durations of waves that they just don't like...
     
  5. whataboutyou
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    whataboutyou Junior Member

    Maybe true, but I suppose I want to look into a bit more before I take this for granted.

    Using this (http://www.go-fast.com/boat_speed_predictions.htm) speed calculator, 15 hp will, let a **4000lb *heavy V-Bottom go 14 mph.
    *heavy v-bottom is the slowest design for the calculator.
    **4000lb is a figure i got from 100lb/ft = 3300lb + 700lb to round out the number

    I'm happy at 5 knots. So it seems feasible to me.

    Another note: 1HP = 550 foot-pounds, an 8 HP motor could lift the boat off the ground without leverage. I'm guessing double that HP can move it on a linear plane, where it's only subject to the friction of the water (which is much lower than gravity).

    And as for no boat being comfortable at rest, or low speeds. Submarines are quite comfortable at rest and low speeds, which is the advantage I'm looking for ;)
     
  6. Rurudyne
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    Rurudyne Senior Member

    You should look at having a bit more oomph or else you may end up hiding behind islands waiting for the tide to change.

    OTOH, around the great loop the current is often with you.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Like many aspects in design, one 'solution' creates another issue - thus all about compromise.

    Splayed out legs, for example, one issue is that the Capt will never know how close to the dock the vessel is when berthing, too much guess work. There are a few examples of swaths like this though......Bob!
     
  8. Rurudyne
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    Rurudyne Senior Member

    Wide angle truck mirrors?
     
  9. whataboutyou
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    whataboutyou Junior Member

    Haha. thanks for all your input in this thread man
     
  10. Barry
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    Barry Senior Member

    The best cross section to minimize the perimeter of a cross section 1 foot long and hence wetted area and maximize volume of a section 1 foot long, is a square, not a cylinder for a given cross sectional area
     
  11. whataboutyou
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    whataboutyou Junior Member

    New proportions

    Re-scaled the model, for stability, about as long, the legs aren't as high, it's wider and the original scale pontoons are used.

    [​IMG]

    [​IMG]

    [​IMG]
     
  12. makobuilders
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    makobuilders Member

    Mr. Whataboutyou, I investigated swath design extensively for something in the 12-15m range but ruled it out for various reasons. I have a practical suggestion, and I'm being serious here not a wise-guy, if you are really serious about building.

    Save the thousands of hours of design time that you would spend (if you have the training) and put those hours into overtime at your regular job. Then hire AdHoc to design your boat for you. He has a wonderful 15m design already built and perhaps could either sell you those plans or redesign a little bit smaller.

    Homebuilding an aluminum vessel of this complexity would be a major undertaking, but if you have the resources then you can assemble a team of certified welders/fitters/etc. and basically act as project manager. I don't know what Canadian labor rates are, but you might build overseas instead.

    If however you don't have deep pockets and want to save money then just go for a monohull in which sea kindliness trumps over accommodations.
     
  13. fredrosse
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    fredrosse USACE Steam

    Air Turbine???

    From Whataboutyou "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."

    That concept is not very efficient, if this would be considered, much better efficiency would result with other drive arrangements:

    Say the windmill puts out 100 units of mechanical energy (shaft power)

    With direct mechanical gearing, either toothed belt or mitre gear drive, efficiency could be on the order of 95%, output to propeller = 95

    However one would probably want some form of variable speed, and in the low horsepower mechanical world, these drives give on the order of 80% efficiency, so overall efficiency about 75%, output to propeller = 75

    Electric drive has a real advantage of the storage battery options, allowing short runs without wind power, and the variable speed option. Again, in the low horsepower world, these drives give on the order of 80% efficiency for the generator, then 80% efficiency for the motor, so overall efficiency about 65%, output to propeller = 65

    The wind turbine driving a compressor, then the compressed air driving an air turbine, provides abysmal overall efficiency. Again, in the low horsepower world, these drives give on the order of 50% efficiency for the compressor, then 30% efficiency for the air turbine, so overall efficiency about 15, output to propeller = 15

    Ordinary sails beat any of these schemes by a wide matgin.
     
  14. Nate57
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    Nate57 Junior Member

    I was watching the R/V Western Flyer (MBARIs 117 ft research SWATH) pull into their base here in Moss Landing CA the other day. They always seem to have a list. They were heeled about 5 deg to starboard as they came in (the sightseeing side) and within 5 min. of making a portside tie up were listing about 10 degs. to port. The small crew offloading?
     

  15. whataboutyou
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    whataboutyou Junior Member

    be cool to see anyway
     
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