Hull shape design advice for 11.5m, 8kts, Fn=0.4

Discussion in 'Boat Design' started by ram68ocean, Jul 12, 2021.

  1. ram68ocean
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    ram68ocean Junior Member

    Well spotted! 100%, it's actually out of Delftship which is more basic. I would rather use Maxsurf.
     
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  2. ram68ocean
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    ram68ocean Junior Member

    Regulation for unmanned vessels is still quite a new territory. There's a lot of work to do in that area and a lot going on from what I have heard.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    A trimaran with detachable amas may well have merit, it might just give you the ultimate stability you need and still be able to fit in the 40 feet container. You could have the amas adjust in height according to the loading of the boat, as the fuel runs down, they go down. Little doubt a 2.2m beam unballasted monohull is going to turn turtle eventually on the "raging main"
     
  4. bajansailor
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    bajansailor Marine Surveyor

    It sounds like you are asking for a lot here!
    So the vessel will carry about 5 tonnes of fuel - I presume diesel?
    What happens if the diesel engine needs some attention out in the ocean, like changing a blocked filter?
    You mention that it is 'controlled remotely from the distance' - but how far away will the operator(s) be? Literally hundreds of miles, and the controls are via satellite communications?
    Are you planning on being able to drive it across the Atlantic (re range) in similar fashion to the Mayflower 400 project?
    They have a recent update on their website - they started off, but are back at their base now, after experiencing mechanical problems.
    Mayflower Autonomous Ship https://mas400.com/
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The 8 knots is the killer. 3-4 and you might be a chance.
     
  6. ram68ocean
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    ram68ocean Junior Member

    Yes, diesel. Will be electric propulsion. But let's assume the generators burning diesel are of continuous rating, if one fails the other one takes over.
    The remote control part doesn't matter much for the design of the boat. Could be via satellites using VSAT. And a local operating fast response system to avoid collisions.
    Atlantic crossing would be good.
     
  7. bajansailor
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    bajansailor Marine Surveyor

    And if the second generator fails, perhaps because you got the dreaded diesel bug in the system and clogged up the filters, what happens then?
    It sounds like you have a lot of heavy redundancy built in to this boat.
    It might then be worthwhile having something like a 'Mini Skysail' to get the boat back home, or at least back to land somewhere (?)
    Home | SkySails Group https://skysails-group.com/
     
  8. ram68ocean
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    ram68ocean Junior Member

    It's just a matter of having larger tanks, isn't it? And it will sink more. I estimated draft change of 250mm, almost one foot in difference between departure and arrival condition.
    Also, It seems it could end up consuming something in the range of 14-16 litres of diesel per hour at 8 knots. Does it sounds right?
     
  9. ram68ocean
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    ram68ocean Junior Member

    Redundancy, good point. Will be key. Having separate tanks and extra generators and some batteries. Personally I think that at some stage is better to have a second boat, and operate together. If one breaks the other will tow it as emergency rescue.
    I like the sky sail idea, thanks. Need to find out how the auto launching and recovery works.
    The boat is getting longer...
     
  10. bajansailor
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    bajansailor Marine Surveyor

    This might be optimistic - especially in the fully loaded condition, which you estimate is about 10" more draft than the 'lightship' condition.
    That works out to about 2 mpg at best - so you need at least 2,000 gallons of fuel for 4,000 miles range, plus a bit extra.
    Say 8,000 litres - and with a specific gravity of about 0.85 for diesel, that is 7 tonnes of fuel that you need to have tankage for.
    You don't want it all in one tank, so you need to have cross-over valves, and facility to transfer fuel between tanks if required in order to maintain optimum trim - and all of this will have to be done by remote control from maybe 2,000 miles away.
    It sounds very complicated.
     
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  11. Alik
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    Alik Senior Member

    We designed USV back in 2013... Not easy task with fuel qty, speed, dimensions - a lot of paramateric study to be done, and clear SOR needed.
    We did 9 and 11m options before the end user could finalize the length to 16m!
     
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  12. Mr Efficiency
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    Mr Efficiency Senior Member

    This reminds me of how Hitler might have specified a bomber to get to America and back, then has to be told it was a tough specification. Maybe this works if the boat goes out and doesn't come home, just sends all the survey results and scuttles itself, no fuel left
     
  13. ram68ocean
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    ram68ocean Junior Member

    Looking good. But these look like fast boats doing 25 knots or more, with planing v-hulls. If it was designed to do 10 knots max the hull will look different, more like a power sailor semi-displacement.
     
  14. ram68ocean
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    ram68ocean Junior Member

    Thanks for your insights. I got a bit lost with those units, but I think I got to the same number at the end, a minimum of 8000 litres = 1760 gallons (which will be all used in operation) + 10% reserve + 10% non-pumpable.
    16 l/h x 500 hours = 8000 litres.
    Then, 16 litres/hours gives me 2.87 mpg (I assume is the land mile not the nautical mile).
    I guess the consumption will drop towards the end of the trip as fuel is consumed and it has less displacement.
    Was thinking of two tanks (P&S) on the same longitudinal but if there's an aft and forward tanks then yes it's probably more tricky to tell the gensets from which tank to pump the fuel. It's doable.
     

  15. container
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    container Junior Member

    Not quite a containerable 40 footer but this 49ft game fishing boat is expected to have a 4000nm range at 8-9kts on 4000l of diesel. Power is a single 750hp shaft drive spinning a large variable pitch prop
     

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