Power Cruiser for Florida/Bahamas

Discussion in 'Boat Design' started by Starhop, Nov 23, 2017.

  1. Starhop
    Joined: Nov 2017
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    Location: United States of America

    Starhop Junior Member

    Okay here we go:

    SOR for M/Y Starhop
    ------------------------
    Must be at least 30 feet
    Must have a range of at least 700 nautical miles
    Must be capable of safely crossing the gulf stream between the Florida coast and Bimini in the Bahamas
    Must be able to support 4 people for at least 5 days without reprovisioning
    Must be stable at sea
    Must draw no more than 5 feet
    Must be capable of carrying, towing, or otherwise transporting an at least 8 foot tender
    Must have a head with a shower (Wet or dry)
    Must be able to be built by a team of 10 people in less than a year
    Should be build for function rather than looks
    Should be a full displacement hull
    Must run at at least 6 knots

    I am not overly concerned with speed or efficiency. My primary goal is to create a exceedingly stable, safe, medium range cruiser of a modest length.

    -------------------------
    I took the liberty of sketching out some *very* *very* rough conceptual plans. These are by no means final, and I'm sure there are a billion things that will make the veterans on here want to face palm xD

    -------------------------
    Rough Sketch for M/Y Starhop

    Length: 32' 4"
    Beam: 11'
    Draft: 5'
    Height from keel (with "masts" down): 16'
    Height from waterline (with "masts" down): 11'

    There may be some inconsistency between decks that I missed. The design changed a lot as I was sketching.

    Main deck and side view:
    [​IMG]

    Below deck:
    [​IMG]

    Any thoughts?

    Once concern I had was free board. I aimed for 4 feet. Is this good enough?

    You will probably have to zoom out some to see both images. Sorry about that.
     
    Last edited: Nov 23, 2017
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Masts meaning radio aerials ? Your range of 700nm is getting "out there", why do you need that much ? A displacement cat would suit most of your specifications, you could get much better speed, but the range specified could be a problem.
     
  3. Starhop
    Joined: Nov 2017
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    Starhop Junior Member

    Yes, radio aerials, radar mounting, and signal flag hoist. My concern with a displacement cat would be the increased beam, but I will certainly consider it. The range was just in case I ever felt confident enough to cross to Bermuda, so its not really a huge requirement. I'll be happy to safely cross to the Bahamas and cruise around there. What speed increase could I expect with a power cat?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    You will certainly cruise a lot more quickly than 6 knots, 15 knots is quite feasible with good economy, provided careful attention is paid to keeping weight down.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I'd tend to agree in as much as a pure displacement mode design limits options, compaired to a semi displacement. With the latter, which is fairly common, you can cruise at twice the speed, permitting outrunning storms, etc., but also throttle back when necessary to shoot inlets or just to save fuel. On cruisers, I've found it's best to have speed options, rather then be stuck in low gear all the time. This is because most tend to try to hit schedules, which are possible with displacement craft, assuming your weather holds. With a semi displacement, you still can hit schedules, but you have the option to punch through a nasty head sea if necessary, without time restraints or if you need to seek shelter from a cell moving though.

    Weight and beam/length ratio will be the biggest considerations you'll need to address in the design, given your SOR. The big, fat boat you've sketched up isn't going to be particularly economical to operate, even at low speeds. Boats of this general size are in the 6 - 10 ton range, which require a fair bit of power to propel. Narrower designs will be much more fuel efficient, even if you have to get creative about elbow room.

    In a nut shell a simple flat bottom boat can offer all that you want and make the build much simpler, though the ride can be uncomfortable at times. If you introduce some deadrise and a more appropriate set of shapes, for sea keeping and comfort, draft goes up, as does the power you need to propel it and her displacement does too. Basically what I'm saying is, you need to find a set of plans for an inboard displacement or semi displacement craft of the length you want. You're not going to easily find the answer to the many design conflicts that will (not if) come up. The arrangement of berths, tankage, etc. can be adjust to suit your requirements without a lot of trouble, assuming you don't stray too far out in the weight distribution arena.

    Consider the Jolly Roger from Glen-L, just to provide an idea of what you can play with. It does what you want, using very little power and likely can be stretched to 33' if you find this absolutely necessary.
    [​IMG]
    [​IMG]
    [​IMG]
    You can change the accommodations as desired, though this is a pretty typical setup.

    Additionally, there are many other designs to choose from and the math is already done for you, such as the TW 28 available from Bateau.com:
    [​IMG]
    [​IMG]
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Woods Skoota 32 is also certainly something to consider. A different boat for sure and untested on the range. Richard suggests it can get 6mpg optimal and I am putting 128 gallons fuel in it. But to be fair, you would need to run optimally all the time for your range minimums. The TW28 would definitely get you further and while the build would be aggressive; if you have a crew of 10, should be doable. I have not seen the Jolly Roger being built by anyone, but people are building the TW28. One was finished in Turkey about a year ago and others are under construction.
     
  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Looking through my papers I have found a hull that may have something of what you are looking for. The general arrangement has little to do with your SOR but the hull shapes could help you, at least, to start playing with them. The ship has 10 LOA, semi-displacement, GRP, and had crystals in the bottom to contemplate the seabed. It is a ship that has been in service for about 5 years on the shores of the Andalusian Mediterranean.
     

    Attached Files:

  8. Starhop
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    Starhop Junior Member

    Do you guys think the best plan of action would be to work from plans at this time? Versus a self design, that is.
     
  9. fallguy
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    fallguy Senior Member


    Sorry, crystals in the bottom to contemplate the seabed? Can you explain better and perhaps a bit on the how? I am not sure I understand.
     
  10. TANSL
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    TANSL Senior Member

    Yes, you are right. In the attached drawings, scantlings, you can check the arrangement of the crystals (polycarbonate, actually). They are in Spanish but I hope you can understand them.
    In the tourist boats the underwater vision has become very fashionable.
    It is a complicated and very interesting topic. Among other things, the designer must demonstrate that, if one of the windows is broken and the compartment is flooded, the ship has enough buoyancy not to sink.
     

    Attached Files:

  11. TANSL
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    TANSL Senior Member

    In general, the designer starts his design based on another similar one. You, who is not yet a designer, should use some previous design.
     
  12. TANSL
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    TANSL Senior Member

    "mirador" = window
    The "mirador" can be incorporated at any time but, first, they must be placed in a completely flat part of the hull and, in addition, they must be protected with various structural measures, additional reinforcements and additional thickness in the area to be cut.
    I can translate for you the detail you need from the scantlings.
     
  13. fallguy
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    fallguy Senior Member

    I changed my mind; the only place I could do it is a small open area of floor and the only places practical are swimmable.

    Apologies to op
     
  14. Starhop
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    Starhop Junior Member

    No need to apologize :)
     

  15. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    I think the biggest challenge would be finishing it in time, a 10 man crew frequently turns into only you working 18 hours a day and way behind schedule.

    Unless part of the challenge is building it yourself, finding an existing hull to finish or rebuild may be quicker.
     
    fallguy likes this.
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