Design Idea

Discussion in 'Boat Design' started by Mik the stick, Dec 9, 2012.

  1. Mik the stick
    Joined: Dec 2012
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    Mik the stick Senior Member

    I have been trying to learn a bit about boat design. I thought

    1. A new design should be better than the boat it is intended to replace.
    2. You must start some where.
    3. Pick a boat that does what you want and make it better.
    4. I want a boat which can go anywhere in the world except the frozen bits.
    Here is my idea REMEMBER IM NOT A NAVAL ARCHITECT.

    The British produced the harbour defense motor launch in WW2. These small boats operated in every theater of war and they did not always arrive as deck cargo. It had a reputation for being very seakindly. 77ft x 16ft x 4.75ft, and 54.3 tons with 8 crew. 260hp-320hp gave 11 to 12 knots. fuel tanks 1650 imp gall. If it was built in aluminium or steel it could turn out lighter with more internal space. It would lose perhaps 2 tons for guns and ammo.

    Starting with the boat from the deck down it could be fitted out in luxury. The above deck supper structure could be lengthened and have a little extra height without compromising its already excellent sea keeping qualities. The opportunity should be taken at this point to make the superstructure a bit more attractive than it was.
     
  2. El_Guero

    El_Guero Previous Member

    The opportunity should be taken at this point to make the superstructure a bit more attractive than it was.

    That might be an understatement.

    You might also want to make it handle waves better. Unless you never plan on being in moderate seas.

    And take off the deck guns .... unless you are going after really big fish.

    :)

    Other than that, I like your idea.

    Wayne

    But, wouldn't a Fairmile A motor launch handle better?
     
  3. tunnels

    tunnels Previous Member

    Photos ???:?:
     
  4. Mik the stick
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    Mik the stick Senior Member

    Thank you for your replies gentlemen.
    The deck IS the gun deck my estimate of 2 tons for guns and ammo should really have been more like 4 tons.
    I will do some scans later today.
    The Fairmile B is my favorite wooden warship, but it would not be better because:-
    At 68 tons and 112ft it would cost a much bigger bag of money.
    Two 630hp engines give it 21 knots, one engine of about 480hp would be required for 15knots.

    I was aiming at a boat of the size of Molokai 65, which I think is one of the best looking boats around.

    PARTICULARS

    Loa 65’ 0”
    Lwl 56’ 7”
    B 19’ 0” hull
    19’ 8” rubrails D 6’ 0”
    Displ. 181,636 lbs. at Dwl
    165,000 lbs. mid-cruise
    Block Coefficient 0.421
    Prismatic Coefficient 0.602 Lbs./inch immersion 4,226 lbs/in
    Displ./Length ratio 406.6 mid-cruise displ.
    A/B area ratio 2.040
    Installed power Caterpillar 3406C, B rating, 440 HP @ 2100 RPM
    Speed 9.0 knots, cruise
    8.0 knots long voyage cruise
    10.2 knots, max.
    Speed/length ratio 1.2 cruise
    Range 3,500+ miles
    Fuel capacity 4,800 gal
    Water capacity 500 gal
     
  5. FAST FRED
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    FAST FRED Senior Member

    The old boats were sea kindly and easy to push because they were skinny.

    Speed is expensive , but less so on a light skinney boat.

    Its been done,

    DashewOffshore.com - the serious cruising sailor's website
     
  6. gonzo
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    gonzo Senior Member

    They also roll to the point that they are not acceptable as pleasure boats. Maybe some kind of active motion control can change that, but it will add a huge amount of stress to the hull and change the dynamics of it.
     
  7. TANSL
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    TANSL Senior Member

    No doubt that will change the dynamics of the hull. For some reason it is called active control of the movement. What I doubt is that "will add a huge amount of stress to the hull". It is sure would be strengthened shell plates and internal structure around the unit, but nothing else. It all depends on how much is "a huge".
     
  8. Mik the stick
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    Mik the stick Senior Member

    Pictures as promised.
    My books don't agree, dimensions should be 72ft x 15ft x 4.6 to 5.5ft
    Motion comfort ratio is about 60 to 71 for 46 to 54tons not bad I thought.
    Capsize Risk Factor goes from 1.28 to 1.21.
    I thought with 4 tons of the deck some weight added due to below deck comforts the center of gravity would be lowered significantly. With modern fuel efficient diesels a tankage of 2600 imp galls would get across the Atlantic at about 9 knots.
     

    Attached Files:

  9. Tad
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    Tad Boat Designer

    Big round-bottom semi-displacement boats are nothing new, here's one built in 1949 and still perfectly maintained. This boat, called Cassiar, was replaced with an 82' version designed by Walter McInnis and now called Black Knight. There are two other 84' yacht versions by McInnis, Lions Whelp and Yorel. There were also several built for Canadian Government service as Fisheries patrol vessels.

    Cassiar.jpg

    0aaaas6.jpg

    Fisheriespatrolboat.jpg
     
  10. gonzo
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    gonzo Senior Member

    Taking weight off the deck will make the motion faster and more uncomfortable. An active stabilizer counteracts the rolling motion. That means that instead of the vessel giving and rolling off the waves, it will remain motionless and absorb the energy. That is a huge stress on a structure.
     
  11. goodwilltoall
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    goodwilltoall Senior Member

    Greetings,

    Look at some of the old Motorboat magazine issues from about 1907. Ailsa Craig is one with 6-1 beam and it has long roll fins at each side. It needed these as a result of it deep hull shape. It raced with 60 hp to bermuda and the runner up Idaho was same length and beam with 25 hp.

    Long, lean boats are better seagoers they just need flatter hulls to deal with rolling.
     
  12. Mik the stick
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    Mik the stick Senior Member

    I honestly did not know that Tad roberts was designing boats like Passagemaker lite. On studying the drawings I thought they are very cleverly designed but not very pretty. When I looked again I thought these boats are different, they have a beauty which is quite unique. Passagemaker lite is my favourite. As an interested beginner I am playing around with stuff he has perfected.

    My design idea is for fun. The HDML was designed by W J (bill) Holt and was his favourite design. I used to think the HDML was a bit of an ugly duckling, my perception has changed a bit. From allied Coastal Forces by Conway press.

    "In a seaway the HDML seemed to posses an unusual harmony of weight, form, bouyancy and hull shape in relation to pitching and speed, which enabled them to move in rhythm with the sea and to make the very best of conditions."

    I think the above statement likely applies to passagemaker lite it is also why I picked the HDML as a design starting point.
     
  13. Mik the stick
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    Mik the stick Senior Member

    I still think my original idea is not so bad. So far the only firm decisions are steel for the hull and decks. I bought Sorrensen's buyers guide which is very very informative. I now know Grp is a better boat building material than I thought. As a boat must displace the weight of every thing in it, my design weighs 2780 lbs so far that is all the stuff you need to live aboard. Cold moulded wood for upper work seems ideal, perhaps it could make a better hull than grp for a small boat.
     
  14. peter radclyffe
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    peter radclyffe Senior Member

    have you seen woodpecker of poole
     

  15. Petros
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    Petros Senior Member

    Many ideas about what makes a good hull has changed in the last century, it seems foolish to spend so much money building a boat around an obsolete design. I suggest you make a list of what you want in a motor yacht and see if there is not already one designed in the last few years, or have a NA design it around your goals using modern materials and construction methods, as well as what modern buyers would find attractive.
     
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