British Coastal Micro Cruiser

Discussion in 'Boat Design' started by stumando, Apr 14, 2008.

  1. rwatson
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    rwatson Senior Member

    Or you could use the civilised measures :)

    My poor math worked out :-
    say a beam of 1.5 metres X 2.7 metres long, by say .3 metre draught X .52 = .63 cubic metres
    1 cubic metre = 1000 litres, and as 1 litre of water = 1 kilo, thats 1000 x .63 = 630 kilos displacement.

    If you allow 200 kilos of you, gear and supplies,
    maybe 200 kilos of boat, to get the draught of .3 metres,
    you would need 200 kilos of ballast.

    Lead is 13 kilos per litre, so say around 15 litres of lead is needed to get this weight of 630 kilos. (say a block of lead 1.5 metres long, 0.5 wide, 0.2 metre deep)

    This could be 15 blocks of 1 Kilo, which would be the most portable type of ballast, which will give you some idea of how much stuff you would need to move around.

    Obviously I am just guessing most of these figures, but this is the method that Alan was describing.

    The Selway Fisher "Pocket 10" uses 175 kilos of ballast for a draft of .7 metres, with a dry weight of 500 kilos - this would be a useful indication.

    Now, you need to work out your stability curves, scantlings (size of material to survive at sea), centre of efforts for sails and hull, and the centre of gravity of the boat...........

    Its a wonderfull exercise. Have fun
     
    Last edited: Apr 16, 2008
  2. messabout
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    messabout Senior Member

    One might be able to find a boat such as the West Wight Potter in England. In the US, maybe a Peep Hen. That would solve the math problems without even trying. The Potter is a capable little boat, has some spartan accomodation, and a proven track record. Best plan is to shop for one of those and be done with the fantasy of designing a boat without benefit of, at least some, design knowledge and experience.

    Take RWatsons curmudgeonly remarks as gospel and abandon the design project. That course of action will ultimately be less expensive and probably more satisfying in the end.
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    Sound but so dull... And if everyone though like that we would be discussing is it better to carv a log canoe with limestone ax with 3' or 3'4'' hickory handle:p
     
  4. stumando
    Joined: Apr 2008
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    Location: south east England

    stumando infant member

    sinking BRITISH COASTAL MICRO CRUISER 585.5 kg w/d

    As the sinking feeling fills my senses, I am thrown into a burning pit of maths and poked with paddles of spite until my dreams are no more than the blackened and torn sails of a sinking vessel once loved, but now forgotten. . .
    But on the bright side
    I am really pleased I put my plans through this forum, although my bubble was burst from a considerable height, I am glad. I can't wait to finish my next set of plans! I have begun already, I am getting excited again, like I did when Talisan first formed in my mind. I hope you Mr Watson sir, and Alan white still visit these pages in a fortnight or so, as I have found you both very interesting and knowledgeable. I will be submitting Talisan II plans, then..
    I know it will take longer than 2 weeks to just learn how to work out my stability curves, scantlings (size of material to survive at sea), centre of efforts for sails and hull, and the centre of gravity of the boat........... But all your words and thoughts on my first design have brought on visions of my next design project, and I found myself reaching for the graph paper. I have some great plans for a 12 foot dinghy that I printed out last year. So all I will have to do, is Design the cabin and rig, which I think will give me much pleasure, and at the same time, provide me with a boat that is safe and still unique, like Talisan I will be studying my stability curves, scantlings etc. during this process, but as you said R, I would be safer in a professional design. For now.


    Thanks once again. stuart


    [​IMG]
     
  5. alan white
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    alan white Senior Member

    I think you did the right thing asking questions, and if you continue to ask questions, you will design and build the boat. It will still be yours from concept to sailing away. I think you sound smart enough to do the designing.
    It's only a small boat.

    Alan
     
  6. rwatson
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    rwatson Senior Member

    Stumando
    You sir, are one of very few who actually read, consider and act on outside advice, without becoming despondant and giving up!

    I cant recall many other occasions I have seen this happen, especially in accepting external advice.

    God knows I wish I could have had that kind of attitude when I designed and built *my* project many years ago - would have saved me a lot of pain!

    Oh - and to calculate the centre of effort of a boat hull, cut a silhouette of the hull out of heavy cardboard, and balance it on a knife. Where it balances - thats the centre of effort for the hull, and the mast is usually a little in front of that line. beats a computer every time. :)
     
    Last edited: Apr 17, 2008
  7. tom28571
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    tom28571 Senior Member

    Yep,

    You are into the most interesting part of the boating thing. By all means continue your quest. I also question your original projection as reasonable or even safe. Look at this as a fairly long path that will not be done in weeks or months. If it only took that long to design a good boat, we would be deluged with design talent. Instead, good designs take a lot of time (read years) to unfold even from an otherwise knowledgeable and talented amateurs board.

    My main question is: why 8':confused: What point does that prove? It's been done many times before and is still a pretty lousy way to find pleasure in cruising. To put a reasonable amount of creature room, stores and gear in 8' makes for a slow little chunk, no mater how superb the design. The nearest thing that looks reasonable to me for your general inclination is Matt Leyden's Paradox or Little Cruiser designs. Brilliant designs in their own way while still more restricted or uncomfortable than most would consider reasonable.

    Read, study, look around, sail some, have fun and see what happens to your dream design in a year or so.
     

  8. alan white
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    alan white Senior Member

    ...And the "lead" of the center of sail effort can vary, but on most boats try 15% or so with the mast straight up and allow for tilting the mast in order to refine the balance. The rudder shape and size can also be played with, and even the bowsprit if you think ahead. A lot of latitude in those few factors. Even body placement, especially on a small boat, will dip the bow or stern, and cause the CLR to shift fore or aft as areas of lateral resistance grow or diminish, so ones position fore or aft can actually steer the boat with the rudder tied off. This is because balance lies between a boats proclivity to either head up into the wind or pay off (so most sailboats are slightly imbalanced to favor heading up into the wind in order to avoid being slammed by the wind on the beam when the sail's hauled close in. While this causes the tiller to have to be pulled up a bit to the windward side in compensation, the slightly turned rudder can actually provide some lift to windward, assisting the keel).
    I would use leeboards on any tiny sailboat. They can be played with a lot and the CLR shifted easily, even under way. Better performance with no loss of interior space.

    Alan
     
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