A 39' "downeast" influenced design - Feedback Request

Discussion in 'Boat Design' started by dobsong, Sep 9, 2009.

  1. dobsong
    Joined: May 2009
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    dobsong Junior Member

    I'm part the way through getting a boat designed and was thinking I sould get some feedback from others before we finalise the design and begin construction (this is scheduled to begin early next year).... So here goes! Any comments, criticisms or suggestions for improvement welcomed.

    She is for open water coastal cruising in Bass Strait, around Tasmania and up the eastern coastof Australia. Most of the time I will use her single handed or with a friend (or maybe two), maybe once every month or two there will be 6-8 guests on board for day cruising.

    Dimensions are 11.9 metres LOA, 11.7 metres DWL, Beam is 3.3 metres and draft is 1.1 metres. Displacement is anticipated to be 6,100Kgs fueled and loaded for cruising. She has a rounded "ducktail" stern

    She will be powered by a 315hp Yanmar and will carry 700 litres of fuel. We are expecting a cruise of 14-15 knots and a top of 19-20 knots. She is to be built using Celery Top Pine (a wonderfully tough timber from Tasmania) in an expoxy composite.

    These are the profile and layout drawings.
     

    Attached Files:

  2. messabout
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    messabout Senior Member

    The profile view shows a very handsome boat. That view also suggests that it will operate in mainly displacement mode which further suggests that the quoted speeds are vastly overstated. Surely you will not need all that power if it is, in fact, a displacement boat.
     
  3. apex1

    apex1 Guest

    Uhhh?

    http://www.balta.fr/lovstar.html

    the most beautiful of her kind as far as I know.
    but what do I know............................................

    Regards
    Richard
     
  4. dobsong
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    dobsong Junior Member

    Displacement? No a semi-displacement

    Boats of a similar size and hull shape easily do the speed I have been advised. e.g. http://www.pbmy.com.au/range38_intro.html

    So I am surprised at your comment. What do you base this on?
     
  5. dobsong
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    dobsong Junior Member

    Yes a lovely looking boat..........
     
  6. dobsong
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    dobsong Junior Member

    Displacement?? (2)

    She has a very fine entry and then flattens out considerably as you go aft - you could call her a semi-planning design.
     
  7. waikikin
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    waikikin Senior Member

    Dobsong, the profile looks nice, I would have assumed the same as Messabout when you track the rabbet line & imagine the buttock lines rising similar, the example Apex has linked is sweet & I admire his taste in that with much more cockpit space with the conventional transom. Are the speed figures as calculated by David? "cos he's known as a pretty cluey guy. All the best with it from Jeff.
     
  8. apex1

    apex1 Guest

    Well as her sister of Patric Balta but tha latter with less than half of the power to the same performance!

    I could do such a boat btw. at about 300.000$ in wood Epoxy
    Finest wood, and prime equipment, and (using now 800 tonnes of Ep resin a year) not the least quality in every aspect.
    This was not a business offer, or a advertisement, just to talk about........
     
  9. dobsong
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    dobsong Junior Member

    Quote

    Is that 300,000 US or Aus - has to be delivered to Melbourne, Australia
     
  10. dobsong
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    dobsong Junior Member

    Speed Estimates

    Yes calculated by David
     
  11. tom28571
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    tom28571 Senior Member

    Well yes, if you apply Crouch's speed formula to the given specs, the top speed comes to a bit over 18 knots. Crouch's is pretty good for a full planing hull, which this is not. The aft hull shows the typical highly warped form of Maine lobsterboats with a fairly flat, if highly twisted, aft run. I am also doubtful of the speed prediction. One caution of the speed prediction is the very steep keel rise aft. If it did get to the predicted speed, I would expect the bow to be way high by over 10 degrees and forward view to be almost non existent. The power to make this speed is another issue.

    Skeptical arguments here are based on scant information and should not be taken as gospel but should cause a deeper study of this boat's potential.

    Beautiful boat, by the way.
     
  12. apex1

    apex1 Guest

    US ex works Turkey.

    Richard
     
  13. dobsong
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    dobsong Junior Member

    Speed and bow rise

    Thanks for your comments Tom - the potential for excessive "squatting" is a concern that we will have to work through
     
  14. messabout
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    messabout Senior Member

    My remarks about speed and power were predicated on the appearance of the afterplane of the boat. To plane or not to plane is closely dependant on the angle of the quarter beam buttock in the run. An angle of four degrees is just about all the rise that might allow planeing performance. The normal planeing hull will have zero degrees of rise and some even have negative rise which coaxes the boat to run on an even keel. The choice of negative angle, or not, is somewhat dependent on weight distribution and sometimes decided on the basis of expected sea conditions ang entry shape. Your drawing shows a rise of considerably more than the optimum. In displacement mode you might expect something on the order of 8 or 9 knots. Probably less except when you are content to pull half the ocean behind you. Be that as it may, it is still mighty handsome.
     

  15. dobsong
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    dobsong Junior Member

    Lines

    My brief to the designer is to optimise for 14 knots - attached is a scanned document of the lines does this make things clearer?
     

    Attached Files:

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