designing a fast rowboat

Discussion in 'Boat Design' started by nordvindcrew, Oct 13, 2006.

  1. lazeyjack

    lazeyjack Guest

    here is my dory, I made two, as a school excercise for the class,
    I found that when rowing the beam severely restricts the pull of the oars, makes your forearms ache because the pivot point is too close, they all need outrigged rowlocks, like a proper race boat
    This 12 footer goes 100 miles with each stroke, I kid you not:)) and is best with a load, my two sons 60kg each an me 90, it is stable
    The lines were by Francis F Kinney in 1946, whio updated Skenes book yacht design and who was a SS draftsman in the 40,s
    I have offsets
     

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  2. melong
    Joined: Aug 2007
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    melong Junior Member

    Yeah I know that design. Nice tender but too short for racing.
     
  3. lazeyjack

    lazeyjack Guest

    it is a hopeless tender! it would swamp getting to an achored yacht
     
  4. melong
    Joined: Aug 2007
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    melong Junior Member

    Really? Looks ok. Kinney seemed to like it. Haven't rowed one myself.
     
  5. DonGreerps
    Joined: Aug 2007
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    DonGreerps New Member

    Peter Gallo of Adirondack Rowing tried hard to sell me an Adirondack Guideboat, claiming it was speedy, etc. I instead bought a wherry from him, and on our particulare lake it handles rough water well, and has proven to be surprisingly fast and efficient. It appears that a hull shape fast on one body of water may not be as (comparitively) fast on another.
     
  6. melong
    Joined: Aug 2007
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    melong Junior Member

    Yep, it's going to depend on the load and the wave patterns. For instance that 18 footer I built only had 9 1/2" minimum freeboard and 15 at the stem. Maximum beam was 32" and BWL just under 23". The boat itself weighed about 120 lbs and was completely open. I'm about 155 lbs.
    It was perfectly fine with just me onboard in all sorts of weather, including 30 knot winds against a 5 knot ebb tide, as long as you knew what you were doing. However it could have done with more rocker in steep short waves and was useless in rough water if loaded with a passenger.
    Rowed like a dream though.:)
     
  7. melong
    Joined: Aug 2007
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    melong Junior Member

    Norvindcrew, I found that Herreshoff boat. The name is "Athelas" and yes, it is a lovely design.
    http://www.sageboats.com/stock/athelas.html
    Too small for two hefty blokes in rough water though. However, if you scaled it up 25% you would have a boat 21'6" LOA and 20'5" LWL. Beam would be 4'8'', which is spot on for 8'4" oars with no overlap on the pull stroke.
    That's handy in rough water if you need to make a sudden correction, or if you just need to pull harder on one side to keep the boat on course.
    Scaling the boat up 25% doubles the displacement (actually x 1.95, but who's counting) which would be right for your load. Freeboard and reserve bouyancy should be ok, although you may need to deck the ends. Ballistic nylon is tough and light.
    I haven't worked out the prismatic for "Athelas" but if that 3hr 15min winning time for the Blackburn was not tide assisted that's an average speed of 6.46 knots. On a 20'5" waterline the speed/length ratio is 1.43, which ideally requires a prismatic of about 0.64 with the LCB around 53.5% aft of the stem.

    Regarding oars, are you using carbon fibre ones? If not, you're wasting a lot of energy over 21 miles. Those things are damned light compared to timber oars and look fine once painted.

    Cheers.
     
  8. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    oars

    we're using aluminun shatf oars, carbon fiber or graphite are out of our price range at the moment. Our new boat will go in for a test dunk in a couple of weeks. It's 20' 3" loa maxbeam is 4' 2" hull only weighs about 85 pounds. I don't know what the numbers are on tat boat that won the Blackburn in my class, but it was designed and built by eye and with two good men at the oars it goes like hell.
     
  9. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    update

    here's where we are on the boat as of yesterday battens to define the shape, botton panel in place and sheer and garboard panels fitted and ready to install in kind of stitch and tape fashion DSC00378.JPG

    DSC00374.JPG

    DSC00379.JPG
     
  10. melong
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    melong Junior Member

    Looks ok. Should go well.
     
  11. nordvindcrew
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    nordvindcrew Senior Member

    0arlocks

    there seems to be a general opinion that off set oarlocks are superior to standard oarlocks. Any thoughts? Also, Leo says that an enormous amount of efficeincy can be lost in the oarlocks themselves. Any comments. We're up to 96% of the speed/time of the only boat that consistantly beats us. Small gains are important at this stage.
     
  12. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    name

    while I'm at it, I know there are some Norweigans out there. We need a good Norse name for our new boat and are open to ideas. thanks
     
  13. melong
    Joined: Aug 2007
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    melong Junior Member

    Sculls and such use the offset rowlocks mainly for pitch control. Standard rowlocks get sloppy as soon as they start wearing, which stuffs up oar pitch. Fixed post rowlocks are supported over their full height so don't suffer from this problem.
    The offset is obviously necessary when you have a full height pivot post.

    The rowlocks that work like normal ones but just have the jaws offset have no efficiency advantage that I'm aware of. It's like the difference between open horns and full circle types.
     
  14. terhohalme
    Joined: Jun 2003
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    terhohalme BEng Boat Technology

    Attached Files:

    Last edited: Aug 15, 2007

  15. melong
    Joined: Aug 2007
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    melong Junior Member

    Nice looking boat, Terhohalme. Care to post some leading dimensions or are they top secret?:D
    I had a look at the English link's small boat rules and I can see the reason for the large beam at the chine (the one metre minimum restriction) but they also say the bow and stern must be raking, while yours appear to be plumb. Have they changed the rules or are you in a different class?

    Btw, you guys are messing with my head here. I'd just about decided to build a kayak and now I'm thinking about a damned rowboat again.
     
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