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Thread: Oar Dimensions

  1. #1
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    I've done a search on the topic and have located the equation used to calculate oar length given a boat's beam. For the boat that I intend to build (beam = 5' 10") the oar lenth comes out to be 11'. I've found designs for oars up to 9' 6" but nothing for 11'. Can an I just increase the diameter of the oar an amount proportional to the increase of the length over the original design(11/9.5)? Or does anyone know of some designs for 11' oars? Thanks.

    W.L.

  2. #2
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    Is this a boat designed for rowing? With that width, you'll have to be sitting up fairly high in order to reach the water unless there is very little freeboard.

  3. #3
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    Sounds like you could use some sweeps. rowable classics may have some old sweep oars that you could modify.
    garland

    [This message has been edited by garland reese (edited 09-10-2001).]

  4. #4
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    Willy, that's a pretty long oar. Can you tell us more about the boat? There was a thread on the Misc. Forum about oar length only about a month or so ago -- did you find that one?

    I think I quoted the Shaw & Tenney formula there, but here it is again anyway.

    The formula that Shaw & Tenney use is based on the "span" of the boat, namely, the distance athwartships between the rowlocks. (This has only some relation to the beam as the rowlocks are not always at the beamiest point.) Divide the span in half to determine the distance fron the centerline of the boat to the rowlock. Because you are measuring parallel to the water, add, say, 2" to that number to give you the inboard length of the oar. In other words, the first measurement is the base of a triangle, and the second is the hypotenuse, which is what you want. The most efficient ratio for rowing is said to be 18 to 7 (7 parts inboard and 18 parts outboard), so the inboard length measured above should be 7/25 of the total oar length. Calculate the full length from there.

    This works for almost all reasonably efficient pulling boats, but boats with a less fine entry, generally use an oar about 6" to 12" shorter. I think myself you could probably be about a foot shorter and be quite safe. If my maths are right, this will in fact be about 9'-6" anyway.

    And should your boat be equipped with two rowing positions, do the calculation for the beamier one.

  5. #5
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    The boat is Iain Oughtred's Fulmar which is a 17' lapstrake sailing dinghy. The oars are just to get me back to the dock in case the wind dies. I don't need anything fancy just something that's functional. If I'm taking the wrong tack here then somebody set me on the right course and tell me what I really need. Thanks again.

  6. #6
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    I asked the question a month or so ago for a larger boat, got some good advice from Mike and others. Does Iain not suggest a suitable length of oar for the Fulmar with the plans?

    Shuggie.

  7. #7
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    Nevermind... I really don't care about this anymore.

  8. #8
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    Too boring? You're fitting a motor? What?

  9. #9
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    Gee, thanks a million, Willy.

    Since I'd already prepared this, I'm going to post it anyway. But please don't expect me to contribute anything further.

    -----------------------

    Well, this is not a particularly heavy boat, Willy. You're not going to need the large sweeps that you might if this were a pocket cruiser. I really think you can throw your formula away here, make the oars 9'-6", and call it quits.

    With those quarters, I think this boat is going to provide a reasonably tiring row anyway. Longer oars, while perhaps developing a little more power, are also going to be heavier in use, and I think that what you might gain on the swings you'll probably lose on the roundabouts.

    Aileen Louisa is 15' long with a 5' beam. Her oars are only 8"-4" long and they're perfectly satisfactory. (She has the true pulling boat's narrow quarters, though, which cuts down the drag quite a bit.)

    Perhaps a four-horse Seagull is indicated?

  10. #10
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    Sorry... let me clarify. Given the events of the past 24 hours my resolve is elsewhere. Right now I'm looking for a flag pole to mount in my front yard so that I may fly the American flag as high and as proudly as I can. Worrying about oar dimensions on a boat that won't be complete for another couple years seems petty and trivial to me in comparison. I also need to go and give blood. Thank you for your responses and I apologize for my lack of enthusiasm at the moment. God Bless America and may His wrath rain down mercilessly on those responsible.

    W.L.

  11. #11
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    Fair enough. I think we probably all echo those sentiments.

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