shoal draft oars sketch

Discussion in 'Boat Design' started by river runner, Aug 10, 2011.

  1. river runner
    Joined: Jul 2011
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    river runner baker

    I finally found the sketch I scanned of my shoal draft oar design. It is pretty rough, but you should get the drift. The blade area is the same on both sides of the shaft. There are two advantages to this design. You can get the whole blade in the water in a water depth of only the width of the blade, which is around 6 inches or so, and second, getting the blade in and out of the water only takes an up and down motion the width of the blade, conserving energy. In the Olympics, the sculls use a much fatter carbon fiber blade that is also at an angle to the shaft, like mine.

    Attached Files:

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  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I see a lot of oars(and paddles) that don't have blade area centerlined with shaft.

    <li class="rg_li" style="width:155px;height:139px;padding:0 18px 0 17px">[​IMG]I used a paddle like this last week on a raft in Class I and II waters. But I wouldn't have noticed flutter because it was mostly a few max effort hard strokes and then pausing, but these paddles are used for regular canoe paddling.

    <li class="rg_li" data-row="1" style="width:258px;height:77px;padding:8px 0 8px 0">[​IMG]<li class="rg_li" style="width:258px;height:93px">[​IMG]<li class="rg_li" style="width: 216px; height: 93px; padding: 0pt 21px;">[​IMG]

    Most of the Hatchet style oars seem to have 60+ % of the area under the shaft. I've only used that type a couple times, but don't remember any flutter, even pulling hard with fairly light grip. Maybe the squared-off face of the oar collar at the fulcrum of the squared off oar lock prevents flutter.

    I do remember getting flutter with a double ended alum and plastic kayak paddle that had a 3-4" 'bite' broken off on one side of one blade.
  3. wayne nicol
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    wayne nicol Senior Member

    hi squidly
    one of the reasons for the cross sectional dihedral , is that it splits the water and allows the water to shed evenly, as apposed to a cupped blade that will hold some water then shed erratically- hence the flutter- i am sure you realise this, but i am curious as to how the cleaver style oars shed the water evenly, is there a different face profile above and below the centerline.
    but that cleaver is still not achieving what runner is trying to do- ie use a shallow water oar.
    the offset canoe /raft blades- i am geussing are offset to allow efficient , vertical power strokes- whilst limiting the need to lean out so far from the craft.
    the other canoe paddles that are interresting, are the C1 race paddles that have a forward bend at the haft, which allows for a more powerful stroke as the paddle passes the body- keeping the blade vertical in the water for a longer time. eliminating the extremely inefficient portion of a stroke where towards the end of an unfeathered stroke, most of the energy is "pulling" the craft down into the water, and not propelling it forward

    runner ,one drawback to these assymetric spooned designs, is that you need to carry two spares. unless of course the blades are going to have the same profile on the face and the back , to facilitate interchangeability.
  4. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    River Runner,

    I measures my hatchet style blades. The depth of blade is 8 inches.

    My suggestion is that you forget about 2 inches less making any difference in wasted energy. In my limited experience you lift the blade much more than that to insure you don't smack a wave on the return. 2 inches at the blade is 0.66 inches at the handles - you would have to be a surgeon to notice the difference in motion.

    Again in my limited experience, the hatchet is easier to hookup at the beginning of the stroke and much easier to extract from the end of the stroke than the wooden spoon blades I also own and actually have to use since my wife has claimed the hachets.

    Don't waste your time, just go buy the hachets. You will be very happy.

    One thing you will notice is that the hachets are so much more efficient at the beginning of the stroke you won't need to worry about the end of the stroke, of course the oars are not vertical like a C-1 so I don't understand the point there.

    Wayne Nicol, do you actually carry a spare? We don't do long cruises so the question has never come up. Not much of an issue for me.

  5. upchurchmr
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    upchurchmr Senior Member

    I just read the whole discussion in the previous thread. For the Hachets I own, the difference in area above and below the shaft line makes no difference (the area is unbalanced). You cannot tell that there is any torque on the shaft- no twisting in your hand. It seems like the torque is so low that it is unnoticable.
  6. river runner
    Joined: Jul 2011
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    river runner baker

    shoal draft oars, unable to post reply

    I have been trying to post a reply to my shoal draft oars sketch thread for several days without success. Possibly because I am the last person on the planet that still has dial-up. So I'm seeing if I can post a new thread to reply to old thread.
    Most of you are missing the point of my oars completely, which is to get more blade area in the water when it is shallow, such as while drift fishing. It is not for racing. I only mentioned the "hatchet" style blades to point out that my design wouldn't reduce performance in deeper water. As for bent shaft canoe paddles, my oars are not bent shaft and serve a totally differnt purpose. Maybe a simple way to picture my oars is to visualize an oar with a large rectangular blade with the shaft right down the middle. Now cut off two opposing corners. What is left is my design.
  7. wayne nicol
    Joined: Dec 2009
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    wayne nicol Senior Member

    in hear exactly what you are saying RR.
    and do think your idea will work well.
    i made reference to the C1 paddle- purely in response to the picture posted above.
    i do realise that niether of them are really related to each other in purpose or application.

  8. Ipikata
    Joined: Sep 2011
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    Location: Australia

    Ipikata New Member

    Hi all,

    I live in the world of 'Olympic' Rowing boats and oars...

    The cleaver oars we now use since around 1990 are obviously one of the most critical parts of equipment. With regards to blade surface area above and below the shaft, it really depends on the the hull and whether it is a 'one oar per-person' sweep oar or a skulling oar. There are many variables as you can imagine but the 3 that are probable of interest to this thread are:

    1. The Angle of the shaft is determined by the handle height within the boat. This depends on the size of the individual.

    2. as for surface area above and below, a longer oar shaft will usually see less of an angle relative to the water line.

    3. The flexibility of the oar shaft is extremely important as ( it was touched upon in a previous post)the, majority of the individual's power applied to the the blade is before the oar shaft itself becomes perpendicular to the run of the boat. Therefore there is wasted force in pushing water 'away ' from the run of the boat. So in utilising a more flexible oar shaft ( and also remembering the boat is at its slowest speed at the catch) the oarsman can effectively transfer energy by bending a composite oar shaft which returns from its state of deformation when the blade running more along the same axis of the boat ( remembering it is quite a large arc the shaft covers).

    One more!

    The shape of the blades are such that when around 35 - 45% of the total force is excerted a low pressure system in the water is created at the the back of the blade ( relative to the high pressure system the face of the blade has created). And there is a, I guess you could call it a 'stalling point' refered to as slippage but after this the blade actually moves forward as well.

    I hope this makes some clarity. English is a very mixed up language!

    Kind Regards

  9. thudpucker
    Joined: Jul 2007
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    thudpucker Senior Member

    I like your idea River Runner. I've been fishing without a motor for the last four years on a small lake. My oars are getting to the 'badly used' situation now and I've considered making new ones.
    Your idea came along just in time.
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