Oars - curved blade vs. flat blade for performance rowing skiff

Discussion in 'Hydrodynamics and Aerodynamics' started by SailorDon, Jun 15, 2015.

  1. Jamie Kennedy
    Joined: Jun 2015
    Posts: 541
    Likes: 10, Points: 0, Legacy Rep: 117
    Location: Saint John New Brunswick

    Jamie Kennedy Senior Member

    Once you understand that graph it kind of makes more sense what the curved blades work better. It is a lot like the breast stroke how your hands can be pushing back even as they are striking forwards and outwards.
     
  2. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    You mean an oar that has a blade articulated to always remain at 90 degrees to the boat's centreline? Yup, it has been done. Rowed like crap.

    http://www.gacooarlocks.com/the-turbo-oar.pdf

     
  3. SailorDon
    Joined: Apr 2013
    Posts: 137
    Likes: 4, Points: 0, Legacy Rep: 34
    Location: Livingston, TX

    SailorDon Senior Member

    Perhaps I am oversimplifying based on the performance of rowboats, kayaks, and canoes that I have had the opportunity to row, paddle, etc. For instance, a one man racing scull goes about 3 times as fast as I can row. That is a lot less drag, and probably much more efficient on the oar blades.

    Consider tying the stern of a rowboat to a fixed dock and the Fig. 8 posted above becomes the following.

    [​IMG]

    My rowing experience lies somewhere between the two figures.

    I don't think I'm getting any lift on the oar blades in the forward direction of my rowing skiff relative to the surrounding water. If you enhance the design for rowing performance and sacrifice load carrying, stability, etc. and you row in the Olympic and collegiate performance category, I can see where the high drag simple analysis of force vectors on the oar blade does not apply.

    If you refer back to my original post, I am not interested in competitive rowing performance, but what I refer to as a "performance rowing skiff". I can cruise at 4.5 mph for a couple of hours non-stop, and I can max out at 6 mph for about 15 or 20 seconds.

    For my kind of rowing design, do curved oar blades improve rowing performance, or is it just an illusion? :)
     
  4. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Only way to find out is to test both types of oar with a heart rate monitor and a GPS under calm conditions.
     
  5. SailorDon
    Joined: Apr 2013
    Posts: 137
    Likes: 4, Points: 0, Legacy Rep: 34
    Location: Livingston, TX

    SailorDon Senior Member

    That was good reading on what works for oar designs.
    Surprising to see that the articulated oar blade design was a poor performer.
     
  6. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    Note of caution: although that bloke's oars obviously make him happy, I have my doubts about some of his theories on why they make him happy. Here's an excerpt from an email conversation I had with him.

     
  7. Jamie Kennedy
    Joined: Jun 2015
    Posts: 541
    Likes: 10, Points: 0, Legacy Rep: 117
    Location: Saint John New Brunswick

    Jamie Kennedy Senior Member

    When I row it also feels like I am tied to the dock. :)

    However, I think it still applies for any boat at any speed as long as the oar is sweeping from say 45 degrees around to 120 degrees or so. In the middle part of the stroke I got that wrong of course and the oar is moving with the water, but in the beginning of the stroke the oar is sort of swimming forward as the blade sweeps forwards but outwards and downwards, and at the end of the stroke it is squeezing the water backwards as it moves forwards but inwards and upwards.

    Here are the dories again...
    https://www.youtube.com/watch?v=_M-qpsIg-6c
     
  8. SailorDon
    Joined: Apr 2013
    Posts: 137
    Likes: 4, Points: 0, Legacy Rep: 34
    Location: Livingston, TX

    SailorDon Senior Member

    The reason I'm searching for an analytical solution to curved vs. flat oar blades is to eliminate the human performance factor.

    I don't have a heart rate monitor. There are too many other variables when I row on the lake that elevate my heart rate and blood pressure. Typically jet skis and 300 hp fishing boats that buzz me while I'm rowing for exercise.
    My heart rate is not a reliable measure of energy converted into rowing performance. :(

    I do keep a data log of all my rowing. That is how I know I have rowed over 2,000 miles. Here is a typical sample.
    [​IMG]

    But the data isn't consistent enough that I can determine which is flat oar vs. curved oar performance. The variation might only be 1/4 mph, maybe 1/2 mph. From a subjective point of view, I think the curved oars give me an additional 1/2 mph rowing speed for the same rowing effort. But that might just be because the curved oars look better. :)
     
  9. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    So if you can't really tell the difference and the curved ones make you feel better, use the curved ones. Easy. :)
     
  10. SailorDon
    Joined: Apr 2013
    Posts: 137
    Likes: 4, Points: 0, Legacy Rep: 34
    Location: Livingston, TX

    SailorDon Senior Member

    That's mostly what I have been doing for the last 1,700 miles.
    But I've always been curious about the hydrodynamics.
    Perhaps this is not the correct forum to post this question.:confused:
     
  11. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    I understand your curiosity. The subject interests me too, and I have looked into it. The problem is that all the research on this has been done for racing shells, since that is where the money is. Any conclusions for slower boats, with or without fixed seats, have to be made be extrapolation.
     
  12. SailorDon
    Joined: Apr 2013
    Posts: 137
    Likes: 4, Points: 0, Legacy Rep: 34
    Location: Livingston, TX

    SailorDon Senior Member

    Rowing seemed so simple.
    1. Oar in water.
    2. Stroke oar.
    3. Boat goes.

    After reading the replies to my inquiry, I find that I might be able to increase my rowing performance by stretching more for the catch since what appears to be an unfavorable angle of attack for the oar blade actually produces lift that moves the oar blade forward with respect to the surrounding water. I never would have expected that.

    A poor understanding of the hydrodynamics of oar blades may have cost me a few hundred rowing miles over the years due to not "stretching for the catch".
    It's good to know I have room for improvement with a better understanding of how the oar stroke propels the boat forward.

    Improved rowing performance is always good! :)
     
  13. upchurchmr
    Joined: Feb 2011
    Posts: 3,226
    Likes: 218, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Have you tried hatchet blades?

    I like them much better than the macons I also have.

    They seem to be most common today for racing.

    Perhaps a more modern blade (newer design) has some virtues.

    But I don't have 2000 miles of experience.
     
  14. NoEyeDeer
    Joined: Jun 2010
    Posts: 983
    Likes: 32, Points: 28, Legacy Rep: 300
    Location: Australia

    NoEyeDeer Senior Member

    I have played around with a long catch and it does feel surprisingly good. One possible (additional) reason is that the increased angle means the blade tends to drop in cleanly with less tendency to backwater. It feels easier to match the blade speed to the water at the catch.

    However, I've found that the increased lean required to do this doesn't feel as good. It's sort of like trying to pick a load up from the ground while keeping your legs straight, if that makes sense.

    Because of this, what I'm currently planning is to build a sliding seat that only has a short slide (around 12"). This will allow the right oar angles (about 70 degree catch and 45 release) with oars that can run at reasonable gearing on the standard rowlocks (on the gunwale, of course) and without such an inefficient body position at the catch. In other words, I should get better performance without having to hack the boat itself since all I need is another drop-in seat, and I won't require outriggers or very long oars or extreme overlaps on the handles.

    The short slide would not only be better for ageing knees than a full slide but will also rowing in normal street clothes. It will also cause less pitching. Downside is less power than a full slide, but OTOH more than a fixed seat. At the moment I'm thinking it could be a good compromise.
     

  15. Rurudyne
    Joined: Mar 2014
    Posts: 1,170
    Likes: 40, Points: 48, Legacy Rep: 155
    Location: North Texas

    Rurudyne Senior Member

    Seemingly small paddle with a feathering mechanism that looks draggy if dipped into the water.

    Now that I think about it this probably would work ... or at least work better than that thing.

    A hollow composite shaft with a mechanical pivot point at the oarlock for the mechanism. The handle and paddle are hinged and are connected by thin rods within the shaft arranged that the active one is kept in tension (you don't want to expose a long thin rods to compression). The goal should not be 100% feathering to stay perpendicular at all times but simply reducing the apparent angle through the whole range, though of course still being perpendicular near or at midstroke. The reason for this last would not just simply be to reduce complexity and weight but I could see it as possibly necessary to maintain comfortable grip (a grip always perpendicular to the centerline seems like it wouldn't be fun).
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.