Stern Extension to Help Rowing

Discussion in 'Boat Design' started by Russ Kaiser, Jul 15, 2014.

  1. Russ Kaiser
    Joined: Jul 2009
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    Location: Winston-Salem, NC

    Russ Kaiser Exuberant Amateur

    I am rowing on a regular basis a 14 foot jon boat - V front, flat bottom with a squared off stern.

    Here is a picture of the boat sticking out of my truck

    https://flic.kr/p/okrHsJ

    The truck and boat are both beauties, three more payments and they're all mine

    Would adding a short removable extension to the stern that tapered up the bottom and tapered in the sides help significantly with rowing effort? When I'm pulling hard, I can hear the water sucking around the back of the boat. I'm thinking about something I could attach at the transom with a couple of deep C-clamps - sort of a spoiler.

    I enjoy the exercise, but I'd like to be rewarded with a bit more speed for my work. I would consider this a temporary measure. I really want to build a dedicated pulling boat, but I have some other projects stacked up in front of it. I figure I could knock a spoiler out in an afternoon once I design it.

    Russ
     
  2. Skyak
    Joined: Jul 2012
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    Skyak Senior Member

    The short answer is that you are most likely dragging the transom and creating an eddy that adds to drag. Your boat is designed for planing with a motor not rowing in displacement. An extension COULD reduce drag by smoothing the transition to the waterline. I am not sure it will be worth the effort. I am wondering if you couldn't achieve the same reduction in drag by improving trim. If you put a video camera on the transom and row you will be able to quantify the eddy drag. Then move weight toward the bow and see if you can't get the transom out of the water. Move your seat or put a weight as far forward as you can.

    If you enjoy rowing and want to build for that purpose I think you would be better off building a pulling wherry. More work but great return.
     
  3. Russ Kaiser
    Joined: Jul 2009
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    Russ Kaiser Exuberant Amateur

    Like This...Maybe

    Thanks for the reply Skyak. I will eventually get a boat built but it could easily take a year before I could get started. Build space would be an issue for an involved project and I really have a lot on my plate right now with house modifications.


    Here is a quickie drawing of what I envisioned; something maybe between 12 to 24 inches in length that would slant the bottom of the boat up above the normal water line and bring the sides in.

    It would be made from 5 panels, open at the top, with the mating panel made to match the existing transom. It would be put together with stitch and glue construction with some very light framing.

    I'm just wondering if something like this would make a noticeable difference.



    [​IMG]spoiler by Russ Kaiser, on Flickr


    Russ
     
  4. Westfield 11
    Joined: Apr 2008
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    Westfield 11 Senior Member

    Why not get another similar boat and cut off the bow and pop rivet it to the stern of the one you have now. That way you would have a double ender. Heck, you could just bolt the two boats together at the transom although it would be a little long....... Maybe a beveled spacer block between the two to compensate for the transom angles.
     
  5. Russ Kaiser
    Joined: Jul 2009
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    Russ Kaiser Exuberant Amateur

    Two boats, that's a bit over the top, don't you think?

    Mating two boats would be insane. I carry my boat in the back of my truck, I don't want to make it any longer, hence making something I can clamp on, field-mountable so to speak.

    I don't want anything that increases the buoyancy of the stern to the extent that the existing middle seat ends up being in the wrong location from a trim standpoint. I'm a big guy and the boat is stern heavy now, so a little buoyancy would be fine.

    This gizmo wouldn't even have be made to the full height of the transom, 6 inches of height would probably do the job. Maybe I will glue some foam blocks to a piece of plywood that matches the transom, shape it and glass it.
     
  6. Skyak
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    Skyak Senior Member

    Russ,
    I am not sure what to tell you because I don't know if or how far your transom is below waterline. A smooth curve up to the surface from tangent to the bottom is all you can do. Nothing above the waterline matters. Tapering the sides does little. I think you might achieve the same result with a jug of water at the tip of the bow if it lifts the transom out of the water.
     
  7. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Skyak, I've been told that the stern at the chine is about 3 inches under the water when I'm in the boat. That means at the keel it's probably about 4.5 to 5 inches down.

    There is absolutely no rocker in this boat at all. I've had my son (90 lbs) on the tiny front seat which is about 2 feet from the stem while I'm rowing. It did make rowing a bit faster but not much. I have put my wife in that seat (we won't discuss what she weighs) and the boat became squirrelly. I figure the water line was about 5 feet long at that point. I don't think a counter-weight at the stem will improve my performance significantly.
     
  8. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Here is some data from one of my better outings - I have about 30 sessions on this same lake, so if it does make a difference, I should be able to tell. Of course you have wind and temperature differences to contend with. I can't wait until the fall so I'm not sweating like a pig while I'm out there.


    [​IMG]StravaData by Russ Kaiser, on Flickr
     
  9. Skyak
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    Skyak Senior Member

    Three to five inches is a big eddy. Your adding a rocker stern sounds like a good fix. The buoyancy aft is also an improvement so foam is good. You could leave a skeg in the center in line with the keel to counter any tracking problem from the shift in trim.
     
  10. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Round the bottom as it comes up, don't leave a sharp break as you showed.
    Anything will help.

    Later make you a Ruth from gentrycustomboats.com
    SOF will be light and cheaper than everything else, unless you set up a cheap canoe to row.

    But if you are looking for exercise, you are good to go :D
     
  11. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    More flat at the back than I thought

    The Ruth is a beautiful boat. Personally I think would like a bit more stability. That or I have to get much better at getting in and out of a boat. I was thinking of looking for something flat bottomed with a good bit of rocker and double ended. Also with sides with enough flair to get the oar lock at a nice width without outriggers. Or maybe I'll make a skinny boat with outriggers and outrigger floats.

    As for this proposed project...

    I just took a better look at the back of the boat and have a few observations. I'll go take a photo of it as soon as the rain lets up and post it. The hull is flatter across the back than I thought. The sharp "V" of the hull flattens as the bottom nears the stern and it's nearly straight across at the transom. So, I'm probably pulling 3 to 3.5 inches of sharp edge through the water.

    Maybe I'll get my son to take a photo from the jetty when I launch next to get the real story. It's hard to determine anything from inside the boat without moving around and moving changes the attitude of the boat.

    The back corners are rounded so that will add a little complexity to the solution - foam is looking better and better. Also, there's an external piece of plywood on the transom to protect the aluminum from mounting a motor. If I attach with clamps to the transom I'll have allow for that.

    Still, I think I'm going to do it. At most the project is going to cost me 30 dollars. I already have epoxy and cloth and plenty of plywood, I just need a sheet of foam and a couple of deep C-Clamps.
     
  12. upchurchmr
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    upchurchmr Senior Member

    [​IMG]
    If you are willing to try those options, consider this.

    You won't be able to take a passenger, they will have to row their own.
    You won't have any extra drag.

    This one goes in my truck bed also.
     
  13. Russ Kaiser
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    Location: Winston-Salem, NC

    Russ Kaiser Exuberant Amateur

    Good idea

    I've rolled this idea around too - you actually have one of these? This one looks like a sliding rig, right? I think my hulls would have to be a tad broader since I'm a tad broader than that spiffy guy in the straw hat. You can tell someone's serious about rowing if they have a straw hat ;)
     
  14. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Pictures of the "Bobr O'Riley" - I think I can get a few more colors on her, don't you? Made in 1973, I think she was painted ever other year since. Honestly, I took about 20 lbs. of paint off of this boat and I'm still working at it whenever I get the power washer out for anything else.


    [​IMG]Transom_outside by Russ Kaiser, on Flickr

    [​IMG]Iso_view by Russ Kaiser, on Flickr
     

  15. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Skyak's suggestion of placing weight right at the bow will make progress easier, unless it also makes the boat wander around. Plonk a full 25 litre water container right up there ahead of the front thwart. Empty it when finished for the day.
     
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