Stern Extension to Help Rowing

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

  1. upchurchmr
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    upchurchmr Senior Member

    I'm not going to tell my spiffy wife you said that.
    She insists on getting covered up to the max.

    Actually I have another for my also "broader" ***.
    This one is 11'x5' with a 6" wide hulls. Its good for about 135#.

    If you really wanted one it would be better to stretch out the length.
    16'x5' with a 6" wide hull would support about 230#.

    A shorter 11'x7' with a 12" wide hulls works for holding me up, but at 5' wide it generated so much wave interference that it was much slower so I widened it.

    It is a sliding rigger, necessary because the ends are so fine that a sliding seat would cause the ends to dive like a submarine.
    With the sliding rigger it stays on an almost perfectly level keel, has no wake, and is easy to accelerate.
    As built it has only 4" freeboard, but the hulls are sealed so waves going over dont matter. Too big and they would hit you in the behind.
    There are a few commercial equivilents, but they require trailers and are 100+# while this is 50# and I think it weighs too much.

    Your boat looks just like what you described, I think the "swim step" extension would make a difference.

    Most people will be uncomfortable perched on the little scull seat. It took a little while to get use to it.

    I do think the wheel mount (aluminum box section) is really ugly and would like to change it.

    Here is a link to a short video of my son in law doing his first 3 strokes ever (don't be too critical of him) https://picasaweb.google.com/114094506422911345287/October92013#5932899349225743634
     
  2. Outlaw45
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    Outlaw45 Senior Member

    Russ, you have a pram in the garage, why don't you row it?
    Outlaw
     
  3. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    My sincerest apologies to your lovely wife, upchurchmr - I thought the shirt was a bit much for a man. In my defense I was looking at the boat :p
     
  4. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Outlaw - the prams were built for the kids, about 33 inches wide and a little less than 8 feet long. Not good for rowing.

    Russ
     
  5. upchurchmr
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    upchurchmr Senior Member

    Russ,

    No issue, its all fun. And I comment on her choice of "coverup".
     
  6. Manfred.pech
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    Manfred.pech Senior Member

    HI Russ, I think it might be helpful to glue a wedge of Styrodur under the stern to lift it and to reduce the whorls/eddies. Two or three inch seem to be enough.
     
  7. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Upchruchmr - what do your cat hull profiles look like, do they have a simple rectangular profile or something wedge shaped. Are there build threads on here for them?

    Manfred.pech - I'm not sure exactly what you're suggesting, could you elaborate?
     
  8. Manfred.pech
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    Manfred.pech Senior Member

  9. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Manfred - that's interesting information but it would be hard to apply to my little boat. For one thing, I slide my boat into my truck stern first so the existing keel strip gets quite a scraping.

    An extension I can clamp to the transom after the stern of the boat is already hanging over the jetty wall makes the most sense for my situation.
     
  10. upchurchmr
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    upchurchmr Senior Member

    Russ,

    The shape of the boat below the waterline is circular sections across the hull.
    The initial shape length wise was also a circular arc, going thru the bow and stern at the waterline, and 3 inches down in the middle of the boat.
    Having no bow or stern in the water made the boat impossible for me to keep it going straight. So I dropped the bow and stern about 1 1/2 inches and faired from the bow to the circular section toward the middle (about 1.5 feet).
    Now is is easy to hold a course, and not too hard to turn.

    This is actually a very easy hull to build, shape wise.
    The cross section shape above the waterline is rectangular. 4" freeboard, and whatever the width of the deck is wide.
    The deck profile looking down is the same arc of a circle as I used for the waterline and the keel line

    If you would like I can make a cartoon to illustrate.
    [​IMG]
    The boat hangs on the fence for storage, here is a picture showing the deck shape from above.
     
  11. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Great cat rowing design

    upchurchmr - thanks for the photo - those hulls on your cat rower are ultra skinny. I think I would submarine that size but I really like your general design. I don't mind building something strictly for rowing since little boats seam to be multiplying around my house with regularity.

    I would be interested in hearing about the wave interference you talked about on the beefier design before you spread the floats apart. Is that a common issue with closely spaced cat hulls?


    On your sliding rig, what is the material of the outrigger beam? Also, what is the material of the rails?

    As for my project, I hope to knock it out, or at least start it this weekend. I will add photos and feedback to this thread.
     
  12. upchurchmr
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    upchurchmr Senior Member

    Russ,

    The same width of the hulls will support you if you extend the hull from 11' to 16', but it won't fit in the bed of the truck. You will have to do something over the cab, but the boat will not be heavy, it's relatively easy to carry and push around.

    Wave inteference in a catamaran is a well understood problem. Most have enough separation and narrow enough hulls to not be really recognizable. When I had 5' width with 1' hulls that only gave 3'separation. When I was pulling hard (for me) I could see 5-7 wave peaks in the water running right down the center. The peaks were actually tall enough to hit the rear crossbeam at the right speed.

    With the 5'beam and 6" hull width, or 4' separation the wave inteference is essentially not recognizable.
    Wave interference represents energy you have to put in the water to make the peak. It will slow you down noticeably.

    That is why for guys like you and I, I suggest longer, but not wider individual hulls. If you are going to carry the boat over the cab, you can always make it wider than 5', but that just adds weight if you don't need the width.

    The outrigger carrying the oarlocks is just a tapered 3/4" ash board. Plenty stiff, but could easily be lightened up with a little cleaverness.
    The rails the foot/outrigger carriage rides on is just 1" aluminum tubing, probably 0.080 thick.
    The most irritating thing on the whole boat is finding wheels to work with the aluminum tubing (I had to hand make mine).
    If and when you might be closer to deciding your next build, I can take more/ better pictures and provide some sketches. There is no such thing as drawings at this time.
    Probably lots of good suggestions for improvements also.
     
  13. Tallman
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    Tallman Junior Member

    I agree that rounding the bottom transition to the upsweep will help. Your ideal option would be to go with a clamp-on version of the front, in foam.

    But that would be long and unwieldy, so a blunter version of the bow, perhaps an 18" projection aft, more if you have room, bringing the bottom into that narrow bow vee as much as possible, curving in the sides, will help. More of a parabola (looking down from above) than a box at the butt end. Something in the direction of a foreshortened Adirondack Guideboat end. The added narrow waterline may also bump speed a tad.
     
  14. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    A quick update

    I haven't had time to start my "spoiler", but I have a bit more data.

    Here is a photo of me sitting in the boat in a rowing position. My wife shot some photos so I would know for certain how much of the transom I was dragging through the water

    [​IMG]Russ_in Boat by Russ Kaiser, on Flickr


    And here is a close up of the water line at the transom. Luckily, I hadn't cleaned up some expoxy runs from a patch I placed on the bottom of the boat and I was able to use the runs and a photo of the boat out of the water to figure out how much transom is submerged.

    [​IMG]Water_Line by Russ Kaiser, on Flickr

    Here is a photo of the transom out of the water with the normally submerged area highlighted.

    [​IMG]transom_WL by Russ Kaiser, on Flickr


    I guess I'm wondering if everyone thinks this is a significant enough area to warrant my effort. The area is about 2.25 inches deep and you can see that it goes almost the entire width of the transom.

    Also, if I added a skeg to this clamp on device, would the drag from that erase the gains from cleaning up the bottom. The normally submerged portion of the keel has just a small keel strip that doesn't provide much directional stability. I'm hoping the slight buoyancy from this device may lift the rear a bit and lengthen the overall water line.

    Thoughts?
     

  15. Skyak
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    Skyak Senior Member

    IMHO, any man that is willing to haul that boat to the water and row it regularly deserves a better boat. Time and effort spent on a rowing needle like Upch. would be better than trying lipstick on this pig. Less storage space and easier hauling are the kickers.
     
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