Stern Extension to Help Rowing

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

  1. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    I love my ugly boat! it will look a lot better when it's painted ;)

    I can throw it in the back of my truck by myself and if it falls out (and doesn't kill anyone) I won't be out anything.

    Believe me, in the next couple of years I'll have something a lot nicer.
     
  2. Skyak
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    Skyak Senior Member

    Personalty I think the surface finish is the coolest thing about your boat. I think someone should buy it, cut it up and sell it as modern art.

    How much does it weigh? Looks like 140#+ to me.

    Cost is less relevant than time, storage, and enjoyment.
     
  3. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    I'm betting it's closer to 100 lbs. than 140 lbs. My son (12 years old) and I can easily pick it up and even though I'm only lifting half of it at a time when I shove it in my truck, it feels pretty light.

    The rib work is much lighter than a new aluminum boat but the skin is probably thicker. I measured the transom skin at 0.100 but I bet the transom is a thicker gauge than the rest of the hull.

    When I first got the boat the seats had nasty brown AstroTurf (glued and stapled!) on the thwarts. There were about 10 makeshift rod holders, hose clamps with sheet metal screws, bristling the gunwale. The entire bottom behind the rear thwart was poured full of bed liner and a large portion of the bottom on the outside was coated with bed liner. It weighed about 200 lbs. and it still leaked like a sieve. I took all of that off and put small glass and epoxy patches over the rib rivets on the bottom. Now it's dry as a bone and about half the weight.
     
  4. upchurchmr
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    upchurchmr Senior Member

    Skyak,

    Wasn't it Herreshoff who had something similar named the "needle". I'm surprised anyone recognized the old boat similarity.

     
  5. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    It was Richard Buckminster Fuller, He was a nut (genius), so you're in good company. :p


    rowing-needle

    Your design is better, cylindrical hull shapes have little reserve buoyancy.
     
  6. Skyak
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    Skyak Senior Member

    The rowing needle is for exercise, with little reserve buoyancy for piercing waves. I figured I could make one with PVC pipe hulls that I could disassemble and store in a small space. Did you see the hydrofoils on Bucky's drawing?
     
  7. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Makes you wonder...

    Foils...whimsy I would imagine. In the video there are two examples, one rowed by a young person and one by Bucky, neither with foils.

    Maybe I'll sketch a version of my aluminum boat with JATO canisters for when I'm bucking a head wind.
     
  8. upchurchmr
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    upchurchmr Senior Member

    Thanks for the correction, I looked through every picture I had and didn't find it.

    You don't need reserve bouyancy if you are wave piercing, just let them roll over the hull.
    But you might get a little wet.
    Mine don't have enough to talk about.
     
  9. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Reserve Buoyancy

    A lot depends on if you're designing the boat for a range of people or just yourself. Your square topped design will have a very predictable response to additional weight. From a performance perspective there is not much difference between someone heavy having two inches of free-board on the floats and someone light having three inches.

    A cylindrical hull profile piles on a lot of whetted area after the water line passes its midpoint for not much return in buoyancy. A cylindrical hull designed to float a 150 lb. person at a point where performance was maximized would have crappy performance if the person weighed 50% more at 225 lbs.
     
  10. upchurchmr
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    upchurchmr Senior Member

    Very similar to my boat shown. That boat was designed for a person of 125#.
    My son at 180# sunk it to only ~2" of freeboard.
    My 230# sunk it to just about the deck line. Not something I would want to use except in a pool.
    That was why I suggested you would need a longer one. But the same length with wider individual hulls and wider total beam would work well, just a little slower. Narrower total beam would be a good bit slower.
     
  11. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Let the games begin!

    Well, I got some time without distractions today so I thought I would start my super high-tech spoiler. I of course waited until Russian spy satellites were no longer overhead.

    I tried a couple of times to sit down and draw exactly what I was going to build and then I finally said, "Screw it, you can get it done quicker by winging it."

    I started with a 1/2 inch piece of plywood with a couple of tabs that miss all the protuberances on the transom. I purchased a couple of deep clamps at Harbor Freight (not bad for junk) and clamped it in place. I made the board a bit big so I could trace the bottom edge of the transom.

    [​IMG]First_Step by Russ Kaiser, on Flickr

    After the bottom profile was duplicated I cut a three pieces of ply 2 feet long for ribs and traced a gentle curve (real scientific) on them. The center rib was made a bit deeper because there is a slight dead rise at the transom and I wanted the top edges to align.

    Then I screwed it all together with some bracing. It may be a bit over framed, but I'm worried about the moment it's going to see when I slide the boat into the water at an angle off of the jetty wall.

    My plan is to sheet the center section with 1/4 inch plywood, then fill in the corners with foam and shape that into a nice transition. Slather with glass and epoxy and call it done.

    I am still considering a skeg attached to the center rib. I'm thinking of using that breakthrough foil shape that was just recently developed called "FLAT". I have to decide soon because a skeg would need to go on before the bottom skin.

    Any thoughts?

    [​IMG]Frame_1 by Russ Kaiser, on Flickr

    [​IMG]Frame_2 by Russ Kaiser, on Flickr
     
  12. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Making Progress

    I decided to go with a skeg. Hopefully that's the right call.

    I got the main pieces of 1/4 inch plywood skin on yesterday and I hope to get the blocks of foam laminated and glued into the corners of the frame tonight.

    After that, there will be a lot of filling, shaping, sealing, glass work, and painting but I hope to make a test row with this gizmo in place on Saturday or Sunday.

    [​IMG]Frame_With_Skeg by Russ Kaiser, on Flickr

    [​IMG]Skinned_1 by Russ Kaiser, on Flickr

    [​IMG]Skinned_2 by Russ Kaiser, on Flickr


    I have a question about cutting foam. A few months ago I bought some fairly heavy nichrome wire and a DC voltage regulator to do some foam cutting. I am wondering if anyone has cut laminated foam, specifically foam laminated with epoxy with a hot wire. How well does the wire go through the epoxy?
     
  13. Skyak
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    Skyak Senior Member

    This is based on theory not experience but epoxy is a thermoset -crosslinked- unlike foam it does not soften much before breaking down. You don't want to try and hotwire cut epoxy. Stick with a single thermoplastic foam like PVC.

    Your add is more substantial than I expected. A following wave could put lots of force/deflection on your clamps.

    Quality work, but IMHO better spent building a boat for your purpose.
     
  14. Russ Kaiser
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    Russ Kaiser Exuberant Amateur

    Skyak, I just want to make sure you understand what I was asking about. I need a block of foam lightly thicker than 4 inches. I was going to use epoxy to laminate two inch foam. I was wondering if the hot wire would go through the epoxy seam. If not, I can maybe use a spray adhesive to join the pieces or I can just use a saw to cut the foam.

    My main rowing lake is very narrow and relatively small. The only waves I have to worry about are boat wakes. Usually folks give me a wide berth and they are limited in horsepower. I plan on putting stringers on the tabs to cut deflection and I may run a stringer from the top of the tabs to the back of the deck. I need to fabricate a couple of hooks on the tabs to overlap the transom so it will be easy to position.

    A friend suggested that studs through the transom would be better than the clamps, but I won't go that route until I've proven that it makes a difference. The clamps will be fine for testing.
     

  15. Skyak
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    Skyak Senior Member

    I don't know epoxy will cause a problem in your application but it doesn't melt and you don't seem to need the strength so it doesn't go well with hotwire. Can you hold it some other way, hotwire, then glue?
     
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