designing a fast rowboat

Discussion in 'Boat Design' started by nordvindcrew, Oct 13, 2006.

  1. NoEyeDeer
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    NoEyeDeer Senior Member

    Yeah I know that mate. I was just curious as to what was the number of panels required for SFA difference in drag. Seven works well for what I want. Could be done with five if I didn't mind extreme flare in the topsides, but I wanted to keep the topsides shape reasonable so seven it is.
     
  2. DickT
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    DickT Junior Member

    Has anyone modelled segmented (maybe vertical multi chine would be a better way to say it) for these types of displacement boats? Intuitively it seems ridiculous because one would expect an eddy at every joint.
    My son is working on a 29' faceted flat carbon fiber panel over steel high speed boat that they've fitted with strain gauges to test slamming loads. The facets make it look like a stealth fighter jet. It planes beautifully but also doesn't make much fuss at displacement speeds, (although with a 496 Mercruiser who'd know).
    I have some 1' by 5' 3mm Baltic Birch with the grain running in the short direction that would bend nicely gunwale to gunwale like a birchbark canoe, or up to the gunwale from a bottom board.
    Just curious.
     
  3. ancient kayaker
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    ancient kayaker aka Terry Haines

    Interesting concept! I’v seen it used for larger boats to create radius chines. Using that method without torturing the ply for a 17' x 30" canoe with a circular arc sheer curve to simplify calculations, the “vertical chine” angle at the sheerline would be 1.7 deg but that is out of the water; it’s only 0.7 deg at the waterline and virtually zero at the keel. It is difficult to believe such minor imperfections would generate significant eddies. Whether you can stand the teasing you will get at the launch ramp is another matter!

    The attached image approximates the results although the FreeShip shading creates a false appearance of scalloping.

    I have shown the first few plank developments from keel to gunnel, but it would probably be easier and stronger if the midship planks went from gunnel to gunnel. You could start midships and work towards the stems, trimming the edges to fit and change to half-width planks if/when waste becomes excessive.

    How would you propose to reinforce the joints? The angle is fine enough to use a butt joint but joints would work and look cool.
     

    Attached Files:

  4. DickT
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    DickT Junior Member

    Very nice! I like the look. I thought butt joints with maybe 2-3" strips of the same 3mm bedded in thickened epoxy as bent ribs covering the joints on the inside and fiberglass cloth on the outside. Decks would be easier to deal with than gunwales and could show off the variegations. Other than that I'd add strength where needed. I think you're right about starting with the midship section and moving towards the ends. It might find a nice prismatic coefficient.
     
  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    The FreeShip design is a bit of a mess now after I added lots of control points to generate the plank developments. Now it's almost impossible to get a really fair hull from it so I won't pass on the file but it is an easy hull to recreate; I used 4 vertical and longitudinal control levels.

    Here are the rough plank developments from bow to midships - assuming a symmetrical hull, revised to show one-piece planks from gunnel-to-gunnel. There is no need to split planks at the keel. The inner lines are the waterlines, just for guidance. I suspect the stem planks may be difficult to shape and might need to be split.

    I think it will need a full mold with a station at each seam, with thickened and waxed edges to allow stapling, then the seams could be epoxied and the hull gently removed from the mold to allow the butt blocks to be inserted. However you may have a better idea how to build it. It is not a good candidate for stitch and glue as a tiny error would have a considerable impact on hull shape, so the developments are not needed.

    With the internal gunnel-to-gunnel butt blocks looking like ye olde fashioned ribs, this boat might have a nice look to it. It reminds me of the cedar rib construction that a few of the classic Peterborough canoe builders made in the late 1800's. The "kinky" sheerline could be smoothed out by the gunnels, or left for dramatic effect . . .

    I hope you go ahead with this, I would really like to see how it turns out. I'd be tempted to try it myself but I already have 2 unfinished canoes which look accusingly at me every time I go into the workshop, a sailboat crying out for a new rig, a bug in my brain for a front rowing rig, and plans to build a long-delayed canoe design as soon as the others are on their way . . .

    Afterthought: 2-3" butt blocks for 3 mm ply sounds like overkill to me. For 3 mm 1" is entirely adequate IMHO, that gives 12 mm glue width to each plank which is thickness x4 - bearing in mind strength is proportional to width squared and cross grain strength is usually around 10% of with grain strength so it still provides 60% margin if executed properly, plus the contribution of the edge-to-edge joint itself. It would look nicer too: the trick is to get the profile right. To do that you can shape the edge of the next plank then cut off the 1" butt block before gluing it . . . ta da!
     

    Attached Files:

  6. DickT
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    DickT Junior Member

    I made a cut and tape model from your drawing and really like it. It occurred to me that in a perfect world the perfectly cut pieces could be taped together in perfect alignment with packing tape on the outside without molds. Then the hull would take perfect shape and stay fair while the butt blocks were put in. There may be a compromise between this and a strongback with a mold at each joint.

    Like you I have many irons in the fire, but I'd like to try this since I'm looking for a lighter hull than my present 85lb 17 footer. I blew out the ligaments in both knees at the end of March and can't throw weight up on the roof rack like I used to.
     
  7. magnus
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    magnus Junior Member

    Trim, multichine, pitching

    and looking for speed at a minimum effort gets complicated.

    Peter Heed would agree in his book "Canoe Racing". He suggest (by my recorded notes: hopfully accurate) that under racing conditions expect a squat of 12-25mm so adjust bow down at rest to compensate. Level at speed gets the best speed. He also mentions what has been discussed that if the bow is too low speed will not suffer badly but tracking is difficult. No skegs or rudders allowed, of course, in canoe racing (unlike kayaks). One obvious advantage canoe racers have is the adjustable seats, even underway: the builder does not have to get it right for all conditions and all weight distributions unlike surfskis and rowing craft.

    If I remember correctly Rick W. thought his 3 panel pedal powered boat was superior to round sections. Rick, (correct me if I am wrong, it would be nice to hear fom you) thought he was getting some hydrodynamic lift, which means bow up to me. We have to remember that Rick and I believe Michlet are designing for constant pitch. My gut says (probably indigestion) roundish sections may have less drag losses with the pitching rowing and especially sliding seat rowing develops, but maybe the proffesionals can comment on that? If race rules are not in the way I like sliding riggers:D
     
  8. nordvindcrew
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    nordvindcrew Senior Member

    race day

    I did the buzzards bay race last Saturday. Really felt lonesome out there. The only rowing boat in the field so 1st place was assured but with no glory. course was 4 mile triangular with a tough 2 mile slog upwind against a 15 knot breeze and 18" chop. I played around with different strokes and found that a short rapid pull moved me along the best. Not being used to that, I got tired quite quickly and had to revert to a longer slow pull. The shorter pull also worked best on the next leg with the wind quartering over the stern on the port side. The last leg (1/2 mile) was straight down wind and the long hard pulls got me clipping right along and surfing with the waves. Made for an impressive look coming across the finish line. Time for me was 52 minutes and 3 seconds. Not great, but I felt OK with it considering the big picture. The new 20' boat is in the final stages of fairing. Priming should begin this weekend. Still need to lower the thwarts but that is a small matter. Brother Dave is fairly well recovered from the saw accident and is starting to get a bit enthused over competing. We both feel this boat will have the potential to win races if we can just get good enough to row her to the max. If I ever finish wiring my house for cable, I'll finally be able to post some pictures of my different builds.
     
  9. dcnblues
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    dcnblues Senior Member

    My buddy Stever and I got you thinking about the dory-stroke! :D
     
  10. nordvindcrew
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    nordvindcrew Senior Member

    dory stroke

    at first, it seeemed like it might be a pain to learn ,but it comes quite naturally after just a bit of practice. The key to it is the right oars. Spoon oars don't do the trick, straight blades ala Pete Culler work better. I've got a bunch of oar shafts all made up and some cedar straight blades mostly finished. Got to get on it as soon as the new boat is done.
     
  11. nordvindcrew
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    nordvindcrew Senior Member

    good day

    We got in a good 4 mile row on sunday then managed to get a coat of paint On the Nordfiord. The results are about what I expected. The boat looks great fron 30' not so good close up, but good enough for the beating it will take.
     
  12. DickT
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    DickT Junior Member

    Lake Champlain Challenge

    Impressive name for a 3 mile race, but it's a lot of fun and we need more rowboats. July 10, 10am registration at Basin Harbor, in Ferrisburg, VT.
     
  13. nordvindcrew
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    nordvindcrew Senior Member

    Lake Champlain Challange

    I put ferrisburg into my GPS. Looks like a 5 hour plus ride. Don't know if I can make it
     
  14. DickT
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    DickT Junior Member

    Yeah it would be a long ride, pulling a trailer over the mountains and all.
     

  15. nordvindcrew
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    nordvindcrew Senior Member

    travel

    If I decide to try to do your race, I will put the boat on racks on the truck. a lot easier that way. I used to visit in Springfield Vt. so I'm familar with that much of the route. Final decision depends on what life throws at me between now and then
     
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