New Racing Canoe

Discussion in 'Boat Design' started by sabsfeigler, Apr 20, 2020.

  1. sabsfeigler
    Joined: Apr 2012
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    sabsfeigler Industrial Designer

    Hello everyone. My name is Sabs, I've posted here before when I was doing my bachelor thesis project building a wooden racing canoe, and now almost 10 years later, I've decided to design another one.

    I still don't really understand a lot of the hydrodynamic theories that I read on here, and from what I see, for designing a racing canoe might it might be more hype than anything. That's why I've come here. For advice and have you guys help me debunk/confirm some of the things happening in the flatwater canoe scene. I'd like to know if what they are doing to the boats is worth emulating, or is it just going to give me a headache to model in CAD.

    Speaking of CAD, I'm going to try to model this in Solidworks, since it is the program I'm most familiar with. I downloaded the newest version of delftship, and I don't know if I need the pro version or what, but I can't seem to turn on the curvature combs for the stations and waterlines. Or at least if I press the button, I have no way of scaling them to anything useable. So if there's a suggestion there, I welcome it.

    But back to the boat.

    The only hull requirements for racing canoes, as mentioned in other threads, is that they are no more than 5.2m long, they are symmetrical across the centre, and that they are convex at all points. I've been eyeing a few books on lofting so that I can be sure I get the lines right, but I haven't committed to anything yet.

    It's been said here numerous times that a flat bottom on this sort of semi displacement hull will not plane, since as I understand it, they are not going fast enough. I also read that the flatter bottom will not stop pitching because that is a result of buoyancy, and if the buoyancy at the bow is the same, then there's no difference.

    Regardless of this, racing canoe manufacturers put flat areas on their hulls, and now on the bottoms of their rowing shells as well. Also, they have started using a reverse bow, with the bottom being near square and the top being sharp, insisting that this will reduce pitching.


    This video gives a good look at the bottom of a rowing shell with this design.


    This video shows the bottom of the new kayaks as they paint them.


    And here they show the boat again (sorry it's in Hungarian) But he mentions that the company has taken a step back from the totally reverse hull, to keep a bit more of an edge on the bottom to keep it running straighter, as well as having a sharp point at the stern, instead of a flat cut off area.

    This was the first generation of that hull design for the canoes.


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    But it was actually so unpopular that they reversed course hard on it and went back to a more traditional design.

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    The question is does this make any difference or is it just marketing? when other boats look like this

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    And like this.[​IMG]

    And is there any benefit to making it look like the Zumwalt?

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    I'm just in the very start of my research for this new boat, so please understand that I am not committed to anything specifically, but if you're going to build a time machine out of a car, why not do it with some style? You know what I mean.

    Thanks for your thoughts, sorry about all the pictures.
    Sabs
     
  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    "This video gives a good look at the bottom of a rowing shell with this design."

    didn't watch the whole vid, but main thing is the bottom is quite flat and sides quite vertical, and the flat is supposed to keep boat from rocking and bouncing as rower's weight shifts, and the sides likewise supposed to be able to move up and down in water without pushing out big energy draining waves at each stroke. Makes perfect sense to me on a boat where the weight is shifting at every stroke.

    Hull does have rounded transition between bottom and sides, so what rocking that does happen doesn't make undo turbulence, so I guess getting these benefits with homemade plywood boat might take some doing. However, when I was playing round with making quick and easy semi-steamlined hull shapes with CAD using simple rounded chamfer feature, it did occur to me that there are pipes and tubes made in all sorts of fancy materials such as carbon fiber that might be used in conjunction with sheet material to make something like this new Neho hull.
    https://michaellorddotme.files.wordpress.com/2016/09/fillet-chamfer.png
    might have give a 1/4 pipe multiple snips to bend similar to this
    http://www.howtospecialist.com/wp-content/uploads/2011/10/dry-wall-arch-0291.jpg
     
  3. messabout
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    messabout Senior Member

    You can easily make rounded chines with a composite structure of ply and strip built chines. With the strip area method you can have any radius or transition from radius that you choose.
     
  4. sabsfeigler
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    sabsfeigler Industrial Designer

    Oh I’m not making a “plywood” boat like that. It will be cold moulded veneers under vacuum so the hullform can be anything really.

    I get that “in theory” these flat edgy shapes make sense, especially for someone like me who doesn’t understand the math behind it, but I’m curious if there is any actual benefit when the speed of these boats is so low and they are so narrow. When you watch videos of these boats racing there is no obvious difference in how much the pitch because each athlete's technique makes their boat pitch differently to begin with.
     
  5. Squidly-Diddly
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    Squidly-Diddly Senior Member

    If you carefully watch single rowing shells (with normal round hulls) on glassy flat water, you should be able to see front wave pulsing with every stroke as weight shifts.
    But what this company should do is set their new design against normal round hull in a video.
     
  6. sabsfeigler
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    sabsfeigler Industrial Designer

    yes I mean one only needs to watch a rowing regatta to see this boat compete against traditional hull forms. I don’t notice a difference when watching.

    In their kayaks, they claim the tumblehome bow keeps the bow in the water, reducing the amount that the boat will pitch from each stroke. But growing up we were always told that getting the bow to lift out of the water was something we should try to do.
    So which is better? Keeping a flat running boat, or having it lift out of the water each stroke?

    And on the topic of tumblehome, like the warship picture, is there any benefit to that shape running the length of a canoe?
     
  7. tlouth7
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    tlouth7 Senior Member

    Old versions of Delftship free definitely allowed use of curvature combs. I recall a problem where you couldn't scale station and waterline combs differently so it was impossible to use both simultaneously.

    Presumably canoes move slightly crabwise, so while you aren't allowed to make them asymmetrical there must be scope to create a design that is optimised for this.

    Fullness and flare in the bow and stern will increase resistance to pitching, but they will also generate waves when pitching does occur. The reverse bow concepts are probably aiming to minimise the energy wasted due to pitching, which is a subtly different requirement.

    We had a big debate on this forum a while back about the relative merits of square or round bottoms (on kayaks?). It all comes down to how much stability you need. Traditional sculls have semicircular underwater profiles and so very little stability. Presumably canoes need a little more and you have to choose how much to get from the profile and how much to get from increased beam.
     
  8. sabsfeigler
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    sabsfeigler Industrial Designer

    As far as my common knowledge goes, square bottoms are more stable but slower due to friction/wetted surface. Stability isn’t such a big issue for racing boats. While you do want it to be predictable in wake, you deal with it as a compromise for speed.

    Beams on these boats is 36-38 cm on average. Basically as narrow as you can so a paddle can be vertical during a stroke.

    so what your saying is that if you overcome the pitching of what the hull can correct for, you’re going to go slower. So it comes down to technique.

    maybe an axe shaped bow would be the best compromise. And the stealth ship remains but a pipe dream.
     
  9. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Since a rowing shell is basically entirely balanced with the oars, and with all this talk about wave piercing bows, you got me wondering about Mono-SWATH rowing shell. However, sitting on a submerged tube might be even bigger problem as far as rocking when the rower shifts weight, so maybe horizontal stabilizer fins, that themselves would add thrust as they bob up and down at the stern.
     
  10. tlouth7
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    tlouth7 Senior Member

    I don't think a SWATH rowing shell would have sufficient resistance to pitching to work well. Wave drag on a shell is already pretty minimal.
     
  11. sabsfeigler
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    sabsfeigler Industrial Designer

    Correct me if I’m wrong but those have to be engineered to be efficient at specific speeds, like bulbous bows, but the nature of racing specifically works against having something be designed for a specific speed. It would be a boring race
     
  12. JRD
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    JRD Senior Member

    Interesting thread.

    All hulls have a speed at which they can be most efficient, all the resistance elements then scale to various powers of the velocity. To win you need the lowest comparable drag at the highest speed your human engine can sustain.

    At top levels of competition the % difference in race times in rowing is tiny. So optimising design for that top speed seems pretty obvious. That said with a long slender hull I imagine the adjustment of shape to meet the key design ratios is incredibly subtle
     
  13. sabsfeigler
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    sabsfeigler Industrial Designer

    That’s the real question here. Does that subtlety make a real difference since everyone will paddle the boat differently. It’s lot like it needs to perform in large waves so pitching due to waves is not an issue.

    The real question here is “does a reverse bow make enough of a difference in keeping a boat at an optimum trim? Or in such a slender trimaran Ama form, is the buoyancy actually going to be overcome by the power of the stroke and weight of the athlete. Is a racing canoe too narrow and run on flat enough water for there to be no benefit?”

    I guess that’s more than one “the question”
     
  14. sabsfeigler
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    sabsfeigler Industrial Designer

    Another question I have is how far back can the widest point of the boat be moved to help reducing pitching, before there is a increase in drag? Some of these boats have their widest point further back or have fuller back sections than others. How much could this help?


    Old boats before the rule change had much wider limits, and didn't pitch as much as todays boats. Is this simply because of the extra buoyancy throughout the entire hull or also due to the placement of this wide point? could this old boat have been even better if the widest point was even further back?

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  15. DCockey
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    DCockey Senior Member

    One reason for the maximum width aft has nothing to do with hydrodynamics. The maximum beam is aft to reduce the beam where the boat is paddled.
     
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