Peter wrote: >>>>>The values you mention for power produced during kayaking seem low when compared to the literature I've read on exercise physiology. I can well imagine that a very fit kayaker would need to be paddling flatout to push a kayak near its hull speed to 5.2 knots. But if the papers/books I'm reading are correct 85 Watts is a level of output associated with exercise on a bike or rowboat that would be sustainable by a reasonably fit human for several hours. I'll quote three examples:<<<<<< Thanks for the examples, they were interesting. However, I think you are comparing apples to oranges here and my figures are correct. The wattage I calculated is how much power (in watts) it takes to overcome the drag on a 40 pound Coaster kayak with a 150 pound load moving at the various speeds I listed (through 59 degree F. water). This is the power needed to drive the Coaster kayak at a given speed, NOT the power the paddler needs to generate to be able to transfer that much power into kayak speed. If the efficiency of transferring the energy through a paddle towards kayak propulsion is 50% (and I think it is even less than that) then the power the paddler needs to generate would be double the power actually required to move the kayak at any given speed. A lot of the power the paddler generates is wasted, which is the basis of my critique of Niel's plan of using gravity to power a kayak. Since a bicycle is something like 85% efficient and powerful leg muscles are used to generate much of those watts I think this accounts for the difference there. From world and Olympic records, I see a top rower can push a rowing shell about 10% faster than a top sprint racer can push a kayak over the same distance. The difference in power that a top rower can generate using leg muscles and a sliding seat is probably over twice what a top paddler can generate. Considering that both hulls are likely pushing their respective hull speeds where (as you can see by how quickly the watts needed for the Coaster shot up with just a little more speed near hull speed) tremendously more power is needed to gain just a little more speed, I think you can see that the rower must be able to generate a whole lot more power than a paddler to go 10% faster. I once owned a Sea Saber, a human powered craft 21' long by 11" wide (with a 9' by 3" wide outrigger for stability 8' to one side) that was, at that time, the fastest human powered vehicle on the water (and was until the human powered hydrofoil craft "Flying Fish" arrived on the scene). Propulsion of the Sea Saber was from pedalling in a recumbent bicycling position driving an 18", high aspect ratio, two bladed prop rotating (through a gearbox and shaft) at 4 times the pedaling speed. The hand operated rudder doubled as the prop shaft support. It was a very elegant design and only weighed 50 pounds total. I witnessed a race between the Sea Saber's builder, with a slightly longer and heavier earlier model (24' long I think) Sea Saber and a racing double scull with two top local rowers that took place on Seattle's Green Lake during an HPV (watercraft) show. If I recall correctly, the distance was over a 1000 meter long straight course. The Sea Saber, with just a single pedaler, easily won the race by a good 20 boat lengths over the double skull. Both craft had the benefit of using powerful leg muscles and also their arm muscles (the Sea Saber guy even had webbing around his feet and lower legs that allowed him to pull up on his--clipped in to the pedals--feet as well as pushing down on his knees with his arms to help him). Given that the double skull rowers were probably generating twice the horsepower (or watts) as the pedaler (and given that a double scull is faster than a single scull) the advantage of the pedal boat must have been in the much better efficiency of a screw propeller vs. oar blades for propulsion and the constant delivery of power from pedaling that could maintain a more uniform (and therefore more efficient than surging and slowing like the rowers) speed through the water. The Sea Saber and its builder also won every Cross Sound race it was entered in, even the one that was held on a very rough and windy day (which was the race that convinced me that maybe we should become the Sea Saber dealer in Seattle). While the Sea Saber attracted a lot of attention when I used it, nobody was interested in buying one even though the cost was not exorbitant at all. I think it suffered from what I have since come to call the "too weird" factor. I could surf boat wakes with the Sea Saber and fairly easily climb up over several transverse waves from directly behind a powerboat to get up to the sweet spot on the second wave behind it. I could never climb over those transverse waves from behind paddling a kayak. As hard as I sprinted, even with a sleek racing kayak, I could never generate enough power towards propulsion by paddling to do so (even though I was one of the fastest, kayak racers--who never had competed in the Olympics, anyway--in the Seattle area at the time). *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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MATT MARINER BROZE wrote: <<<<<Given that the double skull rowers were probably generating twice the horsepower (or watts) as the pedaler (and given that a double scull is faster than a single scull) the advantage of the pedal boat must have been in the much better efficiency of a screw propeller vs. oar blades for propulsion and the constant delivery of power from pedaling that could maintain a more uniform (and therefore more efficient than surging and slowing like the rowers) speed through the water. >>>>>> Great test! I think there's something more to the non-uniform power of the rowers than just the gaps in their power-output. They slide back and forth in their boat, constantly pushing the boat over its hull speed and slowing back down with just their moving mass. That can't be good. Perhaps rowers shouldn't row in sync to avoid that problem - they'd just have to find a way not to bump into each other and get their paddles tangled. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Doesn't work that way. For example, if people paddle out of sync in a dragon boat, the boat does not move anywhere nearly as quickly as if they are paddling in sync. Canoes, kayaks and rowing shells work more like cross-country skis and ice skates, where the glide is very important. Kick and glide . . . stoke and glide . . . You don't get the glide if you don't get the kick, and you don't get the kick unless you are in sync. Richard Culpeper -----Original Message----- From: owner-paddlewise_at_paddlewise.net [mailto:owner-paddlewise_at_paddlewise.net] On Behalf Of Niels Blaauw I think there's something more to the non-uniform power of the rowers than just the gaps in their power-output. They slide back and forth in their boat, constantly pushing the boat over its hull speed and slowing back down with just their moving mass. That can't be good. Perhaps rowers shouldn't row in sync to avoid that problem - they'd just have to find a way not to bump into each other and get their paddles tangled. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Richard Culpeper wrote: > Doesn't work that way. For example, if people paddle out of sync in a > dragon boat, the boat does not move anywhere nearly as quickly as if they > are paddling in sync. > > Canoes, kayaks and rowing shells work more like cross-country skis and ice > skates, where the glide is very important. Kick and glide . . . stoke and > glide . . . You don't get the glide if you don't get the kick, and you don't > get the kick unless you are in sync. Perhaps there would be a market for cars with their cylinder in sync? Anyway: You've got me started on rowing. You shouldn't have. Usually, we measure efficiency by calculating the power needed to propel a vehicle _forwards_. Since rowing boats are going _backwards_, they have a negative efficiency. The exercise is less than pointless. Rowers could dramatically increase their efficiency by dropping an anchor: The efficiency would jump from minus-whatever to zero. Until and unless rowers adapt such simple, cheap and obvious measures to increase their efficiency, there's little point in discussing the finer details. Niels *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
2011/5/2 Niels Blaauw <niels_at_nibla.nl> > > Rowers could dramatically increase their efficiency by dropping an anchor: > The efficiency would jump from minus-whatever to zero. Until and unless > rowers adapt such simple, cheap and obvious measures to increase their > efficiency, there's little point in discussing the finer details. > > This reminds me of the futility of buying the best and most efficient systems for exercise. I have a friend who owns a $5,000 bicycle (which he breaks periodically - but that's another story). I've told him that, logically, he'd be far better off buying an old beater bicycle and riding *that* for exercise instead. Maybe a 1980s Peugeot $99 Shuck's bike with a rusty chain. He's to the point where he has to ride 50 miles or more to get a significant workout. I'm pretty sure I could find a bike that would give him an even better workout and not require him to go so far from home. :D Craig Jungers Moses Lake, WA www.nwkayaking.net & www.bigboxbikes.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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