Aquatic HPVs

DIscuss anything relating to non-standard cycles and their equipment.
james01
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Aquatic HPVs

Postby james01 » 8 Jul 2008, 11:39am

I'm intrigued about pedal-powered boats. Does anyone know where they can be tried out? ( Don't tell me to rent a pedalo next time I'm on the Costa Brava :shock: )

MarySkater
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Postby MarySkater » 9 Jul 2008, 11:08am

I don't know where or if you can try one, but I've always been interested in the Hobie range of pedal kayaks:
http://www.berkshire-canoes.co.uk/hobie-kayaks.htm

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CJ
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Postby CJ » 10 Jul 2008, 1:24pm

Center Parcs used to have some Surfbikes. I had a lot of fun on one at Elveden once. I don't think they have them anymore, but worth a check.

They look difficult, but once you're moving they're as easy to balance as the bikes they resemble, and of course you get a better view than anyone in a canoe or rowing boat.
Chris Juden
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hamster
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Postby hamster » 10 Jul 2008, 4:45pm

Water is sticky stuff and the low power output of a human is not great news - my 30cc outboard does about 16mpg!

Human powered things do OK on flat water, but in a blow it gets increasingly difficult (having once rescued someone in an HPV catamaran near Falmouth with my sailing dinghy.)

Personally (as a qualified Coastal Skipper with DoT certificate) I think they are novelty only.

james01
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Postby james01 » 11 Jul 2008, 1:32pm

hamster wrote: I think they are novelty only.


Better not let this guy hear you say that :D

http://www.pedaltheocean.com/

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CJ
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Postby CJ » 15 Jul 2008, 1:36pm

Chris Juden
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Si
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Postby Si » 15 Jul 2008, 1:46pm

should've watched Scrap Heap Challenge last sunday :wink: Or maybe not....

hamster
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Postby hamster » 16 Jul 2008, 2:30pm

james01 wrote:
hamster wrote: I think they are novelty only.


Better not let this guy hear you say that :D

http://www.pedaltheocean.com/


But compare their times to rowing transatlantic or transpacific and you'll see what I mean. :wink: He has an extremely specialised setup compared to fairly bog-standard rowing boats which are designed more for easy build and seaworthiness. Good luck to him though.

Rowing just seems to be a much more effective way of human propulsion.

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CJ
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Postby CJ » 16 Jul 2008, 4:02pm

hamster wrote:Rowing just seems to be a much more effective way of human propulsion.

According to Bicycling Science, it isn't. Pedalling is a closed-cycle action, in which the kinetic energy of moving parts and limbs is conserved, whereas in rowing there is significant unrecovered effort in accellerating the rower's body and oars.

Where rowing scores over pedalling is the efficiency of the oar blade as a water scoop, compared to a rotating propellor, and the simplicity of the mechanism (a simple pivoting bar) required to connect the human to it. For unless the human sits sideways, you need at least one right-angle drive (many pedal boats have two) to connect the cranks to the propellor shaft, plus loads of bearings, a gearbox, waterproof seals for all of these ...

I think I'd see if I could devise a more efficient form of paddlewheel: one where the paddles pivot so as to enter and leave the water with less splashing and travel through it at a more constant effective speed.
Chris Juden
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thirdcrank
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Postby thirdcrank » 16 Jul 2008, 7:05pm

I'm not much of a telly watcher, so I am often vaguely aware of stuff my wife is watching. Within the last couple of days, I have only caught the tail end of something where a chap somewhere in the East was propelling a boat (utility, not leisure or sport) by pedalling in the conventional way but his effort was transmitted through oars (conventional, except they were attached to his feet rather than his hands) which were then describing large circles, whose lower part was under water.

I've not described it very well but he was converting the leg action of pedalling into a pretty effective imitation of hand rowing. (I don't know the technical terms but where a normal two-oared rower would pull both back together, this chaps oars were both rotating in the same direction but when one was in the water the other was above it.)

hamster
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Postby hamster » 17 Jul 2008, 8:20am

Chris: note I said effective not efficient!

The problem with propellers in things like waves is that they can often end up partly out of the water, plus they (in general) do not steer. This leads to rudder usage to correct yawing, and the angled rudder adds a significant amount of drag. With a slow-moving vessel like a pedal boat, there is not enough speed to make the rudder really effective and this further slows you as very large rudder areas and angles are necessary, especially when moving into waves, which may be doing around 5-6kt in the opposite direction. Of course with rowing you just pull harder on one oar.

There is a huge difference between flat-water speed (where the pedal boat may indeed be faster) and ocean conditions where there will often be waves of 2-3m. For example, as the hull crests the wave, the prop would probably leave the water while the oars (with a skilled rower) would still be biting. Furthermore, a long sleek hull will do well on flat water but having insufficient buoyancy in the ends will tend to dig in and go through waves, resulting in a slower speed than a fatter hull, even though it is hydrodynamically more efficent.

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CJ
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Postby CJ » 17 Jul 2008, 11:43am

hamster wrote:Chris: note I said effective not efficient!

Of course you did, and efficiency is only part of effectiveness. But you said: "Rowing just seems to be a much more effective way of human propulsion." Period. On rough water I'm pretty sure you are right, but on land it is not, and on smooth water it's moot.

The first edition of Bicycling Science had a photo of five girls pedalling a prop-driven catamaran, who had soundly beaten a male-crewed University eight over the boat race course!

Actually, according to Bicycling Science, the action of rowing is potentially more effective and efficient - if the action can be mechanically contained and connected to a flywheel. Although possible this adds huge complexity and weight to an otherwise very simple arrangement, whilst constraining the motion in a manner that cannot easily accommodate individual variations of form and rowing style and robbing it of the facility to raise and lower an oar that is so useful in rough water.

Speaking for myself, as a typical "weedy" cyclist - genetically cursed with narrow shoulders and skinny limbs but having somehow managed to grow some fairly useful leg muscles - I'm a lot more interested in boats I can pedal than anything I have to work with my arms!
Chris Juden
One lady owner, never raced or jumped.

fatboy
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Postby fatboy » 17 Jul 2008, 11:55am

CJ wrote:
hamster wrote:Rowing just seems to be a much more effective way of human propulsion.

According to Bicycling Science, it isn't. Pedalling is a closed-cycle action, in which the kinetic energy of moving parts and limbs is conserved, whereas in rowing there is significant unrecovered effort in accellerating the rower's body and oars.


I used to row quite a lot so have some experience in this. Rowing is actually a fantastically inefficient way to travel and very difficult to master (I know it looks easy but trust me it isn't). The key weakeness are

1. Power is only applied for around 2/5 or 1/2 of the time
2. When not working lots of weight is being moved from one end of the sliding seat to the other (getting this right so as to not stop the boat is quite an art - novice crews often actually go backwards on standing starts because of this). Actually boats using sliding out-riggers have been constructed and they are faster but were banned because they were too good (sound familier?)
3. Feet push againsts a plate the pushes the boat away from where you want to go
4. Gearing is fixed. Darn hard work to get started and can be either frustrating in you've got a tailwind and are geared too lightly or really tiring if you've got a tailwind.
5. You can't see where you are going - I had quite a few nasty prangs because of this! The visibility of the cox is often totally obscured by the crew.

Mind you the few occasions in which you get it spot on the feeling of being in a fast rowing boat is like barreling along at 20mph only since you are right at the height of the water it's more exilerating.

So if you can get the propeller arrangement sussed then cycling should be better - weight stays essentially static, power can be applied at all times and you can see where you are going.
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

hamster
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Postby hamster » 17 Jul 2008, 4:23pm

CJ wrote:But you said: "Rowing just seems to be a much more effective way of human propulsion." Period. On rough water I'm pretty sure you are right, but on land it is not, and on smooth water it's moot.


Sorry, as the context appeared to be about ocean crossings then that was the context I answered.
Frankly human propulsion seems (to me anyway) to be a daft way to cross any ocean when there is wind there for free!

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CJ
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Postby CJ » 18 Jul 2008, 9:41am

hamster wrote:Frankly human propulsion seems (to me anyway) to be a daft way to cross any ocean when there is wind there for free!

Agreed!
Chris Juden
One lady owner, never raced or jumped.