# Pedal Powered Boats

Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

1. ### Guest625101138Previous Member

Mechanical losses ahead of the prop shaft have nothing to do with hull drag. If you have a gearbox efficiency of 50% it would be obviously silly to infer all losses are related to drag on the null. If your propeller was working at 60% efficiency it would be silly to say all losses associated with the propeller could be inferred as hull drag - just silly maths for no meaningful outcome. You must isolate the inefficiency at the source not infer all losses to hull drag.

If your objective is to move across the water with least effort then all that matters is the speed achieved for any given input. So if I can do 8mph for 180W and another boat can do 5.3mph for 180W my boat is superior for the intended purpose.

Efficiency does not come into the performance equation - power in, speed out is all that matters. Efficiency only has meaning if you want to make detailed comparison of each component. This is the point where you need to isolate losses in each component of the system. Inferring mechanical losses in the drive train and slip/drag in the prop to be hull drag simply has no meaning.

The reason why I did the efficiency analysis on the Hobie flappers was to challenge the marketing blurb about them being highly efficient. Their tug-of-war demonstration only has meaning if you want a boat to be good at tug-of-war. It has no bearing on the normal intended use of moving easily across the surface of the water. You would not choose a tug if your objective is fast passages. Hobie have identified a good feature of the flappers and use it shamelessly to market the drive to a gullible public. Any actual use of the word "efficiency" is false marketing. The flappers exhibit poor efficiency.

Rick W.

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### MLampiJunior Member

Dipping rudders are good, but ...

I, too, like the idea of not having drag when you don't need it.

In a cat or tri in open water where you don't need a lot of maneuverability I think they are a great idea. On the other hand, if you want high maneuverability, or perhaps want to employ the rudder as a dynamic stabilizer in rough water for a monohull, then having a fixed rudder directly behind the propeller works very well.

Even at low speeds the prop wash against the rudder can be used to turn the boat much more rapidly. It can also be used to recover some of the rotational energy imparted to the water by the propeller and achieve somewhat higher net thrust.

Michael Lampi

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### MLampiJunior Member

Great Cross Sound Race

Yesterday I completed the Sound Rowers Great Cross Sound Race. My time of 1:15:xx wasn't stellar for the 7.5 mile distance, but then again I did take some 550 photos or so of the other racers. I had lots of energy left over that could have been (should have been?) left on the course.

In addition, I was wearing the Garmin Forerunner 305, and had the cadence and heart rate sensors working throughout. The GPS function seemed to be working reasonably well, too, with no 50 mph stretches.

Using the SportTracks software to analyze the data I took a screen shot and posted it on the SR web site.

The water was rather weird. While it was generally flat and close to high tide, so there should have been minimal current in any given direction, both of the GPS's I had with me and my own sense of speed indicated that some adjacent sections of the course seemed to be slower and some were faster with no obvious reason. The difference in speed was about 1 mph (5.9-6.0 vs. 6.9-7.0). My heart rate and pedaling cadence were the same throughout.

My guess is that in the slow sections some weeds were attached to the rudder or other part of the boat and they let go with no assistance by me, or perhaps an eddy was encountered mid channel.

Michael Lampi

4. ### Guest625101138Previous Member

Mike
You are in some good company with your race times. I get the impression you are more consistent this year.

On rudders - I would not recommend dipping rudders on the Cadence for the reasons you state. One point worth considering is a rudder that can be lifted clear to shed weed. This has been a spin-off with my rudders. I now have nothing underwater at the stern that catches weed. Having the prop right beside me makes it easy to clean. With the local lake in the present low water state it would be annoying if I could not easily clean the prop.

On GPS - were you able to get the speadsheet working? I found the Garmin charts to be limited although they are very easy and fast to use.

Did you see the blue-black boat with the flappers?

I had my first decent exercise for some months this weekend. I managed 20km on Saturday and another 15km yesterday. Start of a long road to get back some fitness. Our weather is now starting to warm up.

Rick

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### beppeJunior Member

Open Waterbike Twin Monohull architecture

Rick and colleagues
I am not at all committed to the catamaran architecture, I like much better the stabilized monohull concept and I agree with you about the superior intrinsic efficiency of monohulls against catamarans, wetted surface and front section issues are unescapable.
Meanwhile, I believe there are a few problems to be addressed in order to satisfy the requirements for the Open Architecture Pedal Boat

http://www.openwaterbike.com/architecture/the-open-waterbike-requirements

within the monohull architecture.
Also, modularity can be more problematic within the monohull architecture then with the cat, and this is a central point for the Open Waterbike project.

Anyway I am very interested in proposing monohull architectures within the Open Waterbike project, the stabilized monohull concept is the best for performance and the possible evolution of stabilizers within the collective project is fascinating.
I would like to submit to you and the the other colleagues the startup concept of a twin monohull architecture as in the attached schema (dwg and jpg, excuse me for the poor quality, I'll provide something better ASAP), with two people on each side of the single hull, each with his or her own drive unit.
This architecture has the advantage of being modular, allowing the usage of OW standard drive units with forward kick-up mounting.
I understand that they are intrinsically less efficient than a single drive unit, but modularity comes at a price, as the enhanced safety of twin independent engines.
Meanwhile a twin boat should have an advantage against a single one, since power doubles, while drag does not.
I believe we can adopt a design power of 200 W for each rider, total 400 W.
I'd like your opinion of this architecture; I don't know if it was already used in the past, I don't recall similar PPBs.
Best
Beppe

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6. ### Guest625101138Previous Member

Beppe
As you increase the crew size in a monohull you can sit the riders within the hull. In this way you avoid the outriggers for stabilising. I have attached concepts for an enclosed 2-man craft and an open 4-man boat. I have also attached a sketch of the in-line pedal stations for such craft.

The 4-man boat has a design speed of 16kph and the 2-man 14kph. These speeds are based on sustained power level of moderately fit crew.

You would not want to hang the riders out on the side of the hull as you add considerable windage. These boats have the ability to move fast so windage becomes a sizable component of drag and needs to be addressed by the design. Windage can actually be less than a single person boat because the riders sit within the hull behind front deck cowling or fully enclosed.

Again this points out the need to isolate and understand the losses within the whole system. If you do not do this you are bound to have a flawed design.

So it would not make sense to design to suit independent drive legs when each rider can simply gang to a single through-shaft using efficient right angle drives. It also allows a single large efficient prop. With a tiny tension strut as opposed to large draggy appendages supporting each prop.

Overall your monohull proposal is a very poor concept. I could not see any good reason to do it like this unless one is wedded to a particular type of drive leg.

Rick

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7. Joined: Aug 2008
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Location: Bellevue, WA

### MLampiJunior Member

Ventilation and cooling?

Rick,

Your enclosed boat designed for two or four people looks like it would be highly efficient and is certainly optimized for speed at low power input. I'm sure it would do pretty well, at least until the pilots collapsed from heat exhaustion.

I'm only partially kidding. One of the things I'm found while pedaling in races is that having a nice cooling breeze and the easy availability of water cooling is important on all but the coldest days out on the water.

If you have no way of getting those breezes to cool off the pilots, and if the water is unreachable for their hands, then they will heat up very rapidly and performance will diminish rapidly.

How does Greg K. do it in his enclosed boat? Doesn't he find himself getting rather toasty, the air stale, etc.?

8. Joined: Aug 2008
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### MLampiJunior Member

That's one way you could put it. For almost the entire race, with the exception of the start and the last part of the finish, I was racing the speed and heart rate reported by the Forerunner, or going slow to take reasonably steady pictures. The times are not out of line from previous years where I actually raced with the field, but ran into more weed problems.

Don't get me wrong - I think your setup is excellent just for those reasons. If I didn't feel the need for a good, strong reverse and dynamic stability forward I'd strongly consider using your type of arrangement.

I did get the spreadsheet open, but I need to spend some more time analyzing the results with respect to power vs. heart rate, etc.

Yes, the Garmin Training Center stuff is pretty limited and a little buggy. The freeware/shareware SportTracks software is much better, but even that I haven't spent enough time with to understand all of its capabilities nor those of all the user-written plugins that are available.

No, that boat didn't show up for this race, either. In fact, there was no other pedal boat of any type at this event. Sigh...

One thing I neglected to mention about Saturday's race, that I touched on a little in my blog and other places, is that I'm beginning to think there is the possibility that the Cadence can actually get on a plane at about 8 mph under certain conditions.

I first noticed this phenomenon last fall when I had a 10+ pound lighter boat and decided to not carry anything else but water, and the canoe paddle I normally kept strapped to the right rear side of the boat for easy access was, instead, strapped to the front cockpit cover. This still allowed for easy access, but the weight was now forward and centered.

At that flatwater race I decided to have a faster start and the boat just moved. My pedaling cadence was quite high and my heart rate was in the 160's. I didn't have a cadence sensor at the time, but I'd guesstimate I was pedaling around 90 to 95 rpm. The GPS had turned itself off, but my sense of speed was that I was going at least 8 mph and my legs were feeling absolutely fine. The OC-6 and everyone else were quite far behind for at least the first half mile when I sort of panicked and thought to myself "1. I don't know where I'm going in these channels and a turn is coming up, and 2. I don't know how I am going this fast and I'll probably burn out even though I'm feeling fine right now.".

It was weird.

Anyway, at the flatwater GXSC in the heavy boat I've been racing all year I had the paddle in front again, but also had the 3 pound camera around my neck. I didn't have the outriggers on it as I have had for most of the other races, either. Anyway, there were a couple of times when it seemed like this boat was almost but not quite in that same mode.

I think that if I had a truly lightweight carbon Cadence I just might be able to get it to plane for most of a race, so long as it was trimmed a little more bow heavy. If so, then the gearing will need to be adjusted from 6.5:1 to 7:1 or higher.

Michael Lampi

9. Joined: Jan 2008
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Location: Massachusetts South Shore.

### tinhornSenior Member

THIS is why your name sounds so familiar to me. I've spent a lot of time viewing your pictures of previous races. (I just moved away from Walla Walla, and was particularly intrigued by NW events.)

That's odd, but this is a great segue for a question I haven't been able to get answered: We know leg muscles are more powerful than arm muscles, but to what general degree? Twice as powerful? More?

I'm curious because I've seen old hpb designs that use the upper body for propulsion when it seems that pedals would have been more effective.

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### beppeJunior Member

Open Waterbike monohull?

Rick
Thank you for your opinion, but this time, I believe, it is off the point.
The examples you give, althought so cool, doesn’t seem to take into account the OW specifications http://www.openwaterbike.com/architecture. As we all know, engineering is about trade-offs between (sometimes contradictory) different goals. This is the case here.
The Open Waterbike, as described by its specifications, is essentially a high-performance recreational boat. It is intended for use in good weather, calm or not so choppy waters, by reasonably fit but not-highly-trained common people who like to stay out in the open. Safety (and the perception of safety) and user-friendliness are as important as performance.
What you propose are essentially canoes in which you sit in a position not so comfortable nor necessarily so efficient. I am a kayaker and a recumbent cyclist; in any canoe you can get wet and capsize also in good weather, if you are not well trained. Your enclosed canoe could possibly need a good ballast and/or floaters for beginners or waves.
A low recumbent position, comparable to that of your drawing with the seat lower than the crank axis, is less comfortable then that of the OW prototype catamaran, with the seat 10 cm over crank axis level (http://www.openwaterbike.com/archit...bike-drive-unit/the-forward-tube-connection/). This could be also more tiring on long distances, even if the effect on performances is not well known.
For recreational (but also for tourism and commuting in good weather) you could prefer to sit higher out of the boat.
Finally, if I remember correctly, the Wavebike twin was a pedal boat in which the riders were not sitting inside the hull, but riding in a traditional cyclist position with high windage, possibly comparable with this of two recumbent riders side-by-side; if I remember well that was possibly the fastest production boat ever.
I agree with you, anyway, about the shortcomings of my monohull design (windage and double drive unit) but the real point is how much you pay for these choices, so I believe that a correct evaluation of the concept should be quantitative rather then just qualitative.
It could be very interesting to compare the canoe design performance and with this monohull concept.
I suspect the loss could be fairly acceptable.
Finally, no, I am not ‘wedded’ to any particular type of drive leg. I am interested in a standard interface for drive units to enable modularity. And yes, I am ‘wedded’ to modularity , the gateway to collective development according with the Open Waterbike concept.

Quandoque dormitat et bonus Homerus ;-)

With high esteem…
Beppe

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11. ### Guest625101138Previous Member

Ventillation is an important requirement as is sun protection. Greg set up a small fan and a couple of vents in the the test boat. His biggest issue with it is that the cabin top is so low that he cannot lean forward.

The concept that has evolved for the ocean boat has a number of port holes that can be opened to get free flowing air. The port holes can be sealed tight for heavy weather.

Greg found the most difficult aspect of the enclosed cabin was motion sickness but this is to be expected for a first time outing in the ocean.

The ocean boat is about 8m long and 1m beam by a bit over 1m high.

Rick W.

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12. ### Guest625101138Previous Member

Mike
There is a target speed around 18kph (maybe higher) where planing becomes less drag than displacement. Probably require around 300W for a very light boat. The most efficient hull for this is shorter and wider than the Cadence. The wide flat aft run on the cadence lends itself to planing though.

You may also find that with very good finish on your hull and increasing beam aft that in smooth water it can sustain laminar flow over a good portion of the hull. When this happens it is like you are on wheels. The smallest of chop upsets it so you can detect the change if you are looking for it.

Rick

13. ### Guest625101138Previous Member

The size of muscles in legs or arms does not have much bearing on it. It is the ability to process oxygen and convert to energy so lungs are the main determinant of performance unless you are just sprinting.

Rowing sculls make use of both legs and arms but they are doing 6 minute events.

Paddling or pedalling have almost identical biomechanical efficiency measured in labs at around 26%. Sculling is lower at around 22% but then there are more muscles involved and it is normally anaerobic so making use of stored reserves.

Rick W

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### beppeJunior Member

catamaran boat data as required

Rick
here are the data you require. My data about this boat include the usuals but also total metabolic power, and they are comparable with those of other boats found in literature, including olymic kayaks. I believe that analyzing these data with your computational tools and extending the results to more efficient PPBs can allow an assessment of the potential of our pedal powered boats against traditional high performance boats.

each hull:
length (WL) = 4800 mm
design displacement= 50.3 l (0,05 m3)
wetted surface 1.13 m2
prismatic coefficient= 0,60
section under WL is semicircular, dmax = 103 mm

hull separation:1.35 m

drive unit:
thickness: 25 mm
wetted surface: 16 dm2

rudder:
thickness: 8 mm
wetted surface:8 dm2

enclosed : dwg files with cross sections

Best
Beppe

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15. ### Guest625101138Previous Member

Beppe
I have attached the reconstructed lineplan of your cat.

It will achieve 10.1kph with 150W in calm conditions providing it has an efficient prop. It will require 245W to do 12kph. By comparison V11J requires 150W to do 12kph - cat is requiring 63% more power than the optimised mono.

An optimum catamaran for 10kph would require 15% less power than your cat.

If you give me some dimensions of your prop I can do a more accurate calculation using it. Need to know the design pitch, overall diameter, hub diameter, blade chord at a few points to get an idea of planform and blade section profile if you have it (Is is based on a symmetrical section or is it an asymmetric profile?)

Rick W.

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