Pedal Powered Boats

Rhinox,

I'm glad to hear your desire to set the design parameters first then optimize a boat around them. It would be good to get an independent estimate of your sustained power output while you are still in the preliminary design phase. Take a bicycle outside on a fairly flat course with not much wind. Measure how far you can go in 30 minutes. Convert to miles per hour. Use a bike calculator like http://www.kreuzotter.de/english/espeed.htm (you can Google other calculators also if you like.) Enter the information for yourself and your bike. Find the power level that matches the miles per hour you calculated. Compare this power level with the reading from the exercise bike for consistency.

Coach Dave

 

With all the talk of high wattage this might be of interest.
note below where I got this from.

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Today's Topics:

1. Matt Johnson First Test of his V15-65 (Rick Willoughby)
2. Matts Boat (Ian Cassell)
3. Re: Matts Boat (Rick Willoughby)


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Message: 1

Matt Johnson contacted me in August 2011 regarding a pedal boat
design suited to his weight and power output. He finally got it on
the water today and posted this video:
http://youtu.be/IL5GBgJbS_4
Matt is the most powerful engine I have done a design for to date so
it will be interesting to follow progress. He is aiming to join Mike
Lampi in the Sound Rowers races when his time permits.

The resulting hull design is based on my V15 series but optimised for
110kg displacement and 300W power. Hull ended up 6.5m long. Matt
chose skin on frame as his method of construction along with a
separate tubular frame and commercial recumbent seat that mounts to
the basic boat. The drive is configured with side-mounted curved
shaft spinning at 7X cadence.

I provided a hub for folding prop and the second set of moulded CF
blades for testing.

The test was impressive but brief because the folding CF blades
snapped when he accelerated for the second run.

Rick Willoughby
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Message: 2

That boat of Matt's really flys, he really
accelerated away fast. Wonder what
speed he got up to. When he has used
it a few times he should be ready to set
a few records. The rudder caused a bit
of turbulence but that is a minor problem.
Hope his boat can stand up to the power
he can put into it.

Ian

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Message: 3


Ian
He pushed up over 13kph easily but said he realised he has some
conditioning to work on by the time he got to the other side of the
lake. The design speed is 4m/s or 14.4kph. He should get to that
with 270W . When he was bike racing he was working in the high
300s. No doubt it will be interesting to follow progress.

I suggested he nurse the blades by staying below 16kph until he had
worked out what needed changing or setting up better. I forget to
tell him not to accelerate hard. Blades broke the second time he
took off to do a pass for the camera. I have tested the new blades
to static load of 120N, which is 50% higher than I was prepared to
take the first set. New layup should be able to take my full power
so will do some flat out sprints with my next set.

Matt will fabricate a set of stainless blades while he is waiting for
my improved CF set. It would be a shame if the blade strength
limited his acceleration.

Rick Willoughby

 

Rhinox,

Coach Dave's idea looks interesting.

The only thing I would add is ride for 15 minutes then turn around and ride back.

This would cancel any grade and wind effect no matter how small.

If you choose to do it, let us know the results.

-Tom

 

Hello Rhinox!

I do not wonder you can do 200 Watts. At your body size, your feet would have to be twice as strong as my feet. As power is force x frequency, twice the force means twice wattage.

A few years ago, I worked on an engine for BMW, delivering 600-700Nm at 3l displacement. This way they could increase power output to 100kW per liter displacement for a Diesel engine, which was thought to be unreachable back then.

As displacement increases at the third power of length, you only have to increase size of a boat by approx. 25%. I think that your weight is advantageous here, as the wetted surface gets relatively smaller at bigger dimensions.

Andreas

 

The human body doesn't quite work like that, though, as sustained power output isn't a function of muscle strength but one of aerobic capacity. It's the ability of your lungs to exchange oxygen and your circulatory system to transport that oxygen that sets the human bodies power limit, which is why it's commonly referred to as the "aerobic limit".

It's the same reason that using big muscle groups, like your legs, doesn't give more sustained power than using smaller muscle groups, like your arms and back when paddling.

It is true that having greater blood volume, lung capacity and heart pumping ability does increase sustained power though.

 

Agreed Jeremy, the only thing I'd add is Rhinox is working beyond his aerobic threshold. His high heart rate, level of fatigue and quite likely "non conversational" breathing rate are strong indicators. I have encouraged him to ease off but the allure of more is better is just to tempting for most amateur athletes.

-Tom

 

I might try this. I know the perfect place to go, its called the Towpath Trail in the cuyahoga valley national park. Its a long, flat, multipurpose trail. Will the calculator do a good job of accounting for my much higher wind resistance than average size folks, and the fact that I ride a mountain bike with hybrid tires and not a road bike?, and probably have higher losses due to friction that newer or higher quality bikes? How would I account for terrain? Its flat and smooth, not really dirt, but its not concrete either.

Also, whats the best/cheapest way to measure distance on a bike? I'm not sure I'll have signposts or other accurate ways of knowing how far I'm going down the trail.



Tom,

Wouldn't you say my workout yesterday was within the aerobic zone? 141bpm is like 75% of my estimated maximum heart rate, and the aerobic zone is supposed to be 65%-80%, right? And actually I was having conversation for about 20min of the time I was in the gym yesterday. I'm sure I hit anerobic especially during interval days or when I'm pushing to max out a 30min personal best, but I'm doing that at most every other day.

I have my own ideas, but I'm curious as to why you would say more is not better? Anaerobic and aerobic cardio both have their place, right?

re: #1395: the resting heart rate VO2max estimator says I'm at 48, but idk how accurate thats supposed to be.

Regarding the heart rate calorie burn estimate, if I change the weight entry to 225lbs and leave everything else the same, the calculation say's I'd burn 429 calories (vs 529 at my current weight). I think that seems like a reasonable difference, as bigger people do burn more calories just by being bigger.

What's interesting is that that number would lead to a 200W generated result using the same 20% efficiency, compared to the 250W I calculated using my current weight. Or, I'd have to be about 25% efficient to calculate the same output power - which it might be a reasonable assumption that weighing less would lead to a higher efficiency since I'd have less useless mass to move around? If I set the same resistance, the output would have to be the same regardless of my weight and the calories I'm burning. Maybe the 200W is the more accurate output number and the 250W is an overestimate because the higher calorie burn is due to my weight and not higher output (or, I'm less efficient now due to being bigger)?

 

Rhinox,

The bike calculators assume a paved surface so your best bet is to stick to the paved sections of the Towpath. The 8 miles north of Thornburg Station are paved according to the website. There may be other paved sections closer to you if you check into it. I experimented with plugging in different rider weights on this calculator http://www.kreuzotter.de/english/espeed.htm and saw that its "effective drag area" increased with weight. If you scroll down the page you can see how the calculator is modeling the various drag factors. Choose the type of bike and tires that match your configuration. To measure distance you can borrow someone's GPS unit for the ride. Another option is to install a multifunction digital speedometer on your bike. They start at about $15 dollars at Walmart. Make sure to calibrate the speedometer to your tires before your ride. I line up the front tire's valve stem with a crack or mark on the pavement or sidewalk, go in a straight line for 10 tire revolutions, mark the ending point, measure the distance, divide by 10, convert to mm, then program that number into the speedometer. Enjoy the ride - maybe this will be the year that you pedal your custom built boat!

Coach Dave

 

Rhinox,

The more fit one is, the higher their aerobic/anaerobic threshold (heart rate that is). There are formulas to approximate which take into account resting heart rate, age, maximum heart rate, etc. I'm a little out of date on the latest ones but you should be able to find them. The best place would be through a human performance lab.

As for the rest, I think you're well on your way to a good understanding of all the variables involved. The biggest message here is the exercise equipment is notoriously inaccurate.

-Tom

 

Hi

I called the folks at Mitrpac to order a 90 degree gear drive today and I was asked which direction I wanted, did I want counter rotating shafts.......I went completely brain dead and coundn't remember which way the props rotate. Still can't!! I am going to use the curved shaft system with the prop pushing the boat. (From either side, don't think it matters to me) The APC I have at home looks like it wants to turn CC when I am standing at the bow looking towards the stern. What are the chances that all potential props for this application will want to turn the same way?

Thanks,

Glen

 

50/50?

-Tom

 

Glen,

Most props are right hand screws. As shown in the diagram when a right hand screw (or propeller) turns in the direction the fingers of your right hand curl it advances in the direction of your thumb. If you are seated in the cockpit of a plane looking forward at a spinning right hand prop in front of you it turns clockwise to pull the plane forward. This is the standard "tractor" prop. If you got out of the cockpit, walk out in front of the plane, then turn around to face the plane you are now facing aft so the prop is turning counter clockwise from your new perspective. If you are at the bow of a boat looking aft towards the stern a right handed prop turning counter clockwise pushes the boat forward.

The less common "pusher" prop is a left hand screw and turns the opposite direction to advance. Unless you have a specific reason to use a "pusher" prop you should use a "tractor" (right hand) prop.

Dave

 

Glen,

If you are making your own prop you could make it left or right handed. If you are buying a ready made prop you will find a larger selection of right handed props.

Dave

 

It's true.

Right hand are by far the most common by a huge factor.

Although, French helicopters are just as commonly the opposite.

Ah, the French.

-Tom

 

Glen:

There is much larger selection of tractor compared to pusher props in all brands of RC plane props. There is a "front" face to the prop with is where the diameter and pitch are stamped. The "front" face should point in the direction of travel, just in case you were not aware. As I recall, one chap on this list mounted it the other way and was still able to power forward, but at much reduced efficiency....


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