A good test!

Human powered boat lake test from Greg Kolodziejzyk on Vimeo.

This morning presented a VERY good environment for testing, and I think I learned a lot. Unfortunately though, she is still not any faster...

I met my brother in-law Cyrille out at the Elbow Valley community lake at 7:30 this morning before the wind started to blow the lake apart. The lake was mirror flat and it ended up being the perfect place to test, as it was easy to do a quick loop, pull the boat up to the dock, make a change and do another quick loop. There was no wind and no current, so the need to repeat every test with an averaged 'out and back' trip wasn't required. I would do a 100 watt 'out' leg, turn around and do a 150 watt 'return' leg back to the dock.

click to enlarge

Rick was exactly right about the self stabilizing features of a pushing propeller. The additional strut that I added to better support the prop actually INCREASED the vibration and made the boat slower due to the drag of that strut. It was faster and vibrated less when I removed the addition. In fact, we found that we could leave the prop strut bracket just sitting on the deck without any fasteners holding it in place, and the prop would still push the boat as fast as it would when the prop bracket was screwed down to the hull.

The additional prop strut was tested and removed

We also found that slight pitch changes to the prop made very little difference to the speed. Neither did slight changes to the direction (right to left) of prop thrust. I brought some clamps with me and we clamped the prop strut bracket down to the deck flange in a variety of different positions which changed the position of the prop. None of these off-center positions made much of a difference to the speed unless it was greatly exaggerated. We also changed the depth of the prop and that also made no difference. This leads me to believe that my prop is OK - it is producing exactly the right power at exactly the right rpm that it was designed to do, and it is able to do it consistently in various configurations. It seems pretty robust and if something in the drive system were responsible for the slower than expected speeds I would expect that the changes we were making today would have a far greater result than they did.

Using my spare prop, I decreased the degree of twist a bit (sorry Manny!). We mounted the 'more grippy' prop to the shaft and it was far less efficient. I produced more power at lower RPM, but the resulting speeds were all lower. Probably due to the inaccuracy of twisting the prop in a vice with wood blocks and a clamp. At least I know now, that the prop Rick designed and Manny CNC machined, is working perfectly as it was designed to.

So, here is where I am at:

1. The speed I need to break Carters record of 245 km in 24 hours is an average of 10.2 km / hr.

2. My average power output over 24 hours (including breaks, coasting, and zeros, etc) is 110 watts.

3. According to Ricks design and his V11, 110 watts should produce 10.8 km / hr which would result in a total of 259.2 km

4. Currently, my version of Ricks V11 goes 9.4 km / hour on 110 watts of power which would equal a total distance of 225.6 km which would be about 20 km short of Carters record.

5. At 150 watts of power, I am currently getting 10.5 km / hour and I am supposed to be getting 12 km / hr. I am about 12.5% slower than Ricks V11 design.

I now know that my lack of speed is probably NOT due to the drive or prop, but probably due to hull drag. The fastest I have been able to go is a little over 11 km / hr and the power required was over 200 watts. Input power over 200 watts produces very little additional speed. Rick can get his V11 up to 16 km / hr! This alone tells me that the drag of my hull, or overall drag is probably the culprit. Here is a speed/power plot - notice that my entire curve is lower than Ricks, which to me, suggests that the reason I am slower is due to my hull speed being lower which could be due to additional drag.

One of the causes of this additional drag could be the outriggers. I am finding it very difficult to balance off of the outriggers. Rick is on vacation right now, so he is unable to offer advice. I played around with trying to balance on the center hull today and found it very hard - even with my new low seat position. We played around with raising and lowering the outriggers and I could not get the boat balanced. You can see in the video that almost always, one outrigger is dragging through the water. The extra drag from this outrigger could be slowing me down, but is it responsible for the missing 12 % ?

Balancing act

Another cause of drag is the flanges on the u-joint that I am currently using. I have ordered a new u-joint that is the same diameter as the shaft and I will replace the fat draggy one when it arrives.

The last refinement regarding drag that need to look at, is the surface finish of the hull. It is far from perfectly smooth, and I wonder if the surface texture of the carbon fabric weave as well as a few bumps and wobblies could be responsible for my missing 12 percent? Also, one of Cyrille's concerns was that the skin of the hull is very thin, and between bulkheads you can depress the hull with your hands. I wonder if the water would have enough force to push the sides in and distort the hull shape? I wonder how I can test for this deformation?

We even placed rocks on the bow and stern to see if weight distribution made any difference. It made it slower.

Click to enlarge

Cyrille enjoying a spin

Labels: ,

16 Responses to “A good test!”

  1. # Blogger "the Dude"

    not sure if I follow , but consider this:

    move the outriggers up out of the water (or remove), only as "emergency floats" so you don't tip over,

    install a front submerged hydrofoil, like dolphin tail. As long as you are MOVING, this foil provides a stable platform, replacing the need for outriggers or ballast. It can be thin but strong, and should have little drag. It functions like a self-balancing gyroscope, in a sense. Not sure what the technical term for it is.

    you get my drift?  

  2. # Anonymous Guus Bonnema

    Hi Greg,

    Looking at the data, you see the difference between the two curves increasing. In the upper curve, the higher the speed, the less increase you get per unit of power input extra. For the lower curve, it looks like per unit of power added the decrease is non-linear.

    I would say in the lower curve something is creating drag increasingly.

    It looks like you have got a very reliable boat. It just is not the fastest in the world.

    However, I expect this to be a good thing. It means that your base is solid. Now what you need to do is spend 80% of your time and effort finding the parts of the last 20% of things that slows it down.

    I expect there will be multiple causes, and you will need to improve all of them in order to get a substantial increase over the 10.2 km/hr.

    From your account, it seems that everything "extra" or "extra advanced" you do causes the boat to slow down. So maybe the adage "less is more" is valid here.

    Greg, I realise looking from a distance is alway easy and I admire your perseverence and will power.

    I can only say, keep it up.


  3. # Anonymous Anonymous

    I had a fiberglass hull and I put an inflatable bags in the hull at 8 psi . It made the hull a lot stiffer.  

  4. # Blogger Bruce

    Hi Greg:

    However counterintuitive it may seem I think those outriggers should be down in contact with the water at all times, not deeply, but enough to completely eliminate the rocking motion. This should provide a bit of lift to offset hull drag, especially if they maintain a slightly nose-up attitude which would keep them planing. In photos from the first test, the boat seemed to trim just a bit bow-down, and seemed to need a smidgen of weight shifted aft to get the bow biting a bit less.

    Also counterintuitively, a rougher, rather than smoother skin can give you less surface drag, because it produces a more gradual gradient of water velocity at the hull/water interface - producing better "boundary flow". Prijon is one kayak manufacturer that takes this approach in production boats.

    It seems you have most of the details pretty much dialed in. I hate to ask, but is the hull itself actually long enough for maximum speed with the power you are putting out?  

  5. # Anonymous Russell

    Greg, my comments come from a sailing background here in Australia, sailing 14 foot dinghies(NS14)
    If you think that the hull has too much drag with imperfections, have you thought of spraying the underwater sections with automotive spray putty, and sanding this back with wet and dry sanding paper, starting with 800 grit and going up in steps to 2000, always using the paper wet. This should give the hull a smooth finish which can be polished with a marine teflon polish, or something similar. The weight increase should be minimal.
    That U joint looks very draggy, have you thought of giving it the heave ho, and use the mid point shaft support to push the shaft into a curve, hopefully finishing with a near horizontal drive onto the prop? Is it that important to finish with a horizontal shaft drive? this may also help reduce shaft vibration.
    Lastly, why not borrow Rick's boat?  

  6. # Blogger Kitlani

    Just a thought: Could you increase the length of the leg stroke by using a more oval (rectangle with round corners) sprokett? The foot on the pedal would travel along a path like the shape of a medicine capsule. Your knees would have to come up farther but you'd have more power at your disposal.

  7. # Blogger Michael Lampi

    Hi Greg,

    From what I saw in the video your hull is generating a bit more waves than Rick's, starting right from the bow.

    Also, if you aren't using a springy prop shaft and instead are using a U-joint, that could also create a bit of drag.

    Lastly, Rick's aluminum skinned hull is by its very nature very smooth. Fast rowing shells and surf skis are also very smooth. You would do well to make your hull as smooth as possible.  

  8. # Anonymous Cyrille

    As we discussed, I also think the rough hull surface and all its imperfections are a large contributor to the overall drag. The surface should be glossy and smooth in order to minimize friction and maximize speed. You need to fill all the cf divots, sand, then gell the hull so that it's glass-like.  

  9. # Anonymous jan lietaer

    Hello Greg
    is it not possible to pull the boat with a rope from an other boat ( as shown below) and to measure the needed force on the rope.


    The ratio between force, speed and power is not that difficult to find out.(basic physica)
    This test would give you certainty about the quality of the hull.

    Jan Lietaer  

  10. # Anonymous jan lietaer

    These should be the force on the rope from the "tugboat":
    Al forces are in Newton

    Power Rick speed Rick force
    50 W 8.10 km/h 1.71 N
    75 W 9.40 km/h 2.22 N
    100 W 10.40 km/h 2.67 N
    125 W 11.20 km/h 3.10 N
    150 W 12.00 km/h 3.47 N
    175 W 12.70 km/h 3.83 N
    200 W 13.20 km/h 4.21 N

    Power Greg speed Greg force
    50 W 7.10 km/h 1.96 N
    75 W 8.10 km/h 2.57 N
    100 W 9.30 km/h 2.99 N
    125 W 9.90 km/h 3.51 N
    150 W 10.50 km/h 3.97 N
    175 W 10.85 km/h 4.48 N
    200 W 11.20 km/h 4.96 N  

  11. # Blogger biff

    I like Jan's Idea, but I would use it as a tool to figure out the drag.

    Since the prop wouldn't be spinning when you are towing the boat, the readings won't be accurate measure of the amount of power required to propel the boat. but if you remove the prop, you would atleast get something and also be able to compare different configurations and determine what increases or decreases drag.

    Here is what I would do.

    First, buff the hell out of the boat and fine tune the bow. I can't stress that enough. I believe laminar flow is a big part of your problem. Epoxy a razor blade (not really) into the front of the boat, and get it so it is borderline dangerous, wax/buff/repeat until the surface is shiney like marble, and there are no inclusions. The leading edge is critical.

    Then get on the water and see how much speed improved. The good thing about that modification is it only requires your own hard work.

    Second, If you are still not seeing the speed you want (and have lots of spare time), tow the boat at a fixed speed (without the prop on) and see how much force it takes at different speeds. If the forces match up with what Jan posted, then your problem is with the drive train. Testing this would require help from a couple friends, a motor boat, and a full test regime to make sure your measurements are accurate. You could test and see how much drag the prop supports produce, you could also scuff up the surface and see how that affects drag, or even try different kinds of waxes / techniques.  

  12. # Blogger "the Dude"

    What you have now is the equivalent of a unicycle with training wheels, great stability for slow movement, but not for smooth sustained speeding forward.

    Lift the outriggers above the water a couple inches or so...

    Install horizontal fins/foils which provide slight lift against your vertical gravitational profile (your inline body above the water surface which is pushing straight down)

    Now your recumbent position (once you are propelling) maintains equilibrium like a bicycle with both wheels and no training wheels.

    The lift to the craft should balance out the added drag, the sum effect is that you (and boat) ride a tiny bit higher and proportionately a tiny bit slower, but synergetically nearly all your energy goes to direct forward motion, rather than side to side wobbling.

    To me this is obvious, and I don't know how the other guy could have been faster without this.

    Just my 2 sense.  

  13. # Blogger "the Dude"

    The Polynesian sailors with their outriggers are dealing with aero~dynamics, like sea birds.

    You pedaling Within while in motion are unlike that, you are dealing with kineto~dynamics, ergo~dynamics and hydro~dynamics. You are far more like a dolphin that swims both beneath, above and at the water surface, sometimes surfing waves, immobilised only during sleep and rest (with the outriggers lowered).

    Within is not a sailboat, but an HPV, a self-propelled water glider.

    (btw, I just happened to see on my way to lunch a kinetic sculpture rolling along, a fine wooden boat with huge horse-carriage wheels on the left and right side rolling along, they convert to paddle wheels when in the water I guess.)

    ok, that's my last centavo!  

  14. # Blogger fhe


    I like the hydrofoil idea (called it airfoil by mistake earlier).
    It appears the problem is not in your prop or prop setup.
    That leaves the hull and I agree with most that it should be as smooth as possible. Roughing it up only works at high speeds (i.e. the dimples that Zipp likes so much).
    Alternatively, the width of your outriggers could play a role. You said they were wider than Rick's and maybe their position viz a viz the bow wave does matter.

    The proof is -as always- in the pudding so testing is the only option.  

  15. # Blogger Jarl

    Maybe something to be inspired by:

    But a true hydrofoil setup is probably (?) not suitable for long distance endurance type of challenges.  

  16. # Blogger Jarl

    Fun hydrofoil ride :-)

    And good luck with your projects Greg, I visit your sites regularly for updates, cool with the inventor+human endurance approach.  

Post a Comment

Subscribe to email updates:

Email :

About Greg video:

    follow me on Twitter

      Adventures of Greg Home
      Motivational Speaker

      featured slide show:

      Archives (newest first)

        Web This Blog

    © 2006 | PedalTheOcean BLOG by Greg Kolodziejzyk.
    motivational speaker
    No part of the content or the blog may be reproduced without prior written permission.