PedalTheOcean.com



THIS BLOG HAS MOVED
adventuresofgreg.com





Strutless bizarreness



I went out to a new lake today and the test results were enlightening. I think I can narrow down the speed difference between what we measure at Elbow lake and both Glenmore reservoir and today's Ghost lake to a preferential current flowing through Elbow lake.

I'll explain: At Elbow, I noticed that my average speed doing a counter clockwise loop around the lake was 11.7 and my speed doing a clockwise loop was 11.1 (km per hour). I assumed this was due to some natural left hand turn tendency of the boat that I was fighting when turning right.

We also assumed that the average speed would be slightly higher when moving in a straight line. At yesterdays Glenmore test and today's Ghost Lake test, this was NOT the case - it was slower in a straight line. We figured that must be due to less drag while turning left and started looking into issues like the strut possibly not aligned and acting like a rudder, recalculating the amount of rudder required of offset the side thrust, and looking at the hull itself.

I repeated a short, 1/2 km loop in both directions today at Ghost lake and was very surprised to measure the same average speed in both directions which was 11.5 kph. This pointed to a current at Elbow being the issue. My average speed over BOTH directions at Elbow just happens to be 11.4 kph - very close to my average today. If we add .1 kph for the smaller flexible shaft to the 11.4 Elbow speed, both speeds are exactly the same.

Elbow valley lake is fed by a small river flowing into the West end. There is a levy that runs under a bridge at the south west side of the lake. The direction of water flow would be from the river then south then south across the lake over the levy. A counter clockwise loop would be taking advantage of this flow whereas a clockwise loop would be fighting the current for at least 1/2 of the loop. There is PLENTY of water flowing right now, as the spring melt is happening. The water level in Glenmore and Ghost lake is very low in preparation for the spring melt from the mountains. Stefan tells me it is creating all kinds of strange eddies and currents. Not the most ideal testing conditions.

This Elbow current result is good news and bad news. The bad news is that my REAL average 150 watt speed is 11.5 kph, not 11.8 like I thought. This could be worth as much as 7 km over 24 hours if I could maintain an ending average of 150 watts (which would not happen). More likely, the difference is probably worth 4 to 5 km over 24 hours. The good news is we found the problem and it isn't anything I can do anything about.

This is bizarre: During today's trouble shooting session at Ghost, I wanted to eliminate the prop strut as the cause of the problems so I just took it off. That's right - there was NO strut holding the prop to the boat - just the shaft. The prop was dangling off the end of an unsupported shaft coupled to my gear box.

The two-blade pusher prop is self-stabilizing meaning that each blade corrects it's attitude when the other blade slips due to changes in the angle of attack (or something like that - I'm regurgitating what Rick told me). I may not be explaining it correctly, but I understand what is happening. This means that the prop will simply start pushing against the shaft and find a horizontal attitude on it's own.

And it works! There was no perceptible difference in feel when I removed the strut, and there was a .1 kph increase is speed due to removing the drag of the strut. Very strange. If you saw it you would laugh and think it is a joke.
This is the strutless prop. No joke! It works!

A nano-second after tripping the shutter for this photo,
a gust of wind came up and blew the boat off the stand
into the water busting my rudder in the process!


Speed data:

date lake power watts wind kph waves rudder prop loop size km loop dir hull floats other SPEED kph
06/05/08 elbow 150 5 ripples big thin .5 counter taped norm
11.1
06/09/08 elbow 150 calm flat big thin .5 counter painted norm
11.2
06/09/08 elbow 150 calm flat small thin .5 counter painted norm
11.7
06/09/08 elbow 150 calm flat small thick .5 counter painted norm
11.7
06/09/08 elbow 150 calm flat small thin .5 counter painted norm prop strut pulled into hull with cord 11.6
06/09/08 elbow 150 calm flat none thin .5 counter painted norm
11.8
06/09/08 elbow 150 calm flat small thin .5 clock painted norm
11.1
06/09/08 elbow 150 10 ripply small thin .5 counter painted norm
11.5
06/12/08 elbow 150 20 waves big thin .5 counter painted norm
11.0
06/09/08 elbow 150 20 waves big thick .5 counter painted norm
10.9
06/09/08 elbow 150 20 waves small thick .5 counter painted norm
11.3
06/09/08 elbow 150 20 waves small thin .5 counter painted skimmers rods 10
06/09/08 elbow 150 20 waves small thin .5 counter painted skimmers no rods 10.2
06/16/08
elbow
150
calm
flat
small
thin
.5
counter
painted
norm
flex shaft & freehub
11.9
06/16/08elbow150calmflatsmallthin.5counterpaintednormflex shaft & freehub11.8
06/16/08elbow150calmflatsmallthin.5counterpaintednormflex shaft & freehub11.8
06/16/08elbow100
calm
flat
small
thin
.5
counter
painted
norm
flex shaft & freehub10.3
06/16/08elbow200calmflatsmallthin.5counterpaintednormflex shaft & freehub13.2
06/16/08Glenmore
150
calmflatsmallthin2
out&back
painted
norm
flex shaft & freehub11.1
06/16/08Glenmore150calmflatsmallthin2.6
out&back
paintednormflex shaft & freehub11.1
06/16/08Glenmore150calmflatsmallthin1.35
counter
paintednormflex shaft & freehub10.9
06/16/08Glenmore15010
ripply
none
thin
.84
counter
painted
norm
flex shaft & freehub11.6
06/16/08Glenmore15010ripplybig
thin
.8
counter
painted
norm
flex shaft & freehub11.1
06/17/08Ghost
150
5
ripply
small
thin
.8
out&back
painted
norm
flex shaft & freehub11.6/11.2 = 11.4
06/17/08Ghost1505ripplysmallthin.52counterpaintednormflex shaft & freehub11.5
06/17/08Ghost1505ripplysmallthin.56clockpaintednormflex shaft & freehub11.6
06/17/08Ghost15010ripplysmallthick1out&backpaintednormflex shaft & freehub11.7/11.2 = 11.4
06/17/08Ghost15010ripplysmallthick.7out&backpaintednormflex shaft & freehub. NO PROP STRUT
11.8/11.2 = 11.5
Observations
1. Every 5 kph of wind equates to .1 kph decrease in speed
2. Big rudder is .6 kph slower than small rudder. Small rudder is .1 kph slower than no rudder
3. Right hand turns dramatically slow the boat down.
4. Paint vs packing tape was worth a speed increase of .1 kph
5. Elliminating the prop strut is worth an additional .1 kph in speed.
6. Counter clockwise loops at Elbow Valley lake are worth an additional .2 to .3 kph average speed due to current (??? need to verify)

Labels: ,

4 Responses to “Strutless bizarreness”

  1. # Anonymous Anonymous

    The Elbow valley lake difference is a result of Corioli force. Same force that gives the northern hemisphere hurricanes and the southern hemisphere cyclones.

    Also our water down here turns clockwise around the plug hole when emptying the bath tub.

    Good to know the offset thrust is not a measurable penalty - as I determined.

    Vic Gazza was the first person to draw my attention to the self-stabilising forces on a pushing prop. Don't go in reverse though unless you support the shaft.

    Rick W.  

  2. # Anonymous jan lietaer

    Just an idea :in the current layout the prop is pushing the boat. Would a layout where the prop is pulling the boat be more efficient???
    jan  

  3. # Anonymous Martin P. Pernicka

    Pulling instead of pushing, interesting inquiry - but for now, the boat will ride in turbulent waters... creating more drag.
    Prop in pushing stage : may lose some efficiency, if unclean boat creates turbulence.
    Not so with your boat, Greg :-)

    There have been many arguments in this field between aircraft designers... Interesting to follow. Each have it's pluses and minuses. Best way? Try & Error, again. For some reasons, pushing is more efficient then pulling in the waters...

    In your search for best prop; did you tried a 3 blades? Adjustable pitch?....
    The the training boat, funny, I would have go for a catamaran style. Lighter, stabler, more out of the water for less drag.

    Keep up!

    Martin, MTL  

  4. # Anonymous Klaas V.

    An other idea:

    If you use a kayak in a white water river, you use your paddle not only to propel yourselve, but also to keep upright. You can get a lot of upright force if you let your blade "skim" (don't know the english word for it, I assume you get the idea) over the surface of the water. Just like you throw a flat pebble on the surface of the water to let it bounce. This causes little drag.

    Would it be an idea to dump the outriggers and make two "skimming" plates? The faster you propel yourself, the smaller they can be.

    The plates must not touch te surface simultaniously: Just a simple touch at the left, following a periode in which the blades don't touch the water at all, a gentle touch with the right blade and so on.

    It should be a very simple to make and test....

    Klaas V.  

Post a Comment


Subscribe to email updates:

Name:
Email :


About Greg video:



    follow me on Twitter





      Adventures of Greg Home
      PedalTheOcean.com
      Motivational Speaker





      featured slide show:



      Archives (newest first)





        Web This Blog



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