I was visited by Dennis and his friend Dafna from Boulder, CO and San Diego respectively. Dennis has been following my progress for a while and was interested in meeting me. Dafna is a member of the Dewalt cycling team. They were passing through Calgary and stopped in to meet me, so I seized the opportunity and dragged them out to the lake to help me through another round of tests.
Since the weather was not as crappy as it’s been lately (rather than high wind, cold and rain we have high wind and cold), the test for today would be to see if the thicker prop doesn’t start to stall when powering into a headwind. After Manny finished milling the prop, he finished it smooth and ended up removing about a mill too much of aluminum from the mid section of the airfoil on the prop. According to the prop data, if it is 1 mil too thin, then it will stall very quickly if if exposed to higher RPM’s. The new prop that I wanted to test today is an extra prop with some small flaws on it that hasn’t been polished smooth, and is still 3 mils thick.
It made no difference to my average speed at 150 watts around my circular course, and the wind was REALLY blowing hard.
I compiled all of my speed data including today’s results into a table which I will start keeping:
| 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 |
| 06/16/08 | elbow | 150 | calm | flat | small | thin | .5 | counter | painted | norm | flex shaft & freehub | 11.8 |
| 06/16/08 | elbow | 150 | calm | flat | small | thin | .5 | counter | painted | norm | flex shaft & freehub | 11.8 |
| 16/16/08 | elbow | 100 |
calm |
flat |
small |
thin |
.5 |
counter |
painted |
norm |
flex shaft & freehub | 10.3 |
| 16/16/08 | elbow | 200 | calm | flat | small | thin | .5 | counter | painted | norm | flex shaft & freehub | 13.2 |
| 16/16/08 | Glenmore |
150 |
calm | flat | small | thin | 2 |
out&back |
painted |
norm |
flex shaft & freehub | 11.1 |
| 16/16/08 | Glenmore | 150 | calm | flat | small | thin | 2.6 |
out&back |
painted | norm | flex shaft & freehub | 11.1 |
| 16/16/08 | Glenmore | 150 | calm | flat | small | thin | 1.35 |
counter |
painted | norm | flex shaft & freehub | 10.9 |
| 16/16/08 | Glenmore | 150 | 10 |
ripply |
none |
thin |
.84 |
counter |
painted |
norm |
flex shaft & freehub | 11.6 |
| 16/16/08 | Glenmore | 150 | 10 | ripply | big |
thin |
.8 |
counter |
painted |
norm |
flex shaft & freehub | 11.1 |
| 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 |
The other test we did was an idea from Warren Beauchamp who suggested that planing skimmers rather than displacement hull floats might be more efficient. He sent me instructions for building the skimmers that he made for his Necky kayak HPB. They are simply two strips of 1″ thick Styrofoam. I was worried that they wouldn’t provide enough buoyancy, so I added some pool noodle foam to the ends of the arms, but thin foam skimmers provided more than enough bouyancy without the pool noodles. I positioned the skimmers to just sit slightly above the water with the tails pushing down slightly to just below the water line. The tails were pushed down using two fiberglass tent poles.
At first they felt really nice – way lighter than the floats for sure. But the tips kept digging down into the water and I thought they were going to snap in half. We pulled the boat out and used duct tape to pull the skimmer tips back – it looked like what Santa would ride if he ever ditched his sled and went the human powered boat route. This worked very well, and I could get up to speed without any issues. My speed was pretty slow though – about 10 kph for the loop rather than 11.3 and I noticed that the tails were really dragging down into the water. We removed the tent poles and went for another run. This time the speed was 10.2 – not much better and probably not worth pursuing any further.
pushing the tails of the skimmers down into the water.
Overall, because of the high winds today my speeds were about .4 kph slower than when it was calm. Over 24 hours that would add up to about 9.6 km if I were able to maintain 150 watts for the entire 24 hours which wouldn’t happen. Also, the winds typically start up in the afternoon and die down after 6:00 pm. If it was very windy for 8 hours of the 24 hour day, and I lost an average of .3 kph, I would loose a total of only 2.4 km. That’s not as bad as I thought it would be.
Because I’ve done two wind tests, I can estimate that for every 5 kph of wind at 150 watts of power, it costs me .1 kph
Adventuresofgreg's Blog 
Hi Greg:
Seeing how little flotation it takes to stabilize this kayak, it seems the amas could be replaced with a pair of relatively small Vee or Tee-shaped hydrofoils. They would provide needed lift, but less drag (especially in choppy water) when they hit waves than the amas. You aren't looking to elevate the hull clear of the water, but only to provide enough lift for lateral stability.
By: b.bolster on June 13, 2008
at 4:52 am
The wide skimmers seem to leave a wide wake–think of a barge vs a boat. I think you want the wake of the boat and the wake of the skimmers/outriggers to cross each other as little as possible. If so, you want both the wake of the boat and the wake of the skimmers to be as narrow a "V" shape as possible. What about longer narrower skimmers/outriggers? Higher hull speed with a narrower wake and the same surface area on the water. Narrow cross country skis are faster so long as they have the same bottom area dimension contacting the snow (cross country skis "skim" the snow similar to your skimmers)–to keep the same surface area narrow skis have to be longer. Also a tapered stern to the skimmers might be more hydrodynamic.
Rick
By: Rick on June 13, 2008
at 12:17 pm
"You aren't looking to elevate the hull clear of the water, but only to provide enough lift for lateral stability." b.bolster
That's what I'd meant earlier.
Hydrofoil. You don't use training wheels at high speed.
By: "the Dude" on June 13, 2008
at 4:59 pm