Faster with three-bladed prop

A close encounter with a rock has brought an unexpected benefit for David on his Sea Eagle inflatable kayak. (See the earlier post for details of his setup.)  The standard two-bladed prop of the 1003 was damaged irretrievably and as we had a three bladed prop available (as standard on the 801) Malcolm set him up with that to get him going again quickly.

We were also wondering how its performance would change with the different prop. Remember that the top speed for this rig with the standard prop was 11km/hr. After testing on Narrabeen Lagoon last weekend , David reports that top speed is now about 12.5 km/hr (6.7 knots) with the three blader. Naturally enough he’s decided to keep that rather than fit the standard one again. For more in depth test results on this comparison see the recent post.

4 Comments:

  1. Some theory on the 801 vs the Cruise 2.0. Assume they both have the same prop (v8/350). The max RPM of the 801 is 700 RPM. For the Cruise 2.0 it’s 1300 RPM. The Cruise would have to reduce its speed by one-half to approximate the max RPM of the 801. Both props are now the same speed. However the Cruise motor voltage is half of the 801’s. The 801 has a two stage reduction which cuts the prop speed in half but doubles the torque. The Cruise has a single stage. So both motors are delivering the same speed and torque to the prop. Ergo there is no advantage to the Cruise at this prop speed. Do you agree? Thanks. Steve

  2. Hi Steve,

    Your theory makes sense to me as far as power to the prop is concerned. That is, there would be no difference in the power being delivered to the prop.

    There could be a difference, probably small, in electrical and drivetrain losses to get to this point. We could speculate that the double reduction of the 801 would introduce more losses than the single reduction of the Cruise. On the other hand, the lower voltage of the Cruise would require higher currents and so there may be more energy lost to heat, perhaps balancing the effect of the reduction.

    In practise it would probably be very difficult to measure the difference.

    Cheers

    Chris

  3. Hi chris ,
    Just a question I was wondering if it was possible to fit a 3 bladed prop to an ultralight and if it would void warranty ? I have a rather long ocean kayak and I would think it would be easy to max out the std 2 blade prop.
    Thanks in advance 🙂

    • Hi there,

      The three blade prop has a different shaft shaft size and so you can’t use it without modification. I couldn’t say if it would void warranty but you might want to think about how you might use your kayak and whether it would offer any advantage. What I notice about typical usage is that when your first get a Torqeedo you’ll want to try it out at full speed to see what it does. Its a guy thing and we like to do that kind of stuff 🙂 But having done that, then we find that we almost never run it at full speed, and what really takes our attention is range.

      With a nice long ocean kayak that is easily driven, you might some nice combination of paddling easily and running the motor on low power to provide some help against wind and tide, or just to make it more pleasant after a long day. I use high power on my various Torqeedo motors only rarely, and then its usually to provide an extra thrust or acceleration, rather than highest speed. At full throttle the battery power get used up much more quickly and for not much speed gain anyway.

      Cheers

      Chris

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