New Prop Concept
05-24-2020, 12:22 AM
#11
Registered
18% 
1.) Prop with no slip have 100% speed.
2.) Prop with 10% slip have 90% speed.
a.) If your prop made 15% slip at cruising speed you have 85% of theoretically slip.
b.) If this new prop go 18% faster, will reach 103% of theoretically speed
Perpetum mobile?
If you have really optimised prop on your shaft will be new prop merhaps better at low speed, but faster you go, worst will be. This loops have to much parasitic drag. Stream flow over this loops you could compare with this https://en.wikipedia.org/wiki/Pitts_Special . No way to be faster at 40 mph+
By surfacing at high speed probably happen the wall like if you want to flight supersonic with old Thunderbolt. Simply no go.
1.) Prop with no slip have 100% speed.
2.) Prop with 10% slip have 90% speed.
a.) If your prop made 15% slip at cruising speed you have 85% of theoretically slip.
b.) If this new prop go 18% faster, will reach 103% of theoretically speed
Perpetum mobile?
If you have really optimised prop on your shaft will be new prop merhaps better at low speed, but faster you go, worst will be. This loops have to much parasitic drag. Stream flow over this loops you could compare with this https://en.wikipedia.org/wiki/Pitts_Special . No way to be faster at 40 mph+
By surfacing at high speed probably happen the wall like if you want to flight supersonic with old Thunderbolt. Simply no go.
Last edited by plavutka; 05-24-2020 at 12:26 AM.
05-24-2020, 12:30 AM
#12
Registered
18%
1.) Prop with no slip have 100% speed.
2.) Prop with 10% slip have 90% speed.
a.) If your prop made 15% slip at cruising speed you have 85% of theoretically speed.
b.) If this new prop go 18% faster, will reach 103% of theoretically speed!
Perpetum mobile?
If you have really optimised prop on your shaft will be new prop merhaps better at low speed, but faster you go, worst will be. This loops have to much parasitic drag. Stream flow over this loops you could compare with this https://en.wikipedia.org/wiki/Pitts_Special . No way to be faster at 40 mph+
By surfacing at high speed probably happen the wall like if you want to flight supersonic with old Thunderbolt. Simply no go.
1.) Prop with no slip have 100% speed.
2.) Prop with 10% slip have 90% speed.
a.) If your prop made 15% slip at cruising speed you have 85% of theoretically speed.
b.) If this new prop go 18% faster, will reach 103% of theoretically speed!
Perpetum mobile?
If you have really optimised prop on your shaft will be new prop merhaps better at low speed, but faster you go, worst will be. This loops have to much parasitic drag. Stream flow over this loops you could compare with this https://en.wikipedia.org/wiki/Pitts_Special . No way to be faster at 40 mph+
By surfacing at high speed probably happen the wall like if you want to flight supersonic with old Thunderbolt. Simply no go.
- test props condition and type.
- they did not comment prop slip...
05-24-2020, 12:10 PM
#13
Registered
I think they made no comment on prop slip because the slip calculation shows all three props with negative slip at top speed. Not possible. I looked up the gear ratio of the engine and it is 1.92. They say all three props have the same 15 pitch. Not likely, and only Sharrow can calculate what they think their prop pitch is.
So, just to get the slip numbers into positive territory I assumed 1.75 ratio and 16 pitch. This puts the three blade props at ~20% slip around 30 mph and ~10% slip at top speed. I can believe those numbers. The same calculation has the Sharrow prop at ~6% around 30 mph and ~5% at top speed. The Sharrow prop is 5-8% slip over that range, as you would expect if you believe the speeds attained at each RPM. A four blade prop woulds also give better slip and speed numbers, but that's not really the point. The amazing result is that the Sharrow prop delivered higher speed with the same fuel consumption. The boat didn't get lighter with less drag, so there had to be more thrust.
Still, if you want to inspire confidence, don't publish numbers that indicate negative slip, without discussing it...
So, just to get the slip numbers into positive territory I assumed 1.75 ratio and 16 pitch. This puts the three blade props at ~20% slip around 30 mph and ~10% slip at top speed. I can believe those numbers. The same calculation has the Sharrow prop at ~6% around 30 mph and ~5% at top speed. The Sharrow prop is 5-8% slip over that range, as you would expect if you believe the speeds attained at each RPM. A four blade prop woulds also give better slip and speed numbers, but that's not really the point. The amazing result is that the Sharrow prop delivered higher speed with the same fuel consumption. The boat didn't get lighter with less drag, so there had to be more thrust.
Still, if you want to inspire confidence, don't publish numbers that indicate negative slip, without discussing it...
05-24-2020, 02:00 PM
#14
Registered
Other issue not discussed is if a just using your numbers for reference) 15 pitch 3 blade WOT is 5000 with 10 slip. If slip is reduced to 5% rpms will decrease do to more load
