Props

[kaypee]

Just as a query to all you prop experts...
When I bought my boat, it was fitted with 13 x 17 SS 3 Blade props on my 100 yammys. On route back through the Sunny Coast I stopped at Solas and naively bought a pair of 13 x 17 SS 4 blades. ( I prob should've tried the 3 blades first) Anyway I fitted them straight away and have been using them for 2 yrs since.

I thought for just a trial I'd try the old 3 blades on the boat for our trip on Friday.
Wow, what a dissapointment.. so here is my question.

How can a prop same size and dimensions 13 x 17 but one more blade, be good for almost 10kph more at top and cruise speed and 0.3KM/L better?? Slip for the 3 blade?? or does the 4 blade prop equate to a bigger pitch 3 blader??

Approx data:
3 Blade
4100rpm - 36kph - 1.3KM/L
4800rpm - 45kph - 1.1KM/L
6200rpm - 61kph - 0.9KM/L

4 Blade
4100rpm - 45kph - 1.4KM/L
4800rpm - 54kph - 1.3KM/L
5800rpm - 72kph - 0.9KM/L

Crazy... Needless to say the 4 blades are back on!!

[Spaniard_King]

The 4 blades are more efficient but load the prop more at the top end.