3-Bladed props = more speed?

[Eric Perez]

Quick question on 3-bladed props...

If I have an X437 and get X speed from it when spun at speed Y.

If I change the prop to X437-3 and motor spins it at same RPM, will the resultant speed be 33% more than before?

What are the rules of thumb on size and pitch when going from a 2 to a 3 bladed prop?

Thanks

Eric (Do the Rigger Dance) Perez

 

[PondSkimmer]

I wish it was that easy! first off it is not possible to have the engine spinn at the same RPM do to the extra amount of drag that has now been introduced to it. Secondly there is no exact math for trasfering from a 2 blade to a 3 blade. If I am wrong PLEASE let me know because i have been missing out for a few years now :'(. I beleve there is more slip with a 3 blade also but i am not positive with that? what boat, engine, and prop are you running? i am sure some one on here has a good recomendation for a 3 blade.

 

[Ron Olson]

Sorry, we all wished it worked that way! Otherwise we would all run 6 bladed props and be 3 times faster! According to the prop chart that I have, they go the same speed. If you go to a 3 blade prop, use the same size as the 2 blade.

 

[Hammerhead]

Three bladed props don't have the speed as a two blade, but they handle corners better on shallow V's than 2 blade props. This is why I prefer them with my Kingcraft over the 2 blade props. The X series octuras seem to get moving if you trim the leading edge lobes a bit.

The V series three blades are seriously fast, but they lift a lot, and cavitate on launch. I have experienced this with the HH.12 and friends have had the same problems with the bigger riggers.

Hammer

 

[Eric Perez]

Ok, so what does the increase in blade area 2 vs. 3 do for you?

 

[Hammerhead]

Sounds like a question for Nitrocrazed. You know with monos, sometimes when you get on the pipe, especially if your over powered, the boat will chime walk. The three bladed props seem to really cut this down. If you try to barrel into a turn will your rock n' rollin', the turn fin is gonna break loose. 10-10-10-10-10-10-10, you win the heat racing acrobatic dive trophy

Hammer

 

[Rob Duck]

I find the rule of thumb to be: A 3 blade is like running the equivalent to one size larger in number. A 437/3 is like a 440. A 440/3 is like a 442. A 457/3 is like a 460,etc. This is just how they load the engine. Generally the 3 blades are smoother and faster in the corners as they are more efficient with the higher blade area.....