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2 blade or 3 blade
05-10-2007 | 07:23 AM
#26
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From: Tottenham/Orillia, ON, CANADA
RE: 2 blade or 3 blade
ORIGINAL: Moppie
I’ve had a number of discussions with guys running full size boats.
They describe a three blade prop as the ideal set up for high speed surface.
The three blade design gives you more water contact than a two blade. Three blades also allow a better use of the air pulled into the prop during its rotation. But they suggest not exceeding three blades for surface running. I’m planning on playing around with both. But as you know props are not cheap and take time to sharpen and balance.
Lets see, 1/12 scale boat running at 35 mph would be around 420mph at full scale. I think I got that right? That’s hauling…
I’ve had a number of discussions with guys running full size boats.
They describe a three blade prop as the ideal set up for high speed surface.
The three blade design gives you more water contact than a two blade. Three blades also allow a better use of the air pulled into the prop during its rotation. But they suggest not exceeding three blades for surface running. I’m planning on playing around with both. But as you know props are not cheap and take time to sharpen and balance.
Lets see, 1/12 scale boat running at 35 mph would be around 420mph at full scale. I think I got that right? That’s hauling…
and if a 3 blade is so efficient. why don't i use on on my boat?
full size boats is what i do best.
also there is more to calculate scale speed then just some simple math.
you have to base it off of a real boat i could have a dingy that does 8 mph or i could have a dingy that does 150 mph.
when you base something of a scale speed then that would have to be the approx speed of its full size cousin.
but if you want to just scale up speed and compare it to nothing then that is what you would do.
05-10-2007 | 09:04 PM
#30
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From: Tottenham/Orillia, ON, CANADA
RE: 2 blade or 3 blade
well first off you can not compare some loud gas boat to a fast electric boat.
you just can't
whether it's on a villain or larger 60 inch HPR 115 hull it doesn't matter. scale is scale and each prop is suited to its own boat.
i'm not really sure where you are going with this.
any boat will and can run a 3 bladed prop. from a 50 mph 6 cell boat to a 40 mph gas boat . and regardless of its power plant
you just can't
whether it's on a villain or larger 60 inch HPR 115 hull it doesn't matter. scale is scale and each prop is suited to its own boat.
i'm not really sure where you are going with this.
any boat will and can run a 3 bladed prop. from a 50 mph 6 cell boat to a 40 mph gas boat . and regardless of its power plant
05-12-2007 | 09:18 PM
#31
RE: 2 blade or 3 blade
When comparing a prop with the same diameter and pitch a 2 bladed prop will have a better top speed in most applications verse a three bladed prop. While running a surface drive a three bladed prop will have two blades in contact with the water at any given time. This will increase the total amount of thrust (acceleration) and increase the total amount of drag. (reduce RPM's)
When you have a 2 bladed prop with a total pitch of 2 inches and you add a third blade to it, the total pitch of the prop will remain the same - 2 inches. In other words the added blade will only consume more power at a loss of speed because of the added resistance of dragging the extra blade through the water.
Why do full scale boaters commonly use a 3 or 4 bladed prop on their full scale boat as opposed to a 2 bladed prop?
Again it goes back to thrust. A 2 bladed prop would need to be much larger in order to produce the same amount of thrust as a 3 or 4 bladed prop outputs. Most outboards would not be able to hang such a large sized prop. Also, as you increase in diameter, prop pitch speed increases. As you approach high values close to the speed of sound the prop nearly loses all of its efficiency making it useless.
In conclusion:
2 blades
- higher top speed
3 blades
- increased thrust - faster acceleration
Ryan
When you have a 2 bladed prop with a total pitch of 2 inches and you add a third blade to it, the total pitch of the prop will remain the same - 2 inches. In other words the added blade will only consume more power at a loss of speed because of the added resistance of dragging the extra blade through the water.
Why do full scale boaters commonly use a 3 or 4 bladed prop on their full scale boat as opposed to a 2 bladed prop?
Again it goes back to thrust. A 2 bladed prop would need to be much larger in order to produce the same amount of thrust as a 3 or 4 bladed prop outputs. Most outboards would not be able to hang such a large sized prop. Also, as you increase in diameter, prop pitch speed increases. As you approach high values close to the speed of sound the prop nearly loses all of its efficiency making it useless.
In conclusion:
2 blades
- higher top speed
3 blades
- increased thrust - faster acceleration
Ryan
05-13-2007 | 01:03 AM
#32
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From: north babylon (long island), NY
RE: 2 blade or 3 blade
that is the last thing i need!! more acceleration
the baot takes of fast enough . so i m thinking more a 2 bladed prop then a 3
the baot takes of fast enough . so i m thinking more a 2 bladed prop then a 3
05-13-2007 | 10:25 PM
#33
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From: Boiling Spgs,
PA
RE: 2 blade or 3 blade
Just ran my Titan 33 on a three blade today. It was sweet, very stable and controlled than with a two blade. Maybe that’s why the big boats use them? I can’t tell about top speed. My next test will be to replace the 2 and the 3 blade and GPS them.
