Results from changing from 3 blade to 4 blade

[parrilladk]

After some info I got from this site I changed my prop and here at the results:

From an older 3 blade (cupped, slightly beat) 13.75" x 15" to a Solas 4 blade 12.75" x 17". I was able to keep the boat ('89 171 Mako) planing at 3200 rpm, keep speeds of 24 mph at 3900 rpm (tubing) and maximum speed of 41 mph at 5900 rpm with the older 3 blade.

With the 4 blade I can keep the boat on plane @ 3000 rpm, keeps speeds of 24 mph at 3400 (tubing) and maximum speeds of 40 mph at 5300 rpm. Maximum speed with the 4 blade when trimming the motor way up though.

I do not run the engine at WOT at all, but I am very pleased about my gain in middle of the road.

Hole shot was VERY good with the 3 blade. With the 4 blade is almost as good but not quite. Still very good for water skiing and tubing.

Turning has improved dramatically with the 4 blade. I can turn much faster and I don't lose grip as with the 3 blade. Dave

 

[Dhadley]

Re: Results from changing from 3 blade to 4 blade

Pretty good results. We'll assume a couple of things. It's an outboard and you didn't change the X dimension (motor height). A couple of interesting things - That's a pretty healthy change in diameter. Normally when going from a 3 to a 4 blade you can raise the motor, that's where you'll really gain efficiency. However, going to that much less diameter may not let that happen although it sounds like you can use all of the trim range. That usually indicates you can go up.

Going up will gain back some of the rpm lost. It may help the holeshot too. Depending on what kind of motor it is, 5300 may be lugging it. You may want to think about getting the rpm back up some so the motor will live a long life.

 

[parrilladk]

Re: Results from changing from 3 blade to 4 blade

Thanks Dhadley,

It is an OB ('00 115hp Johnson). I did not change the height, but I'll explore that possibility. I mainly use the motor in the middle range for watersports. The recommended range for that motor is 4500-5500. It seems to be in the higher end. Dave