# 4 blade versus 3 for 40 merc



## matt_baker_designs (Nov 27, 2012)

I've been looking into prop stuff lately trying to figure out some of the same type of things for my 17ft. tunnel hull. Overall it seems like you are most likely going to loose some top end speed with the 4 blade, but get a better hole shot and plane on lower RPMs. Although, I did read about some people getting faster top end speeds. The difference of speed changing just from aluminum to stainless would be minimal I think, but possibly a touch more from the stainless. Like 1 or 2 mph? From the research I've done, pitch from different prop manufacturers is somewhat unique to each prop, so a different brands of say a 13 1/2 in 21 pitch 3 blade may perform differently, so the only sure way to know is to test the prop out on a particular boat. Which makes figuring out what prop for the boat challenging. I'm trying a 13 1/2 x 21 pitch solas 4 blade for my 90hp johnson to see what difference I get from a 13 1/2 x 19 pitch aluminum 3 blade. I'm expecting to get about 500 RPMs less, lower top speed, better planing, hole shot, and bite when my jack plate is high up. Hopefully I'll get out tomorrow and test it


----------



## steve77777 (Nov 12, 2013)

thankyou also i have a 11.1 diameter and thinking to go to 10 1/2 or 10 3/8 not sure -does anyone know what could change doing this?mainly because most props are not 11.1 x 13p..


----------



## AfterHours2 (Aug 2, 2010)

Just to give you an idea, I run a 25 Yamaha with a 4 blade powertech cupped prop. I also have a powertech 3 blade, both stainless. The pitch is different between the 2 but that's normal when going with a 3-4 blade. The 4 blade performance wise is my favorite prop. Speeds are typically in the 30 mph range but with a jack plate this prop really shines. Boat jumps on plane very quickly, in seconds actually, and allows sufficient water pressure to run in the fully jacked position. I normally run this prop while I fish shallow areas which is 99.9% of the time and it's perfect. If I'm doing long deeper water runs then I can switch to the 3 blade and get every bit of rpms and speed out of the little motor. Speeds jump 3-4 mph and once the rpms are up the boat launches like a rocket. Just not as quickly as the 4 blade. The 3 blade also needs more of the motor in the water to be efficient so shallow planing suffers a tad. Basically, if your not planning on getting an adjustable hydraulic/electric jackplate, tabs or compression plate then a cupped 4 blade may not give you the performance your looking for. It may plane a little quicker and give you a better hole shot but your top end may suffer and you may not be happy with the performance. These are just my findings and I hope they help. It took me a while to get the best pitch for either prop and if you switch sizes make sure you have a tach installed. Without a tach, your tuning blind. Hope this helps..


----------



## CurtisWright (May 9, 2012)

I have a Tohatsu 40 on a 16' tunnel hull skiff.  400lb hull.   I went from the stock aluminum 12 pitch prop at 32mph  to a 4 blade Powertec 10 pitch cupped prop and clocked 28mph.   

I tried the 11 pitch 4 blade and it was too much pitch.  

For me the advantages of the 4 blade outweigh the loss of speed.  I'll list them.

1.  Drastically increased my ability to corner.  I can turn the motor at full throttle all the way without a blowout or the boat sliding.  
2.  Can trim the motor way up and run with the prop sub surface in really skinny water without cavitation and blowout.
3.  Holeshot is way better and can get on plane with less water under me.

Its kinda like having an all time 4x4 vehicle. 95% of the time I wish I had a 3 blade prop, but the 5% when I need it makes all the difference for me.


----------



## steve77777 (Nov 12, 2013)

THANKYOU FOR THE FEEDBACK..


----------

