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Switch from 3 to 4 blade

R

rmm

Regular Contributor
"Have checked with a couple pr

"Have checked with a couple prop shops and gotten varying answers. Anyone done this and is it worth it? Concerned with cruise speed and economy and slow speed handling, could care less about top speed, but want to make sure still turn proper top rpm.

Also what size should be correct, currently running 18x22.5 and achieving about 4200rpm. Boat is a 1988 31' Tiara with 454s and 1.88 trans.

Thanks

Capt. Ryan"
 
if it helps at all my boat is

if it helps at all my boat is running three blade 22x22 at 4400 RPM with a 2.59 trans.

My prop guy said with 4 blades I would want 21x22
 
"Thanks Ted, did your guy give

"Thanks Ted, did your guy give you any feedback if its worth the switch?"
 
"RM:

I think Al went to fou

"RM:

I think Al went to four blades last year and could comment on your desired list. Overall, I think going to four blades will help get you where you want to go."
 
"Ryan,

Did the 4 blade swit

"Ryan,

Did the 4 blade switch last season and LOVED it. However, I knew when we bought these props they were VERY oversized for our needs but we needed a starting point and found it. We run 18 x 21.6 w/ 3 cup in a 34C Silverton and 454's. Our repower was done 5 yrs ago but the PO used the original props which gave us a WOT over 5k. The long and short is.. we find the better size for us is going to be 20x21 NOT the 21x23's we had.

With that configuration we barely made 3400 WOT. SOME drop huh?

AT NO WAKE IDLE: we ran almost 6 knots compared to about 3 or so previously and our top speed prior was near a squirrely 32 knots. The 4 blades gave us about 26 but the WOT was way low. Maneuverability was great. When slow maneuvering you could INSTANTLY feel the turning and movement for really nice control...

These numbers are from a distant memory (last season springtime) My log book has the exact numbers. For what its worth"
 
"RM; I'm in the process m

"RM; I'm in the process myself of switching from 3 to 4 blades. The issue for me is I'm running just 16" diameter wheels, so they are pretty small for the job. If you are DIAMETER limited, AND need more blade area, then you want to go to more blades. Ted has relatively huge wheels, and more blades will likely not improve anything for him. More blades cause more turbulence to the following blade, a bad thing. More blades is a way to increase blade total area, without increasing diameter. It's always a good idea to run the largest dia prop you can, without causing hull slap/vibration issues. That is, maintain tip to hull clearance.
With a 454 and already at 18" dia., going to 4 BL will likely show some better backing and acceleration performance. However, the total drag (blade area) and turbulence (more blades) will work against you. To answer the question "will it be better", may only be answered after a trial in your boat, and only for your particular areas of concern."
 
"Dave,

Very interesting &#

"Dave,

Very interesting (and yes my wheels look absurd when the boat is on the hard).

I am undecided whether I am going to make the transition. a couple of grand for new props and I probably wont see much of a difference. My props are getting pretty chewed up, but one more season may not hurt...."
 
"So I have talked to 2 reputab

"So I have talked to 2 reputable prop shops and gotten 2 different answers when posed with the question. Approached it from the point of having to replace props and so buying one or the other, so not just pushing a sale.

One said 4 will give improved economy and cruising speed and handling, the other said what diver dave said."
 
"Here's yet another opinio

"Here's yet another opinion:

I went from 3s to 4s on mine, but I also went UP an inch in diameter, and DOWN an inch in pitch. This is a 'power' setup vs. a 'speed' setup. (Think lower gearing in a car or truck.)

Adding a blade is like adding an inch or two of pitch.

Jeff

PS: Still pleased with the change, but I got one of the 4 blade props dirt cheap (and one of my 3 bladers was juink). I wouldn't have gone that way otherwise."
 
"Jeff,

When we applied the

"Jeff,

When we applied the GIANT 4 blade props to the boat we dropped over 1400 rpm...NO REGRETS other than the wot shift, for us, was too great... Still looking for 20x21's. I loved the response of the 4 blades"
 
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