do i need a 4 blade prop

[badtip]

My first post here so i'll try to get the info right


2004 bluewater mirage
20' length
30 gal fuel capacity
4 or 5 people usually for wakeboarding
it has a 5.0 volvo penta GXI 270 hp w/SX-M drive 1.60
with the stock aluminum 14-1/4 x 21 2 people WOT is right at 5000 rpm and 54-55 mph.
recomended rpm is 4600-5000
as you add people and gear these numbers fall fast.

i installed smart tabs and they help with planing but my hole shot is not what i would like and it is hard to keep a constant speed of 17 or 18 mph.
so would a 4-blade 19" or 20" be a better prop for hole shot and to hold at low speeds better ?
boat weighs 2500 lbs

ken

 

[steelespike]

Re: do i need a 4 blade prop

What is the max recomended rpm?
Speaking generally; a 4 blade will improve low end performance.
If the max rated rpm is below 5,000 you may want to stay with a 21"
pitch as the 4 blade would drop your rpm closer to its rating.

 

[junior1113]

Re: do i need a 4 blade prop

4 blade 21 should drop about 200 wot rpms. better hole shot and be on plane at lower speeds. top speed would be close to same if not higher. right now your rpms are on the high side. and going down in pitch will result in even higher rpms. four blades are way better imho

 

[badtip]

Re: do i need a 4 blade prop

STEEL, the max rpm is 5000, when reading the info for going to a 4 blade it says i should drop 2" in pitch but i'm not sure.

I was thinking about going with a 4 blade 14 X 20" pitch, i don't run my motor at full throttle, i usually stay between 3500 and 4000.

anyone have any input about the 14 X 20 prop?

 

[hwsiii]

Re: do i need a 4 blade prop

Tip, I would go with a 4 blade 20", as it will keep your RPM right up to the top range of your recommended RPM range in aluminum and keep your speed up as well as decrease your prop slip and increase your hole shot and acceleration all the way to WOT. If you decide on going to a stainless steel prop we need to talk more to be sure you get the right blade geometry for your uses. Your prop slip at this time is right at 11% if your gear ratio is 1.6:1, please verify this, and will be better with the 4 blade.

Prop Slip

H

 

[badtip]

Re: do i need a 4 blade prop

hwsiii, yes my ratio is 1.6:1 and i just placed my order for the 14 X 20" aluminum 4-blade prop, i appreciate the info and am sure the new prop will make a noticable difference in performance, i will let you know the outcome in a week or two.

Thanks Ken

 

[hwsiii]

Re: do i need a 4 blade prop

We will be waiting Ken.


H

 

[ramster]

Re: do i need a 4 blade prop

Which brand of prop did you order?

 

[ChasR]

Re: do i need a 4 blade prop

My experience -
1999 Reinell 203 (20.3')
approx 3350 lbs w/ people and gas
5 liter v-8 and Volvo SX-M outdrive w/ 1.60 ratio
Recommended WOT 4400-4800 rpm
-----------------
Stock prop was 14-1/4 x 21, 3 blade
min plane 2700 RPM
WOT 4800 rpm @ 50 mph
-----------------
New prop - Michigan Wheel Vortex 14-1/4 x 20, 4 blade
min. plane 2600 rpm
WOT 47 mph @ 4600 rpm
-------------------
I lost 3 mph and don't really care about top end that much. The boat gets up on plane faster and has less tendancy to fall off when at min. plane rpm. My primary goal was to reduce cavitation and the new prop virtually eliminated it during "hole shots" and hard turns. A bonus was that I feel the boat doesn't pound as much going over wakes. I believe the extra bite from the 4 blade helps hold the bow down so I don't have to run with the outdrive in the full down position. I'm very satisfied with the prop change.
Good luck with yours,
ChasR