Mercruiser 4.3L LX Alpah one prop questions

[H20Hound]

Here is the scoop. I have a 23ft Walkaround cuddy that has a 14 1/2" x17 aluminum prop. It comes out of the hole nice with just me on board and is respectable with 4 additional passangers. It needs to be replaced and I am ordering an SS.

The boat is used 90% fishing and cruising. I have yet to try an tow a skier for fun. I can only get to 2.6 mph (on calm water) to troll which is a bit to fast and I do not want to decrease the idle. Top speed is 37-38 mph at 4850 rpm based on GPS and my tach.

I am looking at an Apollo 14 1/8" by 19" to slow down idle speed and increase my top end.

Any thoughts?

Thanks!

 

[Bondo]

Re: Mercruiser 4.3L LX Alpah one prop questions

to slow down idle speed and increase my top end.

That Can't Happen,...........

To Slow your troll,.... You need Less pitch.......

To Increase your Top Speed,.....You need More Pitch,.... If the motor has the HP to turn it.....

 

[H20Hound]

Re: Mercruiser 4.3L LX Alpah one prop questions

My thinking was that a higher pitch prop would have more grip planed out at max rpm and less grip at idle, since I will lose hole shot with a higher pitch.

 

[Silvertip]

Re: Mercruiser 4.3L LX Alpah one prop questions

It doesn't work that way but you are certainly free to prove us wrong. Stranger things have happened. The 19P prop is moving more water than the equivalent 17P at the same idle rpm so boat speed is going to be faster, not slower. And the fact that you are going to SS from AL means the SS is likely more efficient which could make the situation even worse.

 

[H20Hound]

Re: Mercruiser 4.3L LX Alpah one prop questions

yeah I see your point. I looked at a diagram this afternoon that helped me see exactly what your saying about pitch pushing more water. I am guessing a 3/8" smaller diameter wouldn't be noticeable either.

I am glad I checked with you guys before running this new prop.

 

[Bondo]

Re: Mercruiser 4.3L LX Alpah one prop questions

Diameter is pretty much Irrevelant..........

It's set by the engineer who designed the prop,+ the profile he gave the blades......

Props are measured,+ sold by Pitch,+ What it's going to be used for..........

There's Really No Choice in Diameter............

 

[H20Hound]

Re: Mercruiser 4.3L LX Alpah one prop questions

Well I tested the 14 1/8" x19 MIW Apollo SS and here is my review.

These are calm water tests done on an inland lake. The boat is primarilty used for great lakes fishing. Engine specs 4400-4800rpm.


17 p aluminum 4800rpm (little throttle left, less that a quarter) top speed of 37 mph and nice cruising speed of 33-34mph (4500rpm) It comes out of the hole pretty good and considerable lift. (25 gal of fuel, gear, plus me). The engine seems on par or a hair over revved at the top end.

Idle trolling speed at 800rpm 2.6mph

19p Apollo SS vented 4700 rpm (minute mount of thottle left, 1/8 or so left)
Top speed of 41 mph and a nice crusing speed of 36-37 mph (4250rpm) It comes out of the hole slower and seems even more so because of the lack of lift. This may be due to the venting? It gets on plane about the same speed has the aluminum. it surprised me that this motor pushes the 19 at the recommended rpm range.

Idle trolling speed at 800 rpm 3.5mph

My conclusions are that I am going back to a 17 and still will stick with SS, just not the same prop becuse I think the venting is actually slowing down the holeshot with my boat design. (picture a 23ft walkaround cuddy, like seaox, trophy, sportcraft ect.)

Any thoughts on the vented vs. non-vented design?

Plus the trolling speed is just way to fast and I am not interested in a kicker right now. I know I know, socks and buckets work help.