The Right prop....

I am looking to upgrade my prop on my boat from a 3 blade to something that is great for tubing/skiing.... I don't know the specs of my current prop but I know that the boat was made in 1971 and the prop has some signs or wear(dings)... What would be the right prop for me? The engine is a 140 hp MErcruiser sterndrive.

 

Need more information about your boat, length, type, make, whatever you can provide in order to determine prop recommendations.

Jango

 

If I may, I would like to get in on this question. I want to do the same thing with my prop. I also have a Mercruser 140 in a 19.3ft 1985 Sunbird model 195 with an Alpha 1 generation 1 sterndrive (don't know gear ratio). I'm in the process of pulling the whole unit out to change the lower shift cable, gimbal bearing, and bellows. At this point changing the prop would be nice before I put it back in the water.

 

Phoenyix, Your gear ratio should be 1.98 : 1. Standard prop could be either a 15 1/4x21 (abt 40mph max)or a 15 1/2x19 (abt 37mph). Pick the appropriate pitch depending on your Boats current speed at max rated rpm of 4400rpm.
See:
http://www.boatramp.com/prop_applet/PropAnalyzerAppletG.html
prop slip should be about 9%
If more power for ski,s, etc.is desired (not top end) drop to next lower pitch, i.e. 21 to 19 or19 to 17.

Jango

 

Thank You ever so much.

Now when I go to the marine store I can sound like I know what I'm talking about.

 

1971 Larson Model 41617 with Mercruiser 140 sterndrive...16' boat.. seats abotu 6 people...

 

Petrey 10, What RPM do you get now? what speed is that? what prop is that?

Why is the prop you got now not ok?

It gets on the plane with 6 people?

 

Petrey10, Your Std Prop is Probably a 15 1/4 x 21p which should provide a top speed w. one person only on board of 40 - 42 MPH @ 4400-4600 rpm.

If these no's seem close to what you're actually getting and are able to easily get on plane, w. 6 people, then a drop in pitch to 19 (15 1/2 x 19p.prop) will provide what you need for skiing etc. 3 Blade should be fine.

 

well I am glad you said that I can get up to 40 mph with this prop because right now it is not running very well and I am going maybe 15mph at full throttle.... I want to get it in the shop but they said it will be at least a 10 days before it gets done which means it won't be done very quickly...i am hitting about 5k rpms and going like 15mph...i had people suggest doing a full tune up and rebuilding the carb...anybody else recommend anything?

 

If you only going 15 mph @ 5000 rpm, either your prop is TOO SMALL,blades are junk and/or the prop Hub is also junk and slipping. In order to get 40 mph, your engine also has to be in TOP condition (almost like new). Also it's a good idea not to run the engine past 4600 rpm and only if it's in Good condition. Good Luck

Jango

 

how do I check if the prop hub is slipping...and what size of prop do I need?

 

In order to minimize damage, if your prop hits a submerged object, The prop has a rubber or similar mat. between the splined hub and prop itself. This "sleeve" is supposed to obsorb the Shock, but often with age etc, it wears out.

With your boat in gear and motor wedged with wood to prevent rotation, try to rotate the prop with your hands (wearing heavy gloves). This will take alot of force, but if it turns at all, the hub is slipping.

My previous post (today 11:33am) outlines the suggested Prop to use. This of course assumes a "tuned engine"

Jango