prop size

[Kent Myers]

i know many people have asked this in the past but what is the best kind of prop and opinions on what would work best for pulling pitch wise for pulling on a 79 85 hp johnson

 

[Dhadley]

Re: prop size

A lot depends on hull design (style of hull) and how you're going to set it up. Obviously the prop that works best for water toys (pulling) on a 21' cabin boat probably won't be the same pulling prop on a 15' Allison.

 

[HighTrim]

Re: prop size

That is a hard question to answer without a little more info.

One of the main goals in prop selection is to determine what prop style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct prop will prevent the engine from over-revving, yet at the same time allow it to reach the minimum RPM where maximum horsepower is produced.

What is your current WOT RPM? Depending on the motor they should be around 5800 to 6200 RPM with todays fuel. If your test results in your being able to over-rev the engine, you need to increase the pitch of the propeller. Increasing the pitch increment by 1" will result in approximately a 200 RPM drop.

Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat, with respect to RPM that is.

You may need 2 props, depending on the activities that you do. Bottom line though is that it is CRUCIAL that the WOT RPM fall within the reccomended specs.

 

[Kent Myers]

Re: prop size

i have no idea the rpm i have to fix that guage to but its a 16 foot v bottom fiberglass hull

 

[Dhadley]

Re: prop size

We'll assume you're talking about pulling a single skiier or a tube, not pulling another boat (using yours for a tow boat). We'll further assume the motor is mounted on the transom and probably all the way down. We'll further assume it's a modified V rather than a deep V.

An awful lot of assuming but I'd probably start with a 17 for a light load or a 15 if you're looking for more pulling power. It'd be best to know where you are (rpm-wise) with what you have.

Obviously some set up adjustment will probably be involved too.