Prop pitch

[Incorrigible]

Engine is a J225TXESS (1991 V6 225hp)

Currently running 20" props. Engines will EASILY push them through the water. Engines will turn at least 6500, depending on trim and loading, I can get them close to 7000 (second I see that? Throttles get pulled back)

My question is this: are outboards the same as I/O's? About 300-400 rpms per inch of pitch change?

If so, I'm looking at almost three inches up....

Mind you: These props came with the engine, so I do not have any other baseline to go by....

 

[Robbabob]

Re: Prop pitch

You are correct about the rpm change per inch of pitch. Also see what type of diameter increase you might make. I think you'll lower rpm by 100 per inch and gain more "digging" power.

Something about the height of the prop (motor of course) with outboards... someone else will chime in about that.

Must be the other owner was pushing more boat or wanted better hole shot over top speed.

Good luck!

 

[rndn]

Re: Prop pitch

If you post this in the prop forum, they will help you get to the right rpm's and the correct style/material prop for your boating needs.
All other things being equal, it's closer to 200 rpm's per inch or prop.

 

[emdsapmgr]

Re: Prop pitch

The factory recommended operating range for that year/model was between 5000 and 6000 rpm. You are best to target your props to run right at 6000 for max hole shot and fuel economy. You are at least one prop size too low. The type of prop you have will make a difference-are you currently running a stainless or aluminum? If it's a 20, could be a stainless. I always recommend propping with just you in the boat with a light load of fuel. That way, when you are with folks and laden with fuel and gear, you won't overrev. If the engines are mounted too high during max trim-you may see a high (7000) rpm which may not translate into any more speed. That could be ventiation due to the props losing their bite.

 

[Dhadley]

Re: Prop pitch

Let's start with the basics. The motor has a rev limiter at either 6200 or 6700, depending on which pack you have. The only way to get to 7000 is to by-pass the limiter. We should verify the tach's accuracy first. Make sure it's set on position 6 then we'll go from there.

 

[steelespike]

Re: Prop pitch

Would help to know what boat?dry weight if possible?Length,beam?Deep V?
What is the speed at max rpm not ventilating(cavitating)?

 

[Incorrigible]

Re: Prop pitch

Rev limiters must be 6700, but both tachs are new, and both give the same reading (switched back and forth to compare each tach on each engine) Possible they are both incorrect, but not likely.

 

[Incorrigible]

Re: Prop pitch

Scarab Sport 29. Don't know weight, but I removed a lot of it. 8' beam, deep V. Speed I cannot remember (Wisconsin weather really sucks)

 

[Dhadley]

Re: Prop pitch

What brand tachs?

 

[Incorrigible]

Re: Prop pitch

Teleflex Marine: Lido Series.

 

[Dhadley]

Re: Prop pitch

Need to get the rpm varified with a shop tach or a BRP tach wired in temporairly. At least verify they are set on position 6.

 

[Incorrigible]

Re: Prop pitch

Both tachs are properly set and are reading accurately.