Prop suggestion 87 offshore 08 etec 250 ho

[Chuck_NJ]

I am looking for a suggestion for a prop for my 87 offshore 24 with bracket and 2008 etec 250 ho. I acquired the boat last year and it has a 4 blade stiletto 14 1/4 x18 but engine was lugging max 5000 rpm engine mounted doin top hole lowest position . Anything over 4600 rpm I would get a overheat alarm temp 185if I backed out to 4500 alarm instantly silenced. Found a 3 blade Michigan aluminum 15x17 thst prop ran past 5600 and did not pass 180 degrees at 5500rpm. I next took my iPhone taped to stem looking at anti cavitation plated and it was below water so I guess I need to raise motor a few holes up

 

[DennisG01]

When you took that picture of the anti ventilation plate (not cavitation, by the way), what kind of speed were you doing? What about speeds with both props in comparison to when/where the overheat happened/didn't happen?

Why would an engine being DEEPER in the water cause overheating? I also don't understand why changing props eliminated the overheat... possibly something else is going on.

But, the engine height has to be figured out first. Prop selection can't be done till that is done.

 

[Chuck_NJ]

Speeds are basically identical. That picture was at 22 knots. The 4 blade would not rev over 5000 rpm it was lugging spec for wot is 5600 which the 3 blade was able to achieve and a little more less lugging I’m guessing less heat. As far as height I was not sure with more metal in water more drag more heat was only asking by no means an expett

 

[Doc Stressor]

The lower the engine the more drag. So the engine lugs harder to turn a given rpm. If it has to work hard enough it will overheat.

I agree that the engine should be raised to the proper height before deciding on the prop. But the 17" 3-blade is still probably going to work better on that hull.

 

[Chuck_NJ]

Thanks will be raising up at least 2 holes to startAnybody have a suggestion on brand and model of prop that would be a good fit for my hi ull engine combo?

 

[Doc Stressor]

No, but in general highly cupped 4-bladed props give better performance with engines raised as high as practical. They do better than standard 3-blade props in aerated water. The downside is a decrease in fuel economy.

You have a pre-SV2 hull that is not too hard to prop correctly. You'll find that the pitch is more important than any sophisticated prop design. As long as you have a prop that will allow you to turn close to the highest recommended rpm without ventilating in turns, you will be good to go.

 

[Shipfaced]

Engine definitely needs to go up before looking at prop size. Went thru this a few times with a couple boats. I currently have a 93 explorer with a 225 etec on a bracket. I have the newer design bracket so not sure if I can tell you what holes to go to but the motor definitely needs to go up. Once you have that at the right hight try a rebel 15 or 17. Might want to change your thermostats in the etec aswell.

 

[DennisG01]

Anybody have a suggestion on brand and model of prop that would be a good fit for my hi ull engine combo?

You're getting ahead of yourself here. You might be perfectly fine with the one of the props you already have. Be patient, wait till you get it to the proper height.

I have to say, I'm surprised that the height, alone, makes THAT much of a difference to cause it to overheat. In theory, I agree - but it just seems strange, you know?

 

[Chuck_NJ]

the oversized prop was lugging big time the overheat went away after prop switched at the same time I saw the height was low not certain if the height has any effect on temp was jusy asking..

the themostats were replaced before the prop switch no change in overheat condition with thermostat replacement.