Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercruiser

[bcox777]

Another weekend out on the water, another issue with my Larson. I have what I think to be a propeller issue however I really dont have much experience with this size boat and engine so I thought I would take the question to the message board for advice. Please see below for the relevant information.

Thanks, Brian


1) Performance issue you are trying to correct.

Low Wide open throttle. Low speed.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.

3-blade Stainless Steel

3) Current prop diameter and pitch (required).

14.25"x22"

4) Wide open throttle RPM and speed with an average load (very helpful)

Last weekend 1900RPM/10 ? 15 mph with extra load of approx1540 lbs (including fuel). Using premium grade 91 octane fuel which was fresh that day. Also cleared out the water / fuel separator that morning.

Recalling this from memory but with less weight approx: 900lbs. I was running about 2500 RPM and 25MPH

5) Engine/drive make, model, year, and HP

Mercruiser 5.7L/Alpha One Gen 2, not sure year, 250hp? Engine compression tested last year and had high compression, Rebuilt carb

6) Boat make model, year, length and weight

Larson 220 Escapade, 1995, 23ft, 3430 lbs / Rated for 2300 lbs (gear, persons, fuel)

 

[steelespike]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

I believe your motor is designed to run on 87 octane but check.High octane could actually be costing a little speed.
I'm not that acquainted with the larger motors but I don't think 3400 lbs should be that heavy for a 260 hp motor.
A 22" pitch might produce sluggish hole shot maybe slow to plane, might struggle with a load but 15 mph seems way slow.
would be nice to see your performance with just you aboard.
At this point I suspect a motor or setup issue. At 2500 rpm you have to make up about 2300 rpm. A 10" reduction in pitch should net about 2000 rpm but would put you at a 12" prop and 4500 wot rpm. Then where do you go to pull skiers a or add more load?

 

[500dollar744ti]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

try a 14.25" x 19p, i have a similar sized boat with a 350 magnum and that prop is what works best for top end and hole shot with average load. i'm going to try a 17p for fully loaded and pulling a skier because the 19P doesn't do well with that.

still sounds like you have a motor issue, when did you last check timing and replace the plugs? with the 19p i get 4400rpm WOT and 50mph with just me on the boat. 45mph with 7 people and 65 gals of gas.

 

[QC]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

I agree on pitch issues, but I also wonder about the data. I can't imagine being able to plane the boat if you also only reach 2500 RPM. A 23 footer and a carb'd 5.7 are looking for 17 inch pitch. The 350 Mag info is probably not helpful as the 5.7L was only rated 235 hp (propshaft) in 94 and 95 (likely engines). She also might be waterlogged to add to the challenge.

 

[QC]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

with the 19p i get 4400rpm WOT and 50mph with just me on the boat. 45mph with 7 people and 65 gals of gas.

I don't want to hijack, but if that data is correct you are overwheeled too I am suspecting your tach is off, or the gear ratio is not 1.5 as I have used. But 4400 RPM at 50 MPH is 5% slip. Tooo good. And if you are only getting 4400 RPM with a light load, then you are in a serious lug condition with the 45 MPH example. This is why I suspect tach as she would be a real pig at 5 MPH less 400 RPM maybe?

 

[500dollar744ti]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

that is quite possible. my 350 magnum is a 1990, the cover on the flame arrestor gives a 270hp rating.

 

[bcox777]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

The boat was about 5000lb total the day I am referencing in the data above. When I have had it out under a lesser load it had no problems planing and moved pretty well. I would like to be able to tell you mph for sure but my speedometer is not currently working.

I will take it out again this weekend and get new numbers with a lesser load. Thanks again for all your feedback and please keep it coming if there are other suggestions. Will also look for the 14.25" x 19p prop and see if there is a performance difference there as well.

 

[QC]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

Try and get speed by GPS. Even a phone GPS would be better than a typical pitot speedo.

 

[Tail_Gunner]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

The boat was about 5000lb total the day I am referencing in the data above. When I have had it out under a lesser load it had no problems planing and moved pretty well. I would like to be able to tell you mph for sure but my speedometer is not currently working.

I will take it out again this weekend and get new numbers with a lesser load. Thanks again for all your feedback and please keep it coming if there are other suggestions. Will also look for the 14.25" x 19p prop and see if there is a performance difference there as well.

A 22p prop is far to large for that boat...there have been a few guys lately running high performance 383 motors and cant turn that much prop. Think 17 maybe 18 id be shocked if it would turn a 19... for a older 5.7

 

[bcox777]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

Finally got out on the water again with maybe a 500 lb load at best and was able to get 38mph on my phone GPS at full throttle. I have also concluded that my tach is off which was suggested earlier. Based on the information you have all given it does sound like a prop issue. Would those of you who responded agree?

Now, the next issue that came up that day is after about a half day on the lake, the engine started to backfire under a load. I was able to run low RPMs fine but when I got on it slightly it started to backfire. In neutral and raising the RPMs I did not have an issue at all. Carb was rebuilt about 16 months ago and have only had about 10 hours of run time since. Could this possibly be a timing and prop issue?

Thanks again for all your suggestions.

 

[Bondo]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

Finally got out on the water again with maybe a 500 lb load at best and was able to get 38mph on my phone GPS at full throttle. I have also concluded that my tach is off which was suggested earlier. Based on the information you have all given it does sound like a prop issue. Would those of you who responded agree?

Now, the next issue that came up that day is after about a half day on the lake, the engine started to backfire under a load. I was able to run low RPMs fine but when I got on it slightly it started to backfire. In neutral and raising the RPMs I did not have an issue at all. Carb was rebuilt about 16 months ago and have only had about 10 hours of run time since. Could this possibly be a timing and prop issue?

Thanks again for all your suggestions.

Ayuh,... Check the contents of the fuel filter,... sounds like ya got water, 'n crud in the fuel system...

16 months, 'n 10 hours is irrelevant, if ya just dumped more crud into it...

Before ya buy any props, Fix the Tach...

 

[QC]

Re: Prop Performance and low RPM at WOT issue on 23ft Larson Escapade 220 5.7 mercrui

Yeah, and 38 MPH may be pretty good considering it isn't running right. We don't know the gear ratio etc. Get her running right, fix the tach, get more data. You are already gaining on it. Just stay after it.