What can I do?

[gunit1400]

I have a 2003 Glastron SX175, 3.0LX 140 hp Mercruiser. It has a 14.5x19p aluminum Quicksilver prop, turns about 4600 rpm wide open and trimmed up nice. But I am only getting 35.3 mph GPS. I keep seeing posts about folks going 42-45 mph in this type boat, even in magazine tests. I can't get anywhere close to that, especially since I am right in the recommended range on rpms. Any suggestions to help me get a little more out of this combo? Four blade prop, different diameter, diameter and pitch change, or just be satisfied with what I have? Any help/suggestions greatly appreciated.

Scott

 

[thompy]

Re: What can I do?

is this speed with a gps, speedos can be considerable off, you rpms sound to be on target

 

[steelespike]

Re: What can I do?

Does the boat respond to trimming?bow comes up.Boat doesn't lay down like its glued to the water? Is the mottom clean no rough or peeling paint or growth?
Do you have a hyrofoil on the outdrive? Is the prop in excellent shape?

 

[gunit1400]

Re: What can I do?

as stated above, 35.3 mph GPS

 

[gunit1400]

Re: What can I do?

"Does the boat respond to trimming?bow comes up.Boat doesn't lay down like its glued to the water? Is the mottom clean no rough or peeling paint or growth?
Do you have a hyrofoil on the outdrive? Is the prop in excellent shape?"

Boat does respond well to trimming, gains considerably in rpms and mph when trimmed from fully down to trimmed correctly. Bow comes up nicely. It is kept on a bunk trailer, bottom is totally clean, no bottom paint, not even any scratches that I have noticed, and I was just under the boat while re-wiring the trailer on Sunday. It does not have a hydrofoil. It does not have any problems planing nor does it show any problem porpoising. In my opinion, the outdrive extends too far for a hydrofoil to be much good for an I/O anyway. As far as the prop is concerned, it has seen its better days. It has quite a few nicks as a result of shallow water in the river and at the coast. That was the primary reason for trying to get all the info I can. I need a new prop, so I may as well get one that could give me the best performance possible. Thank you again for the info.

Scott

 

[steelespike]

Re: What can I do?

You could get the prop repaired and test again.If a prop change is needed you can keep the old prop for a spare.The repaired prop should at least give a good indication of your normal rpm.35 at 4,600 w a 19 seems to me you would have a lot of prop slip.
It seems to me you should be able to run a 21" prop unless the boat is really heavy and or a real deep V.A 21 might struggle for skiing but should reach max rpm range. Do the throttle plates open all the way?Motor in excellent tune?Compression?
Generally a 4 blade will improve low and mid range performance and handling.
It may or may not reduce top speed. On rare occasions I've heard of an increase in speed.

 

[gunit1400]

Re: What can I do?

steelespike,

Thanks again for your input. I was planning on keeping the prop for emergency use only, but hadn't planned on getting it repaired right now. I was acutally wondering if I could go with a 21 but wasn't sure about what the expected outcome would be. I do worry that since I am pulling 4600 WOT now, that a 21 would drop my rpms to the lower end of the recommended WOT rpms, which would take me in the opposite direction from what I am trying to achieve. Am I thinking correctly? Right now, I can swing getting a new prop, but not a prop repair and then a new prop if that is needed. In a perfect world, I would have a shop close by that would allow me to try a couple different props, but we know how that goes......

 

[steelespike]

Re: What can I do?

Not knowing if you might get 4800 or 4900 with a good 19 theres no way to know if a 21 makes sense. I wouldn't do it based on your present rpm.
I still think something is up with your setup.Your dinged up prop? perhaps the
ignition timing,is it set right and advancing as it should?Try running with the motor box open or removed Maybe something is fouling the air.
I would think with a 19 it would zip up to max rpm or really close.

 

[gunit1400]

Re: What can I do?

You know, we had an issue several times last year when the engine would "run on" like my old Chevy would when I turn it off. I know in the old Chevy, it was a timing issue and I was going to check the timing on the Glastron if it continued this year, but it acted fine yesterday on the river. No surging or hesitation. Saturday I changed the oil, filter and spark plugs, getting it ready to take out. So maybe I also need check the timing just to be on the safe side. Does it need to be in the water, to apply the appropriate back pressure, or is this something that can be done while it is on the muffs? I need to find some info on the procedures to check timing. Thanks again for your info, and thought provoking questions.