Prop Question

[Grady fun 5]

My 2011 305 Express has twin 350 yamaha’s. The best WOT is 4900rpm. The props are the Yamaha stainless 19-15.5 could this be the wrong props on this Boat

 

[VeroWing]

Could be, but you need to be sure there isn't any other issues that might affect WOT (wide open throttle) rpms. Things such as: dirty hull bottom, extra heavy load, abundance of water in bilge, boat trimmed incorrectly, engines out of tune, etc all affect top end performance of engines. if all of these are ok, then you should find Yamaha's recommendation for redline rpms, and adjust prop from there. Before I changed props, I would check others with same boat and engines and see what they are running. Also, contact Grady White for their recommendation of props for that hull with those outboards.

 

[DennisG01]

How long have you had the engines? I'd be willing to bet that if you contacted Grady, they could give you some first-hand advice.

But... are you trimming as far up as possible while going WOT (until ventilation or speed no longer increases)? Are the hull/props perfectly clean?

 

[Legend]

Two years ago I repowered my Sailfish with twin F250 4.2L engines. The props were back ordered so I used my old props which we 15 1/4 X 19 and was getting around 4900 RPMs. The new props, 15 1/2 X 17 delivered optimum performance of 5900 RPMs. The thrust and top end improved dramatically. Good Luck

 

[amf282]

I was going to say reduce pitch to 17...Just need to know if it has always been this way or has there been a change. you also may be able to go to a 16.25" diameter, but I would only be guessing on pitch. I know some 350's run 16.25".

 

[seasick]

Two years ago I repowered my Sailfish with twin F250 4.2L engines. The props were back ordered so I used my old props which we 15 1/4 X 19 and was getting around 4900 RPMs. The new props, 15 1/2 X 17 delivered optimum performance of 5900 RPMs. The thrust and top end improved dramatically. Good Luck

This sounds like a perfect example of over propping and over loading. In general, you would expect a change of about 100 more revs per inch of pitch change. You reduced the pitch 2 inches and GAINED 1000 revs!

 

[Grady fun 5]

Could be, but you need to be sure there isn't any other issues that might affect WOT (wide open throttle) rpms. Things such as: dirty hull bottom, extra heavy load, abundance of water in bilge, boat trimmed incorrectly, engines out of tune, etc all affect top end performance of engines. if all of these are ok, then you should find Yamaha's recommendation for redline rpms, and adjust prop from there. Before I changed props, I would check others with same boat and engines and see what they are running. Also, contact Grady White for their recommendation of props for that hull with those outboards.

 

[Grady fun 5]

Thanks for advise, have very light load and pretty clean bottom. I will experiment a little more with various things, but use to get 5500 no problem. May be time to involve Grady. Thanks very much for input

 

[luckydude]

Thanks for advise, have very light load and pretty clean bottom. I will experiment a little more with various things, but use to get 5500 no problem. May be time to involve Grady. Thanks very much for input

I re-propped recently, people here and THT and coastside said talk to Ken Reeves <kr@propgods.com> 941 735 5808

He bumped from 3 to 4 blades and changed some other stuff. I was trying to lift the stern a bit more and stay on plane at slower speeds. I've picked my days so the two trips since I changed it I came in at 38-40mph So I don't know if it made a difference. The next time I go out, which is Monday (ramp was too busy this hot weekend), no matter how nice it is, I'll play around and see how slow I can go and stay on plane.

 

[amf282]

The key is you used to get to 5500 with no problem. Sounds like something else is impacting your performance. I would look at your cruise speed and rpm and compare to what you used to run. I am assuming the props are still in good shape. I would say you were propped pretty good if you used to get 5500 rpms. I would be looking for other issues creating the problem.

 

[DennisG01]

Thanks for advise, have very light load and pretty clean bottom. I will experiment a little more with various things, but use to get 5500 no problem. May be time to involve Grady. Thanks very much for input

By "Grady", do you mean taking it in to your local dealer? Grady, the company, probably isn't the one to contact.

Adding the info of "used to get 5,500" is an important piece... probably should've led with that!

Does "pretty clean" = perfectly clean? Did you physically inspect it or are you just looking at it from the dock?

You either have a mechanical issue or a running surface issue. If it's a mechanical issue, it would have to be something that is affecting both engines and it's unlikely they both have the same mechanical problem. That would then lead to fuel issues as a possible cause.

 

[efx]

If you had 5500, then you are probably propped ok. Personally I prefer to be right at the top of the rpm range (6000?) At wot. which you are close to. Make sure bottom is clean, bilges forward and aft are dry, boat is loaded lightly. Fuel is fresh. You really want to run engines at a high rpm often to keep them in tip top shape. Engines like to be used. If you can’t get the Rpms up, then I would have the engines checked. How many hours are on them? Flywheel replaced on schedule?