Re-Prop or Adjust Height of motor?

[imported_walleyeman]

What should come first? Do you keep purchasing props until you can reach the max WOT RPM range or do you estimate the proper pitch and adjust the height of the motor to hit the max RPM range? Which comes first?

I have been reading quite a bit on here and have learned many things. Thanks to all who are knowledgable and take the time to share. In my situation I have a Lund 1600 Pro-sport with 2007 90hp E-tec. It is on its lowest motor heght setting (motor sitting on transom) and it is propped with a 13.25(I think) x 17 OEM Alum. Prop. It is able to climb to just about 5100 rpms at wot with a full tank of fuel and two adults on board. ( 90etecs are to be run at 4500-5500 rpm's) Its wot speed is 40mph (speedometer) and if I recall it is 37 mph by gps reading. What should I do?

Should I re-prop to a 13.25x15 and probably bump the rpm's up by 200 or should I keep the current prop and raise the motor one notch. (Note: No current problems with ventilation/cavitation at current setting, full trim range is usable)

 

[Dhadley]

Re: Re-Prop or Adjust Height of motor?

Actually that's a good question and it really made me think. I guess it's just second nature for me to look over a rig and start in without thinking. Sometimes we do adjust the X dimension first, sometimes change the prop first. I guess the answer is - it depends.

On your rig I'd start with raising the motor first IF you can use 90-100% of your trim range. And the existing prop is in decent shape. Also since you said the motor is sitting on the transom we'll assume there is no jackplate. Very rare to see a jackplate and an aluminum prop together.

Personally I like to max out the set up with the current prop as long as it's in decent shape. Then go to a different prop.

As starnge as it sounds we sometimes end up going for more pitch to gain rpm. It goes something like this which is kinda like your deal - the motor is all the way down and we're looking for more rpm. Rather than lower the pitch, which can lower efficiency, we raise the motor. That tells us how the hull reacts to X dimension. Once we get it maxed out with that prop we can test a ss prop. Most times that allows us to raise the motor more. Less drag, more rpm. Hopefully we get to a point of using more pitch and get more rpm as a result of less drag.

 

[imported_walleyeman]

Re: Re-Prop or Adjust Height of motor?

Thanks Dhadley, this is exactly what I was looking for. I hope to raise the motor one notch this spring to see what it does.

 

[Dhadley]

Re: Re-Prop or Adjust Height of motor?

Adjusting the X dimension costs nothing except a little time. And can be reversed just as cheaply. Plus it tells you how your rig reacts to that adjustment. Not all hulls are created equally nor are they loaded equally.

 

[imported_walleyeman]

Re: Re-Prop or Adjust Height of motor?

Thanks for taking the time to answer some of my questions. I really appreciate how you guys, and most others on this site ,willingly answer questions to help out rookies like me. (Even though you have probably answered the same question before to someone else!)

 

[Dhadley]

Re: Re-Prop or Adjust Height of motor?

Hey, somebody took the time to answer my rookie questions (and my current questons too). We're just trying to pay back a little.