Prop Slip

[muchco]

I have a Evinrude 150XP on a DC 175 Larson. It's mounted on the Third hole from the top, on the transom. I am running a 13 1/2" X 23 Pitch Renegade prop. The boat runs at 5500 rpm and 51 mph via the speedometer. By my calculations this looks like about 20% slip. Is this acceptable or are there some adjustments or changes I should make? I look forward to your response.

 

[Dhadley]

Re: Prop Slip

I get almost 22% so we're close. Thats not very good but remember youre going by speedo readings. Unless you have a Gaffrig or Nordscog speedo it will probably be off. See if you can get an accurate reading either by GPS or a measured distance.<br /><br />You could use some rpm also. Try going up the last hole to see how the hull responds.

 

[muchco]

Re: Prop Slip

Dhadley, I will get a GPS and recheck the actual speed. I thought that the RPM was good at 5500 being Max. is 5600. What RPM do you suggest I run it at? It's a 1987 Evinrude XP150 Model #E150STLCUR. I will also try running it on the top whole. I had tried a 22 Raker and the RPM was around 5650 trimmed out and approx. the same speed via my speedo. Just curious to know what amount of prop slip should I be shooting for. (knowing that I require an accurate speed to make the appropriate calculation)What type of prop are you running? Thanks for your prompt response to my post. <br />Much-co

 

[Dhadley]

Re: Prop Slip

We set those motors up at 5800 with an average load. Thats where they will live the longest whether your running at wot or in the cruise range.<br /><br />The props youre running are very good props. I like the Stilettos and Turbos too.

 

[muchco]

Re: Prop Slip

Dhadley, On these motors what would you consider the best cruise RPM(most fuel efficent)? Thanks for the response. I will keep you updated.

 

[Dhadley]

Re: Prop Slip

That depends a lot on hull design and water conditions naturally so its really hard to give a specific rpm for every boat and water condition. I think it's kind of a given or accepted "rule of thumb" that somewhere between 60 and 80 percent of wot. <br /><br />Check out the boating magazines like Bass & Walleye or Trailer Boat Magazine. The tests they do list the most efficient cruise for each rig. Makes for some interesting reading.

 

[Dhadley]

Re: Prop Slip

OK, I just grabbed an issue of Bass & Walleye and it happend to be the one where they tested the Verado 250 aginst the 250XS (I know - I know) on identical hulls. The most efficient range for the Verado was 3000 rpm (4.8 mpg / 31.5 mph) and the XS was at 4000 rpm (5.0 mpg / 46.0 mph). Just shows how there can be differences between identical boats with the same (rated) hp motors.

 

[muchco]

Re: Prop Slip

Dhadley, Thanks for the response. I did some checking regarding the tach and speedo readings. I looked at my tach and it was set for 10 pulse 5 pole and it should have been set to 12 pulse 6 pole as per the Teleflex web site. It appears that I will have to go out and do some more testing. With the tach set on the incorrect setting, was the 5550 reading I had higher or lower than actual? I suspect it was higher than the actual engine RPM. This being the case I'm over propped with the 13 1/2" X 23 pitch Renegade. I will be heading back to the lake with a 18 and 20 Pitch Raker and try again. Any thoughts?<br />Much-co

 

[Dhadley]

Re: Prop Slip

Sounds like a good plan. Take the Renagade with you and try it if you have time. The 20 Raker is a great starting point. Dont worry about venting in turns or venting on over-trimming. Right now we want to see how each prop responds to the hull in a general way.