Evinrude Performance

(This is an extension of a previous post)<br /><br />I took my prop to Jeff @ Proptech and he gave me some extra cup and cleaned it up. He indicated WOT should be 5500. I can’t find that, or my gear ratio, in any of my manuals. The performance difference was marginal, especially since I was running 320 lbs lighter. Here is the plot.<br /><br /> <br /><br />When I got home, I raised the engine one hole and went to bed. After Christmas, another plot.<br /><br />I did run without the cowling, steelespike, with no changes. I don’t know how to check the crank seals.<br /><br />Stats:<br />1985 14’ McKeeCraft, new model states 665 lbs<br />Model: E60TLCRE, 1984 60HP Evinrude<br />SS prop: 11 ¾ X 17 with a double cup<br />Tilt and trim is CMC PT-130 aftermarket, 6” setback

Re: Evinrude Performance

Jim.... The 1984 60hp Evinrude hits its rated horsepower at 5500 rpms. Full throttle operating range is considered to be between 5000 rpm to 6000 rpm, not to exceed 6000 rpm.<br /><br />The gear ratio of the 1984 60 hp Evinrude is listed as being 12:29 (.414) in the OMC's 1984 engine brochure booklet. I have no idea what the (.414) pertains to but I feel sure that someone else can explain that.

Re: Evinrude Performance

12/29 gear ratio translated is 1 to 2.4166666 ratio.For every 2.4166666 rotation of crankshaft the propshaft turns once.The .414 translates that the propeller shaft will turn .414 of one revolution for every 1 revolution of the crankshaft.Divide 1 by 2.4166666 and you'll see the (.414) figure.<br /><br />For instance(.333) would be a 3 to 1 ratio.

Re: Evinrude Performance

Jim..... What "ob" said (whew!).

Re: Evinrude Performance

o.b. is trying to say 12 divided by 29 equals .414.

Re: Evinrude Performance

What I was showing was what the .414 meant in rotational terms.

Re: Evinrude Performance

OB.... I knew that. I just couldn't resist a tounge in cheek complimentary zinger in your direction for such a well explained post.

Re: Evinrude Performance

Prop it for 6000. 500 additional rmps is a lot more power. Even when on a plane, most trihulls (like McKees and Whalers) have more wetted surface to push compared to a conventional hull.

Re: Evinrude Performance

Wow.<br /><br />So, if I read this right, my 33.6 @ 5510, with a .414 turn ratio and a 17" pitch prop translates to a slip ratio of...<br /><br /> 5510 RPM<br />x 0.414 Ratio =<br /> 2281 Prop RPM<br />x 17 Inches per revolution =<br /> 38779 Inches per minute<br />x 60 Minutes per hour =<br /> 2326762.8 Inches per hour<br />÷ 12 Inches per foot =<br /> 193897 Feet per hour<br />÷ 5280 Feet per mile =<br /> 36.7 MPH, theoretical, divided into<br /> 33.6 MPH, actual =<br /> 91% equals 9% slip<br /><br />That part I think I understand, even though it took a while to work out the conversions.<br /><br />I went to the speed prop calculator that MG developed using the supplied data and it showed I should be running a theoretical 42 MPH at an overall load of 1100 lbs. Factor in 9% slip and you get 38.3 MPH. <br /><br />Where did I lose 5 MPH? HP?<br /><br />Shouldn't anything about the boat (rough bottom, X-dimension too low, feet dragging in water) show up in greater slip?<br /><br />Does this mean the only thing I need to play with is the engine?

Re: Evinrude Performance

I don't see how the MG method "could calculate to 42 mph theoretical speed when simple mathematics reveals the 36.7 figure posted.Also bare in mind the key word "theoretical" when applying prop pitch to the equation.If one was to get a bit more critical in the exactness of actual speed that the given boat was capable of ,weight alone of the driven load would not be sufficient.One would have to take into consideration the frictional resistance (both air and water) of the driven component. If you consider all of these factors a descrepancy of 5mph is within reason.If you could get some of the cup removed from your current prop you may indeed pick up some rpms that would allow your motor to rap closer to 6000 and realize some additional mph.The 17" prop that I ran on my 83 60hp was OMC's SST single cupped and I was capable of 6000 on a 15 ft. boston whaler sport which had a very low profile.

Re: Evinrude Performance

Good point, OB. I had to go back and look for the differences. The MG spreadsheet uses more information, including a hull shape factor and calculates a different pitch prop (19").<br /><br />In reality, I couldn't turn 5500 with a 19" pitch.<br /><br />I guess I'm proving I have 11 fingers by counting down my left hand to 6 and adding that to my right hand's 5.<br /><br />I won't get to try the raised engine for several days, but if that doesn't look better, I may take a hammer to my cup. It looked real easy when Jeff did it!<br /><br />Is there some way of getting a better feeling about running a 20 year old engine @ 6000 RPM?

Re: Evinrude Performance

What I do Jim is just not leave it at 6000 for extended periods however it's nice to have a few more bullets when you want them.I'm guessing on your 14footer your going to notice some rpm increase with the one hole raise.I recently raised the 70 on the back of my 15 dauntless a month ago one hole to the top position and I was blown away at the incerase in performance.<br />Make sure if you decide to remove some cupping yourself on the prop to insure it is eqal on all three or it'll shake like a dog passing razorblades. A good propeller shop wouldn't charge much

Re: Evinrude Performance

OB -<br /><br />I tend to get heavy-handed with the kids on tubes. That's where I abuse it.<br /><br />Running out to fish or camp, I keep it well under the top end.<br /><br />I'm looking at this thing as if it were a transmission. That may be my problem. Lowering the pitch (or cup) seems like it would lower the speed at any given RPM. The kids want to go fast!<br /><br />We'll see if raising it picks up what I want first. I still have one more hole after this one. At least I now have a good baseline for comparison.<br /><br />Jeff hit me for $50 and cleaned the prop up pretty good. I rushed him and noticed he didn't seem concerned about balance. How is that done?