Reprop report for Johnson 40HP / Lund 18

[Gopher]

I have a 2003 Lund 18 Alaskan with 2003 Johnson 40hp 2-stroke. I mostly take two people and camping gear on trips to our local islands. (high speed cruise, no towing). Initially, the motor turned 5000 RPM WOT with OEM aluminum 15" pitch prop. This is in the middle of the recommended 4500 - 5500 rpm. This year, I swapped to OMC SST stainless prop with 15" pitch. Subjective feel was improved for similar top end speed (around 26 mph via GPS). WOT rpm increased to 5600 rpm. Generously, my local Johnson dealer (thanks, Jacobsen's of Ballard, WA!) let me swap for the OMC SST stainless in 17" pitch. This brought the top speed to 29 mph and dropped the WOT rpm down to an appropriate 5400 rpm. It also "felt" smooth and strong at lower throttle. The extra weight of the stainless prop probably aids this. The boat, with two people on board, accelerates smoothly to upper 'teens mph in a few seconds. Acceleration after that is low mostly because I'm lagging in trimming the hull via trim tabs, not from apparent lack of thrust. These tests were done a large breezy lake with choppy wind waves less than one foot. Runs were made both into and out of the wind.<br /><br />best regards, hugh<br /><br />PS - I probably would have stuck with the 15" stainless prop if it didn't let the engine run too fast. Too bad "they" don't supply props oversize in diameter and let you carefully trim the tips down to dial in exact RPM for your specific combination.

 

[walleyehed]

Re: Reprop report for Johnson 40HP / Lund 18

There really is no "exact" RPM...and 5600 was actually better over-all than 5400, although not terrible, I would consider raising the engine on the transom 1 hole. This will remove some drag (add speed) and get the R's back to 5500-5600, which is better on the engine in the long run.<br />At the same speed, you will be about 100RPM lower at cruise, adding fuel economy. You may be able to raise 2 holes, but test 1 hole at a time.<br />You'd be surprised at the difference it can make.<br />And, as far as diameter and trimming the blades, we accomplish better results by raising or lowering the engine...most cases it will be raising, seldom would there be a reason to lower it.