Question for Dhadley

[dcappotto]

Dhadley,<br /><br />Last year around this time you responded to one of my post regarding an RPM loss on a 1990 22 ft Grady-White with a 200hp Evinrude which had just<br />been rebuilt. I'm getting ready for the start of the new season and I am concerned that I may be lugging this motor. You made note that the RPM loss could be the result of the boat getting heaver over time as well as additional equipment.<br />I'm wondering if its time to try a new prop with less pitch, currently I'm running a 15x17 stainless. I don't think the current setup will allow me to raise the motor a hole due to the cavitation plate being level with the hull now.<br />If you search for "codkiller" with the subject<br />"loss of rpm" you find the previous post you responded to. Any info would be greatly appreciated<br /><br />Thanks<br /><br />codkiller

 

[Dhadley]

Re: Question for Dhadley

The motor can be raised to the point the AV plate is above the bottom especially if setback is involved. Motor height or X dimension largely depends on prop design and its relation to hull design. <br /><br />If youre not getting enough rpms with your current prop, I'd start by raising the motor. At this point we're only concerned about the top rpm changes. We arent concerned about venting on holeshot or cornering. It may not. We're just looking for how the motor responds to top rpms on a given hull.<br /><br />Obviously all this testing has to start with a healthy motor. We should start with the basics. Compression test, make sure the carbs are clean, sync & link, spark check etc.

 

[dcappotto]

Re: Question for Dhadley

Thanks for the quick response Dhadley<br /><br />Setback is not involved, mounted on the transom. Compression is 92 on all six, carbs were rebuild last season, sync & link was done after the rebuild, good spark all around. This motor runs better now than it did when it was new. We plan on running the boat this weekend on the lake to calibrate a newly installed autopilot, I will move it up a hole and let you know the results.<br />What can I expect to pick up in RPM's by moving <br />the motor up one hole?

 

[Dhadley]

Re: Question for Dhadley

A lot depends on hull and prop design and how they react to each other. As a rule of thumb we look for about 150 per hole.<br /><br />Now that just a general rule of thumb. Sometimes more, sometimes less.

 

[dcappotto]

Re: Question for Dhadley

Dhadley I got to run the boat on the lake this weekend. Looks like I picked up about 200 RPM.<br />Now getting 5400 at WOT, GPS says 34.5 knots. What do you think?

 

[Dhadley]

Re: Question for Dhadley

Getting better! Can you use all the trim range?<br /><br />You mentioned the motor was rebuilt. Did you lose the rpm after the rebuild compared to before the rebuild?

 

[dcappotto]

Re: Question for Dhadley

No, I don't think I can use all of the trim range. The way I set the trim is I raise the trim until I start to loose the bite on the prop and then lower it a bit. Is this the correct methord. I would say I am close to using all of the range.<br /><br />I had a lose in RPM before the motor was rebuilt.

 

[Dhadley]

Re: Question for Dhadley

Yes, that is the correct way to set the trim for any given throttle position. Once the motor is at the optimum height for a given prop youll get use of about 80% of the trim range. IE -- if you can trim all the way out without losing bite, you can, most likely, go higher with that prop. We always like to test past what we think is the best height and then drop back down slightly.<br /><br />Since the motor was just rebuilt -- and if its broke-in -- it might not hurt to recheck the timing. If its backed off much it will hurt the rpm's also.

 

[dcappotto]

Re: Question for Dhadley

Ok I will check the timing. So is it safe to say base on the fact I cannot use the full range of trim with the current setup the motor should stay where it is? (one hole higher)

 

[Dhadley]

Re: Question for Dhadley

That'll probably be real close for that prop. If it were mine I'd try it one more hole higher just to see what happens.