Correct motor height?

[GlasV162]

I have a '78 Glastron V162 Futura with a '90 Evinrude 90 hp with a 20 inch shaft and a 17 inch pitch prop. What is the correct height of the motor? I have always heard it should be set so the cavitation plate is even with the bottom of the hull. I'm trying to get the rpms up to the proper wot range, near 5800 rpm--currently I'm only getting about 5200-5300. Thanks.

 

[Dhadley]

Re: Correct motor height?

The "correct" height (X dimension) will largely depend on your prop and how it reacts with your hull design. Not all 17" pitch props are created equally nor do they all age the same. The best thing to do is test with what you have. Don't go spending money on a new prop until you get all you can with this one.

If the motor is down all the way, raise it up a hole or two. Then test and see whaere you're at. Record everything right now and use that as your baseline. Then make one change at a time -- very important, one change at a time -- and record that.

 

[fireman57]

Re: Correct motor height?

That is the usual starting height. Try just trimming it in or out more. dhadley is the most used setup guy on the forum although there are others. One will be along shortly.

 

[Dhadley]

Re: Correct motor height?

dhadley is the most used setup guy

It's been a long week. I feel used up.d

 

[GlasV162]

Re: Correct motor height?

Props don't age the same? If a prop is worn out and doesn't retain its original pitch, would it prevent the motor from reaching the correct range? Also, does the diameter of the prop make a difference in attaining the right rpm range? Thanks.

 

[GlasV162]

Re: Correct motor height?

P.S. I already own a brand new 17 inch pitch prop I bought as a spare. Do you think it's worth trying it, or should I exchange it for a 15 inch pitch to gain rpms? Thanks.

 

[fireman57]

Re: Correct motor height?

Sorry Dale, you type faster than I do. I picked the wrong word when I selected used. I guess I should have said Abused. I know what you mean about weeks like this. I have had days that lasted for a week. Hope all is going well down there.

 

[Dhadley]

Re: Correct motor height?

Lol! Yep, things are fine Fireman, thanks.

As props get older they lose their cup at the tip and some diameter. That lessens their ability to bite or hold water. At first you'll notice a little venting on takeoff or in tight turns. Maybe you're thinking it doesn't lift the boat as well as it once did. Thinner props wear quicker.

What brand and style is the prop you have? A 17 on a V162 should be about right. Have you tried moving the motor up?

 

[GlasV162]

Re: Correct motor height?

It's an OMC 3 blade aluminum prop, 17 inch pitch. Could it be that the throttle isn't opening all the way? I really hate to drop all the way to a 15 in. pitch as it doesn't seem necessary for this size boat. Wil an old prop that is worn cause the motor to not reach WOT rpms? Thanks.