Hi,
First, what a great forum!
A friend just sold me a 1980 Crestliner Nordic 20, with a Mercruiser 140 I/O.
We took it out this weekend, and the top speed is a bit lacking. At WOT, the boat hit about 3500 RPM, and top speed was about 25MPH, with just me on the boat. When 3 more moderately sized people boarded, top speed dropped to about 20MPH max, and only when people were moved toward the bow (see below).
We measured the speed with both the onboard speedometer, and a "chaser" boat, and got approximately the same answers. I trimmed the outdrive full down for this test, as trimming it up reduced the top speed.
The prop has some slight curling and chipping on one of the blades. I am not sure how significant this is.
My questions are these:
a) I plan on replacing the prop to see if that corrects the speed problem, since the prop does have some deformity. Anyone know what pitch should be on this boat, with this power package?
b) Best I can tell from downloading the service manual for the mercruiser 140, the WOT RPM should be in the mid 4K's. So, the RPM is very low for WOT. I assume this is due to either a) the wrong pitch prop, b) the damage to the prop, and/or c) an incorrectly adjusted carb. Any suggestions on that?
Also, I noticed that it was important to position people toward the bow of the boat, or the boat would trim up significantly and slow down dramatically, basically falling off plane. Basically if any adult was at the stern of the boat, it would not plane well. I am considering a Doel-Fin or similar hydrofoil to address this issue?
Thanks for any suggestions!
Bill
First, what a great forum!
A friend just sold me a 1980 Crestliner Nordic 20, with a Mercruiser 140 I/O.
We took it out this weekend, and the top speed is a bit lacking. At WOT, the boat hit about 3500 RPM, and top speed was about 25MPH, with just me on the boat. When 3 more moderately sized people boarded, top speed dropped to about 20MPH max, and only when people were moved toward the bow (see below).
We measured the speed with both the onboard speedometer, and a "chaser" boat, and got approximately the same answers. I trimmed the outdrive full down for this test, as trimming it up reduced the top speed.
The prop has some slight curling and chipping on one of the blades. I am not sure how significant this is.
My questions are these:
a) I plan on replacing the prop to see if that corrects the speed problem, since the prop does have some deformity. Anyone know what pitch should be on this boat, with this power package?
b) Best I can tell from downloading the service manual for the mercruiser 140, the WOT RPM should be in the mid 4K's. So, the RPM is very low for WOT. I assume this is due to either a) the wrong pitch prop, b) the damage to the prop, and/or c) an incorrectly adjusted carb. Any suggestions on that?
Also, I noticed that it was important to position people toward the bow of the boat, or the boat would trim up significantly and slow down dramatically, basically falling off plane. Basically if any adult was at the stern of the boat, it would not plane well. I am considering a Doel-Fin or similar hydrofoil to address this issue?
Thanks for any suggestions!
Bill
