WOT RPMs

[keets]

My boat usually runs around 5,200 rpms wot. However when I took the boat out yesterday I could only hit 4500 rpms max. The boat ran great but took a little longer to get to plane. I have a 2006 sundancer 6.2 liter. The boat is kept in a fresh water slip. Could growth on the props be the cause? Where should I begin to look?

 

[Hampton]

Growth everywhere. Also, different loadings - fuel, water, stuff, people, winds, chop... What is the spec on the books for your engine? 5200 sounds too high. The SR tachs are not completely reliable. Deviations occur. You need to validate the data you had before and the data you are receiving now. Grab a mask and dive your boat. Check for algae/growth all over the bottom. If you have a trailer, yank it out and clean it off, then check again. Keep a log and compare notes. It can help you determine the health of your drive train.

 

[Groucho]

Yup...I agree somewhat, but.......
My guess is the gauge is not reading correct RPM's.
There would have to be a major load to make that much difference, even then you would see the temp gauge alot hotter than normal too.

 

[JeffM]

When was the last time you ran the boat? Has the bottom been painted? Even if it has paint and has been sitting for a while, growth could be the cause. Ablative paint requires use to slough the growth off.

 

[keets]

Ran the boat last night. Hit 5200 rpms again no problem. Most of the time I run my boat around 3900 - 4200. Well I guess I will have to keep an eye on it. Thanks for the replies.

 

[jimdavi]

According to the Merc manual WOT for a 6.2L is 4800-5200 and peak efficiency cruise is 3600-4000. for a 5.7 L WOT is 4600-5000 and peak efficiancy cruise is 3400-3800.