Can't reach max RPMs underway in gear. - Maxum Boat Owners Club

PJHoffnet · 07-01-2017, 11:38 PM

1999 4100 SCA 330 Cummins

No issues last time out, 1 May.

Pre-underway engine start up, warm up, and increase throttle (in neutral) easily reaches max RPMs. Normal temps and oil pressure.

Underway idle/low RPM (10k) run out of no/low wake zones - no issues.

After ~20 min clear of low wake area and throttle up but can't push past ~14k. Temps and oil pressure are normal.

Thought it might be a trim tab issue and I was just not driving out of the hole and getting up on plane. Can't actually see trim tabs, and no remote indication. Checked trim tab accumulator and listened to motor cycle as helm switches are pushed for up and down. All seem ok.

Underway, when transmission is in neutral, still no issue getting to max RPMs.

No black/blue exhaust even at full throttle (in neutral) so seems turbos are ok.

Any thoughts would be appreciated. I have two more days to trouble shoot before this vacation is over and I'll call my maintenance guys to have them take a look on our next time back at the boat.

Thanks in advance.

mmwjr · 07-02-2017, 03:05 AM

First reving an engine in neutral is not good for the engine and it tells you nothing.

When was the last time they achieved proper WOT? Hit anything? Marine growth?

PJHoffnet · 07-02-2017, 03:08 AM

Sorry, noticed a typo in my original post ... missed putting in the decimal point in my RPM reports.

In neutral, idle ~200 RMP, ~3/4 throttle 2,400 RPM easily reached then I back off.

In gear, for low/no wake, about 5 knots ~1/4 throttle ~1,000 RPM. Full throttle 1,400 RPM, only about 7 knots.

Starting to get a feeling that the bottom/props/shafts might just need a good cleaning.

PJHoffnet · 08-09-2017, 02:44 PM

Problem found & corrected. An hour of scrapping made all the troubles go away.

Phillbo · 08-09-2017, 03:22 PM

Wow... when was the last time you had it cleaned?

PJHoffnet · 08-09-2017, 03:56 PM

@Phillbo ... Did a scrape in early March during survey.

mmwjr · 08-09-2017, 10:39 PM

That growth will do it. When last cleaned did you paint the running gear?

jimq26 · 08-10-2017, 01:48 AM

That's a candidate for Eelsnot for sure! The gear snot stuff keeps the little critters off like you wouldn't believe.

PJHoffnet · 08-10-2017, 02:58 AM

@mmwjr & jmq26 - no, haven't begun periodic preventative maintenance, but I've read about the effectiveness of eel snot on the boards. Will read up on application and work it into next short hall or next time on the hard.

PJHoffnet · 08-19-2018, 05:07 PM

Doing house cleaning on subscribed thread that I've left hanging.

I used eelsnot in DEC 2017 - the time after I had the boat out in the picture above. Coated the shafts, props and rudders (used most of a can of running gear eelsnot - 4oz I believe). Pulled the boat to replace zincs in AUG 2018 and there was absolutely no growth. Used the remainder of the can on the props. We did use the boat a lot more frequently (every week or two) during that time period vice the once every couple of months when we had the growth issue so not sure if the use or the eelsnot was the cure.

shrew · 08-20-2018, 03:13 PM

Quote:

Pre-underway engine start up, warm up, and increase throttle (in neutral) easily reaches max RPMs. Normal temps and oil pressure.

OK, since you're closing out old threads (always appreciated), I noticed the statement (above) in the first thread, and thought it was worth mentioning:

1) It is my understanding that you don't bring diesel engines up to operating temp at idle. Run for a few minutes, then put under some load (in gear).

2) It is my understanding that you don't rev diesel engines without any load. Such as bringing to max rpm in neutral.

PJHoffnet · 08-20-2018, 04:15 PM

Quote:

Originally Posted by shrew

OK, since you're closing out old threads (always appreciated), I noticed the statement (above) in the first thread, and thought it was worth mentioning:

1) It is my understanding that you don't bring diesel engines up to operating temp at idle. Run for a few minutes, then put under some load (in gear).

2) It is my understanding that you don't rev diesel engines without any load. Such as bringing to max rpm in neutral.

I've heard the same thing from others - I have changed my way of 'doing business' ... now I just start up and the engines idle while we take off shore power/water and lines and are nicely warmed up before I bump her into gear to head out for fun times.