6CTA 8.3 M3 450 max rpm 2400

[C Wilson]

2001 52 Offshore with 6cta 8.3 m3 450.  31 x 31   3 blade factory installed props.  During the sea trial we could only get 2400 rpm out of each engine?   Any suggestions as to why.  

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[Steve Lewis]

CW,

It dawned on me that I should state that we do realize that the Offshore 52 is a boat that you would mostly run at hull speed or less but has the ability to be run faster if need be.  I have looked at a couple Fleming55’s with Diamond 450’s.  The ultimate goal, if you acquire, should be to go though the entire drive train and make sure that everything is in good working order and then dial in the propellers so that you are able to occasionally run up into the 2200 – 2300 rpm range without causing damage to the engines from overloading.  I am “reading” into your question but that is where we aim to have you “land”.  

If you find that the throttle linkage is moving through it’s full range and the RPM readings are accurate then you can start to look at what would be loading the props and engines.

Pictures of the engines will be helpful in having the Forum determine how hard the engines have been run.  Please make sure that the pictures are such that we can clearly see the entire engine from all angles and we also want to see the exhaust setup.  The collective wisdom of the forum can lend quite a bit from good pictures.

[C Wilson]

Good information. We will go to work on it.  No fuel meters, Next trail we will run through your suggestions. thanks.  

cw

[Steve Lewis]

That is a lot of boat for those engines and there are way too many variables at play when it comes to what can be causing load on the propeller which in turn loads the engines.  Let’s start by having you read Tony’s Tips article about “Props move boats, engines just turn them”.  That will give you a very good idea.  

Are the Tachs accurate?  those are 2600rpm rated engines and Tony recommends prop dimensions that result in 1.05% of rated.  So 2600*1.05=2730+ rpm.  Could be over prop’d, could be inaccurate tachs, could be the throttle linkage…….  All sorts of things.

Did you have a laser tach on the sea trial?  Did the surveyor check deflection for the on engine throttle lever?  Could be all is good in that regard but there is too much pitch in the prop.  Won’t know until you run through all of this.  Also were the bottom and running gear perfectly clean?  I attached my write up on prop tuning.  Give that a read as well.

Does this boat have Floscan fuel burn meters?  

 

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