Looking for Confirmation

[Brian Gaynier]

I have a new to me 1998 Bayliner 4788, here’s what I know:

Port:

• 6BTA5.9-M3 (new long block at some unknown time in the past)
• S/N Unknown – illegible
• CPL assuming 1975
• Hours = Unknown

Starboard:

• 6BTA5.9-M3 (original)
• S/N 45534469
• CPL 1975
• Hours = approximately 2500 and change

Out of the factory the boat had (4) blade 24×24 props and was therefore running in an overloaded state. Paperwork onboard from a previous owner indicates that the props haven’t been reworked to the correct pitch. I know the right answer is to pull the props and have them measured to see what they’re pitched at, and if still at 24 to lower the pitch to 21-22. The gentleman at the boatyard wants me to put it in the water and run it and see how she does. Knowing the right answer, I guess I’m just looking for confirmation.

Additionally, before running those engines, I plan on servicing the heat exchangers and aftercoolers the Seaboard Marine way.

Topic

[Brian Gaynier]

Thank You Gentlemen

Thanks to all, I’ll be following your advice & perform as found testing. I’m going to service the heat exchangers and aftercoolers prior to any in water testing.

[Francis Valerio]

Boats leave the factory brand new and in many cases are overpropped as soon as you load it up with fuel or equipment or whatever it is that you put in your vessel to use it.  SPEED SELLS….PERIOD!  They dont care how it runs when you load the boat up…when it leaves the showroom Everyone loads their boats differently and “as used” weight will more than likely be different from identical boat to its sisters…   With that said, the ONLY way to know is to run the boat and see what your WOT gives you.  Also make note of the different speeds at different RPMs to give you knowledge to talk it over with a good prop guy and then you can also use that info on the Bayliner forums to see if your numbers are in line with others that running “happy boats”he same model and engine configuration.

[Rob Schepis]

Without running them “as-is” , verifying WOT and checking the accuracy of the tachs you are only guessing as to what prop work is needed. 

[Brian Gaynier]

Thanks, I have some reading to do.

Steve,

The 4788 being over propped is a long known issue. So why not measure the props and determine what the pitch is and adjust if necessary instead of another run in an overload condition?

[Steve Lewis]

There is a little more to it……

BG,

I looked your ESN up online with Cummins.  CPL is correct so 6BTA330.  Please find the attached performance chart for the CPL 1975 6BTA330.  That indicates 2800 Rated RPM.  Tony has consistently recommended being able to hit 105% of rated rpm on the mechanical diesels.  That is 2940,  So your “gentleman at the boat yard” is correct to ask for your current performance capability as you are currently prop’d.  Once you have done that, you are correct to state that you should remove the props and get them scanned so you know exactly what you are dealing with and then modify the pitch, as needed, based on your performance runs.  I have also attached my write up on propeller tuning.  It consolidates the stuff that you should search for, about props and loading, on the site into a single document.  Pay attention to the reference to correct propping of a mechanical diesel.

 

[Author]

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