6BTA 5.9 Fuel Burn Table

[Julian]

Hi all,
I just joined as I recently closed on a boat with twin 6BTAs and I found this data sheet for fuel burn, but it seems very optimistic.
https://www.sbmar.com/docs/performance-curves/6BTA%20%5B370,3000,2208,HO,Dec%2000,M-90034%5D.pdf

Does anyone have real world fuel consumption at various rpms?
I have speed and rpm for the boat from the sea trial, but I’m looking to match that with gph for fuel consumption. Thanks all.

Topic

[Mike Pettee]

Not the same hull, but a deep V heavy planing hull with the same 370s.

I spin up to 3150-3200 fully loaded, clean bottom.

I cruise at 2400 RPM, at around 25 MPH (I don’t use knots, sorry)

Until my fuel dock was destroyed in Irma, i filled up every trip on the way home. I can’t give you burn numbers at cruise only, but my runs offshore usually put me in a combined avg burn rate of 1.4-1.7 MPG.

Keep in mind I have short runs to fish. 25 miles puts me past the wall in into 1300 feet of water. But based on the above chart, 1.25 or MPG at cruise.

[Tony Athens]

This is the advise:

You have 355 BHP at 3125-3150 RPM and that is the RPM you want to see…………..

If your prop guy is worth his salt, then he can do this as along as he knows what you have now–2800?..

If your current prop is junk, then you need a new prop that will allow this. We prefer ACME is just about ever case on smaller boats like yours..

Tony

[Julian]

Further propping help

Wanted to follow up in regards to propping.

Ive been reading Tony’s prop article and the cummins pdfs he has posted.
Im waiting to hear from a local prop guy everyone uses.
Right now Im hitting 2800 rpm at wot this is with full fuel tanks and 2 people on board, pressure washed bottom.

I had a captain bring the boat down from Maine to Annapolis in various conditions and he says she planed best at 21 knots and up, which it currently hits at 2300-2400 rpm.
The boat may be a bit underpowered.
He was under the impression that 80% of available rpm was 2200 rpm…18.5-19 knots and a bit below the magic 21 for this hull.
He was afraid to run over 2200 rpm for too long.
Im going to ask the prop guy for 3125-3150 at wot and hopefully cruise speed will be above 21 knots at a reasonable rpm, which Im guessing should be about 2400?
If anyone has any advice I can pass on to the prop shop please let me know.
I will follow up with numbers after the repitching in the Spring.

[Julian]

Will do thanks everyone! 3125-3150 it is.

[Tony Athens]

Julian,

Tell your “prop guy this:

You have 355 BHP at 3125-3150 RPM and that is the RPM you want to see…………..

The “370” number is strictly for “marketing purposes”………..

You can thank me later.

Tony

[Rob Schepis]

Julian wrote:

I’m conditioning props this winter to hit 3000 rpm wide open. They are running 2800 now. I had the engines surveyed by the best Cummins guy I could find and everything checks out.

Well not everything. Quite over propped. Even re-propping to your new target she will still be over-propped. These engines need to spin up to 3-5% over rated rpm without issue. Especially important on a deep V boat with a hump, like a CC.

[Julian]

Thanks Steve. I’m conditioning props this winter to hit 3000 rpm wide open. They are running 2800 now. I had the engines surveyed by the best Cummins guy I could find and everything checks out. I do need to reseal the front cover as there is a small oil leak on one engine. The previous owner had her for a little over a year and sunk lots of money into engine maintenance. New injectors, aftercoolers cleaned, etc.

I surveyed a tiara with the same engines with 900 hours and it had blowby, the turbos were almost done and lots of other issues. Too many people just get on board, start and peg the throttle.

These engines are at 2200 hours and in far better shape. They are the 370hp version.

[Steve Lewis]

Julian,

You might want to post your sea trial info as well as make, model and year of boat and more detail on which 6bta engines you have.

You will want to look at the data plate on your engines and look for the CPL number on those plates and the rated HP and RPM. You will then match all of that to determine which performance curve you should be referencing. For example do you have the 330 or 370 HP version?? Look at the propeller curve. What that curve tells you is the fuel burn rate you should not exceed. This all assumes that you have an accurate method of determining fuel flow for your setup. So you need to follow the advice of all the Seaboard Marine folks on propping a mechanical diesel.

Propping a Cummins Mechanical Diesel Engine

If you follow these recommendations then you should be good. If not, then you need to reduce pitch by having your current props “conditioned” or replaced. You also need to verify the accuracy of the tach so that you are confident that your rpm is being measured correctly.

Adding flowscan fuel flow meters or similar, egt, and boost gauges will give you a very good way to measure the ongoing performance of your particular boat.

There is quite a bit of info to read in the Tony’s Tips section of this site. There is so much that goes into a boat loading a set of props that no one can tell you what your burn rate is. The curve tells you what it should be. You need to measure it some how on your own boat with your own setup under your cruising conditions.

Propellers Move Boats, Engines Just Turn Them

You can spend the winter off season reading up on how these engines are supposed to be operated and maintained so that you will get long life out of them. Depending on how they were treated before you acquired them you may have some work ahead of you. You should become familiar with Aftercoolers, water pumps, turbos, heat exchangers and proper exhaust setups.

The good thing is there is a ton of great info on this site that will make you a more educated operator of your boat and you might be able to get long life out of those engines.

Good luck, keep reading and posting. It helped me learn.

[Author]

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