370 B Cruise Speed - CB 35

[stevediebold]

I have a 2003 35 CB with a Cummins 370B. WOT is 3000 RPMs. Does anyone know what the optimal cruise RPMs are? I have been running at 80% of WOT or 2400 RPMs and generate about 15 knots on average. Read a few other forums that said 400 RPMs below WOT is an acceptable cruise speed. That would be 2600 RPMs and about 17 knots. Interested in what you all think. Thanks.

[sbmar.com]

Steve,

#1--------------Your WOT RPM, loaded the way you use the vessel, needs to be an accurate 3000+ RPM, with 3100-3150 best.........

#2-------------If you can reach rated RPM or more ( remember what I said in #1), then running at 2600 RPM is fine if you find that a better RPM for you.. Your time vs more fuel, and more wear and more and tear on the engine and your boat.. I call that a business decision..

#3--------------If you barely squeek 3000 RPM on a good day or may not even make it there, then all bets are off if you want good long term life spread out over many 1000 hours on your 370's...................Have you had your tachs checked for accuracy ??

It's you call from here.. The 370 is one great engine, but like any engine in this class, overloading will do it in long before it's time..

Tony

[jleonard]

Hey there swabby...glad to see you in this group!! Welcome!

[jruesr]

I have a 1990 sportsfisher 32 that was repowered with a commins 370 B. I cannot get the proper rpm. My gearing is original I believe but cannot be sure. The V-drive ratio is 1.47 and the transmission ratio is 1.12. The boat has a remote V-drive with an intermediate drive shaft connecting the engine and v-drive. My current prop is a 20.5x23 lh, four blade. I recently had the prop re-pitched and the pitch was reduced. I cannot get more than 2800 rpm at full WOT.

Can anyone tell me what the gear ratio is for an albin with a Cummins 370 and what prop size and pitch is correct.

John
Passages III
Punta Gorda, Florida

[Seaslug44]

I have a 1990 sportsfisher 32 that was repowered with a commins 370 B. I cannot get the proper rpm. My gearing is original I believe but cannot be sure. The V-drive ratio is 1.47 and the transmission ratio is 1.12. The boat has a remote V-drive with an intermediate drive shaft connecting the engine and v-drive. My current prop is a 20.5x23 lh, four blade. I recently had the prop re-pitched and the pitch was reduced. I cannot get more than 2800 rpm at full WOT.

Can anyone tell me what the gear ratio is for an albin with a Cummins 370 and what prop size and pitch is correct.

John
Passages III
Punta Gorda, Florida

I have the same boat but with the original 300hp Cummins. My prop is a Nibral Bronze 3 Blade 22’d. x 19”p. I have the same Walters V-Drive with the 1.47 ratio and the same Velvet Drive with the 1.12 transmission. WOT is 22-23 knots at 2850-2950 rpms depending upon the load. Cruise is 18 to 20kts at 2600 rpms (also depends upon the load).

Are you positively sure that you have a 370 Cummins? If you have the engine serial number you can look up all your engine statistics by going to this Cummins website- https://quickserve.Cummins.com/info/index.html and creating a Free/demo account. Then once you are in your free account you can enter your engine serial number and click on "Engine Data Plate" to see your engine info. I bought my Albin second-hand. It's a 1989 but interestingly when I ran the serial number through the Cummins Data base, this is what mine says-

Engine DataplateBASE ENGINE INFORMATION
Upfit Original
Engine Serial Number 44611952
Shop Order # SO52275
Plant CNS - CONSOLIDATED DIESEL CO.
Build Date 07 May 1991
Warranty Start Date 05 Jun 1992
Customer Number 2240
Customer Name
ECM Code Not Available For This Engine
Fuel Pump Part # 3919762
Fuel Pump Calibration
Film Card T
Engine Config # D403017MM12
CPL # CPL970
Marketing Model Name B5.9M (300)
Service Model Name

Under "Marketing Model Name" you should see B5.9M (370) if you truly have a 370hp. As you can see, mine is a 300.

On another interesting note, even though my hull is a 1989, my engine build date was May 1991 and my warranty start date was not until June 1992!! So strange. There are no signs that my boat was ever repowered and according to the person I purchased the boat from (who was the second owner) the boat never was repowered. The boat does have low hours for its model year. Is it possible that my hull was a leftover that wasn't powered until 1991 and not commissioned until 1992??

Anyone have any ideas?

[Seaslug44]

Oh yeah, one more thing regarding cruising rpms... this is right out of the Cummins Manual-

High Output Rating
This power rating is for use in variable load applications where full power is limited to 1 hour out of every 8 hours of operation. Reduced power operation must be at or below cruise speed (rpm). Cruise speed (rpm) is dependent on the engine rated speed (rpm):

Rated Speed (rpm) Cruise Speed (Reduction from rated speed, rpm)
Less than 2800 rpm 200 rpm
2801 to 3500 rpm 300 rpm
3501 to 4500 rpm 400 rpm
4501 to 5000 rpm 500 rpm

[jruesr]

Thanks for your reply.

I would be perfectly happy with the performance of your boat. Maybe I should sell this Cummins 370B and find a nice used 300hp like yours and drop it in. Maybe I could make money on the exchange.

My engine was installed by a boat yard in Ft. Meyers Florida in 2004. They are no longer in business. The boats owner passed away and I bought the boat from his widow after the it sat for a few years with very little use. The boat had 1400 miles on the new GPS log (installed at the same time as the engine). There is no working hour meter. It sounds like the project was not complete. The widow put the boat up for sale with 15 hours on the engine according to her add.

My engine was Remanufactured by Diesel Recon Co
Division of Cummins Engine Co. Inc
San Luis Potose - Mexico

Data plate data follows
Date of Manufacture 10/04/03
CID/l 5.9
Series B
Timing TDC 12 degrees
Firing order 153624
Low idle rpm 600
Engine Serial Number 602244495 60224495
Injector pin 3865968 px
Rated hp 370 at 3000 rpm
Model name 6BTA 370-3000

I WILL TRY YOUR WEB SITE TONIGHT BUT SO FAR NO ONE HAS BEEN ABLE TO IDENTIFY THE RE-MANUFACTURE SERIAL NUMBER. MY Cummins PARTS PEOPLE CANNOT TRACE ANY REMANUFACTURED DIESELS FROM THERE OWN SUBSIDIARY'S.

There is a record (from our propeller company) of the initial sea trials on the boat with this engine and they had the prop pitched to a higher pitch twice in order to reduce rpm. Now I cannot get enough. I had it balanced and brought back down to 20.5x22lh four blade. I still only run about 2850. I am afraid that I will destroy the motor if I don't find out what is going on and fix it. You cannot overload the motor or so I am told. It sure seems like this engine should pull this prop.So far my top speed is 22 kts. I do not care what the top speed is I just want to be sure the engine is not overloaded and that I will not destroy it. I nice 15 kt cruise would be great.

[jruesr]

I changed my prop to an 18 pitch x 23 dia three blade (this was my boats original prop I believe) and the rpm came up to 3085 WOT (wide open throttle) and speed is 22kts. My four blade 22 dia x 20.5 ran at 2650 on the last trial run and boat speed WOT was 22 kts also. My engine will be much happier now I believe. I am not sure what good I am getting from a 370B engine as opposed to the original 300B5.9 like the boat came with from the factory.

Thanks for the help.

John

[Seaslug44]

You are very welcome John. Also, please see my reply to you about the keel panels in the other discussion.

[ctlionsden]

Any chance your tach could be off? Have you checked engine rpm's with another instrument? By now you have hopefully solved your problem, but if not, this may be helpful, since your speeds don't sound that much off the average for the boat.

[jruesr]

The 32 SF was made with an inspection panel in the kiel that covers two cutlass bearings. The panel was missing on my boat when I bought it. After many months of frustration I made covers for this opening and all my troubles went away. The shaking disappeared and the performance increased. Now its a great running boat.

Passages III
John