Cummins 4BTA 140/150hp fuel economy.

[ben2go]

For you guys that have/had the Cummins 4bta 3.9L 140 or 150 hp version, what was your fuel burn rate and boat specs?

 

[O C Diver]

For you guys that have/had the Cummins 4bta 3.9L 140 or 150 hp version, what was your fuel burn rate and boat specs?

18 to 19 HP per gallon of fuel between 1,500 and 2,200 RPM. Until you move to the far extremes of any engine's RPM and HP range, fuel burn is going to be based on load divided by 15 to 20 to give you GPH.

Ted

 

[ben2go]

With my boat, it's looking like 1.5 to 2 gph at 7 knots. If I am to believe the Vicprop calculator, and I do to a point, I would need 44hp for 7 knots. Not bad for a big boat. I took the info from my plans to calculate the prop size and hp requirements. So it should be close. I actually ran the numbers a little high as if the boat was sitting on her max loaded waterline.


The Cummins performance report says the 4BTA engine I'm planning uses 2.4 GPH at 1900rpm with a continuous load. I'll mostly be in the 1400-1600 rpm where torque is at it's peak.



The original version of my boat had a Yanmar 4JH2-DTL 88hp. It's reported to have been under powered for use on the European canals. The designer now recommends 115hp to 150hp and notes this on the plans. Originally he suggested 80-150hp.



I was going to go with a 6BTA 180-210hp and no generator, but my boat has a structural bulkhead right at the front of where the original Yanmar engine sat. I think the boat was designed around that engine. The Cummins six cylinder version (6bt) would land right past the bulkhead so that's a no go without serious design changes. The bulk head supports the pilothouse's forward end.

 

[rslifkin]

From what I'm seeing on the Cummins power curves, you can either get the 4BT non-aftercooled engine at 150hp or a 4BTA (aftercooled) at 250hp. I'm guessing you've got a semi displacement hull based on people finding 88hp underpowered despite theoretically needing half that for 7 kts?

 

[ben2go]

From what I'm seeing on the Cummins power curves, you can either get the 4BT non-aftercooled engine at 150hp or a 4BTA (aftercooled) at 250hp. I'm guessing you've got a semi displacement hull based on people finding 88hp underpowered despite theoretically needing half that for 7 kts?

Full displacement Dutch Teign gravel barge based hull. The 150hp 4BT is aftercooled, at least the ones I am seeing on Ebay. 88hp doesn't go far once you add on accessories like big alternators, hydraulics, and air compressors.

 

[rslifkin]

Full displacement Dutch Teign gravel barge based hull. The 150hp 4BT is aftercooled, at least the ones I am seeing on Ebay. 88hp doesn't go far once you add on accessories like big alternators, hydraulics, and air compressors.

Good point on the extras. And that's interesting. Are the ones you're seeing marine engines or no? I wouldn't be surprised if the marine vs non-marine ones were different in terms of induction system vs hp output.

 

[O C Diver]

Ben2go, the part that you're missing from the Cummins power curve graph is that the numbers are based on fuel consumption for the maximum power the engine can produce at that RPM. If you need less HP at that RPM, the fuel consumption will be less. Think of it like this, with the transmission in neutral, if you run the engine at 1,900 RPM, it's probably only going to consume about a quart to a half gallon per hour because there is no load.

Ted

 

[Ski in NC]

The 4BT has no aftercooler. Generally a good engine rated at 150hp. Do NOT get the 4BTA 250. (the A means aftercooled). The 250 is a problem child, the 150 is rock solid.

What is the length/beam/draft/weight of the boat? 44hp to get 7kts must mean it is pretty big.

The 4BT would be very happy making 44hp all day long. So would a 6BT rated at 210.

If 6BT length is a problem, a ZF 63 or ZF 220 gear is much shorter than a velvet drive with reduction. Might be able to fit it that way.

I'd tend to favor the 4BT for 44hp.

 

[ben2go]

Good point on the extras. And that's interesting. Are the ones you're seeing marine engines or no? I wouldn't be surprised if the marine vs non-marine ones were different in terms of induction system vs hp output.

From my understanding the Cummins B are industrial marinizations. I'm looking at the marine version. Even though I am planning on keel cooling, I would like to have a cooled exhaust manifold and turbo. Some commercial fishing rigs skip the exhaust cooling from my understanding and use a truck or industrial diesel as is.

Ben2go, the part that you're missing from the Cummins power curve graph is that the numbers are based on fuel consumption for the maximum power the engine can produce at that RPM. If you need less HP at that RPM, the fuel consumption will be less. Think of it like this, with the transmission in neutral, if you run the engine at 1,900 RPM, it's probably only going to consume about a quart to a half gallon per hour because there is no load.

Ted

Thanks, Ted. Yeah I'm getting that but at the 1400 to 1600 most seem to be running their engines, I would think it would take 80% of the available hp at that rpm to move a 20 ton boat. The 1900 rpm was the lowest rpm rating Cummins gave a fuel consumption spec for at full load for that rpm of 2.4 gph.

The 4BT has no aftercooler. Generally a good engine rated at 150hp. Do NOT get the 4BTA 250. (the A means aftercooled). The 250 is a problem child, the 150 is rock solid.
Everyone must be using stock photos because I am seeing an aftercooler but you're right.
What is the length/beam/draft/weight of the boat? 44hp to get 7kts must mean it is pretty big.
The boat specs are 45'/12'/30"/39,000 fully loaded. That is misleading though. The actual waterline at 39,000lbs is 40'/10'/36". I took the waterline measurements from the plans and converted them to imperial. The plans are metric, because UK designer. I also rounded up to the nearest foot but the draft is in spec. Light draft is 30 inches. This is what I am shooting for to keep the prop in clean water.
The 4BT would be very happy making 44hp all day long. So would a 6BT rated at 210.
The 4BT is what I have to go with. The structural bulkhead is in the way and the 6BT would go a foot to foot and a half past it into the salon. I could have paid and had the design changed to accept a 6BT but the extra power shouldn't be needed. With conversion rates, I have just shy of $700 in the plans and build manual. Compared to some cheaper plans, I definitely got my moneys worth with Selway-Fisher. I also have access to Mr. Fisher during his business hours and online through various ways.
If 6BT length is a problem, a ZF 63 or ZF 220 gear is much shorter than a velvet drive with reduction. Might be able to fit it that way.
Good point. I need a straight through transmission with no angle and no drop or rise with a 2:1 ratio or as close as possible. I have to maintain the crankshaft center line. With the 4BT specs, a 1.5 inch space between the oil pan and hull puts the crankshaft center line right where it needs to be to spin a 22 inch prop. For every inch I raise the engine, I have to remove one inch from the prop up to two inches. Then the engine comes up through the pilothouse floor. It's looking like the 71/72 BW/VD is going to be my only choice. Once the boat lower hull and keel are built, the engine goes in. If I wait to build it I have to remove the pilothouse and drop it through the pilot house floor. My pilot house is removable from below the windows up. The ones in EU have a pilot house that lowers after the windows are folded in or out.


I'd tend to favor the 4BT for 44hp.

Lowering a Dutchy pilothouse.

 

[O C Diver]

Can you post a link to the Cummins graphs you're looking at. Really think that engine is capable of producing more than 50 HP at 1,900 RPM.

Ted

 

[rslifkin]

The Cummins graphs list a few things for each RPM. Max hp, max torque, max allowed sustained GPH (based on the prop curve) and sometimes prop curve hp. The 2.4 gph at 1900 would be the prop curve GPH, so that's the most they expect the engine to burn at 1900 if propped correctly.

 

[O C Diver]

Here is a link to the performance graph for that engine.

http://tadiesels.com/assets/docs/4BT39_155_performance.pdf

At 2,000 RPM it's capable of producing around 90 HP and consuming 6 GPH (15 HP per gallon). As you reduce HP for the same RPM, the efficiency gets better. The thing to understand is that the "Typical Propeller Curve " in the graph is meaningless for your application as it's mostly likely for a planing hull boat. For a displacement hull boat the curve would be fairly flat, then rise very quickly as you approach hull speed, and almost instantly going off the top of the chart. If cruising speed is around 1,900 RPM, you won't be able to reach maximum RPM before you run out of HP.

Ted

 

[ben2go]

Here is a link to the performance graph for that engine.

http://tadiesels.com/assets/docs/4BT39_155_performance.pdf

At 2,000 RPM it's capable of producing around 90 HP and consuming 6 GPH (15 HP per gallon). As you reduce HP for the same RPM, the efficiency gets better. The thing to understand is that the "Typical Propeller Curve " in the graph is meaningless for your application as it's mostly likely for a planing hull boat. For a displacement hull boat the curve would be fairly flat, then rise very quickly as you approach hull speed, and almost instantly going off the top of the chart. If cruising speed is around 1,900 RPM, you won't be able to reach maximum RPM before you run out of HP.

Ted

That's the graph I used. Speed as suggested by the designer is 6 to 9 knots with the original 88hp Yanmar called out in the plans. I think that Yanmar would be screaming at 9 knots. If I'm not mistaken those Yanmar 4JH2 engines are 3300 or 3600 rpm limit. The vicprop calculator stated a max speed of almost 11 knots with the 150 hp engine. I don't think that's right. I'm hoping my cruise speed is around 7 to 8 at 1400 to 1600 rpm. It would be nice to have a tick more but I'm not holding hopes for that.

 

[rslifkin]

Keep in mind, if you're going to load the engine down with a bunch of auxiliaries, unless you can simulate load well enough to prop it to reach proper RPM with that load, I'd tend to say it needs to be underpropped for running without the auxiliaries powered. So you'll probably be at a bit higher RPM for cruise. Just make sure you reach hull speed a bit before max RPM if possible. And that'll also mean it's running at a lighter load relative to RPM normally, so it'll be less sensitive to changes in load from auxiliary equipment.

 

[ben2go]

Keep in mind, if you're going to load the engine down with a bunch of auxiliaries, unless you can simulate load well enough to prop it to reach proper RPM with that load, I'd tend to say it needs to be underpropped for running without the auxiliaries powered. So you'll probably be at a bit higher RPM for cruise. Just make sure you reach hull speed a bit before max RPM if possible. And that'll also mean it's running at a lighter load relative to RPM normally, so it'll be less sensitive to changes in load from auxiliary equipment.

Good point. The hydraulics will be used for thruster and windlass. The pump will be clutched so it only runs when needed. Same for the air compressor. The engine will be spinning at least one large alternator, but I'm considering two for redundancy. A small 65A to 85A alt for the start batteries and a big house battery alt of maybe 160A to 200A. I'm trying to stay away from having a generator or at least making it possible to have as small of a generator as I can. If I do go with a generator, then the hydraulics and air compressor will be driven by the genny. I'm still working out an electrical system plan so I'll know how much power I need.

 

[jleonard]

Those are tough engines. There are a crapload of them out there in delivery trucks: Frito Lay, UPS, and the like.

 

[Ski in NC]

The ZF 220 and 63 can be bought with no down angle, but all come with a drop center of a few inches. In a new build this should be no big deal as you can locate the shaft log where ever it fits. You can go with in line VD gear, nothing wrong with that, but in a new build you are not so restricted.

On my build the bottom of the gear is 1/4" off the keel and top of engine is 1/4" from deck hatch bottom. Tight!!! I use a ZF 280PL which has no down angle but does have drop center. Was nervous lining things up the final time as I did not have much room to move. It all dialed in just fine. Whoooo. Just had to trim a bit of wood from hatch structure.

On your build, don't cut it that tight!!! Give an inch above and an inch below as clearance to start.

Based on your numbers, still thinking the 4BT 150 should be fine. Use good motor mounts!! (can guide you on that when you get there). A bit shaky at idle, but at like 1600 it is fine.

 

[ben2go]

The ZF 220 and 63 can be bought with no down angle, but all come with a drop center of a few inches. In a new build this should be no big deal as you can locate the shaft log where ever it fits. You can go with in line VD gear, nothing wrong with that, but in a new build you are not so restricted.

On my build the bottom of the gear is 1/4" off the keel and top of engine is 1/4" from deck hatch bottom. Tight!!! I use a ZF 280PL which has no down angle but does have drop center. Was nervous lining things up the final time as I did not have much room to move. It all dialed in just fine. Whoooo. Just had to trim a bit of wood from hatch structure.

On your build, don't cut it that tight!!! Give an inch above and an inch below as clearance to start.

Based on your numbers, still thinking the 4BT 150 should be fine. Use good motor mounts!! (can guide you on that when you get there). A bit shaky at idle, but at like 1600 it is fine.

The way the design is around the deadwood, the prop can't move up or down without going smaller. The rudder is an outboard design and uses a lower keel horn/keel shoe to hold the bottom of the rudder. The prop is fully protected. The design is such that if I try to raise or lower the engine much, a redesign will be in order for the pilothouse and engine room. It's complicated to explain without viewing the plans. It's also why I think the boat was partially, if not fully, designed around the Yanmar.