Yanmar v Cummins v ...

Jeff F said:

Don't forget fuel delivery. The injection pump is likely a limiting factor. Also cooling capacity, exhaust sizing, and power delivery - you'd need to change props and/or gear ratio, maybe beef up shaft size, etc. These components are (or should be) integrated into a complete system. Trying to get more max power is not as simple as it might appear.

Click to expand...

Sigh, thank you. I'm finding that even a minor change ("minor" to me!) isn't easy.

So you'd probably recommend against it?

mcarthur said:

Consumption is total, adding the two.
Speeds are when both are running. I believe it's possible with the gearbox to freewheel with a shutdown engine, so the lower two speeds could possibly be done with one engine (at different consumptions; the hulls are hard chine and deep so there would possibly be little rudder needed to keep a single engine on track).

Click to expand...

I am not sure how you captured the total burn of these two 135 hp Perkins.
I think that it say max fuel burn is 3 liters per nmile at 13 knots.
That would be 3 X 13 = 39 liters per hour or 10.3 gph if I did the math correctly.
How do we explain two 135 hp diesels of that vintage consuming 103 gph at WOT?

270 total hp divided by 10.3 gph = 26.2 Hp per gallon of fuel per hour.

The Perkins consumption curve for the 1000 series M135 shows 21 L/hr at 2400rpm. For two engines, that's about 42 L/hr. For 13 knots at 2400rpm, that's 13nm/hr. 42/13 = 3.2L/nm.

Don't know where you go the 103gph!

mcarthur said:

The Perkins consumption curve for the 1000 series M135 shows 21 L/hr at 2400rpm. For two engines, that's about 42 L/hr. For 13 knots at 2400rpm, that's 13nm/hr. 42/13 = 3.2L/nm.

Don't know where you go the 103gph!

Click to expand...

"Don't know where you go the 103gph"
That would be 10.3 not 103.

"2400rpm (as close to WOT as we get), 13kn, near 3L/nm"
So when you posted these numbers they were not collected on your boat/engine they were just imputed from an engine curve?

If you are utilizing any of these numbers as a benchmark for future alteration it is very important that they are correct otherwise any future work based upon these numbers will be worthless.

FWIW - if you are firewalled at 2400 and expecting your fuel use to follow a typical exponent curve you will be way off base.

mcarthur said:

The Perkins consumption curve for the 1000 series M135 shows 21 L/hr at 2400rpm. For two engines, that's about 42 L/hr. For 13 knots at 2400rpm, that's 13nm/hr. 42/13 = 3.2L/nm.

Don't know where you go the 103gph!

Click to expand...

Hello Mcarthur - just checking in to see if these figures are collected on your boat/engines or are they from an engine fuel curve found online.

"2400rpm (as close to WOT as we get), 13kn, near 3L/nm"
So when you posted these numbers they were not collected on your boat/engine they were just imputed from an engine curve?

Sorry smitty...
The numbers are from the boat itself (two motors, 2400rpm, 13kn, around 3L/nm counting both motors). I only went to the engine data and curves to check against the 103gph - I much prefer 10.3gph (phew!).

You had asked "How do we explain two 135 hp diesels of that vintage consuming 10.3 gph at WOT?" and I was explaining it by a) that's what the boat gets (actual), and b) that's what the engine manufacturer quoted (theoretical). So I'm not seeing the problem...

mcarthur said:

Sorry smitty...
The numbers are from the boat itself (two motors, 2400rpm, 13kn, around 3L/nm counting both motors). I only went to the engine data and curves to check against the 103gph - I much prefer 10.3gph (phew!).

You had asked "How do we explain two 135 hp diesels of that vintage consuming 10.3 gph at WOT?" and I was explaining it by a) that's what the boat gets (actual), and b) that's what the engine manufacturer quoted (theoretical). So I'm not seeing the problem...

Click to expand...

You have an actual measured fuel consumption of 10.3 gph at WOT for both (2) 135 hp earlier Perkin diesels.

That would be 270 hp total being produced by 10.3 gph which is almost 60% less than the hp which you could/should expect from those engines burning 10.3 gph.
I believe it would be important to figure out why your fuel burn (and therefore HP) differs from the expected amounts.
These numbers are being utilized by you to guesstimate the relative speeds of increased hp in the boat so the benchmarks are very important.

smitty477 said:

You have an actual measured fuel consumption of 10.3 gph at WOT for both (2) 135 hp earlier Perkin diesels.

Click to expand...

Yes (well, close enough to 10.3 but I wouldn't swear to the final decimal).

smitty477 said:

That would be 270 hp total being produced by 10.3 gph which is almost 60% less than the hp which you could/should expect from those engines burning 10.3 gph.

Click to expand...

I'm not sure why you would say that - this number are almost precisely what Perkins themselves say the engines should get at the hp and rpm! If you look at the consumption curves in the previous Perkins link, 11gph is EXACTLY what Perkins say at a 2.8 prop curve (21L/hr per engine). I'm pretty happy with a range of 10-11gph given I haven't measured the prop matching the engine to it's 2400rpm (or rather 2600rpm) maximum.

smitty477 said:

I believe it would be important to figure out why your fuel burn (and therefore HP) differs from the expected amounts.

Click to expand...

I don't see any difference though in real versus expected amounts!

Also, you say that the "26.2 Hp per gallon of fuel per hour" would be "60% less than the hp which you could/should expect from those engines". I've tried to find other (non common rail!) engines that would be more efficient and more powerful, but haven't found much more than a 5% better consumption.

• Have you got any data on other engines which show a much better consumption?
• Also, have you an example of other engines (or the Perkins data) that would move from 60% hp-generated to 100% hp generated at the same consumption? This would mean they're generating about 44hp per gallon of fuel per hour. I realise these would be on entirely different boats and slightly different prop curve, but you clearly have some in mind since you mentioned the 60%...

mcarthur said:

Yes (well, close enough to 10.3 but I wouldn't swear to the final decimal).

I'm not sure why you would say that - this number are almost precisely what Perkins themselves say the engines should get at the hp and rpm! If you look at the consumption curves in the previous Perkins link, 11gph is EXACTLY what Perkins say at a 2.8 prop curve (21L/hr per engine). I'm pretty happy with a range of 10-11gph given I haven't measured the prop matching the engine to it's 2400rpm (or rather 2600rpm) maximum.

I don't see any difference though in real versus expected amounts!

Also, you say that the "26.2 Hp per gallon of fuel per hour" would be "60% less than the hp which you could/should expect from those engines". I've tried to find other (non common rail!) engines that would be more efficient and more powerful, but haven't found much more than a 5% better consumption.

• Have you got any data on other engines which show a much better consumption?
• Also, have you an example of other engines (or the Perkins data) that would move from 60% hp-generated to 100% hp generated at the same consumption? This would mean they're generating about 44hp per gallon of fuel per hour. I realise these would be on entirely different boats and slightly different prop curve, but you clearly have some in mind since you mentioned the 60%...

Click to expand...

Lets forget about other boats and prop curves for just a bit here.
If your actual real life measure of fuel burn is 10.3 total for both engines then you are 'making' maybe 185 hp tp go 13 knots.
At this point you are contemplating adding hp to go faster based upon your baseline measurements.
If you are only using 185 hp now where is the other 85 hp?
Is there a problem with the engines, tachs, throttle controls, props, etc?
On the other hand if you are firewalled and the fuel burn is really much more than 10.3 gph then you believe you are measuring then the boat 'requires' more hp to do the 13 knots. How much more depends upon what your engines are really burning.
FWIW _ if you can only achieve 2400 rpm on an engine that is rated at 2600 rpm your fuel burn will not be nearly at the curve on a graph for that engine.... it will be much higher and maybe full fuel loads are present. The engines are overloaded in those cases.
FWIW - your Perkins engines will achieve about 18 hp per gallon of fuel used per hour on a good day, most other engine brands will be close to this number as well. That is why I am asking where has the hp or fuel gone.

So if your fuel burn monitoring is correct and your tachs are correct there is good reason to doubt your baseline numbers which you are utilizing to plan all other options. Solving for the problem you have would be the most important item before planning any other changes in the future.

Do you have any tests done with sister boats to yours with fuel burn numbers?
What exact make ,model, and year is this boat?

whew

Reworking the boat's existing Perkins to add turbocharging and maybe after cooling is a big, big chore and is best done by pulling the engines and sending them to a shop. That will cost almost as much as a new or remanned engine because all of the special parts: turbo, after cooler, etc. will have to be bought one off and installed with very skilled labor.


It would be much better to buy a pair of say new factory reconned Cummins 6BTA engines and install them with the necessary upgrades to prop, prop shaft, transmission, etc. You will have a completely new drive train with engines that are one step below state of the art as opposed to two steps with the reworked Perkins. That won't be cheap either and here in the US will cost about $40K per engine.


So think about buying that boat and adding $80k vs buying a boat with that power already installed. It almost always is cheaper to do the latter.



David

Ouch David, you know how to prod correctly!

I was looking at secondhand 6BTA's for $19-22k, but of course with all the attendant issues of no warranty, condition and age.
Then there's the cost to remove the existing engines and replace.
There may be some money to be pulled back by selling the existing motors?
I also assume the cost to remove and replace entirely depends on the location and access, but would anyone like to hazard a guesstimate of hours or cost, especially if it's not easy to access? Not easy in this case are in the middle of the two hulls of an aluminium catamaran, with best access either with a big chainsaw or somehow onto the inside bridgedeck and then up and out the back door ...

"I was looking at secondhand 6BTA's for $19-22k,"


Try looking in Boats and Harbors , should be 1/2 or 1/3 of your quote each.

djmarchand said:

Reworking the boat's existing Perkins to add turbocharging and maybe after cooling is a big, big chore and is best done by pulling the engines and sending them to a shop. That will cost almost as much as a new or remanned engine because all of the special parts: turbo, after cooler, etc. will have to be bought one off and installed with very skilled labor.


It would be much better to buy a pair of say new factory reconned Cummins 6BTA engines and install them with the necessary upgrades to prop, prop shaft, transmission, etc. You will have a completely new drive train with engines that are one step below state of the art as opposed to two steps with the reworked Perkins. That won't be cheap either and here in the US will cost about $40K per engine.

So think about buying that boat and adding $80k vs buying a boat with that power already installed. It almost always is cheaper to do the latter.


David

Click to expand...

Agreed David - but if I were going to actually cruise utilizing more than maybe 200 hp per engine over long periods I would not choose the 6B.
If I were not going to utilize near 200 hp for longer periods of time I would likely stay with the existing installed power.
And if I were to consider running a 6B at power at 30-35+ ho per liter I would be adding pyro and boots gages and making them a priority check during operations.
YMMV

mcarthur said:

Ouch David, you know how to prod correctly!

I was looking at secondhand 6BTA's for $19-22k, but of course with all the attendant issues of no warranty, condition and age.
Then there's the cost to remove the existing engines and replace.
There may be some money to be pulled back by selling the existing motors?
I also assume the cost to remove and replace entirely depends on the location and access, but would anyone like to hazard a guesstimate of hours or cost, especially if it's not easy to access? Not easy in this case are in the middle of the two hulls of an aluminium catamaran, with best access either with a big chainsaw or somehow onto the inside bridgedeck and then up and out the back door ...

Click to expand...

Hopefully the 6BTA numbers above are for a pair.


I have seen lots of references to the cost of Cummins factory recons. They run about $25,000 bobtail. A new transmission will cost about $4K, a prop shaft about $1K, a new prop maybe $2K. So $27,000 for major parts. Lots of minor ones that will add up as well.



It is impossible to say what installation labor will be. I have seen monohull projects reported on boatdiesel that cost more than $5,000 for a single. If you have to take a saw to the hull, that can double.


David

Both Kevin and Gary on this site have repowered their Cummins powered boats and have the figures at hand.
Perhaps if Mcarthur started another thread just on the Cummins 6B repower costs they will chime in with the extensive details I know both of them have.