HelloBoat
New member
Hi,
I am having a few questions regarding engines, ideal usage and limitations and was hoping there were some folks on here with the experience and willing to explain. Currently I am in the process of buying a boat and want to make sure I know the limitations beforehand.
Almost all boats I come across have engines with an E Rating which seem to be the standard for pleasure craft. For this example let's go with the Caterpillar C12 ACERT 715hp but I doubt Volvo etc is any different.
Manufacturer reports a top speed of 30kn with a cruising speed of 25kn.
So first I look up the engine specs:
Source: http://www.bmgs.com.tr/doc/GucSistemleri/Marin/Marine-Engines/C12/C12-ACERT-715-MHP-spec.pdf
And then I look up the engine rating and it states:
So now I am trying to figure out what to make of this.
1) I am trying to find out if I understand this correctly. I have seen an example that used fuel usage to calculate the load factor. So for this engine, it would use 138L per hour at full speed. So if you go on an 8 hour cruise and burn a total of 400L of fuel, you can calculate the load factor as 400L fuel burned / (138L per hour x 8 hours) = 36%. That would mean that for this engine to reach the maximum load of 30% you can burn 41L per hour which according to the Maximum Power Data table is about 1100 rpm. This is almost idle speed and makes absolutely no sense to me. Any points on this and how I should interpret the term load factor is very much appreciated.
2) Then onto Time at Rated RPM; so if I understand correctly you are allowed to go up to 2300 rpm, which would be full speed, every 30 minutes per 6 hours. I assume anything above that would cause excessive wear? And after that 30 minutes, what would be an acceptable engine speed to continue, how much rpm do you go down?
3) The engines are supposedly designed for 250 to 1000 hours per year. Now let's say you use them 1500 hours in a year, is that an absolute no-go or is this doable if you shorten your oil change intervals and calculate that some additional work would likely need to be done.
4) Is it normal to change oil that frequently? Every 250 hours is not particularly a lot of time. I would have expected modern engines to be more durable to be honest. Can't see a diesel generator or a truck changing oil that often to be honest.
5) I have read that if you run low rpm on diesel engines you may have incomplete combustion and get exhaust deposits. I have seen statements that describe this as running below 20%, is that a fair number?
6) And lastly, is the rule of thumb that cruising speed is generally 200rpm less than the maximum engine speed?
Sorry for all the questions, just trying to gain some additional knowledge here
I am having a few questions regarding engines, ideal usage and limitations and was hoping there were some folks on here with the experience and willing to explain. Currently I am in the process of buying a boat and want to make sure I know the limitations beforehand.
Almost all boats I come across have engines with an E Rating which seem to be the standard for pleasure craft. For this example let's go with the Caterpillar C12 ACERT 715hp but I doubt Volvo etc is any different.
Manufacturer reports a top speed of 30kn with a cruising speed of 25kn.
So first I look up the engine specs:
Source: http://www.bmgs.com.tr/doc/GucSistemleri/Marin/Marine-Engines/C12/C12-ACERT-715-MHP-spec.pdf
Code:
...
C12 ACERT® MARINE PROPULSION
715 mhp (705bhp) 526 bkW
Displacement........................................11.95 L (729.23 in3)
Rated Speed................................................................2300
Refill Capacity
Cooling System.....................................45.0 L (11.9 gal)
Lube Oil System..................................... 28.0 L (7.4 gal)
Oil Change Interval..................................................250 hrs
...
And then I look up the engine rating and it states:
Code:
E Rating (High Performance)
% Load Factor: up to 30
% Time at Rated RPM: up to 8
Typical Time at Full Load: 1/2 hour out of 6
Typical Hour/Year: 250 to 1000
Typical Applications: For vessels operating at rated load and rated speed up to 8% of the time (up to 30% load factor). Typical applications could include but are not limited to vessels such as pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats. Typical operation ranges from 250 to 1000 hours per year.
So now I am trying to figure out what to make of this.
1) I am trying to find out if I understand this correctly. I have seen an example that used fuel usage to calculate the load factor. So for this engine, it would use 138L per hour at full speed. So if you go on an 8 hour cruise and burn a total of 400L of fuel, you can calculate the load factor as 400L fuel burned / (138L per hour x 8 hours) = 36%. That would mean that for this engine to reach the maximum load of 30% you can burn 41L per hour which according to the Maximum Power Data table is about 1100 rpm. This is almost idle speed and makes absolutely no sense to me. Any points on this and how I should interpret the term load factor is very much appreciated.
2) Then onto Time at Rated RPM; so if I understand correctly you are allowed to go up to 2300 rpm, which would be full speed, every 30 minutes per 6 hours. I assume anything above that would cause excessive wear? And after that 30 minutes, what would be an acceptable engine speed to continue, how much rpm do you go down?
3) The engines are supposedly designed for 250 to 1000 hours per year. Now let's say you use them 1500 hours in a year, is that an absolute no-go or is this doable if you shorten your oil change intervals and calculate that some additional work would likely need to be done.
4) Is it normal to change oil that frequently? Every 250 hours is not particularly a lot of time. I would have expected modern engines to be more durable to be honest. Can't see a diesel generator or a truck changing oil that often to be honest.
5) I have read that if you run low rpm on diesel engines you may have incomplete combustion and get exhaust deposits. I have seen statements that describe this as running below 20%, is that a fair number?
6) And lastly, is the rule of thumb that cruising speed is generally 200rpm less than the maximum engine speed?
Sorry for all the questions, just trying to gain some additional knowledge here