Maintenance Cost Diesel vs Gas

I have had a few 6-354 Perkins diesels and the key spots to check on them are the exhaust manifold , the rotary injection pump and the injectors. Other than that is they have good compression and show no heavy smoke/soot they should be goods to go. In Perkins engines they make a right and left hand rotation - do you have one of each or do the transmissions reverse one engine. The reveres rotation engine should be denoted with a "U" in the serial number("4-154U").

Hope this help;s
 
"Fuel % vs max HP curve fuel or prop demand fuel curve?"

I believe it is against their (Volvos) standard prop demand of 2.5.
But that does not help me use this information well either as the pyro and real fuel used at each recorded rpm is what would help me.
 
Agreed strange , but if that is the vase then at 3000 RPM it is at 51% load.
Puzzling that it does not follow their own curve. I haven't backed into what curve it is following though.
 
Back to the original thread.

I have owned small and large diesels and small and large gas. Diesels cost more IMO but cost is not why people buy diesels. The cost calculation only arise when someone wants to justify not going to diesel

In my observation diesel is far superior to gas and I would always choose diesel if it were available but gas is the only answer for some applications such as OBs and I would go with gas if I were to buy an OB with full knowledge of all the problems I was getting into. There isn't much choice in the 25' range inboards either.

In all my years messing with boats I have never heard anyone say they wish they had gotten gas instead of diesel while the reverse is usually true.
 
"Agreed strange , but if that is the vase then at 3000 RPM it is at 51% load.
Puzzling that it does not follow their own curve. I haven't backed into what curve it is following though."

Hello Bruce - I think the report above shows a % load of 77 and 80% at 3,000 rpm's.
If they are utilizing the 2.5 curve (which we do not know) that would be near 9.8 X .80 = 7.84 or 51% as you say.
As I have learned the hard way there is not one boat that follows these curves for more than a couple 100 rpms - the loading curves are just about worthless to me anyway.
But the other readings do not all align with that either - in any case a key reading on these higher HP engines is the pyro temps which they like to keep pretty low in these applications. Combustion temps and extracting heat is the demon that you deal with in the higher HP higher rpm diesels.

Hope this helps
 
quote:
Originally posted by smitty477

I have had a few 6-354 Perkins diesels and the key spots to check on them are the exhaust manifold , the rotary injection pump and the injectors. Other than that is they have good compression and show no heavy smoke/soot they should be goods to go. In Perkins engines they make a right and left hand rotation - do you have one of each or do the transmissions reverse one engine. The reveres rotation engine should be denoted with a "U" in the serial number("4-154U").

Hope this help;s

Click to expand...
To the best of my knowledge all Gulfstar 36 MarkII's with Perkins use both counter rotating engines and the transmissions are both the Borg 71C's and use identical rotation(also they have no Vee drives). It's the way all (35) were built between 1975 and 1976. They are a bit tricky when it comes to docking depending on wind and tide.
I hear many people with the 36's alternate between using one engine at a time on long cruises 15 minutes on the port then 15 minutes on the starboard. It doesn't damage the transmissions as long as the motor not being used is running at idle.
Bill
 
quote:
Originally posted by smitty477

"Something weird about the load numbers. I would not expect load to be so high well below wot"

Its fuel load % related to that specific rpm.

"not to hijack the topic, however I am looking for two very, very important data
Pyrometer temp and Boost pressure."

Agreed 100% on pyro readings as they are key - boost is on the far left column.

A guess would be that they recorded the port engine first.

Click to expand...


BST - NOW I see it !

RWS
 
I agree exhaust temps would be very useful as would fuel flow. With all data collection there is no way to determine MPG or best engine operating RPMs unless that data is displayed elsewhere.
 
The evc displays those numbers. I will try to add those values next year but I can say at 3150 I am burning about 23gph and doing 28mph.
At wot it is burning 29gph and doing about 34mph.

3150 seems to be best cruise for the boat with best fuel economy.
 
"The evc displays those numbers."

Does your EVC display EGT?
Using the numbers supplied so far you have these calculations....
Cruise at 3150 / 23 gph yields an engine load of 75% and a hp extraction of 59 Hp per liter of engine displacement.
The tech specs on full fuel burn call for 15.2 per side at 3,500 rpms or 30.8 gph total.
Boost is higher than the 2.5 and 3 prop curves within the mid range.
The tech spec sheet for that engine can be found here.....

http://www.volvopentastore.net/files/t_ips400_4.pdf

Installation of boost and pyro gages would be a plus for this application,I have installed them on my last 3 boats at a cost of less than $400 each boat and they were very informative about engine conditions in real time. Really helped me with my engines....

Hope this helps
 
quote:
59 Hp per liter of engine displacement.
Click to expand...
cruising!!!

Those rascals are working.

I wonder why Volvo show both 2.5 and 3 exponent when they make the drive?? Are there prop options?

Running at 67% load sounds decent until I realized those are 300 HP WOT engines at 81 hp per liter.!

That is beyond my experience.
 
quote:
Originally posted by CurrentSea

The evc displays those numbers. I will try to add those values next year but I can say at 3150 I am burning about 23gph and doing 28mph.
At wot it is burning 29gph and doing about 34mph.

3150 seems to be best cruise for the boat with best fuel economy.

Click to expand...


I don't agree with this. These engines are 5 rating engines, That is the equivalent of E rated CATS. I would never run these extended cruising at 3150 RPMs or near 75 or 80% of max load. For limited time on plane its OK, but if you are cruising distances or using your boat a lot, that is way over the E rating.

These engines are also producing a lot of HP per liter. I cruise my 3208s at 60 to 65% of max load and that is about 28 HP per liter. The published E rating guidelines are 1 hr of 12 hrs at max load (same as Volvo 5 rating), which is nuts to do, but they also require a time average power target of 33% of full load. So cruising at 80% of max is OK if you spend a lot of time at hull speed, but if you cruise and plane a lot, your MOH and major service intervals will be substantially shortened.
 
This is my first diesel boat and I am no expert, but I have been told by a few Cat certified techs that running my 3126's at 80% or less when cruising, will make them last a very, very long time. So at the beginning of the season I make sure I am reaching the recommended WOT (2850) on both engines with boat fully loaded. It took some prop work to get her dialed in. I then run her at 2100 to 2300 99% of the time. She ain't fast, but she does purr.

With that said, assuming your volvos are similar to my Cats, if your WOT is 3,570 you should cruise at 2,850 or less.

There are 2 major advantages to slowing down:

1. less wear and tear
2. the journey will last longer

I guess the same could be said for life!
 
"This is my first diesel boat and I am no expert, but I have been told by a few Cat certified techs that running my 3126's at 80% or less when cruising,"

I am pretty sure when they said 80% or less they were talking about % of load not percent of rpms.
The propeller load put on engines is not linear compared to rpms. We can speak about % of load in both hp and gph as either can describe the amount of work, heat, and stress imposed on the engines. Curentseas engines are very efficient for 4 stroke diesels and convert 1 gallon of diesel to a bit more than 19 hp per hour so that is the conversion ratio. It is also variable by rpms but only slightly as seen in that tech article above.

Hope this helps
 
Smitty:
i think 80%rpm, with proper propping, produces something in the order 60% load +-depending on prop curve.
 
"i think 80%rpm, with proper propping, produces something in the order 60% load +-depending on prop curve."

Hello Bruce,

That ratio often does not work with various boat/engine trans and prop combinations.
It makes a great deal of difference as to how high the engine is tweaked and propped before you apply the 80% or 60% rules.
One good example would be the above speaking about the DD6V-92's - they came in so many Hp variations that the 80% & 60% rules cannot apply to each of them even though they are basically the same engine.

Hope this helps
 
60% is simply the top curve exponent applied to the rpm
 
The duty cycle you bring up isn't often talked about and presents a very different picture of allowed operation. Do Volvo have that spec on their ips
 
Duty cycle is routinely used to characterize marine diesel usage in commercial applications and many pleasure vessel engine manufacturers do as well. I do see WOT duty cycles listed in the Volvo literature but not routine use duty cycles. CAT and others use long term cycles and even more important use total fuel consumed as the main criteria for usage. My 3208s have a MOH evaluation at 30,000 gallons. So at the recommended 30% of max load, that means ~ 9 gals per hour to achieve 3000 hours. The point is that the engines run fine and don't overheat ect. if run at 80% of max load, nut if you travel long distances or use the boat a lot, say one covers 2500 miles per year, then how the boat is run will dramatically affect the number of hours one might reasonably get out of an engine.

Assuming the ratings for Volvo are similar to other major diesel engine manufacturers, then their 5 rated engines will have similar duty cycles. I just find the routine comments that 80% of max load is OK, this really depends on how the boat is run if one expects to get thousands of hours between MOH. I have had a few CAT mechanics say it is fine to run the boat at 80% load or at 2400 RPMs, but the CAT literature is clear on the amount of fuel burned versus major service and this specifically agrees with duty cycle numbers.
 
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