Cruising RPM, Hrs, GPH, and longevity Tug and Cut diesels

[BB marine]

Brian, this is nothing new to you. Its just another guy expressing your point of view in his own way. I thought others might enjoy the read and perhaps extend the life of their engine.

https://www.sbmar.com/articles/engine-l ... e-loading/

Tony Athens has good opinions and information based on years of experience. Notice in his article he his speaking of high hp per liter engines. 50 to 60 hp per liter. The D3 220 = 91.6 hp per liter, 200hp = 83.3 per liter, 150 hp = 62 hp per liter. D4 260 hp 70.2 hp Liter, 300 hp = 81 hp, 320 = 86 hp liter. The engines listed are among many small displacement high hp engine that are well designed, reliable power plants but require more thought in operating them if longevity is important to the boat owner. As Tony pointed out. "The “EXACT MATH” that typically comes from prop calculators, graphs, architects, builders, etc. when figuring a prop size is much more likely to lead to “running on the edge” or worse, than yielding the correct prop size to insure good engine life in relation to performance. Nothing can replace “on board” engine monitoring and the understanding of (all) engine operational parameters during normal operation…nothing".

This is the point of this thread. Many could care less. I get it, it's a boat, start it and throw the throttle down. If it chokes I'll fix it. Many don't know they rely on the factory to advise. The factory boat builders concern is we want performance numbers ( hull speeds high, it is great for marketing) I was told by a customer service representative from Fluid Motion when I was doing my PDI ( dealer could not do it, didn't know how to) make sure your rpm is 3900 rpm. I told him that I was 4130. He responded back you should increase pitch the boat will go faster. (really!!!) I am just providing an awareness to those who may not know or do not have an opinion of the subject. It is not expensive to tune your prop if it is in good condition. If it is not it should be tuned and repaired for more reasons than just rpm. It cost me $75.00 to have an adjustment done to my prop. I may not be done but I'm close. It takes me no more than 1/2 hour to pull and install my prop.

 

[FWTMD]

Yes, yes, and yes to all of the above.

Brian, we all owe you a thanks for patiently educating a lot of us on the topic.

Frankly I have you to thank for leading me toward searches for more info on the topic, over a period of weeks, which led me that piece. It wanders me into pieces focused on different engine makes, but its all just a different flavor of the same issue.

You will also note he is big on engine room heat, air circulation, and keeping things dry from water (especially salt water). Another of your points.

 

[NorthernFocus]

Brian, this is nothing new to you. Its just another guy expressing your point of view in his own way. I thought others might enjoy the read and perhaps extend the life of their engine.

https://www.sbmar.com/articles/engine-l ... e-loading/

That was a really well written article on the subject. With his example he made a good point about the realities of boats going through multiple different owners in a relatively short span of time and differences in how they treat/operate the equipment. I think the article can be simply summarized as "props don't kill engines people do" 😉

 

[FWTMD]

With his example he made a good point about the realities of boats going through multiple different owners in a relatively short span of time and differences in how they treat/operate the equipment.

I have been going far afield in my reading lately. And viewing. I watched a good YouTube a week ago where a mechanic was discussing what engine hours really mean on used boat values.

His point was that it kinda means something, and is kinda pointless.

Take Boat A where an owner runs the stuff out of it but doesn't maintain the engine. He just wants to show up on the weekend and run it. Hard. After 2 years stuff starts to break down and he sells it rather than deal with the maintenance. He's frustrated that it takes the time and money. That boat will show up as having low hours and only 2 years old. And it may well be a bad buy.

Take Boat B. Used by an owner who maintains it. He's thoughtful and careful about monitoring engine health, and hits all checklist items when they come up. He flushes the heat exchangers. He runs mostly near displacement speeds. After 10 years of use he has hours on it. That engine will probably be in better shape than the 2 year old engine.

Its the "rest of the story" that hours don't reveal.

 

[FWTMD]

And something else that Brian edged into.

The Volvo Penta's have a lot of HP compared to its engine mass / weight. That's great to stuff the engine into boats without giving up power.

That also means its more fragile than bigger chunks of iron with lower HP.

How does that come into play in the real world?

I was looking at specs on the Cummins QSB6.7 line. It has bigger dimensions. Heavier. Operates at lower RPM's generally. While the Penta's have a 100 hour service interval, the Cummins have a 250 hours / 1 year interval. So take a trip and its 12 days of 8 hours on Penta, or 31 days on Cummins. You do have 4 zincs on the Cummins that need to be changed out at 100 hours or 3 months.

Fluid isn't wrong to go with Penta. That Cummins simply won't fit into the Ranger or Cutwater designs.

But owners do need to be aware of the tradeoff. That HP into the small size and weight means they just have to watch the temps, the prop loads, honor the service intervals, and keep an eye on it generally. Running it constantly at the edges has its own price.

 

[scross]

This has been an informative thread!
As a result of reading the potential impact of having a prop set to deliver the 4,000 rpm that my Yanmar 4BY2-150 should achieve at WOT, I tested the boat at WOT today. First time in 5 years it’s been at WOT. I normally run at 2,300 to 2,800 for normal cruising and at 3,200 when I need to be covering miles in a reasonable amount of time.
Today at WOT my 17x14 with .105” cup Acme prop delivered 3,950 rpm at cruising weight - 40 gallons fuel, half fresh water, half black water tank, dinghy on swim platform and all the stuff inside we take cruising with us. The top speed was 14.6 knots at slack tide with two runs in opposite directions. Coolant temps did not climb above 196 degrees in the 10 minutes it was at WOT.
We have 756 hours on the 4BY2. Hull is pretty clean as only in salt water for a week after cleaning the bottom over the winter while trailered.
Based on this test I don’t think my prop needs any adjustments. And I don’t think I’m running the engine hard based on my normal cruising rpms.
So, did I understand the jist of testing at WOT to be sure my prop is properly set?

 

[FWTMD]

Brian will answer I'm sure. But that sounds right to me based on my reading. The idea is to prop so you are "at" or "slightly above" the rated RPM. Seems like you are close enough to "at" to be good to go.

Better, your normal cruise is at roughly 60% of peak capacity which should do good things for engine life too.

My 2 cents.

 

[FWTMD]

But also, the received wisdom is to run it hard for some time at the end of a long day's run at low to moderate RPM's to burn off any soot that accumulated on the turbos. Running easy helps the overall engine. Burning off the soot preserves the life of the turbo.

 

[NorthernFocus]

...
So, did I understand the jist of testing at WOT to be sure my prop is properly set?

Almost. Yanmar's literature describing their engine ratings says:

...When combined with a correctly matched propeller which allows the engine
rated rpm to be achieved in a fully loaded vessel state, the reduced-power
operation can be at or below 100-200 rpm of the rated speed.

So a "proper" WOT test is with tanks full plus all cruising gear and normal number of people aboard.

Volvo specifically states:

Propeller Match
The propeller must be sized to allow the engine to operate slightly above rated rpm under
the boat’s most severe load conditions: full fuel and water tanks, stores aboard for
extended voyaging, and adverse sea conditions.

So it sounds like you are still slightly over propped.

Regarding the overall topic of this thread what the whole issue of engine longevity comes down to and what Brian explained in terms of fuel burn is "Load Factor". This is in the "fine print" when pleasure vessel engines are being discussed. For commercial marine engines the information is more readily available. In the fine print in Yanmar literature they state the Load Factor rating for pleasure craft engines is 30-40%. There doesn't seem to be a true industry standard for pleasure vessels load factor but every manufacturer that I've researched varies somewhere between 30-40%.

The definition of load factor is as follows.

Load factor is the actual fuel burned over a period of time divided by the full-power
fuel consumption for the same period of time. For example, if an engine burns 160
liters of fuel during an eight-hour run, and the full-power fuel consumption is 60 liters
per hour, the load factor is 160 liters / (60 liters per hour x 8 hours) = 33.3 percent.

So the true operating limit of marine engines for long life is load factor. They each have their descriptions something like "one hour of every eight can be at full rated HP" and "reduced load operation is at 10 percent below full load rpm" or something such. But those numbers taken alone are way above the design load factor of the engines. Bottom line is that average over time(engine hours) if you are burning more than 30-40 percent of full load gal/hr you are shortening the service life of the engine.

 

[scross]

Thanks Dan!
I was at about 8,900 pounds all up weight for the test. With my towing limits I know the weights on this boat really, really well. My max cruising weight is closer to 9,250 pounds so I was a bit light from max but close to average cruising weight for me.
Yeah, I may be a bit over propped. Another 100-150 rpm from the prop would help. Will look into getting that done while the boat is in WA.
How difficult is it to pull the prop? Special tools needed?

 

[NorthernFocus]

How difficult is it to pull the prop? Special tools needed?

If it hasn't been pulled in a while a wheel puller and probably a torch are necessary. Honestly as close as you are with WOT and with knowledge I wouldn't make it a high priority. Sizing to WOT is the industry way of idiot proofing. If you run by gph rather than rpm you can live with a marginal prop.

I run the same size wheel and am way over propped. But I run 95 percent of the time at hull speed. My average load factor is below 20 percent. So who cares? I will re-prop some day simply to be able to go slower at idle.

 

[BB marine]

Based on this test I don’t think my prop needs any adjustments. And I don’t think I’m running the engine hard based on my normal cruising rpms.
So, did I understand the jist of testing at WOT to be sure my prop is properly set?

Correct propeller selection in the marine recreational industry as always been done by using WOT Max rpm as the mark. The engine manufacture gives the recommended WOT rpm and recommends that the engine is operated with a prop selected to provide this rpm range. Normally there is 100 +/- figured into the equation. The reason for this is it helps the boat owner from chasing the under/over prop condition. If a boat is loaded light and turns 3900 rpm it is in range but when loaded it is out of range. If a boat is loaded light and turns 4130 when it is loaded heavy it should be close to range. In your case testing your boat the way you use it loaded and still maintain the factory recommended range +/- 100 rpm plus you operate your engine at or below 40% average load if you did the calculations. Being slightly over propped during heavy sea conditions, currents and wind really is not an issue because you are so close to the mark.

In my case I want to run in the higher percent range. The C26 is underpowered for what it was designed for. I have to run 3550 to maintain 14kts .Which is slightly over 75% load but at the end of the day the overall average on the engine clock divided by fuel burn puts my average operation at just below 50%. The fact that I want to run harder makes it crucial to maintain a slightly under propped boat. I use RPM operation as a general throttle position but really refer to fuel burn GPH to rate my actual engine load. It can vary. On a flat day 3550 rpm may burn 8.9 gph. On a day with 2' to 3' swells and a 1' to 2' chop I may be burning 9.5 to 10 gph. 80% load is a bit much to expect on a continual basis for a 2.4 L engine rated at 220hp. So I back down the throttle a bit. Having changed the cup slightly I'm hoping helps. Time will tell I have not been on a trip where I have to run hard yet since the change.

I believe that regardless of what rpm you operate at if the engine is not capable of turning the manufactures recommended rpm you are not running the engine within the parameters that the engine was designed to run. An engine that is designed to by the manufacturer to burn 2 gph at 2000rpm but because it is over propped burns 2 gph at 1800rpm. While only running at a low percentage of load is still running at a higher load at that rpm than it was designed to. This is the theory that the manufactures use. Most boat owners think it just matters when you are running the boat hard. While I agree with Dan it's not going to kill the engine. It just is not going to be operated to design. The issue though comes into play with the average boater that doesn't know anything but push the throttle and go. Or the boat owner that buys the boat from the guy that has an over propped boat because that's how he liked to run it at low rpm. He/she got better fuel economy running at hull speed. The new boat owner buys it and runs it hard well over propped. The longevity of that engine is reduced dramatically.

As Dan has posted on this thread a few times props don't kill engines the people that operate them over propped do.
That is what this thread is about.

Removing the prop can be an issue if it has been on for a long time. I recommend servicing the prop as a preventative maintenance item. Having worked in the industry and removed props that have never been removed before (years) It can be costly. In some cases after removal of the prop there is damage to the taper from crevice corrosion. It's one of those things if you hit something with your prop how hard is it going to be to throw your spare prop on? If you remove it periodically it is not hard at all to pop off the taper. Below is a photo of a prop puller I made it works well. the rangers and Cutwater in boards have limited clearance between the prop hub and the log where the cutlass bearing is.
gallery2.php?g2_itemId=47958

 

[scross]

Thanks Brian and Dan!
Ran my WOT test again today. Average was 3960 rpm with 100 more pounds of water on board but 15 degrees cooler outside. Fuel flow at WOT was 8.0 GPH. Turbo boost was 22 psi.
My normal cruise is at 2.5 GPH which is about 32% of WOT fuel flow. I do run the engine up for short periods when cruising at lower RPMs but an not religious about it.
I’m not sure the prop has ever been off in 11 years. I guess a competent prop shop that has loads of experience in removing props would be better than me doing it after all this time.
Thanks again for the great info!

 

[ALICE J]

Update from Alice J. 2011 RT 27, Yanmar, BY4 180, about 2260 engine hours. At a suggestion from a fellow Tugger, I had the injectors pulled. Several had some carbon buildup at the base of the nozzle. Testing them, two absolutely had to be rebuilt or replaced. The other two should be rebuilt. New are about $4500, rebuilt about $1800. Yes, Yanmar suggests pulling and testing them long before 2200 hours. I did not notice any black smoke, but did see a slight film on the transom, but my numbers were normal to me. Over the next couple of weeks I will run the boat almost naked from the cruising mode and post the numbers; then load it up and see what's on the horizon. With the rebuilt injectors may I expect any dramatic differences from my previous numbers? If the electronics monitor the injectors, would the electronics adjust for worn injectors? But a larger question, what would happen if the injectors were not rebuilt? but just ignored. :roll: What is the relationship between the RPM, Load, Hours, GPH, and proper injectors? :ugeek:

 

[BB marine]

It sounds that your injection inspection and rebuild is based on preventative maintenance. I do believe the ECM will make adjustments that are within the parameters and after that if a injector has failed to the point that the engine starts hard, run rough, smokes or there is signs of fuel contaminating the oil there would be a code that indicates a misfire or low fuel rail pressure.

What is the service interval for the injectors?

If the injectors were ignored I believe you would eventually know once one of the injectors completely failed or failed to the point of poor engine performance, rough running or hard starting. If you oil sample the report would most likely indicate elevated fuel % in the oil.

Bad injectors would effect all RPM, Load and GPH. Hours ?? maybe if the engine was run for a long time with leaky injectors diluting the oil with fuel. Cylinder wash could occur reducing the oil lubrication on the cylinder walls.

I would guess that all four of your injectors are boarder line. If lower rpm operation was consistent maybe carbon fouled. Just guessing I don't know. I'm sure the injector rebuilder can give a report. It would be interesting to see what his/her thoughts are.

Your unloaded Sea trial and then loaded will be a good indicator of how much additional load we put on these engines. Fresh from the factory New boats are propped correctly but in most cases marginally correct. It is up to the boat owner to take over after equipping the boat for there usage.

 

[Miss Stress]

Just a note from a new (to us) 2017 C28 owner.
I don't know for fact the prop pitch, but WOT will turn just over 3500 with 75% fuel, 1/2 water, empty holding tank. 28.5 to 29mph GPS.
Not much food or gear on board, as we have pretty much been just day-sailors learning our new boat.
I will say that the trim gets pretty squirrely with full down deflection at WOT. However, this gives maximum speed.

 

[KlaassyC]

First report on our new to us 2018 C28. 1/2 fuel, full water, 25hp kicker on swim platform, 2 passengers.
Max Rpm 3530, speed 25 knots
High Cruise 3000 rpm, speed 16-18 knots 8 GPH
Slow cruise 1400 rpm, speed 6-7 knots, 1.2 GPH
Temp 185 steady.


Sent from my iPhone using Tapatalk

 

[mlanger]

I just took delivery of my boat and will be monitoring performance at various RPMs over the next few months to get my best cruise RPM, best slow cruise RPM, and best "get there faster" RPM.

Meanwhile, I attended the Volvo session at the Ranger Tugs/Cutwater Rendezvous in Roche Harbor last week and the Volvo guy recommended running a D4 or D6 at 80-90% RPM. I'm looking forward to getting a good idea of how fast I can cover water (and burn fuel) at that RPM.

 

[BB marine]

Meanwhile, I attended the Volvo session at the Ranger Tugs/Cutwater Rendezvous in Roche Harbor last week and the Volvo guy recommended running a D4 or D6 at 80-90% RPM. I'm looking forward to getting a good idea of how fast I can cover water (and burn fuel) at that RPM.

I would have to disagree with the Volvo tech. The right answer if you want to maintain longevity of the engine is NO MORE than 90% of WOT for extended periods of time with a variation of rpm between 85% and 20% rpm. Recommending to run a 3.7L 4 cylinder 300 hp diesel at 90% RPM of max RPM is a marketing statement. Yes you can do it but the longevity will be decreased. A D4 300 hp should turn a minimum rpm of 3500 rpm. Preferably 3650 rpm. It is rated at 3500rpm. Meaning the max continuous rpm to operate the engine at would be 3150 rpm ( If your max RPM is 3500 rpm on that given day) Meaning when you change the loaded weight of the boat, more passengers, full fuel, full water, a little slime on the bottom you need to run the engine up to max rpm and confirm what Max rpm is. Then adjust your max 90%. rpm. You will be surprised how much it changes if you have a prop that is marginally over propping the engine. Most Rangers and Cutwaters are marginally over propped. Most folks don't operate their engines at this max load. I'm not a max rpm fan for gaging what is the max rpm I can operate the engine at. I use fuel burn as my gage. Fuel burn equates closely to engine load. A good high cruise speed would be operating the engine at between 70% and 80% load. Most Volvo Penta EVCs will show engine load. It is close but I feel fuel burn is more accurate. The amount of fuel burned is the energy used. A Volvo Penta D4 300 hp burns about 15 GPH WOT. A good max cruise speed fuel burn would be around 10 to 11 gph. The engine would be loaded to about 70% load. Using this fuel burn number as a max cruise speed will be consistent no matter how you are loaded. What will change is speed and rpm. The load will be the same. You may find that if you are loaded down with extra passengers or gear. Your fuel burn is 11 gph but your speed and rpm has dropped.

Many folks have stated I run at 3150 all the time. I ask even when you are loaded heavy? The answer often is "it doesn't matter that is 90 % of my max rpm". I question again ,"even when you are loaded heavy?" The answer normally is why ?. My answer is if the load changes the engine is loaded more and often it will not tun 3500 rpm @WOT . It may only turn 3375 rpm . So you would be running the engine closer to 95% of max rpm. If you use fuel burn as your gauge the engine load will be consistent 70% to 75% load burning 10 to 11 gph and the engine longevity will be maintained. I don't sell Volvo Penta products, or represent them. This is my opinion of how to operate an engine. Your boat high cruise speed may be a little slower but your engine may last a little longer for you or the next owners.

 

[tranmkp]

Late on this trread ~ regarding engine loading and life

I was told this by several Volvo car and Mac truck reps regarding the Volvo turbo/supercharged engine. I was curious about the reliability compared to the red/silver blocks. Remember these are 2 liter engines putting out ridiculous horsepower. There is a lot of case pressure. Told the the engines are fine for suburban use but are having issues in mountainous states - blowing seals from lugging them up mountains