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Old 07-25-2014, 06:26 PM   #21
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Originally Posted by psneeld View Post
Has anyone here reported actual numbers they derived from overpropping?

I would love to see some real data.
As a matter of fact, I do have some real data to share. Last year I switched from a 17x13 DynaQuad 4-blade prop to an 18x14 DynaJet 3-blade prop. According to all of the prop calculators, Michigan Wheel and my local prop specialist, the new prop should have been 2" over-pitched. Otherwise, it was an ideal prop.

I installed it and ran for several months, then had 1" removed and found it to be perfect.

My engine's pleasure duty specs are 56 hp @ 3,800 rpm. The hull speed (SL=1.34) is 7.02 kts.

Before (17x13DQ 4-blade):
6.90 kts @ 3900 WOT
6.80 kts @ 3500 High Cruise
6.60 kts @ 3000 Cruise
6.00 kts @ 2500 Cruise
5.00 kts @ 2000 Economy

After (18x14DJ 3-blade) Overpropped:
7.20 kts @ 3650 WOT
7.20 kts @ 3500 High Cruise
6.80 kts @ 3000 Cruise
6.60 kts @ 2500 Cruise
5.90 kts @ 2000 Economy

After (18x13DJ 3-blade) Re-Pitched to Optimal:
7.30 kts @ 3950 WOT
7.10 kts @ 3500 High Cruise
6.85 kts @ 3000 Cruise
6.55 kts @ 2500 Cruise
5.70 kts @ 2000 Economy

Obviously the first prop, the DynaQuad 4-blade, was not well suited to the boat at all.

The last two sets of numbers for the DynaJet 3-blade are really interesting. Overpropping by just 1" of pitch reduced WOT by 300 rpm, but the improved performance at lower speeds was minimal. Each prop was evaluated with 2 2-way passes of 1/4 mile each in protected waters. This really is comparing apples to apples. This was the same prop with 1" of pitch removed. What a difference, and now the engine operates within in the manufacturer's recommendations and I sleep better.

Larry
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Old 07-25-2014, 07:11 PM   #22
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...

My engine's pleasure duty specs are 56 hp @ 3,800 rpm. ...
Makes me wonder. The "sweet" spot on my JD 4045 is 1600-1800 RPM out of a maximum of 2400. Will it last longer than a higher-speed engine?
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Old 07-25-2014, 07:53 PM   #23
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As a matter of fact, I do have some real data to share. Last year I switched from a 17x13 DynaQuad 4-blade prop to an 18x14 DynaJet 3-blade prop. According to all of the prop calculators, Michigan Wheel and my local prop specialist, the new prop should have been 2" over-pitched. Otherwise, it was an ideal prop.

edited for brevity

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Old 07-25-2014, 08:30 PM   #24
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I will have an opportunity to provide real world data between slight over prop and propped to achieve max rpm this October. Unfortunately, the overprop measurement will be with a dirty bottom and the no overprop measurement will be clean and slick. But there may be some data of interest to come out this exercise.
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Old 07-25-2014, 11:00 PM   #25
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Makes me wonder. The "sweet" spot on my JD 4045 is 1600-1800 RPM out of a maximum of 2400. Will it last longer than a higher-speed engine?
Mark,

That's an interesting question. My engine, a Yanmar 4JH3E, is one of the most prolific small yacht diesels in existence. It was used in a very large number of vessels in the charter fleets in the early 2000's. Charter boats are used hard but generally maintained well. These boats can now be found in brokerage and the JH3E's routinely have between 5,000 and 10,000 hours, and are still running well. Anecdotally, they have an expected life of 10,000-12,000 hours or more in service as auxiliary sailboat power, which is tough service. As the engines evolved into the 4E and 5E models, the rated engine rpms have gradually dropped to 3,000. I'm not so sure the high speed diesels are that much less reliable than lower speed diesels, but the trend definitely seems to be toward lower speeds. The high speed Yanmars are definitely known for being a little loud or busy at higher speeds.

The quality and engineering of the 'marinization' and accessories have a lot to do with the longevity of a marine diesel. I found references to the JD 4045 in commercial pump service lasting 15,000-20,000 hours, but none for marine service. I'm sure it is way up there though. I doubt you will wear yours out.

Finally, as we all know, most marine engines in pleasure boats die from deterioration and neglect, than from actual use. OK, big exception for the sportfishing crowd and go-fast guys, but that is another subject entirely.
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Old 07-25-2014, 11:16 PM   #26
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Mark,

That's an interesting question. My engine, a Yanmar 4JH3E, is one of the most prolific small yacht diesels in existence. It was used in a very large number of vessels in the charter fleets in the early 2000's. Charter boats are used hard but generally maintained well. These boats can now be found in brokerage and the JH3E's routinely have between 5,000 and 10,000 hours, and are still running well. Anecdotally, they have an expected life of 10,000-12,000 hours or more in service as auxiliary sailboat power, which is tough service. As the engines evolved into the 4E and 5E models, the rated engine rpms have gradually dropped to 3,000. I'm not so sure the high speed diesels are that much less reliable than lower speed diesels, but the trend definitely seems to be toward lower speeds. The high speed Yanmars are definitely known for being a little loud or busy at higher speeds.

The quality and engineering of the 'marinization' and accessories have a lot to do with the longevity of a marine diesel. I found references to the JD 4045 in commercial pump service lasting 15,000-20,000 hours, but none for marine service. I'm sure it is way up there though. I doubt you will wear yours out.

Finally, as we all know, most marine engines in pleasure boats die from deterioration and neglect, than from actual use. OK, big exception for the sportfishing crowd and go-fast guys, but that is another subject entirely.
All things being equal, the engine that develops its horsepower at lower rpms will experience less wear and last longer that the higher rev engine. Of course all things aren't equal, but you can find 90 year old Atlas diesels turning at 300 rpm still running fine, so perhaps there is something to the idea.
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Old 07-26-2014, 12:01 AM   #27
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All things being equal, the engine that develops its horsepower at lower rpms will experience less wear and last longer that the higher rev engine. Of course all things aren't equal, but you can find 90 year old Atlas diesels turning at 300 rpm still running fine, so perhaps there is something to the idea.
Delfin,

You are absolutely right, but they are, relatively speaking, a rarity in modern boats. Atlas, Gardner, Lister, Petter, some old Volvos, Frydenbų Sabb, and on and on. Love the sound of those low-speed diesels. Unfortunately, their power to weight ratios relegate them to museum pieces by today's standards.

I do wish I had a lower speed diesel in Boomarang. I'm not worried about wearing out the Yanmar, but it sure is loud, and sometimes makes a very unpleasant shipmate. I'm spending a ton on soundproofing right now.

What power do you have in your Romsdahl? In 1970 I had the opportunity to go aboard Torsk in Long Beach. I believe she had Gardner power, but that was a long time ago and my memory might be a bit fuzzy.

Sorry for the thread creep.

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Old 07-26-2014, 12:27 AM   #28
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Delfin,

You are absolutely right, but they are, relatively speaking, a rarity in modern boats. Atlas, Gardner, Lister, Petter, some old Volvos, Frydenbų Sabb, and on and on. Love the sound of those low-speed diesels. Unfortunately, their power to weight ratios relegate them to museum pieces by today's standards.

I do wish I had a lower speed diesel in Boomarang. I'm not worried about wearing out the Yanmar, but it sure is loud, and sometimes makes a very unpleasant shipmate. I'm spending a ton on soundproofing right now.

What power do you have in your Romsdahl? In 1970 I had the opportunity to go aboard Torsk in Long Beach. I believe she had Gardner power, but that was a long time ago and my memory might be a bit fuzzy.

Sorry for the thread creep.

Larry
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She still has the Gardner. Delfin has a Cat 3306 that we run at 1350 rpm and around 3.5 gph.
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Old 07-26-2014, 02:54 AM   #29
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Just to add a wee bit more grist to the mill.
With so many variables of loads, currents, sea temps, salinity, wind, hull cleanliness it's nigh on impossible to get definite figures, at best we get calculated guesstimates. (Governments use these, so you know it's not the actual truth)
The general attitude here of a displacement skipper is to bimble along and enjoy the gentle cruise and rarely think of WOT unless needed for emergency.
The key to engine power is the torque curve, I can get a VW Jetta engine to put out 500 hp and go like the proverbial shit off a shovel, but it wouldn't pull a car trailer up a hill and the engine will be destroyed in a very short time. On the other side of the coin some people are disdainful of the Ford Lehman 120's as 'old iron lumps' but they have torque to spare and with proper servicing will last indefinitely, can be rebuilt cheaply and outlive many's a skipper. If you over slightly over prop you can reduce the rpm by 250/300 which reduces noise/vibration/fuel and run at a 'sweet spot' and you can enjoy a relaxed cruising style.
Incidentally Volvo's early TAMD 60 diesel engines ran at up to 3,800 rpm WOT and were regularly rebuilt, now by changing the torque curve they run at 1950 rpm with a corresponding longer life.
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Old 07-26-2014, 06:44 AM   #30
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>Will it last longer than a higher-speed engine?<

Work out the stroke vs rpm. of two engines

Most engine cylinders wear out in total piston miles , so its easy tofigure
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Old 07-26-2014, 09:08 AM   #31
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LarryM

It seems you did not over prop, you right propped since your engine could reach rated max rpm with the last prop setup. Without fuel burn and %load for each rpm change it is hard to tell what is optimal though.

Therein lies the beauty of new diesels where prop changes, fuel burn, load etc are all available. Eschulman and Twisted have the new boats, now if we could only talk them into spending many thousands on changing props for the benefit of more data, for what purpose again?
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Old 07-26-2014, 10:59 AM   #32
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LarryM

It seems you did not over prop, you right propped since your engine could reach rated max rpm with the last prop setup.
You are absolutely correct, I should have been more precise. My second prop/pitch combination was the one that was over-propped. My third/final combination is as close to perfect for my boating needs as I think I will ever get.

Now, for some noise-cancelling headphones . . . . and another couple of layers of Soundown . . . .

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Old 07-26-2014, 11:58 AM   #33
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FF wrote;
"Most engine cylinders wear out in total piston mile"

I would think the amount of force sideways on the piston to cylinder wall interface would have much more to do w it.

An engine working harder has more combustion force and side loads on the piston due to the offset of the crankpin or rod journal, downward forces of conbustion, piston crown area, stroke ect ect. An overpropped engine having fewer power strokes would need to generate more combustion chamber force and greater side loads on the piston. And the sideloads would produce more wear. A lot more I would think.

The concept that the overpropped boat would have lower fuel consumption at some engine speeds can probably be assumed as having overdrive on a car (or a higher gear ratio) produces the same benefit. The question is how much benefit is there to be had. And of course that needs to be balanced or compared w the benefits of propping the way engineers and engine manufacturers recommend.

But even "good enough for all practical purposes" numbers will be hard to come by as there are so many variables. I wonder how much truth could be had just looking at power output v/s fuel consumption curves? Fuel burn at slightly different engine speeds will have slightly different efficiencies and is obviously one variable but there are probably many more. Fuel burn as reported by a skipper is full of variables and usually not very accurate. The reporting skippers will profoundly disagree of course but they usually won't even know what half the variables are.

To me the amount of reduced fuel consumption is a small benefit to have but I am not the skipper of a Hat w big DD engines. Nore is my boat extremely overpowered. So if I had a motivation to overprop it would be very small.

One catergory of boats that would have large motivation to overprop for reduced fuel burn would be passagemakers. I know little about passagemakers and have no idea if they overprop but knowing would seem appropriate information for this thread. I would think they would need to be powered for low fuel burn so the power loading would fall into a small range. No over powered boats here. Since really rough going would definitely come to pass and at least some extra power would be needed for that so underpowering would not be attractive at all. So .. a narrow range of power loading. Since one would need full power at times I would think overpropping on a passagemaker would be too undesirable to consider.

The KK 42 and W40 are both overpowered w the Lehman so some observations and running numbers could be had here and some passagemaking has probably been done w the Lehman. Fuel burn numbers in those boats during some passagemaking should be better than most. I suspect boats of this type probably just run slower for better fuel burn rather than overprop so they may not have much information re overpropping. And perhaps like me they don't overprop for other reasons.
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Old 07-26-2014, 12:56 PM   #34
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indeed and with overdrive and carbed engines a big loss was pumping losses associated with creating that vacuum in the manifold. Lower RPMs with overdrive reduced those losses.

Diesels run unthrottled so pumping losses are reduced. The idea of running at the point of maximum BSFC has merit but within most reasonable operating ranges it probable is a nearly flat curve.

Over loading increases head and piston temps as well due to lower air flow vs fuel supplied to increase HP for rev up.
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Old 07-26-2014, 01:05 PM   #35
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As well as less coolant circulated and less lube oil circulated.
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Old 07-27-2014, 06:55 AM   #36
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>As well as less coolant circulated and less lube oil circulated.<

So what?

The mfg gives a HP and Torque curve that works for his engine, usually from 1200-1500 up to flank..

As long as all the limits are observed , the engine should lube and cool properly for the life of the engine.

Owners hardly need to second guess the engine mfg to obtain normal service life.

Usually the only hassles are engines that are auto transplants that do not have 4 or 5 service ratings and are light duty at best.

There simply loading to 1 hp per 3 cubic inches of eng disp. will keep the engine intact. when used 24/7.
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Old 07-27-2014, 10:07 AM   #37
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Owners hardly need to second guess the engine mfg to obtain normal service life.
Exactly and for that reason owners should not second guess manufacturers about propping either.
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Old 07-27-2014, 10:57 AM   #38
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As a matter of fact, I do have some real data to share. Last year I switched from a 17x13 DynaQuad 4-blade prop to an 18x14 DynaJet 3-blade prop. According to all of the prop calculators, Michigan Wheel and my local prop specialist, the new prop should have been 2" over-pitched. Otherwise, it was an ideal prop.

I installed it and ran for several months, then had 1" removed and found it to be perfect.

My engine's pleasure duty specs are 56 hp @ 3,800 rpm. The hull speed (SL=1.34) is 7.02 kts.

Before (17x13DQ 4-blade):
6.90 kts @ 3900 WOT
6.80 kts @ 3500 High Cruise
6.60 kts @ 3000 Cruise
6.00 kts @ 2500 Cruise
5.00 kts @ 2000 Economy

After (18x14DJ 3-blade) Overpropped:
7.20 kts @ 3650 WOT
7.20 kts @ 3500 High Cruise
6.80 kts @ 3000 Cruise
6.60 kts @ 2500 Cruise
5.90 kts @ 2000 Economy

After (18x13DJ 3-blade) Re-Pitched to Optimal:
7.30 kts @ 3950 WOT
7.10 kts @ 3500 High Cruise
6.85 kts @ 3000 Cruise
6.55 kts @ 2500 Cruise
5.70 kts @ 2000 Economy

Obviously the first prop, the DynaQuad 4-blade, was not well suited to the boat at all.

The last two sets of numbers for the DynaJet 3-blade are really interesting. Overpropping by just 1" of pitch reduced WOT by 300 rpm, but the improved performance at lower speeds was minimal. Each prop was evaluated with 2 2-way passes of 1/4 mile each in protected waters. This really is comparing apples to apples. This was the same prop with 1" of pitch removed. What a difference, and now the engine operates within in the manufacturer's recommendations and I sleep better.

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Larry, that is extremely interesting data. Do you recall if there was any difference in resonance with the 3 blade over vs optimally propped? What I find very encouraging about your numbers is that the increase in rpm relative to speed is only indicated outside cruising speeds. I intend to have my prop re-pitched this fall and was worried that instead of cruising at 1300 rpm to achieve a certain speed, I would have to cruise at 1550 with the increase in noise, etc. But your numbers indicate not, so thank you again.
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Old 07-27-2014, 11:47 AM   #39
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A realistic cruising speed for a Willard 30 is 6 knots. At six knots on Larry's boat 2100rpm is required whether or not the boat is under propped 150rpm or over propped 150rpm.

So 6 knots is produced w an inch less pitch and less prop load. Less prop load equates to less fuel consumption.

So Larry's boat is more efficient w a 13" pitch prop (a tad underpropped) than with a 14" pitch prop that is a tad over propped.

So Delfin perhaps you'll only increase a small fraction of prop speed you anticipated gaining or possibly none at all.

I always assumed over propping got a bit better fuel burn but perhaps not. Or perhaps I did the number interpolation wrong.
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Old 07-27-2014, 12:32 PM   #40
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A realistic cruising speed for a Willard 30 is 6 knots. At six knots on Larry's boat 2100rpm is required whether or not the boat is under propped 150rpm or over propped 150rpm.

So 6 knots is produced w an inch less pitch and less prop load. Less prop load equates to less fuel consumption.

So Larry's boat is more efficient w a 13" pitch prop (a tad underpropped) than with a 14" pitch prop that is a tad over propped.

So Delfin perhaps you'll only increase a small fraction of prop speed you anticipated gaining or possibly none at all.

I always assumed over propping got a bit better fuel burn but perhaps not. Or perhaps I did the number interpolation wrong.
Eric, I don't think it works that way. More aggressive pitch equals a higher "gear", so to speak, so rpm required to reach a certain speed should be lower with more pitch than less. Flatten the prop and spin it at 1600 rpm and you go nowhere. When I flew, once at altitude I'd feather the prop back, rpm goes down, fuel consumption goes down and speed is maintained. Maybe I'm confused on this, but I thought that was the way it worked on props in air or water.

What's interesting about Larry's numbers is that within the margin of error of measurement, there isn't much difference between the right pitch and one that was more aggressive at the rpm range I care about. But even with his boat, if he put on a 18 x 0 prop, it wouldn't matter what rpm he ran at - he wouldn't go anywhere.
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