Low Powered Cruiser

The way I read it was that he was saying there are only so many "piston miles" available before an engine wears out. But then he said that lower power output will return more "piston miles."

The first satement is wrong, the second is true, that's why I said it was both wrong and contradicted itself.

I can see why you said what you said and I don't disagree with you. But Bob's statement was not intended to be a technically correct statement but simply his way of expressing the notion that the easier you make life on an engine (while still operating it correctly) the better and longer service you will get out of it. The phrase "A piston is only going to go up and down so many times" is something his pilots tended to remember in the context of "don't abuse the engines in the planes." I obviously did

I suspect that in a more technical discussion he may have agreed with your fuel burn or power produced method of talking about potential engine life.

Seems that we're not adequately considering the need to produce electrical power to recharge batteries and power the refrigerator, running lights, air-horn compressor, GPS, cabin lights, depth-finder, radio,*electrical pumps, search light, and radar (while omitting non-essentials like electrical stoves/oven, air-conditioning, and electrical heat).* So, how much horsepower is going to be used to generate power in the typical medium-sized trawler in addition to moving the boat?

how much horsepower is going to be used to generate power in the typical medium-sized trawler in addition to moving the boat?

Most small boats have a hard time using the full output of a 6KW noisemaker.

Engine sizing to create a noisemaker is 2 HP per KW.

So the actual load will be less.

Efficiency does play a part in HOW you chose to create the energy.

My preference would be a 300A 24V alternator and a 4KW inverter and load sharing.
Bigger boats can parallel the inverter is needed.
Advantage , the ability to charge a massive batt set quickly in coastal cruises.
Inverter sine wave electric will operate big morors with efficiency.

Offshore choice for the longer passage folks would be a Hyd power pump and a 4KW or 6KW power pack. This could be driven by the noisemaker / get home as needed.

markpierce wrote:So, how much horsepower is going to be used to generate power in the typical medium-sized trawler in addition to moving the boat?

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Read the dataplates and add the power requirements. Figure out how much you want to consume at any given time and for how long. Figure out how long and by what means you want to power those consumers. Think about how, and for how long, you want to charge batteries.

You need to convert it all to a common unit, Watt, BTU, hp, whatever you feel comfortable with and go from there. Remember that everyone of those units comes on board at the fuel dock unless you have a long extension cord.

Mark - Consider two alternators, a Cummins is easily set up for this. That way you can easily split the load to batteries on one and other stuff on the other. Two 120 amp units would do it nicely - as rickB and FF note, add up your* loads plus assume you will be (through the inverter) cooking your potroast in the sink, coffee pot on, microwave doing bagels and hairdryer running etc*while underway.

FF wrote:

Most small boats have a hard time using the full output of a 6KW noisemaker.

Engine sizing to create a noisemaker is 2 HP per KW.

So the actual load will be less.

Efficiency does play a part in HOW you chose to create the energy.

My preference would be a 300A 24V alternator and a 4KW inverter and load sharing.
Bigger boats can parallel the inverter is needed.
Advantage , the ability to charge a massive batt set quickly in coastal cruises.
Inverter sine wave electric will operate big morors with efficiency.

Click to expand...

My boat will have a 24-volt system with an 8KW toroidal isolation transformer.* Don't know what the amperage of the alternator is.

So, with an 8KW transformer, as much as 16 horsepower would be needed from the engine, representing 18% of the maximum horsepower output of an 85 hp Deere??

*

Do you realize*that your last post made absolutely no sense at all?

An isolation transformer is only needed when the engine is off and you are plugged into shore power. I suggest you source and engage a GOOD proven*marine electrician to assist you in this effort and ignore all of us.

Yeah.* I'm going to find out the alternator's capacity.

The main/only engine's alternator is 70 amps.* How many horsepower is needed for that at maximum drain?*

The engine*will be*a John Deere 4045D.* It is rated at 84 hp or 63 kwh.* Maximum*rpm is 2500, with a*4.4 gph fuel consumption.* Low idle is 700 rpm and peak torque is at 1400 rpm.

Thanks.

-- Edited by markpierce on Tuesday 12th of October 2010 01:35:06 AM

Mark,Is your JD bigger than the 4 cyl Lehman? (253 cu in)

Eric, the Deere 4045 is 4.5 litres, or 275 cubic inches.* Each bore is 4.21 by 5.0 inches.

Rechecked and found this note from the builder:

"The engine for your Coot is a* JD*4045DFM70 engine, 80HP(60KW) @2500RPM . This is the only John Deere marine engine that meets emission requirements without a turbo."* (In the context of the Coot.)


It has the same size cylinders as the 4045D*but is rated*at 80 hp (60kw), with peak torque of 218 lbs. at 1400 rpm.* Consumption at max. rpm of 2500 is 4.6 gallons per hour.

http://www.deere.com/en_US/rg/ESC/SpecSheet/MarineProp/4045DFM70_A_S0_R0.html

Note that the manufacturer lists a less-than-or-equal-to 65% typical load factor.


-- Edited by markpierce on Wednesday 13th of October 2010 09:48:14 AM

"The main/only engine's alternator is 70 amps. How many horsepower is needed for that at maximum drain? "

IF you have a 24V system it will be operating at 28.8V in order to charge the battset.

70A x 28.8V = 2,016 WATTS.

OR 2KW .

Noise maker builders figure 2 hp per KW , but that's for longer life , the actual hp draw is lower (depending on efficiency of generation only about 1.3hp needed) but even at the 2hp/kw , its only 4HP, no big deal with an 80HP engine.

Your Hyd system will take more if its working hard , a good engine drive refrigeration system will be pulling 10 hp into a warm eutetic plate , only 1 or so after a couple of hours.

A cruising AC source , perhaps 4 to 6KW , will drag down the engine more.

Have you sprung the bucks for a CPP ? (controllable pitch prop?)

They are fantastic for economy , but depending on how many hours a year you operate , are usually not cost efficient of anything not commercial.

THE CPP would probably allow you to cruise at 1400 or 1500RPM , good heavy load , low rpm for nice and quiet.

-- Edited by FF on Wednesday 13th of October 2010 08:32:53 AM

So, now I'm down to an-engine-burnout 56 hp for propulsion,*which gives me a*36-hp-max.-"typical-usage" engine.

No fancy propellers --*Don't need the additional complication*nor do I see a positive cost-to-benefit return.*

Don't need the additional complication nor do I see a positive cost-to-benefit return.

For a 100hour a year typical pleasure boat , the return would be the quiet , not the fuel consumption pt extended engine service life.

One of the Aqua Drive setups also requires the thrust bearing ,

and with soft mounts and 2 inch soundown the noise can be brought down to a gentle level.

The air intake also needs noise consideration , usually baffles.

FF, Mark,I posted a paragraph twice last night. I punched the wrong button while previewing a picture and a power outage got the 2nd. BAD blow last night.
The air intake. Yes I need to get something. Seems to me I should be able to make one.
Wish I had an old Buick oil bath air cleaner. My plastic eng mounts work very well but I've got some rudder vibration issues now. I knew it was coming but thought it would be later.
What a wonderful engine Mark. 80 hp engine * * *....drop down 400 rpm and you still have 76 hp! FFs going to fall off his stool when he hears my next comment. This engine may be good to over prop. I'm sure you'll never need all that auxiliary stuff at the same time so you've got 20 hp to burn. If over proping interests you, you may want to check w JD. You will have a new and different continuous rpm rating and quite likely some engine speeds you should never use but if there ever was an engine that could gracefully be over proped you may have it. The JD is probably not the most efficient but very user friendly. I wish all our engines had balancers. I would gladly pay for them in weight and dollars. On motorcycles some weren't very effective and others turned a shaker into an electric motor.
Some observations:
The JD is about the same weight as the old Ford 80 but looks a bit larger. Less hp per cu in w almost the same compression ratio. May be the same CR as the turbo version of the same engine (I think it's 135 hp). I didn't know there were modern engines w that low of a comp ratio. Perhaps there are special parts (like rings) in this engine to cope w the low temperatures from low output. If you talk to JD you may ask them if there are any unusual features that allow this engine to pass Tier2 regs. I'd like to hear their answer to that. I wonder what they mean by "Typical full-power operation (hr) 16 of each 24".
Sounds like you could run it 16 out of 24 hrs at WOT. Most on this forum think that would wear it out quickly. I think my Mitsu says run it at WOT for no more than an hour at a time. And I think that's more typical. I'm sure this is a wonderful engine Mark and I would'nt replace it w a smaller Isuzu either.

nomadwilly wrote:*I didn't know there were modern engines w that low of a comp ratio.

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??*

Eric

Low RPM does not necessarily mean low temps. I can't speak for the 4 cyl JD, but many marine engines today are set up to use a circulating coolant/oil HX or other means to keep oil temps up. At 1400 RPM and 20% fuel burn*my engines maintain 175 degrees for both water and oil.

In my last post I was referring to low compression Tom. Could you explain that a bit more.

Rick * * What was the meaning and purpose of your last post?

17.6:1 isn't a particularly low compression ratio. Compared to some tiny automotive engines or other portable power units with ratios in the low to mid 20s perhaps it seems low but the economics support lower CR for marine engines that are not considered disposable.

Another way of looking at it is, if it starts, it has enough compression.

nomadwilly wrote:


... I wonder what they mean by "Typical full-power operation (hr) 16 of each 24".
Sounds like you could run it 16 out of 24 hrs at WOT. Most on this forum think that would wear it out quickly.* ...

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I've sent JD a query.

*

Rick,I'm mostly familiar w 20 to 55 hp engines and all that I can recall have 22 - 23 to one compression. Diesel may not be so but I think gas engines are more efficient w higher compression. Something I've wondered about that you may be able to enlighten me on is the pre-combustion (swirl chambers) on many of these engines. It seems my old Yanmar w direct injection started really easily and didn't have heaters/glow plugs. What do they have to do with tier2 regs? I would think the pre-chambered engine would start better but the reverse seems to be true from my experience.

markpierce wrote:


nomadwilly wrote:

*
... I wonder what they mean by "Typical full-power operation (hr) 16 of each 24".
Sounds like you could run it 16 out of 24 hrs at WOT. Most on this forum think that would wear it out quickly.* ...

Click to expand...

I've sent JD a query.


The response I received was: "Thank you for your message. The best source for application information is the John Deere Power Systems distributor that serves your area."

Not helpful. ...* Common sense tells me to avoid high rpms.* But I conclude that 1400-1600 rpms will be "comfortable" with the engine.



*

"Common sense tells me to avoid high rpms."

You need to operate at the RPM that will develop the required power.

Rated RPM on a commercial diesel is its life , not a "high RPM'.

And rated RPM is frequently the lowest fuel burn per HP.


The common "rule of thumb" is 80/90.

80% rated load at 90% rated power, to "live long and prosper".

Hard to imagine that operating at maximum torque (at substantially below maximum rpm) is harmful to an engine.

markpierce wrote:Common sense tells me to avoid high rpms.* But I conclude that 1400-1600 rpms will be "comfortable" with the engine.
Hard to imagine that operating at maximum torque (at substantially below maximum rpm) is harmful to an engine.

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What is the fascination with max torque?

I wonder if your new boat can even get off the dock on 5 hp. How comfortable is that?

Mark -**You cannot go wrong by propping by the book, especially with a new TierII JD. In general, the book says to select a prop size*to allow full RPM to be achieved. Underpropped means you cannot achieve full RPM and overpropped means you achieve more than full RPM.

This assumes you have a fully loaded vessel with PTOs, and other parasitic drags operating as designed.

RickB wrote:



What is the fascination with max torque?

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I like the sound of it.*