Questions about Diesel power curves

[Kurt]

OK, I'm confused (so what else is new?).

Attached is a graph showing the power curve for the Yanmar 6BY260 engine. I have a couple of questions about its interpretation and operation:

1 - Is the minimum engine speed 1000 RPM or is that just for purposes of the chart?

2 - Why is there a difference between the crankshaft power rating (red) and the prop power rating (blue)? i.e. Why are the curves essentially inverted and so much different? The fuel consumption curve (not attached) essentially follows the prop power curve, which is what you'd expect.

Here's a link to the PDF from which I got the graph:

http://www.yanmarmarine.com/products/pdf/BY/6BY260.pdf

[Mistress]

the 1000 rpm is for basis of the chart. I suspect there's some standard (SAE/ASTM, etc.) for where the chart begins.

The crank hp is just that. What the engine is CAPABLE of delivering at X rpm.

The prop doesn't use all the available hp until it's maxed out (WOT). So the prop curve is the hp required by the prop. The fuel curve follows the prop curve as the fuel req'd is based on the load/demand on the engine.

The fuel curve assumes the boat is properly propped (achieves WOT rated rpm plus a little)

[Kurt]

Thanks Steve...

That makes sense - don't know why I couldn't get my thick brain around that on my own. Out of curiosity, what's usually the idle RPM on Diesels? e.g. I run my 351 Ford at between 600 - 650 with a boat speed of around 5 to 5-1/2 Kts.

It seems that those new 260 HP BMW/Yanmars (4000 RPM max., ~760# eng + trans) would do pretty well in a later (8-1/2' beam) 20 or 22 ft hull with a 1:1 trans turning a 14 x 12 or 14 x 13 prop. I currently have a 14 x 11 and the 260 HP on my gasser spins up to around 4400 RPM WOT.

The Yanmar is about 2" wider than the engine I have in there now but I think there'd be room. The eng + trans length is about 1/2" shorter than the Ford and the O/A height is only 1/2" more than what I have now. The engine mounting points don't seem to be too far out of line either. It would seem that speed performance would be just about the same with about a 35% - 40% reduction in fuel consumption at cruise.

The only questions would be if there were a sufficient justification to cough up $20K to make the change (labor = sweat equity) and whether the engine could be mounted at the ~9° angle needed for the 1:1 trans. Of course, there's always the spousal unit to factor into the equation. :rolleyes: Also, they can take all that dress up cowling crap off the engine - I want to see the plumbing - it's like a damn burka! (sp?)

Obviously the justification factor is whether one REALLY wanted a Diesel since it'd be pretty difficult to recoup the $$$ investment in fuel savings unless the boat were used a few hundred hours/year, for many years.

This seems to be a parallel thread to Tunaman's 22' Diesel discussion. Probably should have put it there.

[fisholic]

The BY260 idles at 620~640 rpm w/o load (tested it in my workshop last week…). With load it may go up to 700/750 rpm ? we'll see!

I agree that the real thing will be in the water, but for now I can say that it’s amazing how balanced and quiet it is. Playing with the “fly-by-wire” command, going from idle to 2000/2500 rpm suddenly, the engine barely shakes over it’s rubber blocks! And it responds so fast to throttle that it doesn’t look like a diesel…

Regarding $ burning, I did my calculations according to the eng fuel chart and, for my +-300 hours/year and the local gas/diesel difference in cost (about $2 /gal), it definitely pays back. ;)

1996

[Kurt]

Hey Fisholic...

Where's the little first mate we saw sitting on top of the boat when it arrived? She ought to be in there "tuning" that new heart for all those fish she'd gonna catch!

I'd be very interested in the performance numbers when you get it all together and she (the boat) passes her shakedown cruise... :D

[fisholic]

Kurt,

At that time Madalena (5yo) was probably playing with her barbies, that’s what she really likes to do… Her thrill about the 246 is more the ”little house w/ a door, 2 windows and a sunglass roof … w/ a nice small sink… a toilet…and a CD player!”... where she can play with her… Barbies, what else?!
Maria (2yo) is more to the “engineering” and “fishing” side… :D

Regarding my current boating project, I must say I got a bit “stucked”… :confused:
Some hard times at the company, some “technical” dilemmas and a heavy dose of “domestic” affairs…
... Well, about the part of it I can talk about here :D , the “technical” dilemmas are/were, for example:
-Works on the bilge easier to do before the engine on place: Location of the Simrad's Combi-c transducer (?), pre-filtering of diesel (arrived this week from Raccor), exhaust line (still to arrive…)…
-Flexible coupling or not?... I order one (bullflex12 from Vetus) and now that it arrived I found it huge (42lb!) and hard to couple to the transmission…

Next weekend works will start progressing faster (I hope...) and I believe I’ll have some pics to post!

...and most important of all, I'll get closer to the Shakedown! ;)

2009 2010

[Lee Short]

I am just finishing my winter project boat, 1989 26 hardtop w/ Cummins 210.
We are going to get it in the water next week for the first time since purchase. Any tips from you diesel owners as to things to be aware of, or watch out for? The previous owner had rebuilt the engine - it has 3 hours on it. Any advice will be appreciated. The boat is going in Lake Erie so our season is just starting - still canceling baseball games a week ago in Cleveland.
Thanks, in advance,
Lee

[Mistress]

keep an eye on fluids and hoses/clamps. Preferably dedicate one person to obeserve while another puts the boat through it paces. Check your max rpm in and out of gear.

Oh...dont forget to open the main seacock before starting.

[Lee Short]

Mistress, I fired it up yesterday. Ran at 780 rpm idle and 2790 rpm w.o.t.
Is that about where it should be - i was actually expecting around 2600
tops. Thanks. Lee

[Mistress]

2600 is max "rated" rpm. It should be able to beat that by 100-200 rpm (on the water). Sounds like you're dialed in. You can drop the idle to about 700 in neutral (600 in gear) before she shakes too much.

If you can, it's good to check rpm with a photonic tach. They're pretty cheap (~$50).

[Lee Short]

Thanks. We did use a digital tac to record the rpms so we knew how accurate the normal tac was - checked out pretty close.
Another question - the transmission has two hoses (blue, if that makes a difference) leaving it that are plugged. It almost looks like these would have been connected to a cooler at some time. Any ideas what they may be.
I am not aware of the need for a tranny cooler on a boat.
Lee Short

[Mistress]

In my experince. VD's ALWAYS have coolers. Optional on some trans. if the lines are there, I'd imagine it HAD a cooler. I can't see being without one.