Diesel engine/prop/hull efficiency questions

Hi,
RPM Kts GPH
3000 40.2 60.1 91 .67 MPG

Hi,

Again you have posted complete garbage.

The bold type above was extracted from yet another of your increasingly fanciful postings.


It is a well known internet phenomenon to have people plagiarize others work as their own.

It is not the smartest thing to do if you do not understand the underlying technology and try to fluff your way through it in an environment where others of far greater understanding and experience have the opportunity to review and comment upon statements/ posted material

"I figured one would "assume" the statement was regarding the diesel we are talking about in this entire thread, the 16v2000."

You very clearly stated that "diesels" were more efficient below 1000 rpm than at cruise. This says that the BSFC is lower at low rpms, and that is patently false. Again you are confused as to the meaning of efficiency. And that 100 rp,m diesel is the most modern, highly engiineered engine on Earth, it is not a primitive prototype from the 19th century. It is a marine engine used on modern ships. We, including you, have been writing about diesels ranging from 20 or 30 hp up to and beyond the 2000 and 2400 hp versions of the 16V2000.

"The power it takes to turn a given prop is a variable as well."

The amount of variation at any point on its power curve is not worth considering. That is how propellers are selected and with modern engineering, manufacturing, and design capabilities, the data is very reliable for purposes of propeller selection and matching. Again I think you are confusing several issues and elements of engine and propeller operation.

"Also, it will take a different amount of HP to turn the same propellor if there is a different reduction in the gearbox."

The propeller doesn't know what gearbox is turning it. It doesn't care. It will absord X hp at X rpm whether it is driven by an electric motor, a squirrel, or a turbine, or a diesel. The gearbox is there to match the engine power, torque, and rpm to the propeller and hull requirements to obtain the best propulsive efficiency, which is another matter altogether.

"Shaft length, shaft diameter, number of cutlass bearings, number of struts all have an effect on how much horsepower it takes to turn a propellor in a yacht."

Certainly, each of those items increases the amount of power the engine needs to deliver to the shaft in order to turn the propeller at a given rpm. None of those items can reduce the power absorbed by the prop at a given rpm.

"How can you use the same formula across the board? It's impossible."

Because a propeller requires a certain amount of power to turn at a certain rpm depending on its physical properties and dimensions. These properties are well catalogued and very accurate graphs have been developed to provide naval architects and marine engineers with design data.

"... it is proported to decrease fuel consumption and increase horsepower 8%..."

Your belief that a stuffing box can produce horsepower may be an indication of why this thread is so entertaining. Only the engine can produce horsepower and it does so by converting the heat energy in fuel to torque. You might reduce the torque required to turn the shaft at a given rpm by reducing friction along the shaftline and thereby save fuel but you won't reduce the power absorbed by that prop.

"So how can you use the same formula for every single yacht?"

We aren't. We are using the data that engine manufacturers derived through testing to determine fuel consumption and power output. We are using the data developed by propeller manufacturers and fluid dynamicists to calculate the amount of power a propeller will absorb. How these elements combine in the real world is determined through tank testing and fine tuned in the field but all the tuning in the world will not change the fact that it requires X number of BTUs to turn a prop and we do not have the technology yet to achieve the fuel burns you first claimed. Especially from an engine operating at the lower left corner of its envelope.

If someone would like to instrument your amazing vessel and show me that it only takes 10 or 15 hp to turn the engine itself, the gearbox and accessories, the shaft, and finally that big prop at whatever rpm equates to moving that boat at 9 knots through the water then I will gladly eat my words and be very impressed. I love being impressed by technical achievements and progress. I don't mind being proven wrong, it's how I learn. So prove me wrong.

Hi,

Marmot- I take it that this is the Engine you have written about above.

It certainly has impressive dimensions and specifications.

I remember this engine being described as thing of the future when I was doing my last stint at college.

At 7780 HP per Cylinder and with the 14 Cyl version consuming a mere 1660 Gals an hour there won't be many of these babies fitted to yachts.

http://people.bath.ac.uk/ccsshb/12cyl/

What is so hard to figure out, 3000 rpms, vessel speed 40.2 knots, 60.1 GPH, 91 decibles of noise, .67 MPG (40.2 divided by 60.1). GO TO THE WEBSITE AND DO YOUR OWN FUEL CALCULATIONS FROM THE PUBLISHED CHART AND POST THEM HERE IF MINE ARE WRONG.

The link is there, go to the motorboating website link that I have provided with the information and look at the fuel burn charts they have provided for your own. I did not plagerize ANYTHING, I did write in the same e-mail right above the fuel/speed/etc charts, that I calculated the MPG figures based upon Motorboating's test figures which anyone else can do. IT'S A SIMPLE CALCULATION which is accurate.

As for the Sea Force thing. Any reduction in reciprocating mass would increase the HP any motor is capable of making. So could it increase shaft horsepower, sure. That system eliminates, stuffing boxes and cutlass bearings and uses an oil filled system that goes around the shaft and acts like a stuffing box. Oil provides a lot less friction as a lubrication form then sea water does. In some extreme cases could it increase shaft delivered horsepower 8%, who knows.......maybe........

Anyways, all you want to do is SPLIT HAIRS over information that is there.......And, SPLIT HAIRS over the terminology I use. The fuel graphs are there....... The vessel speed vs fuel burn is there....... The 48' searay has around 1100hp in 2 diesels and sips 1.3 GPH at 600rpms, yet burns 60 gph at cruise.

The whole point of this entire deal is the vessel is much more efficient at displacement speeds and combined with the fuel sipping qualities of a diesel installed in a yacht the range figures as published are probably accurate. IT'S MAINLY THE VESSEL IS NOT NEARLY AS EFFICIENT WHEN YOU GO ABOVE DISPLACEMENT SPEED. You so called engineers are too busy focusing on the efficiency of the engines, when the co-efficient of drag of the vessel is the MAIN FACTOR of the Vessel's range. WHICH IS WHAT THIS ENTIRE DISCUSSION IS ABOUT. You could propel that Broward 10knots with WIND power even if you put the proper sails on it. You could never get that broward to it's 30 knots

A couple of guys could pull that 48' Searay through the water at 5 MPH with a dock line (in fact I see guys pulling boats that size in and out of a slip by hand all of the time), I don't care how many guys you get, there is no way humans could get that vessel moving past 10 mph pulling it with a dock line.

Hi,

CaptJ- I will concede that I made an error in what I read as being the MPG in the post I highlighted.

The columns are a bit out of whack and it does look like 91.67 is your calculated MPG.

Oil filled stern tubes are not a new invention. Akerboom have been doing them for years. They have a set of their own issues and problems not found with water cooled shafts. The shafts still run in bearings and instead of a stuffing box they have lip seals at the inner end that also contains the Thrust Bearing and a set of lip seals along with a metal face seal at the outer end.

Yeah, I'm not too familiar with the oil filled stern tubes. I've never run a boat that had them. The largest problem I've had with the dripless shaft seals, is the seal leaking and having the haul the boat because there isn't a spare seal on the shaft. I don't know what maintanence issues the oil filled seals bring, or if they're really an improvement over standard or dripless seals. It sounds like a good idea that should reduce friction.

Hi,

CaptJ- I did a bit of googling for Sea Torque ( Post No 60) and Sea Force (Post No 64) and all I could find was this which doesn't seem to work past the intro.

http://seatorque.com/default.aspx

Is this the place you mentioned in your posts?

Here is a small write-up on them as they are installed in an 80' Roscioli sportfish that Power and Motoryacht did a test on, it has their link (SPOTLIGHT ON: shaft system section of article) It has a picture and it looks to be a well built and engineered system and Roscioli is known for using top of the line components in his boats, but that's all I know.

http://www.******************.com/boat-tests/donzi/2008-donzi-r-80/index1.aspx

Yeah I tried to visit their website and it has a flash intro but then throws an application error http://www.seatorque.com/default.aspx

Hi,

Thanks, I found the review but it doesn't say if this can be used as a aftermarket upgrade or only from newbuild.

If it does away with the Cutlass Brg what is in the strut out by the prop?

From the pics shown it looks like other Oil Filled Stern Tubes with the Thrust Bearing in the housing at the front and an Oil Header Tank visible right above it.

If anyone knows exactly how this system works or has any contact info for the company I would be interested to know what it actually is and does

I don't know....my guess is that they'd use existing parts like struts and modify them, possibly with an oil filled tube or something. It looks like a pretty well manufactured system (based on the photo). It probably could be retrofitted.

I think the marine industry could use more technology in some areas to increase efficiency. I have always wondered why they never went to at least a 2 speed transmission, I know the gear ratio's would have to be relatively close, but for heavy motoryachts and such it seems like it would help top speed/efficiency/and acceleration.

I know the new Cummins Zues drives (and Volvo IPS) are quite a bit more efficient then traditional shaft propelled systems. They've installed the Zeus drives on the '40 Cabo and it performs exactly the same (speed figures) as with the Cat or MAN's making 200hp more. Fuel consumption is quite a bit less at some speeds....because of the HP difference and weight savings and the speed is the same....But a nice comparison on the same boat with zues/man/cat/and yanmars
http://www.caboyachts.com/yachts/40X/documents/StdSeaTrial_C40X5pgs_000.pdf

Seatorque

Just for reference the seatorque website is up and running with a list of customers, recent ones being Fleming, Drettman and Van der heijden steel yachts.
http://www.seatorque.com/