Trawler Forum

Trawler Forum (http://www.trawlerforum.com/forums/)
-   Power Systems (http://www.trawlerforum.com/forums/s6/)
-   -   Propulsion effiency for all rpm. (http://www.trawlerforum.com/forums/s6/propulsion-effiency-all-rpm-18431.html)

gadenors 01-24-2015 10:33 AM

Propulsion effiency for all rpm.
 
Best and effiency for bigger tugs and trawlers.

Sometime ago in december 2014 Guru FF. had interesting post about
CPP propeller.
I have digged and found those mails to get more info, for this matter.

www.frydenbosabb.no Sabb has dealer in USA FL Leerburg.
ask: www sabbamerca@aol.com
www.westmekan.no
Westmekan offer fixed adjustable propeller. (prop.pitch on a slip.)
prop.dia down to 600 mm. = 24" dia. shaft 50 mm.= 2 "

I strongly believe that with HP. from 80 HP up to say 300 HP.
will have a great advantageous, and a far better economy.

Why not give it a try, we seamen are conservative I know, bu still.! :blush:

Nomad Willy 01-24-2015 11:12 AM

I think the efficiency of a CSP may be a catch 22 as the slightly better efficiency at cruise probably lost due to the lower efficiency of the CSP itself.

To get the engine and prop matched at higher speeds and cruise also a two speed gear would be better than the CSP. But there is (would be) a small loss in the gear. I was going to say "to consider" but the loss would probably be too small to consider in a cost effective way. Both the gear and the CSP would be expensive and would require many years of operation to justify the cost over a well engineered straight drive and fixed pitch propeller. Changing to a different style or type of FPP would probably increase cruise efficiency also.

I think a better road to efficiency is to pick an engine that is efficient at the cruise rpm anticipated and optimize all elements for that engine speed, boat speed, boat design at the ideal speed ect ect ect.

Good design and planning of all things should result in the best economy.

The above is "IMO" and my knowledge of CSP is very limited.

Another thought is that more efficiency would/could probably be had reducing the cruising weight of the vessel. That would be much more applicable to a SD hull. But even FD boats are often judged and compared by how much power they have per ton of displacement. Four or 5 hp per ton is about optimized for FD craft and SD would/will require about 1.5 times that or another value depending on hull design ... and weight.

djmarchand 01-24-2015 11:55 AM

Controllable pitch props are expensive and are only available in bigger sizes than most 35-40' trawlers need. And "overpropping" with a controllable pitch prop isn't going to save much fuel, maybe 15-20%.

As Eric notes the better choice is to size your engine for the cruising speed that you need. But this is not always possible.

And finally running a big engine slow isn't going to use that much more fuel than one sized for trawler speed cruising. A modern 2 liter Yanmar common rail 80 hp engine uses about 2.3 gph of fuel at 50% load.

Most trawlers in the 35-40' size range will need about that 40 hp to cruise at 7 kts or so.

A much bigger 370 hp Yanmar uses about 20% more fuel at the same 40 hp power output or about 2.8 gph.

In a typical 200-300 hour per year useage, the cost difference is less than $500.

David

MurrayM 01-24-2015 12:44 PM

Never seen one of these in real life, checked on how much they cost, or reliability, but they sure are cool;

Autoprop: Propellors

https://www.youtube.com/watch?v=xdxY5Q7wXek

Art 01-24-2015 01:10 PM

Quote:

Originally Posted by djmarchand (Post 301529)
Controllable pitch props are expensive and are only available in bigger sizes than most 35-40' trawlers need. And "overpropping" with a controllable pitch prop isn't going to save much fuel, maybe 15-20%.

As Eric notes the better choice is to size your engine for the cruising speed that you need. But this is not always possible.

And finally running a big engine slow isn't going to use that much more fuel than one sized for trawler speed cruising. A modern 2 liter Yanmar common rail 80 hp engine uses about 2.3 gph of fuel at 50% load.

Most trawlers in the 35-40' size range will need about that 40 hp to cruise at 7 kts or so.

A much bigger 370 hp Yanmar uses about 20% more fuel at the same 40 hp power output or about 2.8 gph.

In a typical 200-300 hour per year useage, the cost difference is less than $500.

David

Thank you David. One of the best, clearest accounting yet as to why it is perfectly OK to have larger engines than required to move a boat at only very slow speeds. Hope Eric reads your post. Of course, full D hulls can not make use of the larger HP. But, SD and P hulls sure can!

Nomad Willy 01-24-2015 04:47 PM

Sure Art,
It's OK to do whatever one wants. These are pleasure boats and we pleasure boat Captians have more freedom than any other boat captian.

There are many decisions that we make that may not be made like an engineer would make it but nobody will suffer but ourselves (usually) so we are free to over prop, over power or make whatever modifications we see fit. That's good for me as I like to modify things and do as I see fit. You seem bent a bit in the same direction Art.

David's posted numbers are very good and a lot of good stuff can be learned from them.

David I thought over propping would save 5 to 8%. If 15 to 20% can be had overpropping that would tend to make the practice more desirable for those serious about saving fuel.

djmarchand 01-25-2015 07:14 AM

Eric:

It is hard to say for sure how much fuel can be saved by significantly overpropping an engine. Most marine engine manufacturers like Yanmar only give fuel consumption data based on prop horsepower so it is impossible to see how much fuel would be consumed at a lower rpm but at a higher hp than along the prop curve.

John Deere does give fuel consumption data for both the prop curve and the maximum hp curve. But the scale on their chart makes it difficult to read with any accuracy. And comparing prop hp/fuel consumption with wot maximum hp fuel consumption isn't the right way to look at it. No one should prop their boat so that the engine has to run at wot to reach the cruise rpm they want. Well, I hope not.

But with those caveats in mind, if you look at JD's NA 4045 80 hp engine's prop curve rpm that produces 40 hp it uses about the same 2.3 gph (but at a lower 2,000 rpm) as the Yanmar data given in my previous post. If and this is crazy of course you run the engine at wot, it produces 40 hp at about 1,000 rpm. As close as my eye can read, it is in the same gph ball park.

So maybe the fuel savings aren't 15-20% and may be closer to your number. There must be some fuel savings running at lower rpm as you are wasting less parasitic hp when you turn over the engine slower.

The JD data sheet link is http://www.deere.com/en_US/docs/engi...045DFM5085.pdf

David

gadenors 01-27-2015 06:41 AM

Quote:

Originally Posted by MurrayM (Post 301541)
Never seen one of these in real life, checked on how much they cost, or reliability, but they sure are cool;

Autoprop: Propellors

https://www.youtube.com/watch?v=xdxY5Q7wXek

MurrayM.
Thanks for showing the video clip, I know some here in DK. use Aut.Prop. they praise and are happy with the auto-prop. Good to hear positive respons.
I most admit, that I do not know HOW it Works, maybe an (ARM-CHAIR ENGINEER.) can tell us ?
I am told that, if you slow down your engine, instantly, the pitch are altered to more pitch. but NEVER overpropping, just so the rpm.HP now fits the new slower turn of prop.and less HP.
Brunton Propeller, are an old suppier to fishermen for many years.

FF 01-27-2015 07:56 AM

For the true enthusiast that wants to go out in the Blue Water other choices exist.

ZF makes a 2 speed tranny that could speed up the prop in relation to the engine at cruise speed.

This would load the engine better , although it would be most useful to the oxymoron Fast Trawler with a 300% or more over sized engine .It might get it the range required for a crossing.

Other choice would be a landing craft tranny where two engines (dont have to be same size) can power one centerline shaft . Either can be disconnected under way if desired.

Old stuff 50 years at least so not expensive.

Last I saw in Boats and Harbors a Gov rebuilt set with 2 rebuilt 6-71 was about $6K total on a pallet.

Yes, its probably 5000lbs+ of engine package , so it may not be for the small boat.

I would sell one 6-71 and instead install a 2-71 or 3-71 , depending on cruise power needed.

Figure 20-30HP per cylinder, and remember DD are real engines and LOVE to be loaded to 90% or so.

bayview 01-27-2015 10:03 AM

Quote:

Figure 20-30HP per cylinder, and remember DD are real engines and LOVE to be loaded to 90% or so.
Another diesel myth.
only when they are 30 HP per liter or so. at 60 or more not so much. Thee is nothing magical, or "real" about old DD. They were an excellent design, for the time ,and heavily built but the low HP pre liter of the old engines was the prime reason they last forever. Hop them up and try to run at high HP and life is shortened as with any modern engine. This overloading is also related to over propping but I wont go there........

Art 01-27-2015 11:25 AM

Quote:

Originally Posted by bayview (Post 302387)
Another diesel myth.
only when they are 30 HP per liter or so. at 60 or more not so much. Thee is nothing magical, or "real" about old DD. They were an excellent design, for the time ,and heavily built but the low HP pre liter of the old engines was the prime reason they last forever. Hop them up and try to run at high HP and life is shortened as with any modern engine. This overloading is also related to over propping but I wont go there........

Rule o' thumb on engines... From decades general experience/learning and interactions with qualified engine experts:

- For overall longevity and reduced breakdown/repairs... Keep the available maximum HP output number of an engine at a ratio of 75% or less than its total displacement number and run for long periods at 60% to 75% of its maximum HP. :thumb:

- For sheer Fun, Competition, or just for the Hell of It! - Build that engine-baby to its max HP capabilities and ride her hard! But, have deep pockets!! :D

Art 01-27-2015 11:43 AM

Quote:

Originally Posted by gadenors (Post 302338)
MurrayM.
Thanks for showing the video clip, I know some here in DK. use Aut.Prop. they praise and are happy with the auto-prop. Good to hear positive respons.
I most admit, that I do not know HOW it Works, maybe an (ARM-CHAIR ENGINEER.) can tell us ?
I am told that, if you slow down your engine, instantly, the pitch are altered to more pitch. but NEVER overpropping, just so the rpm.HP now fits the new slower turn of prop.and less HP.
Brunton Propeller, are an old suppier to fishermen for many years.

Don't know what ever became of this:

Mid 1960's around the New England states there was some sort of an extra efficient "self tuning" (quote is my words) prop for outboards that became available. In that it was slightly flexible and could/would modify its pitch depending on rpm at a given speed as well as during thrust from quick acceleration. I never used one and did not know those that did. It seemed to evaporate off the market within a year or two. I read ads and what were basically promotion articles in boating magazines. As I recall its cost was prohibitive for an early teenager like me with 40 hp Johnson on 13'3" Boston Whaler.

I did think the concept was good and that as material technology improved material capabilities that concept should come to forefront as a prop choice. Never heard of it again.

Anyone else recall that prop and its capabilities/material... with better recollection than I?

How about that - a semi-flexible prop material that automatically (and in correct format) self-alters its shape in regards to rpm/torque/thrust?? There would be no moving parts... sort a'!

LarryM 01-27-2015 12:27 PM

Quote:

Originally Posted by Art (Post 302415)
Don't know what ever became of this:

Mid 1960's around the New England states there was some sort of an extra efficient "self tuning" (quote is my words) prop for outboards that became available. In that it was slightly flexible and could/would modify its pitch depending on rpm at a given speed as well as during thrust from quick acceleration. I never used one and did not know those that did. It seemed to evaporate off the market within a year or two. I read ads and what were basically promotion articles in boating magazines. As I recall its cost was prohibitive for an early teenager like me with 40 hp Johnson on 13'3" Boston Whaler.

I did think the concept was good and that as material technology improved material capabilities that concept should come to forefront as a prop choice. Never heard of it again.

Anyone else recall that prop and its capabilities/material... with better recollection than I?

I think you might be talking about the Torque Shift Propellers by Land and Sea. I haven't heard anything about them in years though.

https://www.youtube.com/watch?v=C5niXCY-ikM

Brooksie 01-27-2015 12:39 PM

1 Attachment(s)
I think FF is right that using a 2 speed transmission is the best answer to improve efficiency in vessels our size.
Autoprop could also be an answer but these people don't publish any real number data on their use on powerboats. They mention reduced RPM's at various speeds but nothing on loads or consumption. I would assume their prop load curve is much flatter than a fix pitch and would not sag away from the engine power curve. This should yield good efficiency gains. But again they don't publish anything except anecdotal information.
I contacted ZF about using their 2 speed transmission for increased efficiency as shown in the chart below. As I recall, they said that this is not the way they intend their product to me used and didn't even want to run some numbers for me which they could easily have done.

Art 01-27-2015 01:00 PM

Quote:

Originally Posted by LarryM (Post 302425)
I think you might be talking about the Torque Shift Propellers by Land and Sea. I haven't heard anything about them in years though.

https://www.youtube.com/watch?v=C5niXCY-ikM

Larry - Interesting prop and cool video, thanks!

But, no... the prop I refer to had no moving parts similar to the one you reference.

It was one solid piece of flexible material and looked basically like any other three blade outboard prop. However, the material was a composite of material that could flex. Pictures in magazines it did not look to be metal. They were all white as I recall. I have vague memory of seeing one at a booth in NY Madison Square Garden boat show when I was about 14.

Nomad Willy 01-27-2015 01:53 PM

Brooksie I agree too that the 2speed tx is a good route but only if it's cost effective. And I think it will seldom will be so. Just a straight tx is costly enough.

And I suspect the 2speed tx is probably marketed for fishing or other commercial applications.

Combining FFs old 2engines and one shaft arrangement w at least one of those engines connected to a 2 speed tx could be super for some trawlers. When you switched to single engine shift down and turn the "big" prop handily. Carefully choosing the gear ratios could put you right in the engines sweet spot. You could have both single and twin engine configurations propped correctly and selecting engines, props and gears for low fuel burn great economy could be had.

Don't think there's any of these two in one out gears currently availible though.

FF 01-28-2015 08:42 AM

OF course if you are content with just cruising as economically as possible , a single engine with deep tranny reduction run at the MFG rated sweet spot (as chosen from his fuel map) will require nothing , but a fairly expensive prop.

As diameter gets bigger the price goes way up. Price a 24 inch and 36 inch to see.

Those seeking the ultimate might work in a 2 blade prop too.

OF course a boat set up this way will never pull max rated RPM on the pin.

Want cheapest ? Do that the big boys do almost full power ( 96 to 105RPM) and accept a slow down in over 30K of breeze.

OF course these boats are so optomized for one speed the engine required modification , and different operating techniques to slow cruise at 85 RPM.

Even the bulbous bow needs modification, but when the fuel burn is in TONS PER HOUR,,,,,

Most boats are fitted with ove rsized engines as they are cheaper to purchase for the stock boat builder.

Nomad Willy 01-28-2015 09:49 AM

The "ultimate" FF would be a long and narrow and light boat.

Variations in the propulsion of wide and heavy boats won't get you much. Comparatively speaking long and narrow boats will take you to the moon and beyond.
Think "Stiletto" and then compromise.

Ski in NC 01-28-2015 10:46 AM

Two speed trans is better than one speed, but you are still restricted to one speed or the other. Also, they made them purpose specific to fast planing boats so first gear would get you over the hump, then second gear was for fast planing. The ratios were optimized for that and nothing else. And BIG and EXPENSIVE.

The holy grail is the CPP. Infinite control of pitch, infinite control of engine load, seamless change of thrust direction. The stuff that gets gear-heads all excited!!

But CPP's are complex, expensive, hubs are bulky, room needed in ER behind engine for control hardware, still really need a clutch of some sort, and did I mention expensive??

As much as I like the CPP, it simply does not pass the cost/benefit analysis for boats such as ours in a typical duty cycle. Wish it did, and wish I had one.

Art 01-28-2015 11:45 AM

Gear Heads Unite!

Maybe I heard an answer to this back in the 70's. However, in 2015 with new technology having improved things...


Why is it not possible to design have an "automatic" hydraulic marine transmission that shifts forward gear ratios depending on throttle applied and/or rpm/speeds attained?


Is it a torque or prop size conflict? Each trany's ratios/shift sequence would probably need to be specific to (i.e. matched to) boat and engine/prop combo attended.


That said, it would seem that a base unit could be produced that has adjustable ratios built in so it could be relitively easily adjusted to meet needs apparent for a boat and to also match engine/prop needs.


Projection: Let's say it's somewhat like a three speed auto trany. Left in 3rd it runs through all 3 of its gears as you increase throttle and speed. If you want to have a bit more acceleration capability at any time while traveling at mid-range cruising speed then leave it in 2nd gear. If you want to shoot out of the hole then use 1st gear and manually walk it up as rpm reached redline. Also, not unlike autos why not have a passing gear that when cruising at mid-range speed drops it into 2nd for faster acceleration when you gun the throttle.


Seems fuel efficiency may be able to be improved and boat handling may be easier under certain circumstances. However - I'd hate to have the trany shifting gears while I was working hard not to breach in big waves/rough seas. Then of course it could be left in 1st gear or have a locking affair that held it in 2nd or 3rd so automatic shifting no longer occurs.


Happy Transmission Daze! - Art :popcorn:


All times are GMT -5. The time now is 02:47 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012