Page 1 of 5 12345 LastLast
Results 1 to 10 of 48
  1. #1
    Join Date
    Nov 2001
    Location
    Medway
    Posts
    17,597

    Default A few moments to spare from earning money to pay for the boat ?

    Worth a quick browse
    Its American of course, we in UK do not seem to have anybody with the clout to cover this sort of thing at all.
    Its basically about modern marine engines....
    electronics and weird complicated drive systems still to come ?
    Also a bit on engines and props.
    We have come on with car technology to give reliability and longevity, why has marine engineering produced such fragile and delicate solutions to same problem ?

    https://www.sbmar.com/articles/prope...ust-turn-them/




    https://www.sbmar.com/articles/marine-age-the-real-age-of-a-marine-diesel-engine/


    Last edited by oldgit; 11-10-17 at 08:33.

  2. #2
    Join Date
    Mar 2002
    Posts
    14,359

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by oldgit View Post
    Also a bit on engines and props
    ...
    https://www.sbmar.com/articles/prope...ust-turn-them/
    The old adage "Propellers Move Boats, Engines Just Turn Them" always make me smile a bit, 'cause it's often used as if most people would think to run their mobos with no props.

    I'd be tempted to argue that neither engines nor props do anything at all.
    It's the helmsman mind what REALLY moves the boat: his/her hands, the throttles, fuel, engines, shafts and eventually propellers are only there to translate his/her wishes...

  3. #3
    Join Date
    Sep 2016
    Posts
    2,485

    Default Re: A few moments to spare from earning money to pay for the boat ?

    sbmar are the absolute gurus of marine diesels especially Cummins

  4. #4
    Join Date
    Sep 2002
    Location
    South
    Posts
    14,715

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by MapisM View Post
    The old adage "Propellers Move Boats, Engines Just Turn Them" always make me smile a bit, 'cause it's often used as if most people would think to run their mobos with no props.

    I'd be tempted to argue that neither engines nor props do anything at all.
    It's the helmsman mind what REALLY moves the boat: his/her hands, the throttles, fuel, engines, shafts and eventually propellers are only there to translate his/her wishes...
    Ultimately it's energy from the Sun that moves the boat.
    But turning up the Sun a few degrees to compensate for end-of-season fouling might not be the best approach.

  5. #5
    Join Date
    May 2001
    Location
    London/Antibes
    Posts
    21,382

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by MapisM View Post
    The old adage "Propellers Move Boats, Engines Just Turn Them" always make me smile a bit, 'cause it's often used as if most people would think to run their mobos with no props.
    Me too. It's an overused phrase and is a bit mickey mouse. No worries.

    The bit I've quoted below is good though, and right on the mark. I have Cat C32 @1622hp and one of my mechanics implored me to run the boat harder to do more running@70% load factor. It's good for the engine and avoids bore glazing, he said. I asked him if he gave same advice to owners of the same engine in 800hp - 1925 hp versions. "Yes of course" he said. I tried to explain what is nicely put in the bit quoted below, but he didn't get it. Jeeze, there is so much carp talked about this 70%/bore glazing topic so it is nice to see this author getting it correct.

    Quote: You have a new 50,000 lb 45 Ft “East Coaster” with a new QSM11 Cummins rated at 450HP at 2100 RPM and the vessel uses 10 GPH at 12 K’s at 1600 RPM & 800 RPM propeller speed (2:1 gear ratio) – A tad better than 1:1. You are one Happy Camper because you got all the performance you wanted and at 12 K’s, your engine is only loading to 45%, just loafing along.

    Now, to make my point, I go down to the vessel and reprogram the ECM for a 300HP at 1800 QSM Fuel Curve Rating. The owner takes the boat out the next day and brings it up to 1800 RPM and looks at his gauges. “WOW” he says – All of a sudden he sees a 70+% load on the engine yet the RPM, GPH & vessel speed is exactly the same. What happened? Actually nothing that matters has happened at all. We are still extracting the EXACT same amount of power from the engine – the “circumstances” for rotating that prop at that prop RPM has not changed so the vessel is performing at that RPM exactly as before. What has changed is, now we are asking the engine to deliver 70+ % of it’s AVAILABLE POWER. So the load % on the engine in relation to that AVAILABLE POWER is much higher. Does that mean we are adding more “wear & tear” to the engine and the engine may not last as long running it at 70+% load versus well under 50% ??

  6. #6
    Join Date
    Mar 2002
    Posts
    14,359

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by jfm View Post
    Jeeze, there is so much carp talked about this 70%/bore glazing topic
    Agreed wholeheartedly.
    20 years ago, my old lady was built with a massively oversized powerplant (2x350hp Cat 3116), because that's what her first owner asked, and the builder had zero interest to convince him that he could have spent less for the much smaller engines he used to install on similar size boats.
    As a result, the boat spent 99% of her life cruising at 8kts and running at 1600rpm or so (out of 2800 max), which according to Cat prop demand curves means 65hp out of 350 max.
    Not only that, but my own calculations based on actual fuel burn show that those curves actually overestimate the prop demand on that particular hull, which doesn't need more than 40hp each side, if that.
    Now, after 20 years of this treatment, all cylinders should be bore glazed to death, according to many folks.
    And they could well be, for all I know (never removed the injectors - let alone heads - to have a look inside).
    What I know for sure is that the engines run as well as they did on the first seatrial I made back in 2000, they never missed a beat, and they smoke even less than many much more modern electronically controlled engines, with zero oil consumption.
    If that's the result of running engines at ridiculously low load factors, I can live with that.

    Incidentally, since by running the DP at D speed her engines would be spinning at even lower rpm/load (8 kts being just a tad above idle), I thought to ask the chief engineer of the MAN distributor whether this could be problematic, and he confirmed me in written that MAN does NOT give any restriction to how long the engines can run at or just above idle.
    He just suggested to bring them up to "turbo whining noise" for 10 mins or so every few hours.
    Which btw means just 1500rpm or so, still well below 70% load...

    That said, as I said in a previous thread, the real challenge with properly performing P hulls is to resist the temptation to go faster...
    ...Particularly after having experienced the smooth, quiet and stable cruising of stabilized D boats!

  7. #7
    Join Date
    Aug 2012
    Posts
    3,287

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by jfm View Post
    Me too. It's an overused phrase and is a bit mickey mouse. No worries.

    The bit I've quoted below is good though, and right on the mark. I have Cat C32 @1622hp and one of my mechanics implored me to run the boat harder to do more running@70% load factor. It's good for the engine and avoids bore glazing, he said. I asked him if he gave same advice to owners of the same engine in 800hp - 1925 hp versions. "Yes of course" he said. I tried to explain what is nicely put in the bit quoted below, but he didn't get it. Jeeze, there is so much carp talked about this 70%/bore glazing topic so it is nice to see this author getting it correct.

    Quote: You have a new 50,000 lb 45 Ft “East Coaster” with a new QSM11 Cummins rated at 450HP at 2100 RPM and the vessel uses 10 GPH at 12 K’s at 1600 RPM & 800 RPM propeller speed (2:1 gear ratio) – A tad better than 1:1. You are one Happy Camper because you got all the performance you wanted and at 12 K’s, your engine is only loading to 45%, just loafing along.

    Now, to make my point, I go down to the vessel and reprogram the ECM for a 300HP at 1800 QSM Fuel Curve Rating. The owner takes the boat out the next day and brings it up to 1800 RPM and looks at his gauges. “WOW” he says – All of a sudden he sees a 70+% load on the engine yet the RPM, GPH & vessel speed is exactly the same. What happened? Actually nothing that matters has happened at all. We are still extracting the EXACT same amount of power from the engine – the “circumstances” for rotating that prop at that prop RPM has not changed so the vessel is performing at that RPM exactly as before. What has changed is, now we are asking the engine to deliver 70+ % of it’s AVAILABLE POWER. So the load % on the engine in relation to that AVAILABLE POWER is much higher. Does that mean we are adding more “wear & tear” to the engine and the engine may not last as long running it at 70+% load versus well under 50% ??
    Afaik its 70% loading of the continuous duty cycle 24/7 for your engine at its specific revs.

    Eg: The Cummins b series is rated at 425hp in the swift trawler 34, but at 200hp continuous duty. the bigger c series at 625hp in some planing boats, but at only 300hp continuous.

  8. #8
    Join Date
    Apr 2011
    Location
    Boat- SoF
    Posts
    2,912

    Default Re: A few moments to spare from earning money to pay for the boat ?

    He asks this ----

    "Does that mean we are adding more “wear & tear” to the engine and the engine may not last as long running it at 70+% load versus well under 50% ??"

    Interesting to see oil analysis of both engines the 30 % and 70 % + every 200 hrs for the 1st 2 K .

    I'd rarther be running the one as a keeper - long term with the 70 % load .
    Reason is based on the better ring fit minimising harmful products ( through lower combustion temps ) contaminating the oil .
    The reason you change marine diesel oil frequently is not cos it's lost its lub power ,viscosity etc. It's to dilute flush out harmful products of combustion that get past the rings , until it's reached optimal operating cylinder temps
    The cylinder pressures and temps are waaaay higher in a diesel than a typical petrol ,so the rings like everything else at the sharp end expand a lot more than in a petrol .They are relatively loose when cold or not @ designed operating temps .
    Petrol is a volatile air fuel mix and relatively clean burn at lower cylinder temps / pressure so low revs or tick over ,because the temp range is small the rings fit , not much stuff in the chamber gets into the oil -- that's why when you dip a petrol the oil is still a nice golden honey colour .
    In a diesel it's black straight away after the 1 st few start ups cost the rings are loose ,because of the wider range of temps they have to work in .
    I fact modern diesel oils ( that's the diff between petrol / diesel oil ) have active detergents added to in theory pick up these toxic combustion products that escape through the rings from the chamber at low temps.
    So really it's down to how effective your oil can cope with the extra contamination from lower speed - read loose fitting rings if run a big Hp marine diesel out of its let me call it comfort zone. 80 %
    80 % load being the general consensus for longevity - I picked up from various American marine Diesel engine forums - happy to share here
    Not worried about bore glazing that's a none issue in my mind in a leisure boat .

    @ mapisM re MAN ticking over , the EDC variant manual specifically says in more than one occasion to avoid tick over for longer than 5 mins ,infact it reccomends turn off .
    This is not quite the same as engaging first click or running @ D .
    I know you have not got EGT , or load gauges , but it's amazing seeing these two delta,s change ,how fast they change too particularly coming off the plane to tick over D entering a marina .560 @ 1800 rpm - 80 % load ...... to 250 @ 600 rpm -20 % load 1 st click 8 knots D speed if you like ........ to 125 @ tick over in N .zero % load in the berth .
    EGT literary drops / moves with the " stick s " so does load
    Also the cooling system is set up for planning , 86 in the summer 84 winter planning drops to 81 summer and last week 79 ,by the time we at the berth .
    However I find 825 rpm gives 50% load and just over 9 knots - that's my D speed ,but EGT , 325 --- 350 ish --- bit low
    So in effect I,am extra comtaminting my oil, based on the fact the ring fit is not as good as it would be @ 560 ?

    Does that bother me ?
    Well having thought long n hard about it and read around the subject --- let's just say I have set my cruise speed on the load gauge this season .... no prizes for guessing folks 80 %

    MapishM if you are serious about running around at D ( low loads ) it may help to NOT bother cleaning
    the props during the season as again it's amazing what prop fouling does to load .

  9. #9
    Join Date
    Apr 2011
    Location
    Boat- SoF
    Posts
    2,912

    Default Re: A few moments to spare from earning money to pay for the boat ?

    deleted as double post -- took too long typing ^^^
    Last edited by Portofino; 12-10-17 at 04:56.

  10. #10
    Join Date
    Aug 2012
    Posts
    3,287

    Default Re: A few moments to spare from earning money to pay for the boat ?

    Quote Originally Posted by Portofino View Post
    He asks this ----

    "Does that mean we are adding more “wear & tear” to the engine and the engine may not last as long running it at 70+% load versus well under 50% ??"

    Interesting to see oil analysis of both engines the 30 % and 70 % + every 200 hrs for the 1st 2 K .

    I'd rarther be running the one as a keeper - long term with the 70 % load .
    Reason is based on the better ring fit minimising harmful products ( through lower combustion temps ) contaminating the oil .
    The reason you change marine diesel oil frequently is not cos it's lost its lub power ,viscosity etc. It's to dilute flush out harmful products of combustion that get past the rings , until it's reached optimal operating cylinder temps
    The cylinder pressures and temps are waaaay higher in a diesel than a typical petrol ,so the rings like everything else at the sharp end expand a lot more than in a petrol .They are relatively loose when cold or not @ designed operating temps .
    Petrol is a volatile air fuel mix and relatively clean burn at lower cylinder temps / pressure so low revs or tick over ,because the temp range is small the rings fit , not much stuff in the chamber gets into the oil -- that's why when you dip a petrol the oil is still a nice golden honey colour .
    In a diesel it's black straight away after the 1 st few start ups cost the rings are loose ,because of the wider range of temps they have to work in .
    I fact modern diesel oils ( that's the diff between petrol / diesel oil ) have active detergents added to in theory pick up these toxic combustion products that escape through the rings from the chamber at low temps.
    So really it's down to how effective your oil can cope with the extra contamination from lower speed - read loose fitting rings if run a big Hp marine diesel out of its let me call it comfort zone. 80 %
    80 % load being the general consensus for longevity - I picked up from various American marine Diesel engine forums - happy to share here
    Not worried about bore glazing that's a none issue in my mind in a leisure boat .

    @ mapisM re MAN ticking over , the EDC variant manual specifically says in more than one occasion to avoid tick over for longer than 5 mins ,infact it reccomends turn off .
    This is not quite the same as engaging first click or running @ D .
    I know you have not got EGT , or load gauges , but it's amazing seeing these two delta,s change ,how fast they change too particularly coming off the plane to tick over D entering a marina .560 @ 1800 rpm - 80 % load ...... to 250 @ 600 rpm -20 % load 1 st click 8 knots D speed if you like ........ to 125 @ tick over in N .zero % load in the berth .
    EGT literary drops / moves with the " stick s " so does load
    Also the cooling system is set up for planning , 86 in the summer 84 winter planning drops to 81 summer and last week 79 ,by the time we at the berth .
    However I find 825 rpm gives 50% load and just over 9 knots - that's my D speed ,but EGT , 325 --- 350 ish --- bit low
    So in effect I,am extra comtaminting my oil, based on the fact the ring fit is not as good as it would be @ 560 ?

    Does that bother me ?
    Well having thought long n hard about it and read around the subject --- let's just say I have set my cruise speed on the load gauge this season .... no prizes for guessing folks 80 %

    MapishM if you are serious about running around at D ( low loads ) it may help to NOT bother cleaning
    the props during the season as again it's amazing what prop fouling does to load .
    On a new factory block they hone the shiny inside of the cyclinders with cross-hatch groves; in the old days it was done with rough emery paper, nowadays they use a special gizmo. The purpose of the crosshatch honed surface is to retain oil to keep the rings lubricated as they slide up and down the bores.

    Slow running produces lots of soot which cloggs up the honed cylinder surface.....no oil retained in the crosshatched surface .....rings wear down....loss of compression which produces even more soot and carbon.

    This vicious cycle leads to early engine rebuild.
    Last edited by rustybarge; 12-10-17 at 10:20.

Page 1 of 5 12345 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Find Boats For Sale

to
to