Diesel Engines

[wooster]

Hi all,

I'm a bit confused. I keep reading online that

1. Marine inboard diesels last up to around 8,000 hours - I'm imagining an ex-hire would easily run this up in 8 years. However, I know of plenty of boats whose engines are way, way older than this.

2. Older diesels like BMC or Perkins can be continually rebuilt so that very often they last for decades but this is not true for modern diesels, the likes of Nanni. I don't really undesrstand why this should be true. Is it bogus?

3. Engines that are not used frequently eg as liveaboards for a few years are likely to be in worse condition than those used daily for reasonable running times ( ie enough to get them warmed up) This makes sense I guess.

The above would lead me to believe that buying an ex-hire boat with say a 10 year old Nanni would be a poorer bet than buying an old BMC diesel of 30 years old. Also, it would be better to avoid a privately owned boat that has been used only occasionally in favour of an ex-fleet example which has had a hard working life but been well-serviced unless it was a Nanni in which case the engine would have to be less than 8 years old.

Is this actually likely to be  true? Surely it is possible to rebuild modern Nannis etc just as easily as the old BMCs etc  so this idea that modern diesels aren't as long-lasting as the old ones is not correct.

 

 

[Vaughan]

1/. An average season's hire use is around 700 hours.  With the Perkins, yards would try to rebuild them every 7 years in rotation.  The important thing with the older engines is regular oil changing, especially the Perkins.  In this case an ex hire boat engine can perhaps be trusted better than a private one but that is only a generalisation.

2/. The Nanni (and Beta) can be re-built and I have done so but it is not economical as the parts would cost more than an exchange engine.  Exchange units are available from Nanni.  These engines do last for a very long time though, if you change the oil regularly.  15,000 hours is no problem, it seems!

3/. This can only be a generalisation as it depends how the owner has looked after it.  It is true that running in neutral to charge batteries without a load on the engine, can glaze the cylinder bores.  This is no problem on a Perkins, we have found.

There is no hard and fast rule for this.  You have to look at each individual boat and consider its history.  Buying an ex hire boat from a reputable yard (dare I mention Stalham?) is a good bet as the engine has been maintained and they will also offer a fair and comprehensive after - sales service.

[RumPunch]

I looked at this and my initial thought was 'only 8000 hours' my car's done 260000 miles. 

Then I did some sums, and depending on what I called my average speed was looking at 5 to 8 thousand hours.

Kind of puts it into perspective 

 

[BroadAmbition]

I was informed that our Beta which we bought brand new in 07,  if properly maintained should be good for a whopping 30’000 hours, Really?
 

After fifteen years running  and approaching 4’000 Hrs internally still as good as new. Takes an age for new oil to become coloured enough to see it on dipstick easily. Under rocker cover it’s still shiny bright with no black build up or discolouration. Start up and cold running, there is no white / black smoke ever. It achieves maximum rpm whenever asked to do so and will stay within heat limits even when flat out all the way over Breydon. 
 

Servicing has been meticulously carried out by just one ‘engineer’ from new - Me!  I go beyond the standard of course. Every major service I use flushing oil (not the additive) and apply ZX1 

This Beta will outlast us - he says optimistically 

Griff

[MargeandParge]

We have only heard and are totally unqualified to comment. An old Gardener engine in a bus would burn about half a gallon of oil every day of its life new or old had to be changed very regularly because while that engine was a-warming and swelling with the heat all the carbon twas being created and getting past dem piston rings and amixing up wit lube oil sludge up de old sump. The early Perkies  used to be pretty good at it.

Along comes yer new fangled stuff (kids can mess up an oil changers livin.)  Tighter tolerance's less movement from hot to cold, better filters,  thinner oil so it was where it should  be quicker and running  at the proper viscosity straight away and ding dong 200hrs between oil changes. A lot of hire yards only change the oil once a year in a modern engine as Vaughan says 700 to possibly 1000hrs.

Just our opinion

Regards Marge and Parge

[Vaughan]

3 minutes ago, MargeandParge said:

We have only heard and are totally unqualified to comment. An old Gardener engine in a bus would burn about half a gallon of oil every day of its life new or old had to be changed very regularly because while that engine was a-warming and swelling with the heat all the carbon twas being created and getting past dem piston rings and amixing up wit lube oil sludge up de old sump. The early Perkies  used to be pretty good at it.

Along comes yer new fangled stuff (kids can mess up an oil changers livin.)  Tighter tolerance's less movement from hot to cold, better filters,  thinner oil so it was where it should  be quicker and running  at the proper viscosity straight away and ding dong 200hrs between oil changes. A lot of hire yards only change the oil once a year in a modern engine as Vaughn says 700 to possibly 1000hrs.

Beautifully put!  And all true!

I would just say that the Perky 4108 should have an oil change every 100 hours, as per the manual.  150 hours will do, but no more, or they will sludge up.  I have seen them with so much black sludge around the rocker shaft that when you take the cover off, the shape of it remains there in the sludge, just like a jelly mould!  If you then turn the engine over on the starter, the jelly wobbles about as the rocker arms move up and down in it!

[WherryNice]

7 minutes ago, Vaughan said:

Beautifully put!  And all true!

I would just say that the Perky 4108 should have an oil change every 100 hours, as per the manual.  150 hours will do, but no more, or they will sludge up.  I have seen them with so much black sludge around the rocker shaft that when you take the cover off, the shape of it remains there in the sludge, just like a jelly mould!  If you then turn the engine over on the starter, the jelly wobbles about as the rocker arms move up and down in it!

I had an old Ford Fiesta that was just like that when I went to adjust the valve clearances, took ages to scrape, hoover and wash it all out followed by an oil change every month for quite a few months with the cheapest possible oil to clean it out. It lived on though, for quite a while:)

[wooster]

I'm a mechanical illiterate so it was possibly a naive question however, thank you all for your thought - provoking replies. I started trying to educate myself via google and ended up with more questions than answers

I also started to wonder. How many horsepower do you need for the Broads. My boat has twin engines and they are rated at 50HP apiece (if I am right) they barely go above idling for 90% of the time. I'm sure this isn't good for them but that's what they do.  IIRC when I had a share in Lightning  ( a 42 ft cruiser ) it's engine was much less powerful. I seem to have an idea that it's pretty average for 42ft boats to have 40hp diesels in them and so I'm way overpowered. I have two questions from this.

1 what is the ideal size engine for a 42 ft boat. This might be another simplistic question so apologies if so.

2. is idling diesels constantly a bad thing. I'm sure I have had this disxussion before but would like to hear current hought on the subject.

Thank you for my education

[Vaughan]

1/. This depends on the hull, and what you want to use it for.  Broads cruisers are displacement hulls, which will not lift out of the water and so will not go faster than their hull speed.  Broad Ambition, for example, has perfectly adequate power with a relatively small engine and even goes to sea on occasions.  If you want your boat for towing, then you need a more powerful engine.

2/. Yes, in general, it is a bad thing, especially if they have turbos.  On the Thames I have seen big twin engined Brooms that moor in Penton Hook marina and hardly ever leave.  They venture out once a year to go upriver for Henley Regatta and the whole of Penton Hook lock disappears in a cloud of white smoke!

[Jbx5]

Don’t mention the white smoke Vaughan ! Big twin engined 1970s Broom with 3ft of exhaust pipe either  side moored just behind us last week at Bramerton literally filled our aft cabin and surrounding area with smoke, you couldn’t see anything  Good job there’s no immersion tests on boats! (Or should there be as these things would have no chance of passing).

John

[BroadAmbition]

 immersion tests

Ha Ha - Love it - Immersion tests?

Griff

[Smoggy]

My engines are turbo'd and after a spell of river speeds the first throttle up produces huge clouds of blue smoke, the oil seal in a turbo is a piston ring type affair and needs a bit of pressure to seal it so when the turbo isn't spooled up oil seeps past into the compressor side and collects till the first time it's run hard enough to suck it through then the fog billows for a few seconds then clears, at river speeds mine puffs smoke worse when passing moorings as I drop the rpm right down, once back up to 1200 rpm it's better, never seems to use much oil though but it only takes a tiny amount to produce a lot of smoke.

My old volvos are renowned for grey/white smoke on cold startup but they were known for it from new, I think there were a few design tweaks on the later 41's that reduced it.

I like to get out to sea for a good run when I can or a thrash across breydon if the weather's iffy.

As for immersion tests, last time mine was immersed it floated just fine.

[Jbx5]

Did you like that Charlie 

these new glasses are  really good 😂😂

 

[Cheesey69]

Diesels liked to be worked hard and if not generally glaze ( fill in) the micro valleys and ridges of the piston bore that help form an oil seal on the piston rings. 
Once glazed smoke, oil consumption and harder starting follows. Can’t fix it without a head off glaze busting. 
so an engine on the smaller side working hard is better than one this having it easy. 
 

[annv]

Hi Wooster you cant compare diesel car engines to boat engines.  boat engines are slower userly max RPM.2800rpm cars are 6,000 rpm with constant changes in speed, and all year running ie cold winter tick over in traffic. a diesel that is charging battery's should be at a speed in that the engine doesn't shake often 1,000rpm. regular oil changes with good quality oil and a filter at least once a year before lay up are essential. John

[wooster]

Thank you once again. I didn't know about hull speed. Out of curiousity what hp does Broad Ambition's engine have, and  what would an average broads cruiser's approximate hull speed be, perhaps using, as an example Lightning, which, I believe, is a 42 ft Broom Commodore?

Sorry if I seem like an annoying student here 

[BroadAmbition]

Originally when R641 Broad Ambition was Star Supreme 1, then Superb Heart, then Superb Gem then Ivy Lady she was fitted with a 34hp Perkins 4108 running through a Borg Warner 2;1 reduction G/box driving a 3 blade 16" propeller

She still has the original G/box and propshaft

We installed a brand new Beta Marine 50hp along with a four blade prop in 07

Griff

[BroadAmbition]

[grendel]

 

Hull Speed Formula

Theoretical displacement hull speed is calculated by the formula: velocity in knots = 1.35 x the square root of the waterline length in feet.

[grendel]

so lightning at 42 foot (say 40 foot at the water line)

√( 40 )   ×   1.35= 1.35 x 6.325 =8.54 knots = 9.83 mph

water rail 26 ft

√( 26 )   ×   1.35 = 1.35 x 5.1 = 6.9 knots = 7.94 mph

although with just a 19hp engine water rail really tops out about 7mph.

this shows that a large engine is not necessary to reach displacement speed, but for example take Broad Ambition above, the 4 blade prop and 50hp engine do give excellent manouverability.

[NeilB]

Mine has a slightly sorry for itself and oily 4108, it's only making around 7.5mph and 2,600 rpm but I think it's still restricted from it's hire boat days.  I've not actually checked as 7.5mph is plenty but now the thought is in my head I'll have to take a look now!  

The prop is buggered but as they took a similar sized chunk out of each blade there's virtually no vibration!

I ordered a new engine yesterday, just awaiting a delivery date so we'll see how she goes with 50hp and a 4 blade prop.  Anyone know what an Alphacraft 42 Centre cockpit weighs?  Surveyor said 6,500 KG and I might try asking Herbert Woods as they have some in hire still and use a crane for lifting out.

Need the info for my prop calculation.

 

[Vaughan]

7 hours ago, BroadAmbition said:

It's worth looking at some of the other Broads features which can be seen clearly here. 

The hull rises gently up almost to the waterline at the stern, which greatly reduces the stern wave. That long, prominent keel is what makes her so easy to steer and keeps her in a straight line, along with the very large rudder which means she can still be steered easily when drifting in neutral.

See how the long keel is dead flat on the bottom, to allow the  boat to be hauled up a slipway on "greasy ways". That hole in the metal, just where the skeg joins the keel, is called a snore hole, where a winch cable is attached to a pin, for hauling her down the slip when launching. There wlll be another one at the bottom of the stem, for hauling her out.

And look at that shallow draft! Less than 2'  6", I would guess.

[Vaughan]

4 minutes ago, NeilB said:

Surveyor said 6,500 KG

Might be, but I would allow for 10 metric tonnes, to be safe.

[Smoggy]

It's not just how much hp to reach Hull speed but how much hp to stop it from hull speed in a hurry, the later being greater. 

[BroadAmbition]

There is indeed another snore hole at the bottom of the stem.  They were both used in anger when slipping at LBBY a few years back

The Rudder is not the original one.  It had a slightly smaller trailing edge and was not raked up to match the sweep of the hull, made of cast iron with side ribs and also was a 'Top Hanger' 

I altered the top rake, extended the trailing edge by 2" fitted 2 x bronze washers underneath the blade so the weight is now on the bottom.  Made of S/steel it is both lighter and stronger. It improved handling no end, is a breeze when tight manoeuvring and going astern.  4 x blades with 50hp means stopping in a hurry is now easily achieved too.

Drawbacks? - We keep the bowden cable well greased along with the rudder pin to reduce friction as much as possible - We have overdone it!  The prop wash now turns the helm ever so slightly, whilst underway.  This is arrested cured by a friction thumb  k n o b  at the helm that is backed off prior to berthing manoeuvres.  This enables you to 'Set' the helm and won't turn when hands free, makes for easy cruising on the straight reaches of the rivers

Griff