Engine size versus displacement

[Pen n Ink]

As a part of a discussion I'm in the middle of having, the horny old question of engine size has come up and I don't know the answer but I'm sure that someone will.

 

Assuming a modern engine (Beta, Shire etc) revving at oomphty thousand rpm as opposed to one of the old timers, can anyone advise on the appropriate engine size for the following, assuming that the boat should have enough power to fight (almost) the worst tidal stream it is likely to encounter on the inland waterways.

 

70' narrowboat, with a draft of 30". Originally set up for a 23" propeller. I've worked out in my thumb-in-bum calculation that the displacement will be around 28 tonnes.

 

So - what does the panel think - recommendations for engine size, gearbox, and propeller size?

[ditchcrawler]

I would suggest a proper engine and the big prop, not a modern 5000 rpm job

[Bee]

Cor, what a lot of variables. First thoughts, whatever comes along that's affordable. Second thoughts, that Beta JD3 (?) The brave option is some sort of old thumper, more easily sourced from our Dutch friends.

[NB Lola]

40-45 hp 150 prm hydraulic. We have a canaline and it's perfect for our needs, part river part canal. Our engineer loves it, easy to service and touch wood, very reliable. We idle at 700 and canal top line at 1400, rivers depends on flow and bywash but Trent can take 2000 easily. It can get to 2500 no bother.

[GUMPY]

Ok my boat is only 60ft

50hp beta driving a 19x14

On canals

Tickover is about 2mph

1200rpm is really as fast as you would want to go 3.9mph

On rivers

1500rpm is 5+mph

2000rpm is 7mph

 

What would I do? if you have a seperate engine room then a jp or similar driving a 23x19 with big blades

Failing that a Beta tug with a similar size prop.

[nicknorman]

More importantly, make sure whatever engine is installed has adequate cooling ie an adequate skin tank if it is indirect water cooled

[NB Lola]

More importantly, make sure whatever engine is installed has adequate cooling ie an adequate skin tank if it is indirect water cooled

Agreed, we had to fit a new external skin tank.

[FadeToScarlet]

72', 25 ton 3' draft.

 

Currently a Lister LPWS4, which is 40hp.

 

On a 20" prop, I think, and well overproped so it can stall if not revved when going into reverse.

 

But easily adequate power to do 11kph in deep water, and to tow with. You've just got to rev it a lot which I don't like.

[Alan de Enfield]

I currently have a 'surplus' Lister LPWS4 complete and marinised, and a reconditioned PRM 150 gearbox that I will be putting in the 'for sale' section when I get home

 

If you want to get ahead of the pack drop me a PM for more details prices etc.

[larkshall]

Someone has missed a point here. What is the power and, or torque of the power unit.? The motor in my truck for instance, max power at 1800 rpm, max economy at 1600 rpm. Max revs 3000 rpm. Which is revving the guts out of it. Same with boats really. Yes poodle around the ditches at 700rpm, screw the gonads off it at 3000rpm on rivers?. Think you need two different motors, or a multi speed gearbox

[Alan de Enfield]

Here is the Hp and Torque at various revs for the Lister LPWS engines ( 2, 3 & 4 cylinder)

 

www.listerpetter.nl/download/DAT-LPWS4-V.pdf

 

Cut & Paste it into Google to get the Pdf

Edited July 10, 2015 by Alan de Enfield

[DHutch]

Power=torque*speed , hence with the right gearbox and prop it all comes out in the way.

 

The extra dimension however is the shape of the torque curve, which is often where the newer engines fall down as they can have quite narrow 'power bands' or in other words not a very flat torque curve.

 

 

Daniel

[larkshall]

Here is the Hp and Torque at various revs for the Lister LPWS engines ( 2, 3 & 4 cylinder)

 

www.listerpetter.nl/download/DAT-LPWS4-V.pdf

Only lister petter, no real engines? Cummins, Detroit diesel etc?

[Alan de Enfield]

Only lister petter, no real engines? Cummins, Detroit diesel etc?

 

I was tempted.

 

I know a man who knows where there are dozens (maybe 100's) of Perkins 4108 engines that have been sold off by the MOD - they were used as Donkey engines to start 'real' engines.

[Dinz]

Gosh! In days gone by a fully laden managed on 1 horse power and very little 'talk'[torque]

How times have moved on.

[colinjw]

Only lister petter, no real engines? Cummins, Detroit diesel etc?

OMG. I haven't worked on Detroit Diesels for years.

Or what about EMDs then?

Another piece of brilliant American engineering. NOT!!!!

[larkshall]

Rather poor or distinctly agricultural US engineering than ours anyday. It's all AF for starters

 

 

Btw it's cummins anniversary this week think it was tuesday

[Giant]

Gosh! In days gone by a fully laden managed on 1 horse power and very little 'talk'[torque]

How times have moved on.

 

There is a rule thrown around for leisure barges of 1.5hp per tonne of displacement.

 

By that logic we should have about 100hp. We have 30hp, which is what she was built with, and she moved 100 tonnes of cargo with that setup.

 

I guess nobody ever gets in trouble for erring on the powerful side, so the recommendations creep upwards and upwards over time.

[blackrose]

As a part of a discussion I'm in the middle of having, the horny old question of engine size has come up and I don't know the answer but I'm sure that someone will.

 

I tried to get aroused by this thread but soon realised that perhaps you meant "thorny" old question...

Edited July 11, 2015 by blackrose

[blackrose]

Power=torque*speed , hence with the right gearbox and prop it all comes out in the way.

 

The extra dimension however is the shape of the torque curve, which is often where the newer engines fall down as they can have quite narrow 'power bands' or in other words not a very flat torque curve.

 

 

Daniel

The torque curve is fairly flat on my Isuzu 55.

 

I've often read on this forum that once an engine has reached maximum torque it has also achieved maximum power, hence the common trend for builders to over-prop canal boats on the basis that they will seldom be used at max torque.

 

However, my experience on rivers differs, and repitching my prop so that higher revs could be achieved (beyond what is required for maximum torque), has resulted in a lot more power from a modern engine.

 

Yes, power = torque x engine speed (rpm)，but what some people overlook is that if the torque does not drop off significantly (at rpm beyond max torque), there may still be additional power to be gained at higher revs.

Edited July 11, 2015 by blackrose

[NB Lola]

I keep my life simple cos my job is complex. My boat engine is right cos I can go past boats on tickover and everyone is smiling. I can wander along canals and not create a wash as well as see the lovely world we have. I can pop along the Trent enjoying the scenery knowing my engine is good enough to help me when I need it to, like getting into Trent lock under control and not looking like an over revving dummy- I like my engine so much I might give it a name like?

Edited July 11, 2015 by NB Lola

[Pen n Ink]

I tried to get aroused by this thread but soon realised that perhaps you meant "thorny" old question...

That well known speeling error, fat thumb, or autocorrect... I did notice afterwards but thought I'd leave it as a cross between thorny and hoary!

[Pen n Ink]

This is all illustrating why I've asked the question in the first place beautifully!

 

So to clarify, what I am asking is - with a "modern" engine as a given, fixed factor, does the fact that the boat has a third greater draft than most new hulls have a significant effect on the power required?

 

The answer I seem to be getting is that on canals most modern boats are way overpowered anyway, so - no, but that still leaves my question unanswered in respect of sufficient power to deal with a significant tidal stream. The "1.5HP per ton(ne?) rule would still only show a requirement for 42HP, but will that make sufficient headway against a (say) 7 knot current?

[NB Lola]

In my view, yes

[GUMPY]

Very very few narrowboats or widebeams will make headway against a 7knot current.

Those that say they can are probably lying.