Russell Newbury DM2

[Martin Harris]

Hi all. Newbie here. I am in the process of buying a trad Narrowboat with a RN DM2 engine.

 

what are they like? I know they sound great, but are they ok for going up the Severn from Gloucester to Tewksbury and then on the Avon to Stratford?

And any other information would be lovely.

many thanks 

martin

[Jen-in-Wellies]

Welcome to the forum.

Do you have a beard? Do you smoke a pipe? You won't be allowed to buy it if you don't. Sorry, but them's the rules! 😀

Some more serious and knowledgable people will be along shortly to actually answer your questions.

[matty40s]

So long as you follow the flood warnings, yes, a DM2 is more than capable of enjoying every navigable canal and river that a narrowboat with a Beta or Isuzu engine can.

Theres one (58ft) in this marina that in 26 years has been along every inch of EA and CRT waters, some many times, including the Wash and Severn down to Portishead....and has also been trapped for short periods on the flooded Soar, Nene and Avon!!

Edited March 2 by matty40s

[Tony Brooks]

28 minutes ago, Martin Harris said:

Hi all. Newbie here. I am in the process of buying a trad Narrowboat with a RN DM2 engine.

 

what are they like? I know they sound great, but are they ok for going up the Severn from Gloucester to Tewksbury and then on the Avon to Stratford?

And any other information would be lovely.

many thanks 

martin

 

If the engine, gearbox reduction( if any) and the prop are well-matched to the boat then in summer you should be fine, as long as you learn to recognise when it is time, current wise, to stay tied up and wait for the current to abate. Boating on rivers is more about reading the water and good watermans ship.

[David Mack]

I have done both of those river sections and more in a boat powered by a National 2DM, which is the same engine as the RN DM2, but built under licence from the RN company. Absolutely no problem with having sufficient power.

[IanD]

A 20hp DM2 or similar will happily run all day at full power/rpm without overheating or making you go deaf, because that's what they were designed to do in working boats.

 

A modern engine like a Beta 43 is theoretically double the power at maximum rpm, but most people with any mechanical sympathy wouldn't run them this fast due to noise and vibration, anything above 2200rpm is rarely used for any length of time -- and at this speed with a matched prop it'll be putting out about 20hp... 😉 

 

(which is also why sustained 15kW is fine for electric/hybrid boats like mine, about as far as you can get from a trad with a DM2...)

[booke23]

23 minutes ago, IanD said:

A modern engine like a Beta 43 is theoretically double the power at maximum rpm, but most people with any mechanical sympathy wouldn't run them this fast due to noise and vibration, anything above 2200rpm is rarely used for any length of time -- and at this speed with a matched prop it'll be putting out about 20hp... 😉 

 

Your figures are miles off! A Beta 43 with matched prop makes 20hp at 1100rpm and about 37hp at 2200rpm. 

 

Edited March 2 by booke23

[IanD]

22 minutes ago, booke23 said:

 

Your figures are miles off! A Beta 43 with matched prop makes 20hp at 1100rpm and about 37hp at 2200rpm. 

 

 

No it doesn't, the power/torque curves are what the engine can put out on a dyno -- only the fuel consumption curve is with a prop load. Prop power absorbed (and fuel consumption, approximately...) is proportional to rpm^3, see the blue curve here -- 15kW at 2200rpm is 20hp, like I said... 😉 

 

 

Edited March 2 by IanD

[Dorlan]

We never had any problems on the Severn or the Avon with our RN DM2 powered, 70' narrowboat, when we were moored on the Avon at Tewkesbury.

Edited March 2 by Dorlan

[MtB]

The DM2 is a terrible engine, take it out!

 

I'll give you fifty quid for it, as a special favour...

 

 

[captain birdseye]

I've been up and down the Severn and Avon a few times on my boat with a DM2 in. You can fly along. Join the Russell Newbery Register, the members have a wealth of knowledge. I'll be down on thew Avon this summer as their annual get together is at Evesham.  

Happy boating, and enjoy it

[magnetman]

I ran a DM2 on a 55ft trad narrow boat for 12 yars. Most of this was cruising around the system. It was a nice unit I would not moan about it. A bit noisy but mine was in an unusual engine room which did not have a cabin behind it.

I suppose having a luxury Boat with one of these contraptions at the age of 21 and free from encumbrances was a little unusual and could lead to different experiences. 

 

If I was doing it again I'd just put a jap kubota in there with similar torque and sensible propeller. .

The RN makes a nice sound in theory but can be a nuisance. It depends what you do with the Boat. I did excessively large number of hours which tends to make the noise seem worse. 

 

I can still hear the galloping horse and visualise the following up crankshaft. 

 

Nice units and of course very traditional but I would rather a DM3 myself. 

 

There will be questions about whether it is an Altricham unit or an Essex made unit or god forbid a Vero Engineering version made in Southampton. 

 

I had an Essex unit and felt very good about it. PRM 160 the God of marine gearboxes. 

 

 

 

 

Edited March 2 by magnetman

[Mike Tee]

Mine was a Southampton made engine and never caused any problems - wish I still had it. Have a BD3 in one boat and a Petter PH2W in the other - similarly no problems but out of the 3 I’d rather have a DM2

[Martin Harris]

Thank you everyone. So it seems the DM2 will be ok 😊

 

we’ve had two boats b4, plenty of journeys to Stratford from Saul junction.

 

that was 10 years ago and never had a RN engine and so exited 😊

[booke23]

5 hours ago, IanD said:

 

No it doesn't, the power/torque curves are what the engine can put out on a dyno -- only the fuel consumption curve is with a prop load. Prop power absorbed (and fuel consumption, approximately...) is proportional to rpm^3, see the blue curve here -- 15kW at 2200rpm is 20hp, like I said... 😉 

 

 

 

Why do you say a 20hp RN engine can actually produce this power at full rpm, while a Beta 43 can't? 

[MtB]

15 minutes ago, booke23 said:

 

Why do you say a 20hp RN engine can actually produce this power at full rpm, while a Beta 43 can't? 

 

Its not that it can't, I suspect its that the Beta 43 is usually installed over-propped for comfortable quiet revs in normal cruising. Which also means it won't go up to max revs and max power. 

[booke23]

14 minutes ago, MtB said:

 

Its not that it can't, I suspect its that the Beta 43 is usually installed over-propped for comfortable quiet revs in normal cruising. Which also means it won't go up to max revs and max power. 

 

Maybe that's what he means. I have a Beta 30 with matched prop and it will only rev to it's peak torque rpm of 2600rpm.....it's still producing 24 of it's 30 horses though. 

[MtB]

48 minutes ago, booke23 said:

 

Maybe that's what he means. I have a Beta 30 with matched prop and it will only rev to it's peak torque rpm of 2600rpm.....it's still producing 24 of it's 30 horses though. 

 

No such thing as a "matched prop". Prop sizing is a balancing act of conflicting parameters. 

 

If you over-propped yours a bit more you could have lower engine revs and less noise for the same cruising speed. Cost would be even lower peak revs and power. You'd probably get better brakes as well as quieter cruising though. Depends what's most important to you.

[IanD]

18 hours ago, booke23 said:

 

Why do you say a 20hp RN engine can actually produce this power at full rpm, while a Beta 43 can't? 

 

I didn't say that. I said that a Beta 43 with a prop matched to full power (43hp at 2800rpm) will be putting out about 20hp at 2200rpm, because that's how propellers work, see posted curves. Obviously you could run it at maximum power/rpm if you wanted to but every boat I've ever been on with this engine (or similar ones) would be pretty damn noisy both inside and outside the boat if you did...

 

17 hours ago, MtB said:

 

No such thing as a "matched prop". Prop sizing is a balancing act of conflicting parameters. 

 

If you over-propped yours a bit more you could have lower engine revs and less noise for the same cruising speed. Cost would be even lower peak revs and power. You'd probably get better brakes as well as quieter cruising though. Depends what's most important to you.

 

The definition of a "matched prop" is one which absorbs the full rated power of the engine at maximum rpm (or rpm for maximum power output it if this is lower). At least, that's the definition that engine suppliers and marine engineering uses... 😉 

 

As you say, many boats are "overpropped" -- meaning, bigger pitch or diameter than a "matched" one -- so the boat is kept quieter by running at lower rpm for a given power level. So long as this isn't overdone not much top end power is lost, and even less off maximum boat speed.

Edited March 3 by IanD

[Martin Harris]

Thank you so much everyone 😃