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Replacement engine HP size - advice pls!


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3 hours ago, Tony Brooks said:

How about an ex ships lifeboat Bukh DV20 or DV24. They tend to be low hours and heat exchanger units are available but direct cooled ones convert to skin tank easily enough. Usually low hours. The downside is that work will be required to fit it but I doubt any more than for the Vetus and like many direct injection engines my DV36 tended to smoke on idle and under low speed light loads.   I suspect the Petter is also direct injection so may also tend to smoke at low speed and power in good condition.

 

I you used @RLWP (MES Midlands) to overhaul your engine he may well do the measurements and then advise/discuss with you what needs to be done and this may make a perfectly adequate job less costly. As long as your engine starts well from cold and has good hot at idle oil pressure I have seen nothing in your first post that suggests it needs and overhaul. Of course, we don't have all the advice you may have been given by "experts" but we don't know how good that advice is.

 

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Just now, ditchcrawler said:

 

 

I know you posted that which is why I added (MES Midlands) to show we were both talking about the same person and that person was known to the forum. I thought giving the @RLWP link would allow the OP to send a PM via the forum.

  • Greenie 1
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The comments about HP not being the only measurement for comparison are borne out with my engine, a Perkins 4108M, which is factory limited to 2,100 rpm and only rated at 28 bhp.

It has plenty of power at 11-1200 rpm to propel a 57ft boat, and on several occasions, has towed similar sized craft without having to increase the revs noticeably. 

 

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33 minutes ago, Ex Brummie said:

The comments about HP not being the only measurement for comparison are borne out with my engine, a Perkins 4108M, which is factory limited to 2,100 rpm and only rated at 28 bhp.

It has plenty of power at 11-1200 rpm to propel a 57ft boat, and on several occasions, has towed similar sized craft without having to increase the revs noticeably. 

 

 

Power is simply torque x speed so is a measure of both torque (the useful stuff) and how high the manufacturer dares to set the maximum revs. There are many little motorbike engines that will easily produce 50Hp but they do this only by having a very high rated speed, they would be useless in a boat.

 

..............Dave

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2 minutes ago, dmr said:

 

Power is simply torque x speed so is a measure of both torque (the useful stuff) and how high the manufacturer dares to set the maximum revs. There are many little motorbike engines that will easily produce 50Hp but they do this only by having a very high rated speed, they would be useless in a boat.

 

..............Dave

 

But because of things like air intake throttling and poorer scavenging the torque starts to fall off at higher speeds and it starts to do this while HP is still increasing  because of the higher speed, despite a lower torque. In displacement craft it the torque that takes president over HP which is why the WOT revs is usually lower than those delivering maximum HP.

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6 minutes ago, Tony Brooks said:

In displacement craft it the torque that takes president over HP which is why the WOT revs is usually lower than those delivering maximum HP.

 

 

My WOT is at 2600rpm

 

At WOT I am getting 143hp whilst at 2000rpm I am only getting 110HP

 

At WOT I am getting just over 300Nm torque whilst at 2000 RPM I am getting max torque at 385Nm.

 

Torque is 'what we need' (and at 'low rpm').

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I note that in your second post you mention that you have had the injectors "refurbished" but you still have grey smoke.

 

So before you go any further might I suggest that you get a compression test done?

That will involve the removal of the injectors at which time you can have them checked for correct pressure settings and having the correct pintle nozzles for this engine.

 

"Grey smoke" is a subjective term, it could mean unburnt fuel or lubricating oil  blowing by the pistons and/or vallves. Having the injectors checked will confirm/eliminate unburnt fuel, the pressure test will indicate to some extent the condition of the bores.

 

A low compression pressure reading will compromise the combuustion process and cause loss of power. Yup! I'm back on about my old friend called "TORQUE". Torque is almost directly related to piston area and the pressure created by combustion. Pressure x area = force, (torque), leaky bores = loss of pressure = loss of torque. Or wot TB said. 

 

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You haven't said much about the boat and it's value. If it's an old (not historic) boat it maybe not worth spending much money on refurbishing or changing your engine. If you can't do the work yourself your are likely to end up with a large bill one way or other from a boatyard. The Petter is an old engine and unless it is in a show engine room probably doesn't add much value to the boat when you resell it. Most old boats end up as CCers in London and the engine is the last thing people worry about as long as it works. Get a diesel engineer to look at the engine. If it is just worn it may go on for many years providing you maintain it. Remember it's bound to smoke and leak oil. I remember a young lady who ended up spending nearly 60K on a Springer, including changing the engine that was OK and ending up with a boat worth only 20K

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35 minutes ago, Alan de Enfield said:

 

 

My WOT is at 2600rpm

 

At WOT I am getting 143hp whilst at 2000rpm I am only getting 110HP

 

At WOT I am getting just over 300Nm torque whilst at 2000 RPM I am getting max torque at 385Nm.

 

Torque is 'what we need' (and at 'low rpm').

Unless you've got a variable pitch prop, this can't be correct.

 

If your prop is absorbing 143hp/300Nm at 2600rpm WOT, it will only absorb about 65hp/178Nm at 2000rpm, because that's how props work -- assuming absorbed power is rpm^3, which is confirmed by many measurements.

 

The fact that your engine is capable of producing 385Nm at 2000rpm doesn't matter a jot, because the prop won't absorb this.

 

This is why all the "it's torque at low rpm that matters, not power" talk is just wrong, any book on naval engineering will show that it's power that matters. At low rpm you need very little torque to turn the prop.

 

Yes a bigger slower prop is better than a smaller faster one, but this doesn't alter the way that prop power changes with speed, it just changes the prop efficiency.

 

A variable pitch prop changes all this and allows more engine torque/power to be used at lower rpm, but very few narrowboats have these fitted... 😉

Edited by IanD
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2 minutes ago, IanD said:

Unless you've got a variable pitch prop, this can't be correct.

 

If your prop is absorbing 143hp/300Nm at 2600rpm, it will only absorb about 65hp/178Nm at 2000rpm, because that's how props work -- assuming absorbed power is rpm^3, which is confirmed by many measurements.

 

The fact that your engine is capable of producing 385Nm at 2000rpm doesn't matter a jot, because the prop won't absorb this.

 

This is why all the "it's torque at low rpm that matters, not power" talk is just wrong, any book on naval engineering will show that it's power that matters. At low rpm you need very little torque to turn the prop.

 

Yes a bigger slower prop is better than a smaller faster one, but this doesn't alter the way that prop power changes with speed, it just changes the prop efficiency.

 

 

I'm quoting the manufacturers graphs.

The manufacturer also recommends shaft and prop size (25" at 2:1 and 33" at 3:1)

 

I actually have 22" x 18" which seem to work well enough.

At 5knts I'm doing 1500rpm at a theroretical 30hp per engine and using 5.4 litres per engine.

 

Maximum hull speeed is 8knts which is achieved at 2000RPM, so anything above that (RPM, HP or Torque) is irellevant.

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7 minutes ago, IanD said:

This is why all the "it's torque at low rpm that matters, not power" talk is just wrong, any book on naval engineering will show that it's power that matters. At low rpm you need very little torque to turn the prop.

 

Quite correct. What makes larger displacement engines appear to be more powerful is that they work over a lower range of speeds and that coupled with a larger prop improves the performance on canal boats. A small engine with a big reduction gearbox offers the same torque as a larger one for a given horsepower. Maybe it doesn't sound so nice. The Ideal solution is to have a variable speed drive if you want to load the engine at lower speeds. Otherwise the cube law propeller loading meets the power output curve at only one point when you achieve maximum power which also defines the maximum torque.

  • Greenie 1
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8 minutes ago, Alan de Enfield said:

 

 

I'm quoting the manufacturers graphs.

The manufacturer also recommends shaft and prop size (25" at 2:1 and 33" at 3:1)

 

I actually have 22" x 18" which seem to work well enough.

At 5knts I'm doing 1500rpm at a theroretical 30hp per engine and using 5.4 litres per engine.

 

Maximum hull speeed is 8knts which is achieved at 2000RPM, so anything above that (RPM, HP or Torque) is irellevant.

Yes, the manufacturer's graphs show what an engine is capable of. But with a fixed-pitch prop you can only choose one RPM at WOT -- this can be anywhere from the peak torque point (2000rpm in your case) up to peak power point (2600rpm in your case).

 

If you size the prop for WOT at 2000rpm you're not using the maximum power of the engine -- which is fine, if that's what you choose to do, it'll mean quieter and lower rpm when cruising but a lower top speed. If you size the prop for WOT at 2600rpm you'll use all the engine power and get maximum top speed, but when cruising more slowly rpm will be higher, as will noise and probably fuel consumption.

 

So overpropping -- which is what you've chosen to do -- loses some top speed, but lowers rpm/noise/fuel consumption when cruising more slowly. It's common on narrowboats for this reason.

 

None of which changes the fact that "high torque at low revs" is useless in a boat, without a variable pitch prop 😉

2 minutes ago, Mike Adams said:

Quite correct. What makes larger displacement engines appear to be more powerful is that they work over a lower range of speeds and that coupled with a larger prop improves the performance on canal boats. A small engine with a big reduction gearbox offers the same torque as a larger one for a given horsepower. Maybe it doesn't sound so nice. The Ideal solution is to have a variable speed drive if you want to load the engine at lower speeds. Otherwise the cube law propeller loading meets the power output curve at only one point when you achieve maximum power which also defines the maximum torque.

Or a variable pitch prop... 😉

 

[no I'm not seriously suggesting this is a good idea on the UK canals]

Edited by IanD
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4 minutes ago, IanD said:

Or a variable pitch prop... 😉

The best solution is to use a hydraulic drive with a variable displacement pump. I agree that a variable pitch prop wouldn't last too long.

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47 minutes ago, Mike Adams said:

You haven't said much about the boat and it's value. If it's an old (not historic) boat it maybe not worth spending much money on refurbishing or changing your engine. If you can't do the work yourself your are likely to end up with a large bill one way or other from a boatyard. The Petter is an old engine and unless it is in a show engine room probably doesn't add much value to the boat when you resell it. Most old boats end up as CCers in London and the engine is the last thing people worry about as long as it works. Get a diesel engineer to look at the engine. If it is just worn it may go on for many years providing you maintain it. Remember it's bound to smoke and leak oil. I remember a young lady who ended up spending nearly 60K on a Springer, including changing the engine that was OK and ending up with a boat worth only 20K

 

There is a lot of good sense in this post. Its one reason I think to be really helpful, rather than just answer the question the OP asks, I feel we need a lot more information or to be absolutely sure that the OP has been advised by an experienced and diligent engineer.

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30 minutes ago, Mike Adams said:

The best solution is to use a hydraulic drive with a variable displacement pump. I agree that a variable pitch prop wouldn't last too long.

Perhaps best if you have *very* deep pockets, and don't mind the higher fuel consumption because of drive losses...

 

The other reason for using them used to be a quieter boat because you can get the engine cocooned somewhere away from the steerer, but most (all?) boaters who see this as important are now going for electric/series hybrid boats which are much quieter still, and more eco-friendly. But also even *more* expensive... 😞

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1 hour ago, Mike Adams said:

You haven't said much about the boat and it's value. If it's an old (not historic) boat it maybe not worth spending much money on refurbishing or changing your engine. If you can't do the work yourself your are likely to end up with a large bill one way or other from a boatyard. The Petter is an old engine and unless it is in a show engine room probably doesn't add much value to the boat when you resell it. Most old boats end up as CCers in London and the engine is the last thing people worry about as long as it works. Get a diesel engineer to look at the engine. If it is just worn it may go on for many years providing you maintain it. Remember it's bound to smoke and leak oil. I remember a young lady who ended up spending nearly 60K on a Springer, including changing the engine that was OK and ending up with a boat worth only 20K

 

It's not an old historic boat. It's  45FT Hancock and Lane with Norsman Hull that was built in 1978. It is a CCer in London but the engine has not been working properly since I bought the boat... so I do worry about it! It has always emitted a cloud of smoke from the exhaust that changes in colour and intensity - blue, light grey or white - but mainly blue. I was recently reported to CRT by a landlubber whilst in Central London for 'gassing his flat' whilst running the engine to charge my batteries one evening, because of the blue smoke coming out of the exhaust. There is black residue collecting around the exhaust outlet on the boat exterior which I assume is from burning oil. When I top up my engine oil it disappears by the end of the day after cruising, because it is leaking oil from multiple places, including the air filter. There was also an issue with power - the boat would not increase speed despite the throttle in a high position, this has improved slightly with the injector refurbishment, and injector pump refurbishment, as one injector had not been firing for a long time. The lift pump has also been replaced as this was leaking heavily. The flooring around the engine is stained black from oil leaks over the past 42 years. The engine shakes the whole boat when running.

 

I have had 4 marine engineers look at it now, all of which have high recommendations from other boaters. 2 of which said that the injectors should solve the problem and the engine might be worth keeping as Petters were good in their day - the injectors haven't solved the problem. The most recent engineer said he could do a compression test and the engine would most likely need a full 'top refurbishment' or words to that effect, but the cost of the compression test along with the work would be about £2.5k,  and so already I'm at the price of a refurbished newer engine model, minus installation fees. Finding the survey from 1999 was the last straw as this confirmed that the exhaust has emitted a blue smoke since the engine was first put in the boat. So if it has always had problems, is an old engine that doesn't add any value to the boat, why would I throw more money at it attempting to fix something that has never run well?

 

Tbh I just want something that is reliable and runs without giving me a headache from the fumes and a lot of anxiety when cruising. The hull had high readings on it's last survey and the boat itself is sound, but I got the boat for a very low price through a family friend who was aware the engine was troublesome. So no 60k scenario here (fingers crossed)

 

Any other details needed?

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16 minutes ago, Vixen2021 said:

I was recently reported to CRT by a landlubber whilst in Central London for 'gassing his flat' whilst running the engine to charge my batteries one evening, because of the blue smoke coming out of the exhaust.

Bloody nimby - a good dose of noxious exhaust fumes and an incessant gentle roar from a nearby malfunctioning engine never spoilt anyone's evening...

 

:banghead:

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Posted (edited)
2 minutes ago, Sea Dog said:

Bloody nimby - a good dose of noxious exhaust fumes and an incessant gentle roar from a nearby malfunctioning engine never spoilt anyone's evening...

 

:banghead:

Lol. I think he’s really disheartened to realise he has to share his £1 million flat that overlooks the canal with the boats that live on it!

Edited by Vixen2021
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24 minutes ago, Vixen2021 said:

Lol. I think he’s really disheartened to realise he has to share his £1 million flat that overlooks the canal with the boats that live on it!

 

 

And it is against the law for him to 'make smoke' but boaters get away with it, - bound to be a bit 'miffed'.

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Ok Vixen, that gives more to work on.

 

Lack  of power despite injector overhaul and blue smoke tends to speak of worn pistons, rings and cylinders but there is no way a top overhaul will solve that but a compression test would rule such wear in or out. That sort of wear will also allow excess pressure in the rest of the engine and that tends to cause oil leaks so that is another thing that may confirm worn cylinders etc.  However, the breather system that is supposed to allow such pressure to escape may be blocked so needs checking. Unfortunately I don't know those specific engines so I can't help with where or how. I hope another member will be along to fill in that bit for you.

 

For information only, a "top overhaul" normally relates to just the cylinder head and valves. Unless the wear is so great parts can not be reused there is no way I can see that getting to £2500. It sounds far more like an "I don't want the job price". If I had the kit and was local so travelling expenses were low I would do a compression test for maybe £100 at London prices. I think an hour of labour should be ample.

 

The "one injector had not been firing for a long time" may well point to a cylinder with low compression but weather that is a valve (cylinder head) problem or pistons etc. I can't say remotely. The fact the engine shakes the boat about suggest it is misfiring and only running on one cylinder but again I can't tell if its valves or cylinders from here. If it is misfiring unburned fuel will be being pumped into the exhaust all the time the engine is running and that will also make smoke.

 

Now the blue smoke ever since the engine was put into the boat. It is all a question of degree and under what conditions the smoke is worst. This gets a bit technical but I will try to explain. There are two types of  diesel engine. Direct injection given best fuel consumption and easy starting but tending to smoke at low speed or indirect injection that tend not to smoke at low speed but use more fuel at higher speeds and are less easy starters. I think yours is direct injection so I am not surprised it has always smoked a bit but I am surprised it starts easily and makes enough smoke to annoy flat dwellers. That degree of smoke again suggest cylinders etc unless you have the wrong dipstick and are overfilling it with oil.

 

White and light grey smoke tends to happen when unburned fuel collects in the exhaust during starting and the vaporises off as the exhaust heats up. That normally clears after maybe 15 minutes of running at speed.

 

Taking t all together I suspect your decision to replace the engine may be correct but I have suspicions about the advice/quotes. I would also want to check the valve clearances first.

 

 

 

 

Edited by Tony Brooks
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47 minutes ago, Tony Brooks said:

Ok Vixen, that gives more to work on.

 

Lack  of power despite injector overhaul and blue smoke tends to speak of worn pistons, rings and cylinders but there is no way a top overhaul will solve that but a compression test would rule such wear in or out. That sort of wear will also allow excess pressure in the rest of the engine and that tends to cause oil leaks so that is another thing that may confirm worn cylinders etc.  However, the breather system that is supposed to allow such pressure to escape may be blocked so needs checking. Unfortunately I don't know those specific engines so I can't help with where or how. I hope another member will be along to fill in that bit for you.

 

For information only, a "top overhaul" normally relates to just the cylinder head and valves. Unless the wear is so great parts can not be reused there is no way I can see that getting to £2500. It sounds far more like an "I don't want the job price". If I had the kit and was local so travelling expenses were low I would do a compression test for maybe £100 at London prices. I think an hour of labour should be ample.

 

The "one injector had not been firing for a long time" may well point to a cylinder with low compression but weather that is a valve (cylinder head) problem or pistons etc. I can't say remotely. The fact the engine shakes the boat about suggest it is misfiring and only running on one cylinder but again I can't tell if its valves or cylinders from here. If it is misfiring unburned fuel will be being pumped into the exhaust all the time the engine is running and that will also make smoke.

 

Now the blue smoke ever since the engine was put into the boat. It is all a question of degree and under what conditions the smoke is worst. This gets a bit technical but I will try to explain. There are two types of  diesel engine. Direct injection given best fuel consumption and easy starting but tending to smoke at low speed or indirect injection that tend not to smoke at low speed but use more fuel at higher speeds and are less easy starters. I think yours is direct injection so I am not surprised it has always smoked a bit but I am surprised it starts easily and makes enough smoke to annoy flat dwellers. That degree of smoke again suggest cylinders etc unless you have the wrong dipstick and are overfilling it with oil.

 

White and light grey smoke tends to happen when unburned fuel collects in the exhaust during starting and the vaporises off as the exhaust heats up. That normally clears after maybe 15 minutes of running at speed.

 

Taking t all together I suspect your decision to replace the engine may be correct but I have suspicions about the advice/quotes. I would also want to check the valve clearances first.

 

 

 

 

Thanks Tony, that’s v helpful and also matches what Mes Midlands said to me on the phone when I called them earlier. I am waiting for a quote from them on Monday to size up what option will be the most cost effective, but this would also mean getting the boat to Leighton Buzzard or more north, which is a bit of a trek with the engine smoking like it is.

 

I suppose I fear going down the Petter refurbishment route and more problems arise afterwards. And then it seems like I’ve wasted a lot of money on nothing and also have to replace the engine after all. But I won’t know until I try. Depends on the quote they come back with tbh


There is a local engineer near where I am at the moment that I’ve heard good things about. I suppose I could ask him to do a compression test, but he doesn't specialise in older engines.

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OK so you need a replacement engine and you need someone to fit it.

1. You will probably get a much better deal/job if you can move the boat out of London to the midlands.

2. I would avoid any recon engine since this is too much of a gamble and the costs of fitting an 'old' engine are the same or more.

3. You may be able to reuse the gearbox if it is something like a prm but not otherwise.

4. Don't get a larger engine than you need 20Hp would be plenty all the time on that boat.

5. Look at something like canaline you might be able to get a deal.

6. Many people might give you suggestions of good boatyards. Give a few a ring.

7. You can probably get at least £500 for your old engine

Hope this helps. Guess at 4K for the engine and 2K to fit it.

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2 minutes ago, Vixen2021 said:

There is a local engineer near where I am at the moment that I’ve heard good things about. I suppose I could ask him to do a compression test, but he doesn't specialise in older engines.

 

Old Lister Petter are a specialist subject a 'bog-standard' spanner man will not know how they work. You need a specialst like MES, or, you will be wasting your money.

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37 minutes ago, Vixen2021 said:

Thanks Tony, that’s v helpful and also matches what Mes Midlands said to me on the phone when I called them earlier. I am waiting for a quote from them on Monday to size up what option will be the most cost effective, but this would also mean getting the boat to Leighton Buzzard or more north, which is a bit of a trek with the engine smoking like it is.

 

I suppose I fear going down the Petter refurbishment route and more problems arise afterwards. And then it seems like I’ve wasted a lot of money on nothing and also have to replace the engine after all. But I won’t know until I try. Depends on the quote they come back with tbh


There is a local engineer near where I am at the moment that I’ve heard good things about. I suppose I could ask him to do a compression test, but he doesn't specialise in older engines.

 

Richard (MES) is a proper old school engineer and I trust him to do a fair job for a fair price. I would also expect any work he does to be good for many years. On the basis of what you said I think a trip up the GU would be most likely to get the job done in the most cost-effective way.

 

One way or another you are going to have to move the boat to  somewhere the engine can be removed from the boat and hopefully you can plug a battery charger in while its away.

Edited by Tony Brooks
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If the parts are available and the engine is designed to be rebuilt ( not some modern asian item that is designed to be thrown away when worn out) it is almost always best to have the engine overhauled.

 

Changing an engine for a new type is expensive,  probably eye-wateringlyà so in congestion charge, emission charge, No Parking COVID London.

 

It is never just the engine purchase.  You are likely to need alterations to the engine bearers, the fuel pipework, the controls,  the wiring, the cooling pipework, the drive plate ( unless you buy a new gearbox and plate with the new engine), the propeller etc., etc.

 

With an overhaul, the engine comes out, it gets fixed, it goes back in.  Nothing apart from the engine and gearbox ( if that needs any work ) need be altered.  The time needed to remove and refit the engine is all you have to pay London prices for. Yes, you have to find a good mechanic, yes, you have to pay him good money and yes,  you have to cough up for the parts. 

 

The Petter PJ was a decent engine, not perhaps as good as the PH because it was more highly loaded, but it was still  well regarded in the plant world and, as you can see with your example, keeps going even when a bit tired.  It is also contemporary with the boat  and plenty powerful enough for 45ft.

 

I would want to get it rebuilt. Tom Pattle at P&S Marine at Watford knows his onions and his old feller cut his teeth on plant of that era.  He  may well be able to help, if MES are too difficult to get to.

 

N

Edited by BEngo
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