Engine revs

Yealm

Yealm

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I’ve just had a new engine put in- beta 25 - in contessa 32.

It’s lovely - really pleased with it. Was wondering what revs I should be running at? It feels very comfortable at 2k, but I get a bit more speed (5-5.4kn) if I go up to 2.3 - 2.5k. Is there a sensible upper limit for cruising ? I’m now on about 60 hours.

Secondly, I seem to be using 1.4 litres/hour - is that typical?

Thirdly, I’m wondering does motor-sailing strain the engine at all? Eg if the sails add an extra knot, does the extra speed through the water strain the prop/engine rotation? And similar type of question- when I’m sailing only, I put the throttle in reverse position (feathering prop) to stop rotation - does this cause the engine any damage?

Many thnaks - sorry for novice engine questions!
 
You should know from information given what the maximum revs should be. In my case it is 3400, and the engine was run up to ths before I took possession. In my Volvo they recommend a cruising speed of 500 rpm below maximum, ie 2900 which is quite high. I also understand that you should not 'run in' a marine diesel, so I would expect that you should be thinking about running at something like 2500. I normally cruise at about this when not sailing but have done 2700 for 24 hours.
 
johnalison said:
You should know from information given what the maximum revs should be. In my case it is 3400, and the engine was run up to ths before I took possession. In my Volvo they recommend a cruising speed of 500 rpm below maximum, ie 2900 which is quite high. I also understand that you should not 'run in' a marine diesel, so I would expect that you should be thinking about running at something like 2500. I normally cruise at about this when not sailing but have done 2700 for 24 hours.
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Just checked manual- the only reference I could find to revs was in a table - max torque @ 2.4k revs. Is that relevant to what typical/max revs I should be using?
 
Yealm said:
Just checked manual- the only reference I could find to revs was in a table - max torque @ 2.4k revs. Is that relevant to what typical/max revs I should be using?
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Not directly, but you will need an engineer to tell you what the relationship might be.

As for motor-sailing, the trouble is that it is not straining the engine enough, so it will take longer to reach working temperature and be working at lower than ideal revs. There is a similar problem when you are forced to motor slowly, as when going through the Dutch canals sometimes. An additional problem when motor-sailing can be that the angle of heel may be more than the engine will allow to allow proper lubrication. In my case the maximum angle allowed is 15 degrees, so there are times when it is worth taking in a precautionary reef. As for whether to lock the prop by putting the gear into reverse, this is widely practised, including by me, but it appears that it doesn't apply to all engines, so you need to refer to you manual or look for one of many threads on the subject in these forums.
 
johnalison said:
Not directly, but you will need an engineer to tell you what the relationship might be.

As for motor-sailing, the trouble is that it is not straining the engine enough, so it will take longer to reach working temperature and be working at lower than ideal revs. There is a similar problem when you are forced to motor slowly, as when going through the Dutch canals sometimes. An additional problem when motor-sailing can be that the angle of heel may be more than the engine will allow to allow proper lubrication. In my case the maximum angle allowed is 15 degrees, so there are times when it is worth taking in a precautionary reef. As for whether to lock the prop by putting the gear into reverse, this is widely practised, including by me, but it appears that it doesn't apply to all engines, so you need to refer to you manual or look for one of many threads on the subject in these forums.
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Thnaks - that’s amazing advice! Will chat to the engineer :)
 
The general advice is to run the engine continuously at half its rated output which on your engine equates to approx 70% of maximum revs which is around 2400 rpm. You should also be able to reach at least 3400 and hull speed in flat water. The figures you quote show your prop is about right, and cruising at the higher revs (2300-2400) is spot on. suggest you also from time to time on every passage run for a short period at full revs. These engines do not like low load running so avoid motorsailing where you are boosting speed under sail as you are not loading the engine properly.

Your fuel consumption is also spot on.
 
Tranona said:
The general advice is to run the engine continuously at half its rated output which on your engine equates to approx 70% of maximum revs which is around 2400 rpm. You should also be able to reach at least 3400 and hull speed in flat water. The figures you quote show your prop is about right, and cruising at the higher revs (2300-2400) is spot on. suggest you also from time to time on every passage run for a short period at full revs. These engines do not like low load running so avoid motorsailing where you are boosting speed under sail as you are not loading the engine properly.

Your fuel consumption is also spot on.
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Massive thnaks - and reassuring !
 
I am a fan of working diesels fairly hard - I'd regard prolonged 2,000 rpm on an engien designed to max out at maybe 3,400 or 3,600 rpm as substantially too low.

On my own engine with a max of 3,400 I avoid lengthy running much below 2,400, often running at 2,800 for hours if I want to get somewhere. Engine now 13 years old, high hours due to charter use (not sure as *****y Yanmar tacho hour counter dead, as most are) but engine runs beautifully, no smoke, starts instantly.

As a broker I see lots of boats and see lots of engines run: those whose engines have been "coddled" are the ones that smoke and are difficult to start. Especially Volvos. Almost the worst thing you can do to a yacht engine is start up, tickover ten minutes then half a mile out of harbour at low revs then turn off.
 
Yealm said:
Just checked manual- the only reference I could find to revs was in a table - max torque @ 2.4k revs. Is that relevant to what typical/max revs I should be using?
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It's worth knowing, but doesn't define how the engine should be treated. Peak torque revs (2.4k in your case) is the point at which specific fuel consumption is most economical. That doesn't mean that in a boat system it will give you greatest fuel economy, since lots of othe factors apply, but it's a guide.

Beta used to specify running-in stages before full power was asked of the engine. Their commissioning instructions also told you to run the engine flat-out to check the installation and prop suitability. The two are obviously incompatible. Neither their handbooks or installation instructions now mention a running-in regime.

Your practice seems in every way appropriate. As said, it is bad practice to consistently run a marine diesel under very light load, particulalry a new one. But the way you've been using the engine is fine. If you do find yourself for some reason running yours very lightly for extended periods, just give it an occasional ten minutes hard running (aka an "Italian tune"). When started from cold, don't leave it idling while everyone faffs about: it's long-term health will be better if it's put under load as soon as possible and warms up quickly. Most engine wear occurs when it's cold. (This doesn't mean you should thrash it as soon as the key's turned, though.)

As to heel angles when motorsailing, your installation handbook probably tells you 25 degrees either way is OK.
 
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I had always thought that you should cruise at 75% of max power, in my case 16 hp, which would give 12 hp. When I look at my power graph this comes out as 2200 - 2400 revs. Also my engine sounds comfortable at these revs.
 
I fitted a Beta 25 to my Vancouver 27 seven years ago. Whether motoring or motorsailing, I typically run it at between 2200 and 3000rpm, with occasional short periods of full welly, except when in areas of restricted speed (e.g. rivers). Consumption comes out at an average of about 1.4 l/hr.

Re locking the prop by engaging gear when not in use, I do this primarily to get the feathering prop to feather.
 
Refuelled earlier today and checked the logbook since the last topping-up: 18 litres over 12 hours motoring = 1.5l/hr. This is a bit higher than my normal average as I've recently been motoring faster than usual.

Also checked revs at full-welly (underway) = 3,300rpm, so 2,600 typical motoring revs equates to just under 80% of max.
 
Replaced our Leyland 48 with a Beta 35 last winter.
The running in process was simple and was clearly described in the manual. Done 50 hrs now so the 1st service has been done. The recommendation is not to exceed 2800 rpm.
We wander along nicely at between 1800 to 2200. Hull speed is achieved, economy is around 1.5 ltrs per hour and the ammeter and voltmeter both appear happy.
 
claymore said:
Replaced our Leyland 48 with a Beta 35 last winter.
The running in process was simple and was clearly described in the manual. Done 50 hrs now so the 1st service has been done. The recommendation is not to exceed 2800 rpm.
We wander along nicely at between 1800 to 2200. Hull speed is achieved, economy is around 1.5 ltrs per hour and the ammeter and voltmeter both appear happy.
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I can't find any reference to limiting RPM in my Beta 25 manual. I assume this recommendation was from an external source, and just for the running-in period?
 
Indeed, it was the engineer at the boatyard who installed the engine. He also did the initial running in exercise and went through the various bits and pieces that he felt I needed to know such as bleeding the fuel system. This was great for me as I am no great understander of manuals.
 
jimi said:
Yikes I need a smaller engine! Volvo 2040 on 38 foot boat eats 4.5 Ltr/HR!
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Gulp! I've just done a fuel calculation for my season so far and for my 37' 9 tons generally tootling along at c. 6 knots (1650rpm) with a 2112cc engine it's 1.9l/hr - and I thought that was a lot.
I take it you tend to press on a bit?
 
Babylon said:
I can't find any reference to limiting RPM in my Beta 25 manual. I assume this recommendation was from an external source, and just for the running-in period?
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The Beta 35 is 35hp at 2800, it's the top of it's power graph.
But even so, 'hull speed' at 2200 sounds a little low. Depending on what is meant by 'hull speed'.
 
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