More reflections on our prop issue.

In my view if you are not getting to maximum revs at full throttle without having block smoke in the exhaust it look to me as fuel starvation reducing the fuel flow at full throttle.

My engine is slightly over propped and I don't get maximum revs but I do get black smoke at full throttle position
 
Rogershaw said:
In my view if you are not getting to maximum revs at full throttle without having block smoke in the exhaust it look to me as fuel starvation reducing the fuel flow at full throttle.

My engine is slightly over propped and I don't get maximum revs but I do get black smoke at full throttle position
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Why can I get max revs in neutral then?

Bear in mind this is a brand new engine, with a certificate that says it achieved 3,600rpm in the factory under load.

- W
 
webcraft said:
Why can I get max revs in neutral then?

Bear in mind this is a brand new engine, with a certificate that says it achieved 3,600rpm in the factory under load.

- W
Click to expand...

Diesels only need the diesel when under load - ie it is not just the revs that dictate fuel usage. A hard motor into weather will use far more than motor sailing off the wind even with the same revs.

Did the primary fuel filter get changed?

Since you have high speed under tickover, however, the finger is pointed to the prop, I would have thought.
 
webcraft said:
Why can I get max revs in neutral then?

Bear in mind this is a brand new engine, with a certificate that says it achieved 3,600rpm in the factory under load.

- W
Click to expand...


As has been said the engine will need a higher fuel flow rate when under load to attain a set RPM

Th throttle sets the diesel governor to the desired speed which in turn controls the amount of fuel to drive the engine to that speed. If the engine is prevented from reaching that speed the excess fuel will not burn correctly and will manifested itself as black smoke.

I would look at the fuel supply system to ensure enough fuel can be supplied to the engine before looking at the prop/gearbox.
 
Since the drag should be low at tickover speed, you could assume there will be very little slip at that speed, and work out what pitch that implies.
Then see if that's consistent with how the old engine performed.
Then use one of the prop calculators to see whether that's consistent with your engine developing the power it should at the higher RPM.
 
scottie said:
I think that you should forget all the deluge of comments and go back to basics

You have got so many opinions and few facts
And too many different posts coming from different angles
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Basics to me says 6.2kts at 2000rpm says the prop is over-pitched. We should be getting 5kts at that rpm.

How I calculate the prop pitch from that seems tricky. Basically we are travelling about 24% faster than we should be, so instinct says the prop has a pitch of 8 x 1.24, or around 9.5 - 10

It is stamped 9.5, so not too far out.

Tickover in slow ahead gives 2.3kts at an indicated 650rpm, again in the ballpark for 9.5 pitch.

Other people then tell me I should only be losing 350-400 rpm, but we seem to be losing nearer 1000rpm

My thinking is, at 2500rpm we have reached hull speed at around 7 kts (LWL is nominally only 6.43m, but is increase as the boat 'squats'.

No amount of power is going to push a long-keeled heavy displacement boat any faster, so any attempt to increase the rpm and so the boat speed has to overcome the forces generated by dragging a spinning prop through the water in effect backwards. I don't know how much power is needed to spin a prop of this pitch in this condition, but it is obviously more than 16HP.

The fact that there aren't clouds of black smoke is a bit of a mystery. New engine and not running it for long enough seems a possible explanation, but what do I know? One thing I am pretty sure of is that it is unlikely there is a fuel issue, filters are new and the brand new engine produced 3600rpm under load in the factory test before being shipped to Portugal.

- W
 
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Ok but
1 crudely speaking diameter is revs and pitch is speed and your problem is lack of revs although you can compensate to a certain effect
2 no matter the amount of HP a propeller can only absorb A fixed amount of fuel subject to the engine revs remaining static unless you alter the reduction gear and that only alters the revs no matter what HP may be turning the prop
3 there is no black smoke so the prop is using all the fuel it’s getting
4 if you have the same prop as earlier engine with more HP turning it at the same Revs something else has changed
 
I have spoken with a friend I trust. (He is a very competent engineer).

He says if I run the engine at a throttle setting where there is no black smoke and am happy with the speed I am getting I should go sailing now and deal with it later. He says I will not damage the engine.

I am now tending to this way of thought myself. Lifting out again here could be a nightmare, I have only measured the taper on the old shaft, not the new one. This is Portugal, anything that can go wrong will, and the idea that a new prop will not get lost in customs and that it will fit and be fitted in minutes in the slings is hopelessly optimistic.

The only downside is if we ever need to really punch into wind or current we might just need to forget it and go with whatever Plan B is. I have only once ever run the Beta in our other boat flat out for any length of time, and heaving to and waiting was, on reflection, a perfectly viable option.

So that's where I am at the moment. I can live with the high gearing, and especially I can live with the economy of being able to make long passages through offshore cslms at low revs with great fuel economy.

April 5th we are out of here and off to cruise the Algarve until we can fly home without breaking the bank. Earlier maybe if things ease before Easter, but we are paid up to the 5th.

- W
 
webcraft said:
I have spoken with a friend I trust. (He is a very competent engineer).

He says if I run the engine at a throttle setting where there is no black smoke and am happy with the speed I am getting I should go sailing now and deal with it later. He says I will not damage the engine.

I am now tending to this way of thought myself. Lifting out again here could be a nightmare, I have only measured the taper on the old shaft, not the new one. This is Portugal, anything that can go wrong will, and the idea that a new prop will not get lost in customs and that it will fit and be fitted in minutes in the slings is hopelessly optimistic.

The only downside is if we ever need to really punch into wind or current we might just need to forget it and go with whatever Plan B is. I have only once ever run the Beta in our other boat flat out for any length of time, and heaving to and waiting was, on reflection, a perfectly viable option.

So that's where I am at the moment. I can live with the high gearing, and especially I can live with the economy of being able to make long passages through offshore cslms at low revs with great fuel economy.

April 5th we are out of here and off to cruise the Algarve until we can fly home without breaking the bank. Earlier maybe if things ease before Easter, but we are paid up to the 5th.

- W
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Enjoy
 
One comment I would make is that if my boat had a propeller in the condition yours and a hull to match I would expect a drop in revs and speed as the engine would be under extra load. Also are you checking under way or tied to a pontoon? That also makes a big difference especially to a 16 HP engine.
 
That pic was taken before pressure washing and new antifoul. We are very shiny-hulled now.

2600rpm is max under way. At which point we are doing 7 kts through the water.

I can only get 2,350 in ahead tied to the pontoon.

- W
 
Webcraft - if it is any help to you, that is exactly how my boat was set up. I have a Beta 28hp with a Maxprop and when the boat was built (2003) the builders specified a 16" prop. They guys supplying the prop said it was over propped, but this is what the builders wanted. Max revs at 2600 gave 7kn but most of the time the engine ran at 1600rpm and about 5kn. I never saw black smoke and had no engine problems other than running a bit hot when pushing into big seas.
I spoke to both Beta and Darglow and last winter had the prop cut down to 15" and set in line with the Beta table in earlier posts. Now the boat accelerates a bit quicker and motors a bit faster. Sadly the restrictions of last year prevented much testing as by the time I could get out the boat was fouled.
Anyway, the engine covered 800 hours with the large prop without any problems so your problem may not be too pressing and can be sorted out a bit later as you suggest.
 
Disregarding what the ‘ stupid morons’ may or may not have done to the install in a previous life.. I would like to suggest a couple of things to eliminate before guesstimating any more wrt the propellor and gearbox spec .
Things you prob should check anyway as the engine is only one component in the whole fuel/burn /exhaust cycle ..and the ancillaries may well be even older than the Ex Yanmar..
1. You or a chum jury rig a free flowing gravity fed diesel fuel feed from a 5 litre can direct to the filter.
2. You verify that any fuel return pipe can be blown down easily ( might as well check it , right ?)
And 3 . How is the exhaust system ?could it be collapsed , partially blocked , maybe a part melted, part collapsed water trap or a part open exhaust valve on the transom .. any of these would choke the performance when the engine is trying to work under full load ..
...eliminate eliminate .. !

Having written all that , if you are really getting fast cruising speeds at idle then, obv, some ratio in the drive train really is wrong ..

Algarve, Bruce’s yard, cheap flights to UK with requisite parts brought back as cabin baggage, all will be well !
Enjoy the better parts of Portuguese living and coastal cruising eh!
 
Bbm,

Thanks for your excellent suggestions. The exhaust is new, but blowing down the fuel return pipe is an easy enough thing to do, so will check that at some point.

The primary filter in the fuel line is new, as is the piping, so there shouldn't be an issue with that, but again the check you suggest is not too difficult to organise.

And yes, eventually a new prop will be Ryanaired back to Faro - but in the meantime Amlov's report of a similar situation not causing issues is most encouraging.

- W
 
Just to add a bit more information to my earlier post.

The boat is a Starlight 35 and the original set up was 16" by 9.8". This gave a maximum rpm of about 2,600 on the BD1005 engine with 2:1 gearbox and this is about what Darglow had calculated. It was sufficiently odd for them to comment and record this when it was sold to the builder, but the builder maintained this was what they wanted.

With this set up I could cruise at 1800-2000 rpm giving 5-6 kn but as soon as the wind picked up (20kn plus) this slowed to 4-5kn. The engine ran a bit rougher than I would like at the low rpm vibration wise and I felt that if it were running with higher rpm more power would be available.

Beta recommended a 15" by 9" prop when I spoke to them and Darglow much the same. So I had the prop cut down to 15" by 9.2". Now I get about 3300 rpm full throttle and the boat seems to go along better, but I have not tried motoring into stong winds as other than in or out of ports we find we can sail upwind faster than we can motor.

I never had any concerns about the engine with the big prop and Beta seemed quite chilled about it when I spoke to them, with one of their suggestions being that if I was happy with the speed leave it alone. They did say the engine would run slightly hot, as it did a bit, but not enough to worry about. No smoke, no black stains on the transom and no build up of carbon in the exhaust elbow.
 
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