Over-propped?

[sv_telemachus]

Hi all

I think my engine is over-propped, grateful for a sense-check:

• Beta 38 (max rated rpm 3600)
• Fixed 3-blade prop (I don’t have dimensions, but could possibly dive down and measure!)
• Engine reaches 3100rpm in neutral with no smoke
• Engine reaches 5kts (hull speed 6.5kts) in gear at 1800rpm with no smoke
• White smoke in gear from 1900rpm, smoke increasing in intensity to max 2400rpm in gear / 6kts
• New exhaust elbow, heat exchanger flushed, new impeller, flushed seacock with dinghy pump, checked strainer.

Video of the various running states here:

https://imgur.com/a/zPK4Geu

My suspicion is that I’m probably over propped. My questions:

(i) do you agree

(ii) is it harmful to stay at 1800rpm

(iii) anything I can check / do short of a new prop?

Previous owners ran at 1800 for 10 years, prop almost certainly dates back to at least the engine replacement in 2005.

Thanks!

 

[ash2020]

If it's any help, I have a Beta 14, which is rated at 3,000 RPM and a couple of years ago I spoke at length to the tech guy at Beta. He said that it would run at 3,000 RPM all day without any harm.
They really are very helpful there. I would suggest you could give them a call.

 

[Roberto]

In neutral it should reach the maximum rpm, two things come to mind 1. Are fuel filters clean, and 2. does the command cable attached to the injection pump lever allow for its full amplitude movement? You might try and remove the cable and move the lever by hand, careful very small movements can give huge amounts of rpm variations

 

[sv_telemachus]

In neutral it should reach the maximum rpm, two things come to mind 1. Are fuel filters clean, and 2. does the command cable attached to the injection pump lever allow for its full amplitude movement? You might try and remove the cable and move the lever by hand, careful very small movements can give huge amounts of rpm variations

Thanks Roberto, actually yes I believe the throttle handle was replaced a few years ago - could be miscalibrated.

Is that idea separate to the smoking and inability to reach rpm in gear though? I recently replaced the coarse fuel filter, can take another look.

 

[ash2020]

I've had that with 2 boats. Fouled prop. My current prop is completely covered in barnacles and weed after a season in Poole Harbour and in gear it will only reach 2,000rpm.

 

[Tranona]

Yes, it should reach 3600 in neutral, so either there is a restriction on fuelling or your rev counter is wrong.

Difficult to advise without knowing details of the boat. 6.5knots is a very low hull speed for a sailing yacht that needs 38hp. That implies an LWL of about 22' which means a short very heavy boat. My GH 31 has a LWL 28' and hull speed of 7.4 knots which with a displacement of 5.3 tonnes needs 27hp. So I am assuming your boat is 35' LOA+ and displacement of 7 tonnes+ and should have a hull speed of closer to 8 knots

The sort of speeds you are getting definitely suggests overpropping, irrespective of what the rev counter says the actual revs are. To get even a rough idea of what size the prop should be one needs to known LOA, LWL, Beam, Displacement and reduction gear ratio.

With the correct prop you would expect to get hull speed at above 3300rpm and 6 knots at 2400rpm

This, of course assumes a clean bottom and no prop fouling.

 

[LittleSister]

If it's any help, I have a Beta 14, which is rated at 3,000 RPM and a couple of years ago I spoke at length to the tech guy at Beta. He said that it would run at 3,000 RPM all day without any harm.
They really are very helpful there. I would suggest you could give them a call.

A Beta 14 is designed to rev to 3,600rpm, not 3,000. It produces its maximum power of 13.5hp at 3,600rpm. At 3,000rpm it can produce only 12hp.

Are you sure you don't have a Beta 10, which is basically the same engine, but limited to max revs of 3,000rpm, at which it produces 10hp?

 

[sv_telemachus]

Yes, it should reach 3600 in neutral, so either there is a restriction on fuelling or your rev counter is wrong.

Difficult to advise without knowing details of the boat. 6.5knots is a very low hull speed for a sailing yacht that needs 38hp. That implies an LWL of about 22' which means a short very heavy boat. My GH 31 has a LWL 28' and hull speed of 7.4 knots which with a displacement of 5.3 tonnes needs 27hp. So I am assuming your boat is 35' LOA+ and displacement of 7 tonnes+ and should have a hull speed of closer to 8 knots

The sort of speeds you are getting definitely suggests overpropping, irrespective of what the rev counter says the actual revs are. To get even a rough idea of what size the prop should be one needs to known LOA, LWL, Beam, Displacement and reduction gear ratio.

With the correct prop you would expect to get hull speed at above 3300rpm and 6 knots at 2400rpm

This, of course assumes a clean bottom and no prop fouling.

Thanks Tranoa,

Boat is a Nic 35. Data suggests:

LOA:	35.25 ft / 10.74 m
LWL:	26.75 ft / 8.15 m
S.A. (reported):	551.00 ft² / 51.19 m²
Beam:	10.42 ft / 3.18 m
Displacement:	15,650.00 lb / 7,099 kg
Ballast:	7,200.00 lb / 3,266 kg
Max Draft:	5.50 ft / 1.68 m

Hull speed is more like 6.9kts, corrected*

Prop is clean from the GoPro in the sea, and I antifouled about two months ago so is pretty good shape.

I can dive to measure the diameter, not sure how I measure pitch though?

 

[sv_telemachus]

(Also to ask a novice question - what is technically causing the smoke under higher rpm, is that water vapour or unburnt diesel from extra load?)

 

[B27]

If you can find out what your prop is and what the gearbox ratio is, then you can put that into an online calculator or tow and see if it's sensible.
Measuring pitch underwater is a big ask, your best hope is to read what's stamped on the prop boss.
But taking pics might give a rough idea by comparison?
Is it a plain 3 blade or what? Folding etc props can be worn out and inefficient, props can get bent etc.

When you say 'it reaches 3100RPM in neutral', is that as fast as it will go, or just as fast as you care to rev it?
If it won't rev any faster, that would probably either be fuel starvation or the governor/speed control needing adjustment. The video shows IMHO that there is no shortage of fuel going in. The white smoke is likely unburned diesel, the black smoke, partly burned diesel.

I presume nothing has changed in the time you've known the boat? If tis has got worse, it's not the prop.

5 knots at 1800 suggests the pitch might be a little high but not much.
It's a big engine for a boat of that LWL, so it should cope with a bigger pitch, people sometimes pitch props to work nicely getting adequate power and lower RPM from a bigger engine, people do not always seek to use max power.

Unfortunately I suspect a significant problem with the engine.
However , finding out the prop dimensions or swapping the prop for a known one on the small side would clarify that.

Bad fuel might be a possible cause, can you rule that out? Maybe some clean fuel and some injector-cleaner-snake-oil? This might be seen as unlikely, but it's cheap to try.
Beyond that, maybe it's time to have the injectors checked and cleaned etc. I wouldn't do that without trusting the fuel in the tank and that the pipe work etc is clean.
Lack of air getting to the engine? Choked filter, engine box vent. Check the cheap things!
I once spent a long time working on an engine to eventually find the airbox had been put together wrong strangling it! A partly blocked exhaust can do non-intuitive things too.

 

[Tranona]

Thanks Tranoa,

Boat is a Nic 35. Data suggests:

LOA:	35.25 ft / 10.74 m
LWL:	26.75 ft / 8.15 m
S.A. (reported):	551.00 ft² / 51.19 m²
Beam:	10.42 ft / 3.18 m
Displacement:	15,650.00 lb / 7,099 kg
Ballast:	7,200.00 lb / 3,266 kg
Max Draft:	5.50 ft / 1.68 m

Hull speed is more like 6.9kts, corrected*

Prop is clean from the GoPro in the sea, and I antifouled about two months ago so is pretty good shape.

I can dive to measure the diameter, not sure how I measure pitch though?

Yes, 7 knots and needs 32hp to achieve that. With 38hp you should be able to get 7.2 knots. Crucial now is the reduction ratio. No point in measuring the prop until you know that. For example with a 2:1 it is likely to be 14or 15" with a 2.5:1 probably 17". There are different shaft layouts on Nic 35s depending on which gearbox arrangement you have - V drive or straight. Not sure what reduction ratios are fitted but if you have the standard TMC 60 box that comes with the beta it is either 2 or 2.5.

The smoke is unburnt fuel because you are "asking" for more power than the prop can absorb so the governor is overfuelling

 

[neil_s]

Dirty bottom? Even a layer of slime makes my motor do that.

 

[sv_telemachus]

If you can find out what your prop is and what the gearbox ratio is, then you can put that into an online calculator or tow and see if it's sensible.
Measuring pitch underwater is a big ask, your best hope is to read what's stamped on the prop boss.
But taking pics might give a rough idea by comparison?
Is it a plain 3 blade or what? Folding etc props can be worn out and inefficient, props can get bent etc.

When you say 'it reaches 3100RPM in neutral', is that as fast as it will go, or just as fast as you care to rev it?
If it won't rev any faster, that would probably either be fuel starvation or the governor/speed control needing adjustment. The video shows IMHO that there is no shortage of fuel going in. The white smoke is likely unburned diesel, the black smoke, partly burned diesel.

I presume nothing has changed in the time you've known the boat? If tis has got worse, it's not the prop.

5 knots at 1800 suggests the pitch might be a little high but not much.
It's a big engine for a boat of that LWL, so it should cope with a bigger pitch, people sometimes pitch props to work nicely getting adequate power and lower RPM from a bigger engine, people do not always seek to use max power.

Unfortunately I suspect a significant problem with the engine.
However , finding out the prop dimensions or swapping the prop for a known one on the small side would clarify that.

Bad fuel might be a possible cause, can you rule that out? Maybe some clean fuel and some injector-cleaner-snake-oil? This might be seen as unlikely, but it's cheap to try.
Beyond that, maybe it's time to have the injectors checked and cleaned etc. I wouldn't do that without trusting the fuel in the tank and that the pipe work etc is clean.
Lack of air getting to the engine? Choked filter, engine box vent. Check the cheap things!
I once spent a long time working on an engine to eventually find the airbox had been put together wrong strangling it! A partly blocked exhaust can do non-intuitive things too.

Thanks B27, much appreciated:

• Gearbox is a Z15 (MIV) V-drive, found a stamp that says 2.13 ratio.
• Picture of the prop attached if helpful - unfortunately nothing showing scale
• 3100 RPM is max the lever will go in neutral, it sounds quite happy, good waterflow and no smoke. But doesn't reach 3600 RPM.
• I can't rule out bad fuel but the tank is nearly empty after a run down the Iberian coast so I can get it checked out.
• Not new and previous owners running at 1800RPM suggests a historical issue to me?
• Why do you suspect a significant problem with the engine?

Thanks again!

Yes, 7 knots and needs 32hp to achieve that. With 38hp you should be able to get 7.2 knots. Crucial now is the reduction ratio. No point in measuring the prop until you know that. For example with a 2:1 it is likely to be 14or 15" with a 2.5:1 probably 17". There are different shaft layouts on Nic 35s depending on which gearbox arrangement you have - V drive or straight. Not sure what reduction ratios are fitted but if you have the standard TMC 60 box that comes with the beta it is either 2 or 2.5.

The smoke is unburnt fuel because you are "asking" for more power than the prop can absorb so the governor is overfuelling

Thanks Tranoa, that's very helpful. Apparently the ratio is 2.13. It's a Z15 (MIV) V-drive.

I see similar numbers using the Vicprop calculator - a 3 blade prop should be 15.1 x 8.2. That doesn't sound unreasonably inconsistent with the prop size in the photos.

What do you suggest? Potentially fuel and injectors as above?

Dirty bottom? Even a layer of slime makes my motor do that.

Can check, but I think it's pretty clean!


***

 

[sv_telemachus]

Merged above

 

[sv_telemachus]

Merged above

 

[robmcg]

If you were over propped, I would expect to see black smoke rather than white smoke coming from the exhaust. White smoke is either unburnt diesel (it usually lingers in a long trail behind the boat) or steam which tends to dissipate quite quickly.

 

[B27]

Thanks B27, much appreciated:

• Gearbox is a Z15 (MIV) V-drive, found a stamp that says 2.13 ratio.
• Picture of the prop attached if helpful - unfortunately nothing showing scale
• 3100 RPM is max the lever will go in neutral, it sounds quite happy, good waterflow and no smoke. But doesn't reach 3600 RPM.
• I can't rule out bad fuel but the tank is nearly empty after a run down the Iberian coast so I can get it checked out.
• Not new and previous owners running at 1800RPM suggests a historical issue to me?
• Why do you suspect a significant problem with the engine?

Thanks again!

That prop does look quite coarse pitch. The reduction ratio is quite low.
Not reaching 3600 RPM in neutral could well be a complete irrelevance.

A lot of people cruise at revs not far from 1800. On my boat, it's lazy but very economical, no wash, quiet, "why hurry anyway, we're happy out on the water" mode. 2100 in flat water is fast cruise. That's a Beta 14 on 27ft LOA.
When I did a quick sea trial of my but, the esteemed previous owner was appalled at me wanting to try more than 2500RPM, but it did 3200 happily despite the hull looking like a saag bhaji.

The smoke suggests something is quite badly wrong.

Your boat is, with respect, heavy and an old fashioned shape with a short waterline. It is not in the game of going fast under power. However it ought to do 5.5knots with no fuss.
I made some guesses about hull-body draught and waterline beam, put them in the calculator at vicprop.com and got answers around 5.3 knots for 15HP. So your big engine should have enough torque to cope with the prop being a bit wrong. Quite a bit wrong.

With my boat, a previous surveyor had noted the prop dimensions which was a useful bit of data.

I think it's good to understand where you are before trying to move.


It is not impossible that previous owner re-engined the boat and kept the old prop or used some random prop, because he was not sure what prop to buy (or other reasons). So he has a new engine that starts, he's happy pottering at 1800RPM quietly and there is no urgency to buy the optimum prop.
It's a sailing boat, have some respect and buy a folding prop.

 

[Tranona]

How long have you had the boat and has it been like this all the time? You say it was re-engined in 2005 and I have difficulty in accepting the prop being wrong and not being corrected . 5 knots at 1800rpm is about right. 2200rpm should give nearer 6 knots which agrees with what you are getting, but you should still be able to go over 3000rpm to get 7 knots (even if you rarely use it).

2.13 is an appropriate reduction - I guess the boat originally had a Perkins 4 108 which would be governed to around 3300rpm. Any bigger reduction would require a bigger diameter prop and you would have tip clearance problems.

Everything points to the propeller being right and the inability to rev being with the engine, particularly as it won't seemingly achieve governed maximum with no load.

Criminal to hang that drag inducing prop on such a boat, particularly if you are going to make full use of your Hydrovane and go long distance cruising. Speak nicely to Father Christmas and treat it to a Featherstream like mine. Not only will you get better performance under motor (assuming the motor is fit) but it will add 15 miles or so to your daily runs.

 

[Bilgediver]

Lots of ideas being floated about however to take the subject any further and understand the figures we need to be clear about the position of the speed lever on the governor in relation to the stop screw. You mention the speedlever pushed all the way in one post but do not confirm if it is the lever you hold or the lever on the governor which is all the way. is the lever on the governor hard up against the stop screw when the speed lever at the helm is at full speed. If you make a small adjustment to the stop screw on the governor does the engine respond accordingy and speed up. Can you borrow a
stroboscope or maybe try an app stroboscope to confirm the actual engine speed.

Your Hull and prop could be fouled. Is this having an effect?

If the load IS limiting the revs then you may be overtorquing the engine and this condition should be avoided to minimise excessive cylinder wear.

If the engine is overloading at lower revs than indicated by the propeller curve then it may be possible to improve the situation by having ghe existing propeller modifiedto defectives reduce ghe pitch. I have done this with shipspropellers and it works. There are various companies around ghe coast of ghe UK and possibly even in your area that are capable of this,
Before we go any further we need to confirm what actual speed you are running at and adjust the high speed setting if necessessary. . If your speedfigures are correct then confirm the state of the Hull and prop before considering the modification to repitch ghe prop.

Meanwhile you are doing no harm running at 1800rpm. I am pretty sure that what you reference to as white smoke is steam and is more prevelant and visible at this time of the year especially on a cool evening.

 

[jwfrary]

I expect the Rev gauge might not tell you tge whole truth as on a beta they are run from the alternator, so that could well need calibrating before you make any diagnosis based on it.

Where as black smoke comes from overloading, white smokes can be from over fueling. This could be caused by a few things.

1. Restricted exhaust. Beta require a 50m. Exhaust on that engine from elbow to transom. I'm suspicious that yours is smaller from the video.

2. Poor injector spray pattern. Easy to check/have rectified.

3. Pump timing both retarded and extream advanced timing can cause white smoke and low power.

4. It's not uncommon for yachts to be intensionally overpropped for the purpose of reducing the crusing revs. I don't agree with the practice but when it's requested I generally adjust the pump so extra fuel cannot be applied past the prop loading curve. (on ecu controlled engines some call it the smoke curve!)

5. Being at the end of the season we are at, are you sure you haven't just got a lot of fouling!