Mermaid turbo 4 low power, black smoke.

[Keith-i]

I don’t know if it helps your quest but before we re-engined Island Girl she was running a 20x17.75 propeller on the original Ford engine (single). I believe the engine had been tweaked with possibly a different turbo and fuel governor to make around 230hp from the original 190hp if memory serves me right.

 

[Bill W]

I don’t know if it helps your quest but before we re-engined Island Girl she was running a 20x17.75 propeller on the original Ford engine (single). I believe the engine had been tweaked with possibly a different turbo and fuel governor to make around 230hp from the original 190hp if memory serves me right.

Hi Keith,
Thanks for the input. I’m not sure it would directly translate with Island Girl being single engine and Gracie Jay being a twin, though they are both CI32. I think prop size and pitch are worked out by hull type, weight, number, max revs and hp of engines and gearbox ratio.
Using a free online prop calculator I can only get a result which gives less than 16knots, which is clearly nonsense because she will do 20 plus in her current state and previously is said to reach 23knots. Personally, I’d be happy with 18knots or so and cruise at 15.

 

[stone beach]

Port engine will rev to 2300+ under load. Starboard engine will only reach between 1900-1950. Port engine has 1.5:1 box. Starboard box is 1.46:1.
Starboard turbo reaches around .5-.6 bar about 1700 revs but does not increase much if at all beyond that.
Manufacturer's max revs for the Ford Dover-based Mermaid Turbo Four is 2600. I think they will hit 3000 out of gear but I didn't like to scream the guts out of them with no load. I was informed that they were supplied as reconditioned 170hp units but it could be that someone has tweaked the pumps to get a bit more.
The port engine will reach at least 2300, maybe a little more if the starboard one was reaching those revs too.
The turbos are the correct ones for these engines, KKK K26.
The engines are said to be low hours and were factory recons fitted in 2009. They don't seem to be worn out. They don't smoke much on startup, sound healthy and don't burn oil. No sign of breathing from the crankcases.
The turbo on the port engine spins very freely, the starboard one very slightly less so.
I'm leaning towards it being excessive pitch on the starboard prop as the main cause, with possibly a tired and leaky turbo adding to the mix.
The boat is afloat at present, so checking the pitch will probably have to wait for some settled weather and putting her aground. We'll then do a quick and dirty pitch check using a straight edge and carpenter's sliding bevel to compare the blade angle of the two props. We might also be able to contrive a method of working out the actual pitch without removing the props.
In the meantime, we might try swapping the turbos over between engines and see if that has any effect on either of them.

you didn't mention the port max boost pressure...."Starboard turbo reaches around .5-.6 bar about 1700 revs but does not increase much if at all beyond that"....but I am assuming it is about the same.
I doubt you will learn anything meaningful from a rough pitch check, I've tried that myself and ended up with more questions than answers ! they both need to be put on the correct machine for pitch check and adjustment.
If you are happy using the boat as is until you take it out for winter lay up I don't think you will do any harm as long as you treat the Starboard engine as max revs 1800 ie stop before it reaches overload condition and you can probably put the port engine's speed up until you have balanced the boost pressures. This should give you balanced output from both even though their rpm is different, assuming the engines are in equal condition, a leap I know but you have to start somewhere.
The port prop needs about 10% pitch reduction and the starboard one should be matched to the port. I'm afraid this prop adjustment stuff is trial and error when you are dealing with old equipment. It isn't that important as long as you operate accordingly. Full rpm less than 10% of the time and cruising at less than 90% of max rpm...the max rpm you can do with existing props, not the max rated speed. Personally I would go a lot less than that with an old boat.

 

[david_bagshaw]

Might be a long shot, collapsed or collapsing exhaust hose?
loose baffle in a collector box?

 

[Bill W]

you didn't mention the port max boost pressure...."Starboard turbo reaches around .5-.6 bar about 1700 revs but does not increase much if at all beyond that"....but I am assuming it is about the same.
I doubt you will learn anything meaningful from a rough pitch check, I've tried that myself and ended up with more questions than answers ! they both need to be put on the correct machine for pitch check and adjustment.
If you are happy using the boat as is until you take it out for winter lay up I don't think you will do any harm as long as you treat the Starboard engine as max revs 1800 ie stop before it reaches overload condition and you can probably put the port engine's speed up until you have balanced the boost pressures. This should give you balanced output from both even though their rpm is different, assuming the engines are in equal condition, a leap I know but you have to start somewhere.
The port prop needs about 10% pitch reduction and the starboard one should be matched to the port. I'm afraid this prop adjustment stuff is trial and error when you are dealing with old equipment. It isn't that important as long as you operate accordingly. Full rpm less than 10% of the time and cruising at less than 90% of max rpm...the max rpm you can do with existing props, not the max rated speed. Personally I would go a lot less than that with an old boat.

Port boost gauge is unreliable due to poor quality wiring, which is on my increasing long list of jobs for the winter layup. Currently it reads lower than the starboard turbo at around .4 bar.
I’m not entirely happy to continue using the boat as it is. I might manage one more trip at reduced revs next weekend , weather permitting, then get her lifted at first opportunity after that. I have been running them up to 1900 port and 1800 or so starboard but will take it easier than that.
I agree that a slight reduction in pitch would allow the port engine to get closer to max rated revs but maybe not as much as 10 percent. I’m mindful that the port engine is currently doing more work to carry the starboard one, so there could be more revs available once the port one is doing its fair share.
I also concur with your thoughts about running well below max output. I’m no boy racer and quite content to go 14or15 knots. The wife would like to go faster but understands that the fuel cost goes through the roof, if not the implications for older machinery.

 

[Bill W]

Might be a long shot, collapsed or collapsing exhaust hose?
loose baffle in a collector box?

Possible, but I think unlikely as there is good flow from both exhausts. We can’t really take the exhaust hoses out and check the insides while she is afloat, but will do so over winter ashore.

 

[stone beach]

"Port boost gauge is unreliable due to poor quality wiring, which is on my increasing long list of jobs for the winter layup. Currently it reads lower than the starboard turbo at around .4 bar"
I was quite surprised to read you have electric gauges, thought they would have been straight mechanical type. You could consider temporary swopping the wires at whichever end is easiest. Might give you some idea of accuracy of reading.
If it is reading correctly the low Port side reading also points to imbalanced power and supports a prop issue theory.

To explain why I am banging on about boost pressure.
The best indication of engine load is exhaust gas temp (EGT) before the turbo. But I believe you won't have such a read out.
Turbo is spun by heat energy of the exhaust, therefore turbo works harder, = spins faster, with higher EGT. In the absence of an EGT reading you can get some idea of which side is working hardest by comparing boost pressures, the side with the higher boost is the side working harder, obviously this assumes everything else is equal, maybe a bit of a stretch with an old boat but you have to start somewhere.

 

[Bill W]

"Port boost gauge is unreliable due to poor quality wiring, which is on my increasing long list of jobs for the winter layup. Currently it reads lower than the starboard turbo at around .4 bar"
I was quite surprised to read you have electric gauges, thought they would have been straight mechanical type. You could consider temporary swopping the wires at whichever end is easiest. Might give you some idea of accuracy of reading.
If it is reading correctly the low Port side reading also points to imbalanced power and supports a prop issue theory.

To explain why I am banging on about boost pressure.
The best indication of engine load is exhaust gas temp (EGT) before the turbo. But I believe you won't have such a read out.
Turbo is spun by heat energy of the exhaust, therefore turbo works harder, = spins faster, with higher EGT. In the absence of an EGT reading you can get some idea of which side is working hardest by comparing boost pressures, the side with the higher boost is the side working harder, obviously this assumes everything else is equal, maybe a bit of a stretch with an old boat but you have to start somewhere.

Yes, they are electric gauges with a pressure sensor on the inlet manifolds. Good idea about swapping the wiring to check what they read with the same gauge but obviously there's no guarantee that the senders are accurately sensing the pressure.
Please do continue to "bang on" about boost pressure. You are doing a grand job helping me to get my head round this conundrum.
You are right, I don't have EGT sensing and as the manifolds and turbos are freshwater cooled, there's no way of testing it that I can think of..

 

[david_bagshaw]

Yes, they are electric gauges with a pressure sensor on the inlet manifolds. Good idea about swapping the wiring to check what they read with the same gauge but obviously there's no guarantee that the senders are accurately sensing the pressure.
Please do continue to "bang on" about boost pressure. You are doing a grand job helping me to get my head round this conundrum.
You are right, I don't have EGT sensing and as the manifolds and turbos are freshwater cooled, there's no way of testing it that I can think of..

Dont know about mermaid, but sabres have a small stub, going into the exhaust manifold which isnt cooled. An infra red thermometer, aimed at the cyl head flange would give an indication, and comparison with the other engine, if not the actual egt

 

[david_bagshaw]

Just re reading this thread,
1 I take it the fuel filters have been changed, along with the pre filters.
I have had occasions where the filters are moderately soiled, work fine at 3/4 power , but there is just not quite enough flow for full power.
2 Is there a good supply of cool air at the intake, as i clearly remember my tutor (worked for Mercedes marine dept in the 70s) telling me of boat builders complaining of lack of power, for the missing horses to bolt out of the stable when the engine room floor was lifted.

 

[Bill W]

Just re reading this thread,
1 I take it the fuel filters have been changed, along with the pre filters.
I have had occasions where the filters are moderately soiled, work fine at 3/4 power , but there is just not quite enough flow for full power.
2 Is there a good supply of cool air at the intake, as i clearly remember my tutor (worked for Mercedes marine dept in the 70s) telling me of boat builders complaining of lack of power, for the missing horses to bolt out of the stable when the engine room floor was lifted.

I checked pre filter/water trap and changed the twin CAV filters. Fuel looks bright and clean and best part of 1000 litres has been through the tanks this season, unfortunately some to be wasted as oily soot. There are two bilge fans fitted to the air intakes, one blowing in, the other out. There appears to be a good supply of fresh air via intakes in the. Superstructure and additional louvres in the hull topsides.
We have run her at high revs with sole hatches up and the smoke is unchanged.

 

[Bill W]

Update: I managed to contact the last but one owner. He confirmed that the props had not been reduced in pitch and they were 20x21.5 when he owned her. He also said that max revs under load was just under 2400, so the 2350ish the port engine can reach is about right.
It’s looking increasingly like a turbo problem.