Prop pitch vs Diesel WOT revs.

Latestarter1 said:
I AM suicidal now offset rudder hand grenade discussion has been lobbed in!
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Ok, let's pretend I didn't mention it... :D
The question about why inward on the OP boat still stands, though. :confused:
PS: thanks for the explanation on BW velvet drives, interesting stuff.
 
coastwise said:
Nothing to do with "pitch issue", but you say you prefer inward turning props rather than the conventional counter-rotating outward turning on this boat. Why this preference on this boat?
Paul
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Sorry, typing too fast here. My mistake in my post #16 above. I mixed up in/outward when typing/thinking. What I should have said was was "which would helpfully convert you from your current inward turners to outward turning" and not "on this boat you want inward turners imho". Sorry for mistake and for creating confusion
 
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OK truce......No, I have no clue as to change to conventional wisdom of outward turning props and I did not spot it on the OP's very clear and graphical post however looks like he has got what he has got, and it is new right handed prop.

Staying away from WOT on port engine is certainly sensible as this represents around 90% engine over load.

Going outward turning is double bubble on new props as well as messing with gearboxes.
 
Sooooo

To clarify.....

stbd:
Engine: CW
Engine seen from rear: ACW
Gearbox in reverse is same rotation as engine ie ACW (seen from rear)
Gearbox ratio 2.1:1
Prop 18" pitch ACW (Left hand)

2600/2.1*18

@WOT 2600 prop movement is 22285" per min ignoring slippage

Port:
Engine: CW
Engine seen from rear: ACW
Gearbox in ahead is oposite rotation to engine ie CW (seen from rear)
Gearbox ratio 1.91:1
Prop 20" pitch CW (Right hand)

2600/1.91*20

@WOT 2600 prop movement is 27225"

explains why port will only rev to 2200 as it is very overpitched

Now reverse ratio of either gearbox or prop (but one only)

Stbd
2600/2.1*20=24761

Port
2600/1.91*18=24502

Near enough matched (but as a guestimate WOT would be around 2400)

So if props were swapped gearbox would also have to be configured to run in opposite direction to still drive prop forward, but that will change ratio thus we have moved gearbox ratio with prop to take us back where we started apart from now having outward rotaing instead of inward (red herring)

Upshot looks like when props were speced the Left and right orientaion were mixed up

Upshot of the upshot
Buy a new port prop

Using Stbd as a datumn
22285/2600*1.91=16.37"

But as the same rotational orientaion as the exixting

ie Right hand (I prefer CW) 20 dia 16.37 pitch
This would (thoertically) allow the engine to rev to 2600

Clear as mud (or that brown slimey stuff we get on the Medway)
 
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Rocksteadee said:
Just to chuck another spanner in the works......have you tried swapping rev counters?
The port could be reving to 2600 without you knowing
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if you go that route, how about replaced alternator pulley / or alternator giving wrong readings? There was such a case mentioned a couple of months back iirc.
Need a strobe light and something to check against the rev counter or best one of these s/w that by "listening" to the engine print the revs. Pitty I couldn't find one for android mobiles...

If there is an award for most difficult/technically challenging thread of the month I think it should go here...

V.
 
virtuvas said:
if you go that route, how about replaced alternator pulley / or alternator giving wrong readings? There was such a case mentioned a couple of months back iirc.
Need a strobe light and something to check against the rev counter or best one of these s/w that by "listening" to the engine print the revs. Pitty I couldn't find one for android mobiles...

If there is an award for most difficult/technically challenging thread of the month I think it should go here...

V.
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If yours is the type which comes off a connection on the alternator could the drive belts be slipping?
 
Rocksteadee said:
Sooooo

To clarify.....

stbd:
Engine: CW
Engine seen from rear: ACW
Gearbox in reverse is same rotation as engine ie ACW (seen from rear)
Gearbox ratio 2.1:1
Prop 18" pitch ACW (Left hand)

2600/2.1*18

@WOT 2600 prop movement is 22285" per min ignoring slippage

Port:
Engine: CW
Engine seen from rear: ACW
Gearbox in ahead is oposite rotation to engine ie CW (seen from rear)
Gearbox ratio 1.91:1
Prop 20" pitch CW (Right hand)

2600/1.91*20

@WOT 2600 prop movement is 27225"

explains why port will only rev to 2200 as it is very overpitched

Now reverse ratio of either gearbox or prop (but one only)

Stbd
2600/2.1*20=24761

Port
2600/1.91*18=24502

Near enough matched (but as a guestimate WOT would be around 2400)

So if props were swapped gearbox would also have to be configured to run in opposite direction to still drive prop forward, but that will change ratio thus we have moved gearbox ratio with prop to take us back where we started apart from now having outward rotaing instead of inward (red herring)

Upshot looks like when props were speced the Left and right orientaion were mixed up

Upshot of the upshot
Buy a new port prop

Using Stbd as a datumn
22285/2600*1.91=16.37"

But as the same rotational orientaion as the exixting

ie Right hand (I prefer CW) 20 dia 16.37 pitch
This would (thoertically) allow the engine to rev to 2600

Clear as mud (or that brown slimey stuff we get on the Medway)
Click to expand...

Well kind of, and I like your summary.

Not sure if I am 100% in agreement with your terminology.

#1 Propellers are ALWAYS named either LH or RH not CW or ACW as you put it.

#2 All engines (exept some Detroit 2 strokes) are shown on spec sheets with rotation from the REAR, either counter clockwise (CCW) the norm, or clockwise (CW) some older 'handed' engines.

#3 Gearbox rotation is as engine in ahead position (position A) again viewed from the rear. Only BW produce gearbox which reverses engine rotation in ahead position. (position A).

The OP himself has got in a bit of a muddle by stating STARBORD gearbox BW assembly #10-18-106 1.88:1 is running in reverse but states that is the LH prop. In reality starboard engine has standard BW assembly #10-18-107 2.10:1, engine is CCW therefore so is output coupling, hence LH 22X18 prop which seems there or there abouts. QED inward turning. Port engine (CCW) has reverse rotation BW #18-10-106, hence RH prop on PORT side.

No real point in discussing tacho as engine will NEVER produce enough power to respond to demand of a 22X20 wheel at rated rpm. Perhaps I a little goofy when I assume people are smart enough to calbrate their tachos as the first step in troubleshooting?

What does concern me is that the Perkins dealer who supplied the engines should have signed this installation off for activation of warranty, engine reaching rated speed at WOT is an absolute requirement, calibration of tachos is part of same engine sign off, what happened in this case?
 
Just to try and tidy this up.
The engines will both rev a tad over 2600 when not in gear and no load...

Think I am going to leave everthing as it is with the exception of repitching or replacing the port hand prop to the recommended finer pitch !
 
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17" here we come !

The engines "feel" OK together right up to 2100 ish and its fairly obvious if one or tother is bit down on rpm .
We have done around 200 hours this year and all seems alright until you go to WOT. Starboard engine just whizzes up there but the port struggles to pull more than 2200.
 
If I remember correctly you had the engines installed new.

Still stuggling to understand why Perkins commissioning technician did not 'knock' the installation for not meeting required standards?? Remember to dig out the report and keep it safe, any subsequent engine damage due to overloading is down to signing this installation off.

Installation review should have also commented on inward turning props as this is uncommon.
 
As the boat was a home build job over thirty years ,suspect the installation of shafts and engine/gearboxes could have been several years apart.Lord only knows when the props were added.
Although out of interest,as we have all and every single invoice to do with the build from hull /flybridge moulding in 1973 right through to last couple of stainless nuts and bolts in 2004,will see when propulsion was installed.
Doubt that Perkins or any of its agents ever got anywhere near the boat.
The bits concerned.
DSCN5993.jpg
 
Remember that there may be a pair of second hand props out there for little more money than just one, plus having them graunched and machined to to suit.

Good luck and post your results when you are sorted.
 
Thanks Latestarter1 .........now about this pair of mufflers I want to install ....... .The manual mentions something about 3" of mercury .
 
oldgit said:
Thanks Latestarter1 .........now about this pair of mufflers I want to install ....... .The manual mentions something about 3" of mercury .
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Yep 3" of Hg @ WOT is pretty much the industry standard for back pressure.

Expect you have 31/2" or 4" exhaust system. Rather than screw around with gauges yet.... work on the basis that every 90 Degree elbow costs you 1/2" of back pressure, visual check of exhaust design will give you decent guestimate.
 
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