New props, now not quite running at max revs

simonfraser

simonfraser

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KAD 44 EDC, B5s, which i knew might be slightly over propped

Max revs in slightly choppy waters 3500
Needed a little bit of trim tab, with the trim completely up in a flatter stretch, it picked up to 3600

Not planning to run it at full throttle for any time, 3000 revs gives a good turn of speed without excessive fuel consumption
No overheating during the above 30 mins run, i have an exhaust temp gauge too

Any long term issues running this setup at 3000 revs for an hour or so ?
 
Iirc KAD 44 should max out on prop at 3800 and be limited to about 3950 by governor.

is your hull absolutely spotlessly clean ?
 
simonfraser said:
KAD 44 EDC, B5s, which i knew might be slightly over propped

Max revs in slightly choppy waters 3500
Needed a little bit of trim tab, with the trim completely up in a flatter stretch, it picked up to 3600

Not planning to run it at full throttle for any time, 3000 revs gives a good turn of speed without excessive fuel consumption
No overheating during the above 30 mins run, i have an exhaust temp gauge too

Any long term issues running this setup at 3000 revs for an hour or so ?
Click to expand...

Was there a particular reason you over propped?
 
Hull def clean, trailer based

Likely being a bit inaccurate with the revs, the limiter did cut out at 3600 with previous B2s
Have had the rev counter to bits to change the LCD display a year or so ago, for this you have to remove the pointer
I suspect 3600 = 3950
I can check it via the supercharger i now realise, this is cutting out at about 2000 revs from memory, will check
What revs is the supercharger cutting in / out ? Failed to google that just now :(

My B2s were stuck on the shaft, needed an anode change, the forward prop had to be cut off
Was offered a set of B5s as in two pairs for a good price
Happy with that change for the moment
I can sell the B5s and change to ? For little money, gotta start somewhere
 
Use the hand held tach to test your dash tach . When alongside with no load set rpm at say 1000rpm on dash tach and jump down and check on engine. Repeat at say 2000 ,3000 rpm etc noting how far out your dash tach is then either correct the dash tach or note the correct reading v recorded reading
The engine wont take any harm being reved no load for a short tach check
 
simonfraser said:
Have had the rev counter to bits to change the LCD display a year or so ago, for this you have to remove the pointer
I suspect 3600 = 3950
Click to expand...


2nd the above comments. Get a hand held tach. with the the boat in neutral rev up to about 3k rpm on the dash tacho and validate against handheld tach. Calibrate dash tach. Verify again against 1k rpm and 2k rpm. If they are out as well then work out the graph line error or set to be accurate at max rpm.

NOTE! if the alternator has ever been changed there is a very good chance it was installed with the pulley wheel it came with. If you are taking tach readings from the alternator rather than ECU (not sure on KAD44's so worth checking) then make sure you have the correct alternator pulley on. I had an alternator changed on my KAD 42 twins. Gave me a headache for a long time until I realised what had happened.

Pulley part no. 841813
 
There may be some confusion here. There are no tensioner pulleys on your alternator belt. The pulley you are after is the one that attaches to the alternator itself. Think of a bicycle with gears. The pedal crank gear remains constant but small increments in size on the rear wheel gearing system have a huge effect on how fast the back wheel spins. (multiply this by thousands and you can see why the alternator pulley needs to be an exact diameter to get correct rev readings accurate)

this is only valid if you are taking rev readings from a alternator signal post and not the ECU.

Can somebody with a KAD44 confirm which it is please?
 
Last edited:
C. your hand held laser tacho will probably come with a bit of reflective tape. Place a small strip of the tape on C
 
tnx Bruce, very helpful as usual :)


this is from a volvo agent who i asked what prop to buy:

I’m glad to hear you’re now obtaining better performance with the B5 propellers. I think there is more performance to be gained from C4 or J5 series propellers however it’s a significant improvement on the 22 knots you were previously getting.

A max RPM of 3500 is 300 RPM down on the mid range recommendation for full throttle so yes it is now over prop’ed however it isn’t going to cause damage to the engines. It will mean the engines are slightly overloaded and will therefore have a negative effect on fuel consumption.

My suggestion would still be to change the propellers to J5’s or C4’s in time but for now 24knots @3000 rpm is good.
 
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