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donradcliffe · 01-12-2018, 15:01

Quote:

Originally Posted by Atravan

Is this donradcliffe number? I need donradcliffe user contact data. I am sorry.

Private Message sent to you.

BlueChicago · 01-12-2018, 15:04

Quote:

Originally Posted by Scubaseas

Yes, Either supply water for salt inlet pump or take the impeller out. You can verify tach operation long before the fresh water cooling system will get hot enough to worry about. The exhaust won't heat up that fast either. Just don't run it more than about 2 minutes tops. Should take about 30 seconds to comapre your tach to an external (usually optical) one.

Scubaseas,

I'll ask the yard if they are okay with this. If so, I may give it a try.

Thanks

-BC

BlueChicago · 01-12-2018, 15:12

As I think about this, I may just have a conversation with the yard, as they installed this engine (though it was prior to my purchasing the boat).

Also, I may contact the prop distributor to see if they can provide a way to confirm the pitch is actually what was specified and sold. Also, to let them know that there may be an issue.

I am really hoping that I can learn what is wrong before the boat is put in the water this coming spring.

Thanks to all for the assistance.

-BC

**Wotname** · 01-12-2018, 20:36

As others have posted, remember the basics.

The engine has a designed max rpm of 3,000 rpm and the governor should prevent it from exceeding that - regardless of prop or anything else i.e. even in neutral and at WOT, it should not exceed that figure.

If it is showing 4,000 rpm, either the tachometer is wrong or the governor is wrong.

Don't worry about the prop, worry about the tachometer calibration first and if proven the engine is truly running at 4,000, worry about the governor.

morribabes · 02-12-2018, 01:34

Try this https://www.tinytach.com/diesel-tinytach

Scubaseas · 02-12-2018, 03:41

Wotname: If it is showing 4,000 rpm, either the tachometer is wrong or the governor is wrong.

True if in neutral.

Prop should limit speed of engine in gear and cruising at max throttle. Yes there is a governor that should limit it to about 3200rpm. But the prop if pitched properly will also limit the upper end engine speed to about 3000rpm.

**Wotname** · 02-12-2018, 04:15

Quote:

Originally Posted by Scubaseas

Wotname: If it is showing 4,000 rpm, either the tachometer is wrong or the governor is wrong.

True if in neutral.

Prop should limit speed of engine in gear and cruising at max throttle. Yes there is a governor that should limit it to about 3200rpm. But the prop if pitched properly will also limit the upper end engine speed to about 3000rpm.

Actually always true. The OP reports his engine has an indicated engine speed of 4000 rpm. There are only two things that account for that figure.

Faulty tacho or faulty governor.

The prop cannot cause excessive rpm (i.e. that which is well and truly above the designed max rpm as determined by the engine designer).

**Wotname** · 02-12-2018, 04:23

And I highly doubt the governor will be faulty though it is possible.
I reckon NoTies nailed it in post #2 - get the tacho checked.

Scubaseas · 02-12-2018, 04:28

It's a New prop.

If the pitch is way low it would allow the engine to run at a higher RPM. I agree the governor should limit the engine to about 3200rpm but even if the governor were broken, if the prop was pitched right the engine would not be able to make more than 3000 to 3200rpm in drive.

Ideally you pitch your prop to run your engine at wide open throttle to be near the spec rpm for that motor. The difference between a 10" pitch and a 16" pitch can be as much as 1200rpm or more. Note this varies widely depending on prop design, diameter, speed etc.etc. but you can vary the top engine speed in gear by changing the pitch of the prop if no governor is involved.

OP likely has a tach that is not reading right. The governor should be around 3200 rpm on that engine if I recall. But if he can actually make 4000rpm then both the governor and the prop pitch would have to be off.

NoTies · 02-12-2018, 10:32

I wish people would stop blethering about the prop. IF the engine is in fact developing over 4000rpm in neutral and it's not as faulty tach setting then the engine will be developing more power (until it disintegrates) therefore of course it will rev higher in gear as well. Forget the prop, forget the shaft, forget the reduction, forget everything except having the tach calibration checked in the first instance.

FlyingScot · 02-12-2018, 10:51

What does your manual say? Yanmar manuals can typically be downloaded.
My Yanmar 3YM30 manaul says the following:
"It is recommended that new vessels be propped so the engines can operate 100 to 200 rpm above the maximum rated output power engine speed (3700 to 3800) to allow for some added weight and hull resistance.
The engine must be able to reach Maximum Rated Power engine speed (3600) under full load at all times."

3600 rpm on mine is the maximum and 3400 is the maximum continuous rating.

I suspect your tachometer is wrong. Check it's accuracy. But you definitely should read your manual and not overspeed your engine short of a an actual emergency.

kmacdonald · 02-12-2018, 11:02

Quote:

Originally Posted by NoTies

I wish people would stop blethering about the prop. IF the engine is in fact developing over 4000rpm in neutral and it's not as faulty tach setting then the engine will be developing more power (until it disintegrates) therefore of course it will rev higher in gear as well. Forget the prop, forget the shaft, forget the reduction, forget everything except having the tach calibration checked in the first instance.

Max power is usually developed below max RPM's. Power would drop off considerably above max spec RPM's which strongly suggests the tach is wrong if it's reading 4000 RPM's in gear. As others have said, it's pretty clear the tach is wrong.

NoTies · 02-12-2018, 11:29

Quote:

Originally Posted by kmacdonald

Max power is usually developed below max RPM's. Power would drop off considerably above max spec RPM's which strongly suggests the tach is wrong if it's reading 4000 RPM's in gear. As others have said, it's pretty clear the tach is wrong.

Of course Cummins may be wrong. Don't confuse power/rpm over continuous power.