When is a rumble not a rumble.

[kennyh]

How much of a rumble / vibration should I get from a Volvo D4?

Should it be super-smooth at 3000rpm or should I expect a bit of vibration felt at the helm / stern area?

 

[jrudge]

This is a general answer as I don’t have d4 but d12

The vibrations on a boat will vary with speed, load sea state, degree of prop and shaft fouling and where in the boat you are.

I would think that “ silky smooth “ is rare ( they are truck engines !) but equally you should not have tour fillings being shaken out.

 

[BruceK]

Diesels can be a bit lumpy but also dont forget at certain revs your boat may start a harmonic resonance. On mine just shy of 3k rpm the little topside recess, next to the far side throttle that allows you to get your hand in to push in the button on the throttle to rev in neutral, well that whistles slightly as the air in the cavity behind resonates to the engine rumble as the tubo's come on song. I kid you not, a whistle, like somebody barely cracked open a window in a car going down the motorway. Drives me nuts. So I never cruise at that speed.

 

[[2068]]

When my starboard D4-260 generated vibes, it was because the boat ended up sitting on a prop at low tide, and the prop went out of alignment on the hub.

A visual rotation check clearly showed it was wonky.

I sent the prop off to be re-hubbed, and it’s smooth again.

VP props should be nicely balanced out of the packet, unless you have damaged or dissolved them.

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[kennyh]

When my starboard D4-260 generated vibes, it was because the boat ended up sitting on a prop at low tide, and the prop went out of alignment on the hub.

A visual rotation check clearly showed it was wonky.

I sent the prop off to be re-hubbed, and it’s smooth again.

VP props should be nicely balanced out of the packet, unless you have damaged or dissolved them.

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Interesting point about dissolving them - I recently stripped mine post some pretty good fouling and there was some pitting on them.

The thought of having to buy new props brings tears to my eyes!

Question is whether running with a rumble / vibration is (seriously) detrimental to the longevity of either the drive or the engine?

 

[[2068]]

The engine won’t mind much, but the trim rams, steering rams, mounts, pins, etc. are all going to suffer if the vibration is serious.
If it’s only slight vibration, then probably not.
A D4/DP-H should be pretty smooth if it’s all working properly.

A good prop company should be able to check the prop balance for not too much £££.

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[kennyh]

The engine won’t mind much, but the trim rams, steering rams, mounts, pins, etc. are all going to suffer if the vibration is serious.
If it’s only slight vibration, then probably not.
A D4/DP-H should be pretty smooth if it’s all working properly.

A good prop company should be able to check the prop balance for not too much £££.

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I don’t think it is too serious - I’ve a jaunt from Oban to Crinan tomorrow so will take a call if I need to lift and remove props for balancing (hopefully not)!