Seahorse Marine Diesel Duck Vibration - Advice needed

[Terra Nova]

Originally Posted by SeahorseDD54201

...The whip bearing is a water lubricated Duramax...is inacessible in the middle of the stern tube, which in turn sit inside and inaccessible in the long keel

Originally Posted by SeahorseDD54201

...I don't think torsion is a problem. DD462 do not vibrate and have the same shaft and similar power characteristics. The only difference is DD542 has a longer shaft...

Duh! You don't see anything wrong here?

[SeahorseDD54201]

Originally Posted by Sailmonkey

A longer shaft will also need to be more resistant to torsional loading. It’s longer, so is able to twist more than a shorter shaft while maintaining the same angular deflection per length.

Come to think of it, the formula published at Aquamet website for determining shaft diameter does not take account of the shaft length. Length comes into the picture only in determining the location of bearings.

Is there a formula that determine shaft diameter, accounting for torsion due to a longer shaft ?

[Bill Seal]

Just ruminating here...
Could you put 2 "whip" bearings on it at unequal spacing so there can't be resonance between the two halves? Think guitar string.
As for inferior materials, modulus is modulus regardless of ultimate strength, (i.e. chrome moly is no stiffer than mild steel, just don't try explaining this to a race car driver/owner.)

[Pelagic]

Originally Posted by SeahorseDD54201

Hello Pelagic:

Thanks for sharing the experience at Translift, and I may well drive the boat over for their help. My boat is about 45 tons, and I hope it can be accommodated.

Checked with Watercraft re weight limit.

They said 40 tons but my 50% load displacement is 44 tons.

When I lifted in March 2017, with full Fuel (2400 liters) their gauges said 38 tons.

The Travel Lift is rated 50 tons

[SeahorseDD54201]

Thank You for checking at Subic !

[boden36]

I do not know your layout, so this suggestion may be impractical. Are you able to fit one or two harmonic balancers along the shaft?


Regards,
Richard

[excess_risk]

Wish I could help. I have no experience-backed suggestions.

Would like to hear an update when there is news.

Thanks and good luck!