Opinions requested on running temperature of stuffing box packing nut.

[S1975]

Good Day.

Would be grateful for any comment, advice or experience from my learned brethren as I am not properly familiar with looking after a motor boat

I believe that the packing nut at the inboard end of the stuffing box seal is running too warm, i.e. can only keep finger tips on it for about 1-2 secs, no longer, after cruising at operating speed for 30 mins or so. After my previous sail boat shaft (20 HP engine)this nut seems very warm. This boat, a Saga 29, is single shaft semi-displacement with about 230 HP, a fairly short shaft of just over a metre and cruises at about 14 knots. Stuffing box was well greased with fitted screw down cap type grease applicator near start of season, and topped up since. Hose around inboard side of shaft just aft of packing nut is cool. No significant engine vibration underway above 1000 rpm. Shaft will not turn by hand in neutral (boat afloat) but spins freely when underway in neutral at one or two knots.

Cutlass bearing was replaced this winter when boat ashore by the experienced local engineer as a result of my recent pre-purchase surveyors's observation on same shaft bearing temperature, and engine alignments checked by my engineer and in tolerance. Discussed with engineer after my above observation, he is not unduly concerned as to my continued operation but will do a run with me to observe next week. He is not too impressed by this older type of bearing. Boat out of water next month as I leave to go back to sea for 3 months so will use this period to plan/arrange a fix as necessary ready for autumn cruising on my return.

Thanks in anticipation of any comment, experience or suggestion.

All the best.

S1975 (David)

 

[Baddox]

Could the nut be too tight, compressing the packing and causing heat through friction? Is stuffing box set up to allow a slow drip of water when the prop shaft is turning?

 

[prof pat pending]

That's way too hot, mine runs cold and dry.

As said above, it sounds like the nut has been done up too tight, the friction will be wearing into your shaft, which obviously isn't good.
You might get away with backing off the collar a bit and adding more grease, don't be tempted to take the packing out if the boat is in the water ... unless you know exactly how to repack it under pressure

 

[fergie_mac66]

That's way too hot, mine runs cold and dry.

As said above, it sounds like the nut has been done up too tight, the friction will be wearing into your shaft, which obviously isn't good.
You might get away with backing off the collar a bit and adding more grease, don't be tempted to take the packing out if the boat is in the water ... unless you know exactly how to repack it under pressure

+1 is it dripping when shaft turning

 

[Piers]

Sounds like its too tight. Should run at warm at the most. If it's hot, the grease can be cooked thereby compromising the water seal capability. Is there any evidence of anything but water escaping into the boat from the seal?

Not knowing your specific installation, adjusting would normally be done by slacking the nut a 'flat' at a time to adjust. You should be able to turn the shaft when the engine isn't running and the boat's not making way, albeit a bit stiff.

 

[S1975]

Many thanks everyone, useful information, advice and experience. That nut/bearing to my mind was uncomfortably warm. I will now get on with resolving the issue and post the outcome.

Thank you again. It is good to have so much experience and advice readily available.

S1975 (David)