............. yes, for good health, about four to five times a day is good.
However, for a number of years I have been chiming in here on packing glands leaking and the fact I have run mine bone dry almost from the day I bought the boat new in late 1998 as a '99 model H310. As mentioned in several old threads, back in 1999 I discovered that if the stuffing box were packed with teflon impregnated flax, I could hand tighten the gland to the point where there was no water dripping and yet the gland stayed cool to the touch. Why so when this spells sure disaster for others ?
Many have said dry glands are a recipe for disaster or worse: the shaft will score, the packing will burn, the honey on the boat next to me will stop wearing short shorts, and my brother-in-law will come to live with us.
Biblical prophesies have nothing on this bad boy.
I've heard it all and I can't say I understand any of it:
Seems like every statement raises another question.
Well, given the miserable, sodden winters we live with here in Vancouver and having nothing more adventurous to do, I thought I would dig into this packing conundrum and try to make some sense of it. Dry, wet, hot, cold, what's it all mean ? Sleepless nights, irregularity, and quite possibly E.D. I've got to make some sense of this mystery so it's off to the boat to gather a few numbers along with some pictures.
What makes this packing work very nicely without any leakage are such basics as: proper installation, light compression of the packing, ensuring the flax packing is indeed impregnated with teflon, maybe a bit of SYNTEF lubricant during installation .............. oh, and one other thing, the shaft surface speed - the most important detail of all.
Sailboat props turn at reltively slow RPM's with low shaft surface speeds. In the above case, the surface speed of the 1" shaft (while cruising) was 270 ft/min with no damage occurring in over 1700 running hours. I think the photos demonstrate that 270 ft/min is a low enough surface speed to avoid any problems while running with no leakage. However, if the surface speed were continuously increased (as might be found in a high speed power boat with a larger diameter shaft), there would come a point where the heat from the friction would start to cause problems for the packing and ultimately the shaft if run dry. As the above shaft runs at 63 deg. F (17 deg. C) I suspect this overload point would not occur until there was quite a significant increase in the shaft surface speed.
And there you have it ............... "Believe it or Don't"
However, for a number of years I have been chiming in here on packing glands leaking and the fact I have run mine bone dry almost from the day I bought the boat new in late 1998 as a '99 model H310. As mentioned in several old threads, back in 1999 I discovered that if the stuffing box were packed with teflon impregnated flax, I could hand tighten the gland to the point where there was no water dripping and yet the gland stayed cool to the touch. Why so when this spells sure disaster for others ?
Many have said dry glands are a recipe for disaster or worse: the shaft will score, the packing will burn, the honey on the boat next to me will stop wearing short shorts, and my brother-in-law will come to live with us.
Biblical prophesies have nothing on this bad boy.I've heard it all and I can't say I understand any of it:
- I'm told the packing gland has to drip because sea water is a better lubricant than the teflon in the flax (if so, why put costly oil in our engines if water is such a good lubricant ?).
- I'm told the cross sectional area of the prop shaft can't possibly transfer the frictional heat of the rotating shaft into the cold, cold sea. No, it's really the two or three drops per minute of water leakage that carries the heat of friction away (try calculating just how much heat energy three drops of water contains even allowing for a 100 F. deg. temperature rise).
- I'm told the water leakage washes away the shaft scoring carbonates formed by the high temperatures in the gland (but if the shaft and packing never get hot in the first place, how are the carbonates formed ?).
Seems like every statement raises another question.
Well, given the miserable, sodden winters we live with here in Vancouver and having nothing more adventurous to do, I thought I would dig into this packing conundrum and try to make some sense of it. Dry, wet, hot, cold, what's it all mean ? Sleepless nights, irregularity, and quite possibly E.D.
I've got to make some sense of this mystery so it's off to the boat to gather a few numbers along with some pictures.
What makes this packing work very nicely without any leakage are such basics as: proper installation, light compression of the packing, ensuring the flax packing is indeed impregnated with teflon, maybe a bit of SYNTEF lubricant during installation .............. oh, and one other thing, the shaft surface speed - the most important detail of all.
Sailboat props turn at reltively slow RPM's with low shaft surface speeds. In the above case, the surface speed of the 1" shaft (while cruising) was 270 ft/min with no damage occurring in over 1700 running hours. I think the photos demonstrate that 270 ft/min is a low enough surface speed to avoid any problems while running with no leakage. However, if the surface speed were continuously increased (as might be found in a high speed power boat with a larger diameter shaft), there would come a point where the heat from the friction would start to cause problems for the packing and ultimately the shaft if run dry. As the above shaft runs at 63 deg. F (17 deg. C) I suspect this overload point would not occur until there was quite a significant increase in the shaft surface speed.
And there you have it ............... "Believe it or Don't"
