Dripless Shaft Seal vs Dripless packing

zeehag · Aug 13, 2012

i like mine--is dripless packing by gore tex. i use in my ericson and my formosa. on formosa i also use dripless for my rudder post packing. good stuff.

reworb · Aug 13, 2012

I have a Yanmar engine and a Volvo Dripless shaft seal. I was told by a Yanmar factory mechanic who worked on the boat and knew about the shaft seal to leave the transmission in neutral when sailing. Since you said "that rules out a dripless for me" I hope I'm not doing any damage.

I really like having a dry bilge over the wet bilge I had in my previous boat

navigator97 · Aug 13, 2012

I have a Yanmar 2GM20F Diesel and use the dripless packing compound, and have for quite a few years. I too keep the transmission in Neutral while under sail. For packing there are essentially 3 rings of packing. The 1st and 3rd are the Teflon impregnated Flax. The middle ring is the green Teflon Putty that is rolled into a "string and put in as a ring. No drips, no heating, no problems.

Rick I · Aug 13, 2012

Why would sailing with the transmission in neutral rule out a dripless shaft seal. I've done eight seasons with a dripless shaft seal and always sail in neutral.

Steve Dion · Aug 13, 2012

Bill

This is a first that we have heard about this issue. Do you happen to know which brand your friend was using.

The early PSS shaft seal units did not have a hose. The user just needed to "burp" the unit when the boat was relaunched.

Rick D · Aug 13, 2012

Re: re. why not dripless shaft seal if in transmission inneu

Yea, get more details and advise. Whatever kind they had sounds like a positive pressure unit of some type The PSS and others I know of are not pressure and should have no such issue that I can conceive of. However, not 'burping' an old style PSS like mine after a launch will fry it.

gfrazzle · Aug 13, 2012

The hose that is attached to the dripless housing is to vent the water that tends to collect, when motoring in reverse, OUT of the shaft seal. Mine is vented to a collection bottle which I empty from time to time. I sail in neutral with no adverse affect. Either sailing or motoring, the wear on the seal should be the same.

JK_Boston_Catalina310 · Aug 14, 2012

I have seen PSS installed like the OP described on power boats. I questioned one guy and he thought I was crazy for suggesting a mainesail style collection bottle or just letting the little bit of water go into the bilge. He put a threaded barb on the drain to the heat exchanger and connected the tube from the PSS.

To me it makes no sense to connect the PSS to your engine. I am looking at installing a PSS in the next couple of years and plan to do a similar install to MS.

alexco38 · Aug 14, 2012

Connect the PSS to the engine is for high speed (on plane motor boat) application. (Read the manual). When the boat is on plane, the shaft left the water and will not be cooled.

The small hose for sail boat is to vent the air trapped after launch so you don't have to burp. The older PSS has to burp in order to get rid of the air pocket. With air pocket, the seal gets hot. Ask PSS to see if they will sell you a collar with the hose attachment.

Not sure what a bottle is used for. There is no water coming in. Just air going out. The hose must be above the highest water level.

No a drop after 6 years on my boat.

Scott T-Bird · Aug 14, 2012

That's right, there is no diffence between the shaft spinning when sailing and the shaft spinning when motoring. The cooling water comes from the shaft log. The hose is simply to relieve air pressure and allow water into the chamber if it is dried out from a period on land. The hose needs to be connected to the engine cooling system only for a high-speed application.

If the end of the hose isn't placed high enough on a sailboat, the manual says there could be a small discharge of water if a burst in reverse is strong enough, or if sailing at a high degree of heel.

If the PSS began leaking water, it was probably because the set screws were loosened (it's a mistake if somebody loosened them and then attempted to re-set) and the seal was able to back out. You are supposed to get new screws if you ever loosen them. Many people use a locking nut of some kind on the transmission side of the shaft to make sure the seal doesn't move.

JK_Boston_Catalina310 · Aug 14, 2012

I stand corrected on connecting the PSS to the engine. I haven't read the manual because I haven't installed it.

This still doesn't explain why billt1's friend installed it that way on a sailboat. I still stand by that I would not install it that way when I make the conversion.

To the collection bottle, MS said he was having the issue with a small amount of water coming out when in reverse. I have also ready about the issue when healed over and hose end is below the water line. So I plan to follow his installation method.

Rick D · Aug 14, 2012

The Definitive Answer

billt1 said:
A friends boat almost sank recently due to seal burnout on a dripless.

he followed the yanmar instructions and sailed with transmission in neutral. he doesnt nave a shaft lock nor feathering prop so unfoirtunately the shaft spins and the dripless gets no water for cooling/lubrication it will eventually burn out. he confirmed it his did by taking out the dripless and inspecting. during normal operation when engine is on the hose going into the unit carries water from the engine raw water exhaust. You can google to confirm seal burnout if no cooling water supplied

billt1 said:
he had it installed about 4 years ago. I guess it can take a while to fail. anyways water was squirting in from the at a fast rate.

The following is from the PYI, the PSS manufacturer:

Hi Rick,

This will not be the case in a sailboat / low speed application where there
is always water present for lubrication from the stern tube. There will be
no difference when motoring or sailing with a freewheeling prop as the
lubrication is not a positive feed from the engine but from the stern tube.
Depending on what model PSS Shaft Seal you have ('standard speed' (no hose
barb on carbon) or 'high speed' (with hose barb on carbon)) you may need to
'burp' the seal (with standard speed) when the boat is launched (to purge
the initial air that develops in the stern tube / seal). If you are running
a vent line off the carbon (with high speed version) you will not need to
burp the seal as this is the function of the vent line that should be run
2-3 feet above the water line and purge any air that gets into the tube.

I hope this helps and clears things up for you.

Maine Sail · Aug 14, 2012

A few thoughts:

#1 Your friends seal was installed incorrectly for a sailboat. Despite what PYI says, and I have had this discussion with Fred H., some boats are more prone to collecting air in the shaft log throughout the season and may need multiple burpings per year. Our Catalina 36 was notorious for entrapping air in the shaft log and required multiple burpings per season. Short quick blasts from reverse or crash stops can force air up into the log where it can't escape if there is no vent or way out. With the engine shut off this is likely the case, he trapped air and with the engien off lacked water lubrication..

#2 On sailboats the vent is there to evacuate any entrapped air and allow the water to reach the seal and keep it lubricated. Without the vent you may need multiple burpings per year on some boats. Some boats never need more than one burp but all boats are not the same and some trap more air up the log than others.

#3 Many boats with PSS vents suffer from expelling water out the vent tube. It is a matter of the height of the vent tube, your prop, how hard you back down and the gap around the shaft in the shaft log. I have one customer who never new this was happening until his engien got badly rusted. Every time he opened it the engine was dry but it began rusting badly. The engine heat baked off the moisture but left behind the salt. There are a number of ways to deal with this and I've used two that both work well. The bike water bottle and a hydronic heating system air vent both prevent the water from being blasted out of the tube.

#5 Running ANY type of packing gland dry, drip free or unvented CAN result in the seal not getting enough lubrication and you can overheat both a PSS type or standard traditional
packing. Letting a traditional box drip some keeps the air out and also brings fresh oxygenated water to the shaft which helps minimize shaft corrosion up in the log. The vent on the PSS does the same..

Both systems work but installation errors are bad with both systems. Sadly your friend got a poor installation...