PSS Failure on only one shaft

[HeywoodJ]

If the prop hub has slid forward and its face is against the strut then I would suspect that the PSS collar has not budged. Others have suggested the engine mounts, which could be a cause. But my first suspicion with these symptoms would be the shaft coupling.

With the vee drive the shaft end passes all the way through the coupling. The shaft is free to slide forward until the prop hub hits the strut, or aft until the prop hits the rudder or the PSS bellows compress completely. If the shaft slides forward in the coupling this opens a gap between the PSS collar and the bellows, that looks line the collar has slid.

We have vee drives, and every time I make shaft adjustments I write two measurements on the bulkhead in front of the shaft; the distance from the end of the shaft to the coupling face, and the distance from the end of the shaft to the bulkhead. This makes it very easy to check for slippage of the shaft inside the coupling. And I speak from experience, I started this notation system after finding a very polished prob hub and strut where the engine was run in gear after the shaft had slid forward in the coupling.

Many of the vee drive couplings I have seen are the compression style (no set screws) and if the shaft diameter/coupling fit is not perfect it is not hard for the shaft to slide in the coupling.

[HeywoodJ]

Another few thoughts:

New PSS means shaft was out of coupling and put back in.

A wrapped line and sudden stop results in extra torque on shaft, which could loosen coupling.

If you have been sliding the PSS collar aft to compensate for a shaft sliding forward then, if you slide the shaft aft you will have to slide the collar forward and there is risk of o-ring damage from the set screw dimples.

[osprey877]

Tie the boat securely to a dock, then have someone alternately rev the engine in forward and then in reverse while you watch what Happens to the PSS., the shaft coupling and the motor mounts. This should tell you where the problem is. Good luck.

[skipperpete]

The big problem with that Vee drive is that the shaft seal (PSS) is under the engine and hidden from view. It also occurred to me that I’ve seen Shaft seals hooked up to the raw water circuit, does anyone know if a dripless seal could be made to leak if the seawater pump pressure was too high? .... just wondering!

[mvweebles]

Originally Posted by rslifkin

Regardless of the PSS issue, if the seal separating is more than your bilge pumps can keep up with then you desperately need to upgrade your bilge pump setup. The factory install on many boats is nowhere close to adequate.

Having seen a PSS failure where collar loosened and slid forward, the amount of water intrusion is breathtaking. It's not a leak but rather equivalent of a hole. "Gushing Water" is not an overstatement. Bears little resemblance to a conventional packing gland with packing removed. Surprising how much water can pass the cutless bearing.

I agree that few boats have dewatering capabilities that include a holed hull. Frankly, off the shelf pumps are designed for serious dewatering.

I recently went from PSS (face seal) to Tides (lip seal).

[rslifkin]

Originally Posted by mvweebles

Having seen a PSS failure where collar loosened and slid forward, the amount of water intrusion is breathtaking. It's not a leak but rather equivalent of a hole. "Gushing Water" is not an overstatement. Bears little resemblance to a conventional packing gland with packing removed. Surprising how much water can pass the cutless bearing.

I agree that few boats have dewatering capabilities that include a holed hull. Frankly, off the shelf pumps are designed for serious dewatering.

I recently went from PSS (face seal) to Tides (lip seal).

I agree, it's a lot of water. But in my mind, pumps should be sized to a failure of the largest hole below the waterline. So a broken off engine intake through hull, missing transducer, or missing prop shaft in most cases. Being able to keep the water level down and buy some time while you find and band-aid the problem is huge.

[AKA-None]

Originally Posted by rslifkin

I agree, it's a lot of water. But in my mind, pumps should be sized to a failure of the largest hole below the waterline. So a broken off engine intake through hull, missing transducer, or missing prop shaft in most cases. Being able to keep the water level down and buy some time while you find and band-aid the problem is huge.

My current pump was almost able to keep up when the shaft pulled fully out of the hull and stopped when it hit the rudder
A lot of water comes through a 1+ inch diameter hole

[SVTwilight]

Originally Posted by juliogustav

Thank you all for the response. I believe the issue might be the engine mounts. They had been replaced 3 years ago, but maybe with the folding prop, v-drive, length of shaft, strut placement, and folding prop, there is just to much opportunity for the shaft to move. Something is causing the pss to push apart. An no one has mentioned water pressure of why one side would be an issue. Give me a few months and I will get back with you. As for a pump. I have two submersible pumps. A PSS failure can create quite a bit of water coming into your boat. New PSS, setscrews, shaft coaler, good allen wrench have all been used. Thanks

I have used PSS for years across 3 different boats. The stainless collar ring should hold, but yeah they can slip. I always place a shaft zinc next to the stainless collar. No more slipping.

[RedneckRedcoat]

Make sure you put some locktite Blue on the second set of grub screws and also make sure you tension the bellows to the correct tension.

We learnt the hard way after the installer of our PSS did not follow the instructions.

I’d also make sure you got the right diameter stainless steel collar for your shaft and the o-rings inside the collar are also changed out.

Like others I’d be more concerned with you shaft being able to move sounds like the coupling is not set right or the bearing has gone out

[Distant_Shaws]

I have a PSS seal where the collar moved when motoring.

The grub screws are stainless steel so quite soft and do not really bite into the shaft like a

HT grub screw would.

I fitted a split collar on the shaft to prevent the PSS collar moving.

No movement since.

I have a flanged pillar block to take the thrust and prevent the engine taking any thrust and moving allowing the PSS seal collar to move and allow water to enter.

[PMac456]

I put a zinc collar in front of the stainless ring...just as backup. Never an issue!

[Mark Johnson]

Put a zinc on the shaft as a stop. 10 years is the life of a bellows. Change it out.

[Jim Cate]

Does anyone know why PSS uses this kinda mickey mouse set screw system instead of a single long screw with a head incorporating seizing wire or a lock nut? This seems to be standard on lots of shaft couplings and other hardware and is (IMO) less prone to failure.

Jim

[colinalleck]

Just wanted to check that you are using 2 set screws in each hole ie 4 in total with loctite ?

Cheers Col

[juliogustav]

Skippepete, thank you for the help. I have attached some pictures of the engine mounts with descriptions on each photo title. All my PSS issues have been with the starboard side. What do you think of the mounts? The newer ones had been done by the local boatyard. The older ones (over ten years old) have been done by the older owner. The previous owner new a ton about catamarans but has since passed away, so I cannot ask him about the mounts.