This is from PSS installation instructions. I have a PSS seal on my inboard and has a pressurized system to feed water for lubrication. Method B in the instructions. If for some reason the dynamics of your hull around the exit point of your prop shaft causes a vacuum during running, it could create a dry seal. I would then go to method B to pressurize the system.
From the instructions:
15. Plumbing the system:
15A. Low speed boats
Under 12 knots of boat speed under power).
Note:Sailboats or displacement powerboats with a powering speed below 12 knots can use either method A or B.
Using a 3/8 ” ((8 or 9 mm)ID “underwater rated ” hose ((not provided with the PSS), connect the hose to the hose barb fitting installed on the carbon and secure the hose with two (2)hose clamps.Run the hose to a point in the boat at least two (2)feet above the waterline,making sure that the hose does not apply any load on the carbon part of the seal.Keep the hose as close as possible to the centerline of the vessel so the top of the vent hose is never below the waterline,even if the boat heels.Secure the hose in place with the necessary fittings that insure it will not pull free and drop.This hose is now a venting hose that will help ensure that no air is trapped in the seal.
WARNINGS: Do not run a loop at the top end of the vent hose as it could start a siphon action in some extreme conditions.Also,make sure the vent hose is properly secured from falling below the waterline.If the vent hose were to fall down below the waterline, water would come in the boat.Also,do not plug or block the end of the vent hose,as this would prevent the line from venting.
Over 12 knots of boat speed under power).
Note:Boats that can exceed 12 knots on a single engine must run a crossover line between seals to ensure both seals maintain water flow. For high-speed vessels it is required that a water supply be plumbed to the PSS for the purpose of cooling and lubricating the seal faces (i.e.,at over approximately 12 knots of speed a vacuum is created in the stern tube and water is drawn away from the PSS resulting in a loss of cooling water that may cause the carbon to over heat).There are multiple sources of water for this supply.The following are a few non-exhaustive examples. These are examples only and they may or may not apply to your particular boat.
-T-off the engine raw water-cooling line.(Note:T-kits are available separately from PYI, Inc for internal hose 3/4",1",1 1/4",1 1/2")
-Thread a barb fitting into the drain plug of the heat exchanger if applicable.
-Thread a barb fitting into the drain plug of the exhaust manifold if the manifold is raw water-cooled.
-Add a small scoop under water for keel-cooled boats or t-off another water pick-up.
(Note:A valve must be installed to regulate the water flow as too high a water flow may over pressurize the PSS seal).Use an appropriate “underwater rated ” hose from the fittings on the boat and the fitting on the PSS and secure them with two (2)hose clamps at each end.
NOTICE:All plumbing must follow the standards and practices of proper boat plumbing.
For example,if the pick-up on the engine is located under the waterline,an anti-siphon fitting must me installed,in addition to other standards and practices.
16. Testing:When launching the boat,inspect the PSS and make sure the PSS is properly in place.Water should not be entering the boat from the PSS seal area.Run the engine in gear as in a normal operation.It is normal at this time to notice a very fine spray or mist coming from the seal and some carbon dust,as the PSS requires a break in period (see below).The PSS should not be leaking at rest and should never spray more than just a fine spray or mist.
If you hear a high-pitched squeal from the PSS shaft seal during operation,the seal may not be getting water.Review and correct plumbing to the seal.
CAUTION:If the seal has run dry use caution!The faces (stainless steel rotor and carbon)may be very hot.