There are several types of seals, which are divided into two key groups – face seals and lip seals.
Both use an articulated rubber sleeve to keep the water out, and are similar in appearance, but lip seals seal via a lip, or sometimes two, whereas a face seal uses a collar that attaches to a surface on the end of the articulated hose.
Considered the most efficient way to seal a shaft, the PSS (Packless Sealing System) shaft seal is a mechanical face seal, which uses the seal created between the flat surfaces of the rotating stainless steel rotor and the stationary carbon flange. The carbon flange is attached to the stern tube via an articulated rubber bellows. The carbon flange contacts a stainless steel rotor that fits securely around the shaft, and is fastened on with grub screws and seals via two O-rings sunken into its bore. The bellows is installed on the stern tube and is then compressed a set distance by the stainless collar, creating a solid and even seal between the carbon flange and the stainless rotor.
Volvo Rubber Stuffing Box
Volvo Penta’s solution is commonly called a ‘rubber stuffing box’, and is quick and easy to install, and takes up minimal space, as it combines the rubber hose with a lip seal in one assembly, with no moving parts. It has an internal, water-lubricated bearing and lip seals which must be greased annually. It comes with a single, wide hose clip, secured with machine screws, to clamp on to the stern tube. As it does not have a pressurised water feed, after launch, it must be ‘burped’ to remove air.
Tides marine Sure Seal and seriesOne
This is a propeller shaft sealing, which is suitable for a wide range of shaft speeds and ambient operating temperatures, and commonly fitted to power boats, yachts and commercial crafts. Created from fiber-reinforced composite material that is non-corrosive, it is strong, durable and practical, as there are no moving parts. A pressurised cooling water supply is required to lubricate the lip seal and alignment bearing in the seal head. The seriesOne model is produced in the same way as the Sure Seal, yet is designed for smaller, single-engine vessels with stainless steel propeller shafts.