STERN GLAND – EXHAUST ELBOW RISER
After all the problems with the traditional packing stern gland in June, we finally decided to replace the system. This piece of gear had to be removed without taking out the shaft. But on Contessa’s, the shaft can be extracted only if the rudder is down. That meant a lot of extra work for us. Moving the engine a few centimetres forward was much easier. This was done in a couple of hours.
The packing was first removed and checked. It was totally dry and very tight around the shaft. To replace it in the future would have being another complicate task.
The new Radice RMTA shaft seal looks like an upgraded Volvo seal. The main advantage of this system, is the extra water inlet which lubricates the rubber lips. The second inlet with the cap, is there to add grease. Much more simple than our previous packing stern gland, this seal does not drip and does not require any special adjustment. Another main issue on the Contessa, was the outer diameter of the stern tube (38mm) and that was also the reason we chose a Radice instead of a Volvo seal.
On the Nanni diesel engine, the new exhaust elbow is now made of casted aluminium. If our engine was not so much under the water line and especially not so close to the waterlock, we could have kept this exhaust elbow. But the height in between the exhaust and the waterlock had to be increased. On other Contessa’s some of the owners did the same arrangement in order to avoid any sea water flowing back to the engine.
In general, when we dismantle something on the engine, we always note down the position of each part. This procedure makes things much easier when is time to reassemble everything back together.
The new exhaust elbow riser was first designed with PVC plumbing pipes. Those were connected together with insulating tape. As a main flange we used a piece of plywood with the exact thickness.
The mock-up was then taken to the work shop and assembled temporary with few welding points. We used 316 stainless steel pipes with a thick wall and then, tried the part on the engine to check height and position.
The mixer is the most crucial part of the exhaust elbow. It is where the cooling water meets the exhaust gas. Its inner diameter had to be wide enough to allow water coming out.
Then, it was welded with 316 welding rods and polished thoroughly. Well polished stainless steel also prevents rust in the long term.
When the engine is running, the exhaust elbow heats up quite a lot. Therefore, the metal had to be wrapped with special fiberglass tape to reduce the heat transfer.
A last but important step in the exhaust line was the installation of an air vent. This little item, includes a valve which prevents sea water from returning back to the engine when it stops. Ideally it must be installed about 40 cm above the water line. It is also important to clean regularly the valve in order to avoid the formation of salt crystals, which could block the device.