Seawater filter position

[stuey_two]

The instruction manual for my Nanni 3/21 diesel says that the seawater filter must be at least 15cm above the waterline. Can someone tell me why? (The engine was installed by a Nanni-approved dealer- now defunct - with the filter level with the waterline)

 

[Tranona]

Having the filter above the waterline allows you to check and clean without closing the seacock. Also any (unlikely) failure will not result in water coming into the boat. It is useful to have the strainer immediately above the inlet seacock so that you can clear any obstruction by rodding down the inlet pipe.