Is there a minimum length that the marine diesel heater silencer flex pipe can be on either the section after the heater or from the silencer to the hull fitting?

the total combined length of this marine silencer is 1.8 mtrs. There is no statutory minimum length to the input/output flex pipes, more often the exact installation dictates which side is trimmed to suit. For example, often it is required to install pipe downward from the heater exhaust out in a U BEND tohelp prevent condensate returning to the heater - this would require length of inlet being kept similar to as supplied.

Hope that helps a little