Hi Ricre2, I am not quite sure of your description of RISER on your engine
.I assume it to be the salt water
inlet... The use of ordinary aluminium is definitely a NO NO. . Although there is a salt water
resistant aluminium alloy. Copper, Bronze, Plastic, even heavy gauge steel
, are more resistant to salt water
than Aluminium. However if it is the alternative term for the exhaust
pipe, then a fabricated part from ordinary steel
is nearly as durable as cast iron. and far more durable than Aluminium.. H the boat.