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Hi to all, as part of my repaint refit, i am considering changing my rear exit 8inch exhausts to either side exit or possibly underwater exhausts with idle reliefs, i have a Bertram 42 with 465hp 6V92s,and there seems to be varying opinions on whats best, the boat has a large swim platform (as we don`t do a lot of game fishing) and quite a big cockpit canopy all of which helps create negative air pressure and with it the associated back draft of exhaust fumes, which id like to change, any and all thoughts welcomed, and thanks for reading this
Regards Todd

I have a 62’ spencer with 1800 mans with underwater exhaust, all u hear ever is bubbling, never any exhaust smell, idle or cruise. They are also great when deep dropping, no smell or spray when backing into seas. I also have a 31 Bertram with 330 Cummins and side exhaust , have not seen/smelled any exhaust but once a top is installed over the cockpit, the station wagon effect could be possible. I do get some spray in certain conditions when maneuvering during deep dropping.

you have a Spencer!!!!, you have my dream, Oh that`s a boat, ,we just don`t have boats like that down here,, Green with jealousy , that acknowledged , Given the choice which would you go for Under or side, relative costs are quite close so its not a money thing

I don't know the calculations involved for underwater exhaust back pressure---I do remember a local boat in Freeport,NY ---The BOAT----a Hatteras --were the owner converted to underwater exhaust and kept blowing motors---this was 30 years ago--- probably not dealing with the same animal.

Underwater, butCraig brings up a valid point, exhaust pipe size or some other factors may need to be taken into acct. I’m sure others will provide more imput,I’ll see what I can find out

Look at this thread and you’ll get a lot of answers:


31FBC Waterline Change After Repower