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Exhaust skin fitting

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We are needing to change the exhaust skin fitting as we are putting a new motor in and want to make sure the new fitting is approved for Cat 1. The website that details the regulations is in fact not very detailed about what to use. If anyone can enlighten us we would appreciate it. Cheers.

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Ok, I'll put the jist of it here. Just IMO. As always, use my advice at your own risk!


Go for a proper Naval Bronze skin fitting. Some Are chromed, that's ok. BUT be certain that it IS naval bronze - there are some cheap crap brass ones out there!! Yes, I know it's not immersed (mostly), and is therefore not normally prone to electrolysis, but it is a critical through hull that is not normally closed, and can sink you if it fails in choppy conditions - or if heeled on a side exit.


2nd choice would be a GRP one, as they are more heat resistant than the plastic ones, which have been know to melt if the cooling water stops!!


Remember that the installation of the exhaust is a critical thing - diesels don't like water! Make sure your loop goes up nice and high, consider a flap if the thru hull is transom mounted, AND have a way to block it (soft wooden plug, seacock) if it becomes necessary.


There are multiple suppliers of these around, and the engine supplier will have them to I'd expect. GMS in Auckland and Fosters are two...


I'm not aware of any Cat 1 requirements re materials. Tim might come up on here if I've forgotten something that is actually there!



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There are some critical dimensions to a good system - see link:





The waterlock muffler should be in line with the exhaust manifold fore and aft and the muffler should be as low as possible in the bilge and the loop as high as possible. Our installation originally had the muffler on the other side of the centreline. This caused water to enter the engine when the boat heeled as the muffler height relative to the engine was reduced when heeling.

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Thank you everyone for your input. The job is progressing, unfortunately having to return to my paid work is slowing things down :( Rather frustrating with all of the perfect weather we are experiencing in Wellington at the moment. Chees

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