Projects for Renegade, Would like opinions & ideas. reality check.

[polecat]

I'm removing and glassing over all the thru-hulls with the exception of the raw water intake.  While I'm at it I want to move the exhaust and bilge pump thru-hulls from the transom to just under the transom but above the water line - do I need seacocks on these?  When done there will be about 20" from the exhaust output tip to the top of the copper exhaust  tube riser bend.  about 8" more than there is now. The exhaust tip will be about 8" above the water could a rising wave from the stern push water up the exhaust and back flood the engine?

[AdriftAtSea]

Polecat-

I'd install a seacock, or at least a check valve, since there would otherwise be the possibility of the engine getting flooded and hydrolocked via a pooping wave.  I think the check valve would be easier to deal with, since you wouldn't have to "open" it every time, but you'd have to check how it would affect the exhaust flow, since it would increase the back pressure in the exhaust system. 

IIRC, it is generally recommended that any seacocks within 6" of the waterline be equipped with a seacock.

[polecat]

Atsea - From what you say, I'd go with a bronze sea cock.  I've never had much luck with check valves - also no way to tell if it's working or not till your oil turns light grey.  How do you think the PTFE seals will hold up in a hot saltwater/exhaust environment?  A little internal leakage wont hurt anything anyway  - - even with failing seals it will inhibit a high pressure surge from getting over the hump & down to the engine.  Do you know what they made the exhaust tubes out of?  This one looks like copper.  There is a riser of sorts at the exhaust manifold where the water is injected and then it goes slightly up hill till it gets to near the top of the lazerett (This is all 2" copper looking pipe) it isn't thick enough to clamp to it so will have to braize it some way to make attachment to the sea cock.  One lucky thing - the Renegade has a huge lazerett to work in.
jim

[Lynx]

As I recall, Cruising encyclopedia has some words on exhaust thru-hulls. Mostly big boat stuff.

[AdriftAtSea]

Teflon has a pretty high temperature resistance rating...so should probably be fine for exhaust hoses.