Like your project
. I'm doing a similar one, 42' steel
double ended cutter
. Much of my detailing is similar to yours. So I've been looking at a lot of the same questions.
Regards engines, with a metal boat I far prefer keel cooling
to the usual heat exchanger
cooled and a dry exhaust
eliminate the most common failure areas on marine
diesels. And they eliminate the need to buy a marine diesel
. With this setup you can buy an industrial diesel
for about half the cost. On my boat I have a Cummins 3.3L. They are available from 65 to 85 hp, with or without turbo. I bought mine for $3995 brand new from a dealer. They are compact, extremely reliable, and run at lower RPM
than the typical Yanmar
If your hull
type is what I recall
it has a rudder
skeg. This, if it is large enough, can be used as your heat exchanger
. This can be a a very clean setup.
Dry stacks can be run out of the hull
, just above the waterline, just like a wet exhaust
. This is done by cutting a hole in your hull about 1 foot in diameter where your exhaust exits and welding in a circle of 316L stainless, 1/8" thick, into the hole. The exhaust is 316L also and is welded to the center of the stainless plate. The stainless does 2 things: one it allows you to have a bare, non-painted area around the exhaust exit to eliminate heat damage to the paint
, and two the stainless has very low thermal conductivity so it severely restricts the heat which is transmitted to the hull.
There is now an American company which manufactures, in the US, galvanized 1x19 wire. I'd suggest you consider this as an alternative to the usual stainless. If the galvanized is painted with coal tar epoxy
(which has about 10 time the flexibility of standard epoxies and is more resistant to water
permeation) and then has a cover of closely fitting, thin walled UV resistant plastic tubing slipped over it (for UV protection) you will have a rig which is probably good for a lifetime. So long as it is protected from rust, galvanized is far longer lasting and long term reliable than stainless wire. It's also much cheaper. Another benefit to this is that the plastic tube covering is very slick and it reduces chafe significantly.
In the same vein, galvanized rig fittings have much to recommend them. I like to weld them up from 4130 or 4140 steel
. Up the mast corrosion
is not much of an issue, and these will be stronger and longer lasting than they typical stainless fittings.
Where you do need stainless for hi stress areas like rigging
I highly recommend you look at duplex stainless. I use 2205. Rolled Alloys is a good vendor. Much higher strength than the 300 series stainless and much higher corrosion
resistance. This is a far superior metal.