T&T: Prop shaft tube - corrosion

[Mark Andrew]

Greetings all,

Got a 50 year-old Great Lakes trawler (on the blueprints it's called a
'Cruiser') undergoing complete renovation.  Everything inside has been
removed but the main engine.  After sandblasting and epoxy-coating inside
and out (just below the waterline thus far), I'm now dealing with engine
room systems.

The fellows and I working on the boat are sweet-water sailors with little
salt-water experience with the corrosion that exists. So we're trying to
anticipate blue-water cruising requirements.

The system at hand is the sea chest and re-commissioning the plumbing to the
prop shaft tube.  The tube is quite large, and houses the shaft with a
packing fixture just before the transmission, and at the other end, a lead
bearing.  Just ahead of the propeller itself there are two forward-facing
little scoops with a 3/4 inch hole on either side of the shaft tube
presumably to let water in to lubricate the lead bearings.

Just abaft the packing at the inside end of the tube, there was plumbed 1/2
inch piping.  Originally this piping came from the old Kahlenberg engine.
When the previous owner removed the original engine and replaced it with the
Cat3306, he had this plumbing to the shaft tube plugged.

I'm also assuming that the plumbing to the shaft tube provided fresh sea
water to the tube so that stagnant water would fester in the deep recess of
the tube.  We plan to plumb from the seachest strainer thru a small pump
direct to the prop-shaft tube such that every time the engine is turned on,
the pump will create a small flow into the shaft tube.  I figure this was
the original setup.

My question:

How do we ensure minimal corrosion otherwise in the shaft tube?  I would
imagine like much of the boat, there may be a leaded wipe coating on the
steel, but if this isn't the case (and I've never had the shaft out of the
tube), how do most steel boats like this protect an inaccessible,
essentially part-of-the-hull, area like this?  So people paint their shaft
tube?  The tube on the boat is about 6 feet long.

Just wondering what standard practice is.  Worried that the whole boat will
be epoxy coated and the weak point of the hull be become the prop shaft.

Thanks for any ideas or expertise,

Mark Andrew
"Black River"
Holland, MI
56' steel, circa 1955