Thanks to everyone for the ideas on a sacrificial steel strip
beneath the keel. I have just learned this is properly called a keel
shoe.
In my behalf, Bruce Kessler contacted a former Northern Marine expert
familiar with the process, and here's what Bruce reported:
-
Northern originally used to use 304 stainless steel plate which
proved to rust too much, so they then tried 308 and 316 stainless,
but because of the high price of 308 and 316 they are now using epoxy
coated A36 steel.
-
For a Nordhavn 47, the steel should be a minimum of ½ inch
thick. Larger yachts might use steel up to 1½ inches thick.
-
At Northern, the steel which will eventually make up the keel shoe
is cut into sections to fit the keel, with the fore and aft edges
beveled at a 45 degree angle. The steel is then drilled and tapped
for large counter-sunk flathead bolts.
-
Once the steel has been cut to fit, drilled, and tapped, it is
fastened to the boat using the flathead bolts tapped into the
fiberglass keel. In addition to the mechanical bond with the bolts,
3M5200 is used liberally along the entire length of the keel.
-
A means needs to be provided for getting a bonding wire or strap
from inside the hull to make solid electrical contact with the keel
shoe. This is typically done before the 5200 gets into the act.
-
Once the 5200 has dried, the beveled pieces of steel are welded
together to create a single solid unit to make up the keel shoe.
-
When the process is completed, the steel is coated with two coasts
of epoxy primer and bottom paint.
--Milt Baker, N47-32, shipping late April
Thanks to everyone for the ideas on a sacrificial steel strip
beneath the keel. I have just learned this is properly called a keel
shoe.
In my behalf, Bruce Kessler contacted a former Northern Marine expert
familiar with the process, and here's what Bruce reported:
1. Northern originally used to use 304 stainless steel plate which
proved to rust too much, so they then tried 308 and 316 stainless,
but because of the high price of 308 and 316 they are now using epoxy
coated A36 steel.
2. For a Nordhavn 47, the steel should be a minimum of ½ inch
thick. Larger yachts might use steel up to 1½ inches thick.
3. At Northern, the steel which will eventually make up the keel shoe
is cut into sections to fit the keel, with the fore and aft edges
beveled at a 45 degree angle. The steel is then drilled and tapped
for large counter-sunk flathead bolts.
4. Once the steel has been cut to fit, drilled, and tapped, it is
fastened to the boat using the flathead bolts tapped into the
fiberglass keel. In addition to the mechanical bond with the bolts,
3M5200 is used liberally along the entire length of the keel.
5. A means needs to be provided for getting a bonding wire or strap
from inside the hull to make solid electrical contact with the keel
shoe. This is typically done before the 5200 gets into the act.
6. Once the 5200 has dried, the beveled pieces of steel are welded
together to create a single solid unit to make up the keel shoe.
7. When the process is completed, the steel is coated with two coasts
of epoxy primer and bottom paint.
--Milt Baker, N47-32, shipping late April
