Hi Jeff,
I highly doubt that Catalina installed your knot meter. The electronics were installed after the boat was purchased from a Catalina dealer, either by the dealer or by some one the new owner hired after taking delivery of the boat. We have an 88' boat as well (#551) and I know from the filled holes on the cockpit cabin top bulkhead that our boat is on least its second set of electronics. We currently have the Raymarine ST60 Wind and Tridata displays with the corresponding thru-hull sensors and mast head unit that were installed by the previous owner. The thru-hulls in our case are plastic. Typically the thru-hulls and electronics are sold as a package. If the thru-hulls are plastic, I would check with the manufacture for availability of a replacement to have on hand before attempting any repairs. If they are metal then they will more than likely be reusable unless they are severely corroded.
Before going any further you may want to check that the nut holding the paddle assembly into the thru-hull is the source of your leak. Then simply tighten the nut slightly may be all that is required to stop the leak. Let me explain. In our knot meter thru-hull there is a flange nut that holds the thru-hull to the hull and another nut that holds either the paddle assembly or a plug in the thru-hull. This may be the case with yours, but you will have to check your boat to see. Ours is made of plastic and I can hand tighten it to stop it from leaking from when I change the plug for the paddle assemble before we go sailing. If the thru-hull is leaking between the hull and the flange holding the thru-hull to the hull then read the following:
The removal and resealing of the thru-hulls will require a quick haul by a boat yard. The thru-hull can be removed by removing the backing nut and using a jig made from some 2x4 wood and a 12" long 3/8" threaded piece of all-thread, washers and nuts to pull the fitting from the hull. Take the 2x4 stock and cut three pieces of wood from it to make a u-shaped piece that will just straddle the thru-hull from the outside with the verticals of the "U" to be equal to the height of the thru-hull fitting. Now drill a 3/8" hole in the center of the horizontal part of the "U". Now cut a 4" length of 2x4 and drill a 3/8" hole through the center of the "square" side of it. This will be the backing plate inside the boat that will force the thru-hull out of the boat. Take the section of all-thread rod and put two nuts on one end and tighten them against one another to lock them in place. Now take the all-thread rod and a washer and place the washer on the backing plate and push the all-thread through the washer and hole in the 2x4 backing plate. Now take the backing plate and all-thread, and from inside the boat, insert the all-thread rod into the knot meter thru-hull after removing the paddle assembly. Now from the outside of the boat, place the top of "U" shaped piece against the hull while inserting the all-thread through the hole in the horizontal part of the jig. Place a washer and nut on the all-thread rod and tighten the nut until the wood jig is draw to the hull. Now take a wrench and tighten the nut. this may require a helper on the inside of the boat holding a wrench on one of the two nuts tightened against one another to prevent the all-thread rod from turning as you tighten the nut on the outside of the hull. This will extract the thru-hull from the hull, The force required will depend on the sealant used to install the thru-hull. Hopefully not 5200. Once out of the hull, cleanup the hull and the thru-hull and apply sealent and reinsert into the hull and tighten the backing nut. Hope this helps
Paul & Cyndi Shields
