Part of the ongoing maintenance for a 25 year old sailboat is

cleaning the barnacles and critters off of the Data Marine Knot Meter sensor wheel.

     My 1979 Data Marine Knot Sensor was located in the thru hull, under the floor board, just in front of the head door.  You need the supplied extra plug ready to insert in the hole when you remove the speed sensor. This the same plug is also used when having a bottom job done.  You remove the pin in the thru hull, pull out the knot sensor and jam the plug in very quickly.

     You will get wet when you do this. This makes a good visual picture of how fast water would enter from just a 1 1/2" hole.  Now you have the sensor in your hand you can inspect it and give it a good cleaning.

     When I pulled the sensor out it was a mess.  Six months of barnacles and critters. It didn't even turn.  I know you can buy paint just for sensors or even go by the boat yard and and get a small cap full of bottom paint, but every time you paint that wheel you change the physical turning characteristics of it.  The paint builds up and soon the wheel starts to slow down and becomes ineffective.  It's protected but not accurate in it's ability to capture the flow of the water.  I prefer to just keep it clean.  It also gives you a chance to hand turn it and check the meter display.

You'll need some towels to mop up the water, marine grease to lubricate the sensor body when it goes back in, a small screwdriver and a small brass brush (as seen in the bottom right of the picture).

   The sensor is all cleaned and ready to go back in.  Don't be surprised if you find some live critters crawling out as you clean it.  Use the small screwdriver and brush to clean all of the edges of the wheel and wheel housing.  The area under the wheel is necessary to create an even flow of water and should be free from anything living.

     Coat the base down with marine grease to form a good seal with the gaskets.

     Get the towels ready for replacing the sensor in the thru hull.  Just get it in fast.  You can turn it after it's fully inserted.  Can't believe just how fast the water flows in.  The thru hull is positioned about 1' below the water line.

   Turn the base of the sensor until the pin hole aligns up with the mount hole.  Insert the SS pin and check for leaks.  I have attached some Wood plugs with sewing thread in case I need to plug the thru hulls in an emergency.  Low cost insurance for Pearson Thru Hulls that are glassed in and not bolted thru the hull.