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 Posted 6/28/2013

SHEARWATER’S Sacrificial Zincs
By Tom Assenmacher
, VA


Back in August (2012), we received the following email from John Rilett, the owner of MOLLIKETT, a 1981 MK-II Sloop:
“Hi Tom,

I thought I would check in with you and give and update.  My son and I have move Mollikett out to Richmond British Columbia where we hope to do some cruising and where my son and family can use the boat.  We used Joule Yacht Transport to truck Mollikett out west.  They did everything they said they would for the price quoted.  We were very happy with their professionalism.  We are now putting Mollikett back together to get her ready for launch.  Her new home will be Saanich British Columbia. If I could ask you about sacrificial zincs.  Since Mollikett will be going into salt water for the first time she will need some zincs. She does have a prop anode but I don't think that would be sufficient.  Is there one "best place" to install a hull anode and what is the best way to do so.  I can find very little on the net about this topic.  What have you done with Shearwater? John Rilett Mollikett.”

In response, we sent John the following information:

You definitely need to install sacrificial anodes (zincs) to the underwater bronze components of your boat.  We use a  zinc on the prop, along with zincs on the cutless bearing housing; the center gudgeon on the rudder and the rudder shoe.

We bought our 1975 yawl SHEARWATER in 1982 from Whitby Boatworks (the original owner had bought a Whitby 42, and Whitby was brokering a few A-37s at that time. She had been in Toronto since new, and had never seen salt water, and did not have any sacrificial zincs installed.  As soon as we had her delivered to the Chesapeake, we immediately installed a prop zinc. 

The below photo shows the same kind of zinc which we have been using on SHEARWATER for years.  On our boat, there is just enough room at the end of the zinc to clear the rudder.  Most A-37s don't have room to mount a 'donut' zinc on the shaft between the cutless bearing and the prop.  The bronze cone on which the zinc is mounted acts as the second prop (jamb) nut.  Most chandleries carry this assembly.  The bronze cone is reusable, and the zinc fits over the cone, and is held in place by a 1/4" SS Allen machine bolt.  It 's a good idea to put some thread lock compound on the zinc attachment screw so that zinc stays on the cone.  The cones/zincs are readily available in 1" or 7/8" prop shaft sizes.   

The following are some photos from previous haul outs of SHEARWATER.


SHEARWATER's Prop Quite Fouled With Barnacles, Showing The Prop Zinc (Which Needs Replacing), Along With Part Of The Bronze 'Cone'.  Also Is The Teardrop Zinc Which Is Attached To The Hull With Bonding Wire To One Of The Cutless Bearing Mounting Bolts.


Note 'New' Zinc On End Of Prop, And 'Teardrop Zinc' With Bonding Wire To Cutless Bearing Housing Bolt.  Also Note Circular Zinc On Center Gudgeon (Could Also Use A 'Teardrop Zinc' Here).


Soon after we bought the boat, we noticed deterioration of the bronze bolts holding the cutless bearing housing to the hull, and also the bolts holding the two sections of the center rudder gudgeon, along with the bronze bolts holding the bronze rudder shoe to the hull.  These zincs were installed by drilling and tapping a 1/4" hole and using the SS Allen bolt that normally comes with teardrop (or circular) zincs.  The cutless bearing housing zinc was installed by drilling and tapping a 1/4" hole into the fiberglass 'deadwood' just in front of the prop aperture (the glass in that area is quite thick) - it's advisable to seal the zinc attaching screw with a good quality 'marine' sealant to prevent water intrusion into the deadwood fiberglass). 


After we installed zincs in these areas, we have observed no deterioration of the rudder shoe, gudgeon, cutless bearing housing (or their mounting bolts), nor any prop deterioration .  The zincs do require periodic checking and replacement (especially in marinas where there is a lot of 'stray current' or improperly wired dock power)!


Also take a look at the following link on the A-37 web site (http://www.alberg37.org/Project%20DB/ZincSolution2/A37_shaft_zincs.htm) by Gord Martin (MAGGY FIELDS), 


Another View Of 'Teardrop Zinc' On
Rudder Center Gudgeon.  We Drilled And Tapped A 1/4" Hole In The Gudgeon Body For The Zinc Mounting Screws. 




Teardrop Zinc Attached To Rudder Shoe.


(Ed. Note: We should note however, that this is ONLY OUR OPINION on how to protect against galvanic corrosion , but it works for us here in the Chesapeake Bay, and in the Bahamas.)