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Drilling a hole in cast iron keel

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William Matley
1st Mate

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52 Posts

Initially Posted - 04/22/2003 : 21:36:29

If my dad was still alive I'd ask him, but I'll have to rely on the collective wisdom of this group.

I remember from my metallurgy class in college that cast iron has a high percentage of carbon in it and that carbon makes the cast iron keel very hard. I'd like to install a zinc on my keel to protect the cable from corrosion. I just need to drill a small hole to mount the screws. I thought that drilling a hole would be a tough job, it is!

So collective body of great wisdom, lets hear your tricks. What will it be carbide, diamonds, what should I try?

Edited by - on

luckystar
Navigator

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USA
236 Posts

Response Posted - 04/23/2003 : 00:18:36

I, too, will be installing zincs when I haul out and talked to lowell at catalina direct. His advice was to thru-bolt them with 5/16" bolt that they send with the order of zincs. He recommended getting a cobalt drill bit and using a drilling lube/liquid and drilling the hole about 5 in. ahead of the keel eye bolt about 4 in. from the aft edge of the keel where it's only about an inch or two thick. Hope this helps.

Patrick Burnett, Little Rock, AR
S/V Lucky Star #2707 1982 SK/SR<br>
<img src="http://www.proxycreative.com/clients/luckystar/luckystar_0602_sm.jpg" border=0><br>
http://www.proxycreative.com/luckystar.html

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/23/2003 : 06:41:22

William,

I recently added zincs to my swing keel near the lifting cable attachment. I drilled about 1" to 1-1/2" deep, and tapped for 5/16"-NC threads. I attached two pancake zincs with stainless steel allen head machine screws. I don't remember having any problems with the drilling or tapping, although cast iron is a little "crunchy" to tap. Use a good quality sharp tap, cutting oil, go slow, and clear the tap often. Be sure to clean out the hole thoroughly before installing the SS bolt. If there are any metal chips, the SS threads might jamb, making it impossible to remove the bolt later.

-- Leon Sisson

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Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 04/23/2003 : 18:38:00

A few notes on drilling into steel. Dont run the drill at a high speed. Use a sharp bit and take it easy. Another little trick is to put a small "O" ring around the fastener between the zink and keel. This will keep water out of the thread area and make later replacement easy.

Doug&Ruth
Triska (Alberg 29)
Tacoma Wa.

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ddlyle
Captain

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302 Posts

Response Posted - 04/23/2003 : 22:19:18

My personal favorite is to pay someone else to do it.
Last August I had the boat yard put two zincs on my swing keel
(pancake approx 2 - 3 inches in diameter.)
I don't know how they did it, but I sure am glad they did.
I looked at my keel this week for the first time since August
and the zincs were almost halway gone.
My keel looks nice and my cable (I don't know how old it is) is actually still shiny.
My boat was in fresh water from 1986 until spring of '02.
Now it is saltwater and I am painting the bottom (Trinidad SR).
I am going to have two new zincs put on, maybe even a third near the cable. (My first two were up high closer to the top of the keel.)
Zincs are great.

Cap'n Dave
Sailing The Blues
1986 C25 sr/sk #5413

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gerdo
Navigator

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107 Posts

Response Posted - 04/24/2003 : 09:33:30

Bought my 1982 swing keel in March of 2002. It never had zincs on it and had been in salt water (Chesapeake Bay) all its life. It was pulled every winter. Anyhow after reading this site and CD catalogue, zincs sounded like a good idea. I had no problem drilling completely through the keel, first a samll pilot hole and then larger to accept a through bolt for the pancake zincs. They were the 3 inch ones CD sells. I needed a longer bolt than what they supplied. Much to my suprise, when the boat was pulled in December ( it was launched May 1 and pulled Decmeber 5) the zincs were completely gone. The keel was rusted and patches of fairing and bottom paint were falling off or easily removed with a flat blade screw driver. Prior to that with no zincs the keel appeared good. Did this set up some sort of wild galvanic action?

This weekend I am removing all paint from keel and painting with POR 15. CHeck out their website. Then will bottom paint and put new zincs on.

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svmoxie
Past Commodore

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USA
331 Posts

Response Posted - 04/24/2003 : 12:45:25

A huge factor in the life of zincs, and in galvanic action in general, is whether or not the boat is hooked to shore power or even in a marina. A boat that is not connected to shore power, sits isolated on a mooring or a private dock and in fresh water will have very little to no galvanic erosion. However, take that same boat and put it a crowded marina with questionable power grounding in the other boats and in the shore power itself and you could go through several zincs in a month.

Also the differences in the nobility of the metals alone could cause Gerdo's zincs to erode. What type of bolt did you use? If it is stainless then you probably set up your own little circuit between the steel keel (0.79v) the zincs (1.04v) and the stainless bolt (0.24v) in saltwater. (approx voltage in salt water) Those all different enough metals to sacrifice those pancake zincs in short order without ever being connected to shore power. Add a little stray current into the picture and it only gets worse.

There are reams of information available on galvanic erosion. I really like the "Boatowner's Mechanical & Electrical Manual" by Nigel Calder for an comprehensive resource.

The best solution is to be more noble than those around you! <img src=icon_smile.gif border=0 align=middle>

Clif Thompson
Treasurer C-25/250 National Association.
svMoxie '81 25 sk

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.