Bonding Garboard Drain Plug

earlylight · Post by **earlylight** » Sat Dec 20, 2008 7:25 pm

My Sabre 34 has all of the thru-hulls and seacocks bonded to the keel bolts as well as all chain plates, the shaft strut, rudder post and engine. I purchased a bronze garboard drain plug from Hamilton Marine and am about to install it in the side of the bilge sump which is actually the keel stub for the fin keel. There are provisions for 4 #10-24 machine screws to mount it and I will be drilling and tapping the side of the keel to accept these screws. I am looking for thoughts from this group as to whether I should drill all the way through the side of the keel sump for 1 of these screws with appropriate washers and nuts so I can add a bonding wire.

Any advice will be appreciated.

Dick
Early Light
Sabre 34
Solomons, MD

David · Post by **David** » Sat Dec 20, 2008 7:43 pm

I think it is a big mistake to bond the underwater metal on a boat.

JonnyBoats · Post by **JonnyBoats** » Sat Dec 20, 2008 7:58 pm

Tell about a hot potato, you will hear much debate about the merits of bonding, both pro and con. Further there are many, many factors to consider beyond simply protecting metal from electrolysis. Take lighting protection for example.

Without even trying to get into all that, may I suggest that _most_ experts would come down on one of two positions:

1) Do not bond
or
2) Bond everything below the waterline

I think you will find that few would recommend just bonding some of the fittings and not others.

If it were me, and I was not planning on breaking all the other bonds on the boat, I would go ahead and bond the garboard plug as well.

Post by **Tim** » Sun Dec 21, 2008 7:59 am

I am firmly in the "no bond" camp, but since all your other fittings are already bonded, then don't add a new metallic installation without incorporating it into your existing bonding system.

Al · Post by Al » Sun Dec 21, 2008 12:50 pm

Welcome to the group, Dick.

Other members of the group can see Dick's handy work in restoring his Sabre 34 at http://www.geocities.com/earlylight160/

Al Lorman

Quetzalsailor · Post by **Quetzalsailor** » Sun Dec 21, 2008 6:58 pm

I think I'm in the no-bond camp, too. But Johnnyboats and I have boats that were pretty thoroughly bonded when built. I've found that the screws that affix the copper straps to the object, whether stainless chainplates or bronze seacocks (and I'm not going to confuse this post with mere facts), are the first thing to corrode. The screws look as though they're de-zincified, but I can hardly believe that they were brass! Most of the copper is pretty good; some in the bilge have flaked to less thickness; most connections must now have high resistance. Since the current involved in this problem is small(?), I presume Quetzal is very spottily bonded, if at all. Oh good! Something to fix.

I agree that a bonded boat should have new bits added to the bonding system. I particularly think that the garboard plug fitting needs to be permanently affixed to the boat in the same way that other through-hull fittings are seriously bolted to the boat. The four little screws that those fittings come with do not do it for me.

I'd like to have one of these drains but installing the bolts down in the bottom of my hollow keel has me defeated; it's about four feet down from the sole. Driving a plug into a failed fitting down there would be pretty defeating as well.

Rachel · Post by **Rachel** » Sun Dec 21, 2008 9:59 pm

Quetzal,

I don't say this to talk you into doing it this way -- and I prefer through bolting too -- but I will say that it's reasonably common to install those plugs with tapped (into the hull) fasteners and 3M 5200. I've not heard of one failing. I also haven't heard of the plug part unscrewing itself, although I'd be more worried about that (one part failing as opposed to three fasteners plus adhesive)

Again, I'm not trying to get you to do something you're not comfortable with; just mentioning it as a data point. Even if it is perfectly safe, there's no sense doing it if you're going to have to lie awake at night thinking about it.

I might as well put in a "plug" for my favorite, bronze, garboard plug, made by Buck Algonquin and sold for example) at Hamilton Marine. It has a bronze pug as opposed to the more common brass one. I know I've mentioned these before, but I want plenty to sell so that they don't quit making them.

Rachel

earlylight · Post by **earlylight** » Sun Dec 21, 2008 11:23 pm

Rachel,
I already have a brand new Buck Algonquin (totally bronze) garboard drain from Hamilton. I was intending to drill and tap for 3 of the screws and then thru-drill for the fourth (longer) screw to be used for the bonding connection to the keel bolt. I intend to use 3M 4200 fast cure to bed the fitting once I have ground out the recess so I can flush mount the flange in the side of the keel. Fortunately, the keel sump is only about 13 inches deep so access from the inside is quite good too.

Dick Coerse
"Early Light"
1982 Sabre 34 MK I #160
Solomons, MD

Rachel · Post by **Rachel** » Mon Dec 22, 2008 2:34 am

That sounds like a good plan. I should think 4200, Sikaflex 291, etc. would work well. Although that's one of the few places I might use 5200, figuring I would get it out if I had to, and meanwhile I'd want it stuck on but good.

One thing to check: Last year during the installation one of those same plugs, caulk started oozing out where it shouldn't have... After removing it and looking closer, a casting defect was found: It had caused a small hole right where that "keyway" meets the flange. Hamilton Marine happily sent a replacement, but you might as well give it careful once-over first (if you haven't already).

And welcome to the forum :)

Rachel

Hirilondë · Post by **Hirilondë** » Mon Dec 22, 2008 9:18 am

My bronze garboard plug/drain plug is bronze. It is held in by stainless self tappers and Sikaflex 291-LOT. The cap threads are smeared with pump grease each year. It is not bonded. It shows no sign of corrosion after 3 years. If it ever does I will replace it as needed. Draw what ever conclusions you choose, below the waterline decisions have to make you feel safe.

fusto · Post by **fusto** » Mon Dec 22, 2008 10:43 am

After you install it, paint it with a couple coats of interlux 2000 and then some bottom paint.
This will significantly reduce the amount of exposed underwater metal, thus negating the need to bond.

Rachel · Post by **Rachel** » Mon Dec 22, 2008 12:12 pm

I've noticed that all the bronze garboard plugs (that I've found) -- except for the Buck Algonquin -- have brass plugs when you get down to the specs. I'd love to add another brand/model to my "good" list though; Dave, who made yours?

Rachel

David · Post by **David** » Tue Dec 23, 2008 11:24 am

Dick,

I'm curious from the photo in this thread: are you checking the torque of your keel bolts with that torque wrench?

David

earlylight · Post by **earlylight** » Tue Dec 23, 2008 2:55 pm

David,

Yes, Sabre recommends re-torqueing the keel once a year while the boat is on the hard with the weight resting on the keel. If I remembrer correctly the Sabre manual calls for 90 ft lbs.

David · Post by **David** » Tue Dec 23, 2008 3:34 pm

Very impressive that Sabre recommends annual checking. I'm surprised at the low torque value though. What is the diameter of the keel bolts (just curious)? Also, when you check their torque, do you first back the nut off and then retighten (like you would do if you were retorquing head bolts on an engine) or do you just start from their current state and tighten to the specified value?

Thanks,

David

earlylight · Post by **earlylight** » Tue Dec 23, 2008 4:31 pm

David,
The keel bolts are 3/4 inch stainless steel with bronze nuts. I just rechecked my Sabre manual and they call for 90 ft lbs torque. I back them off before torqueing them to spec. and start from the center working alternately toward each end of the keel.

David · Post by **David** » Tue Dec 23, 2008 5:09 pm

Just like torquing a head :)

Hirilondë · Post by **Hirilondë** » Wed Dec 24, 2008 11:59 am

Rachel wrote: I'd love to add another brand/model to my "good" list though; Dave, who made yours?

Rachel

Hmmm, good question. I forget. It has a flush plug that uses a square drive allen type wrench included with it if that helps. Working in a boatyard with an excellent store manager has made me really lazy keeping track of such things. With the recession I have been layed off, or I would check for you.

David · Post by **David** » Wed Dec 24, 2008 1:36 pm

Stay clear of the Perko "bronze" garboard drains, which use brass plugs.

Rachel · Post by **Rachel** » Wed Dec 24, 2008 2:38 pm

Dave,

Sounds like it could be the Buck; or at least your description doesn't rule it out.

Sigh, I'm partially laid off for the same reason. Was originally supposed to be completely, but, for now at least, I'm clinging to 20 hours per week.