*info*  3M Marine Adhesives and Sealants  *info*

(above) - before

(below) - after

The Final Tally:

Through Hull Fittings and Valves: $720.00

Miscellaneous Hose Fittings: $50.00

Sealant and stuff:  $40.00

Grand Total:

$810.00, several bloody knuckles, a smashed finger, a lump on the head, and the better part of a week of labor.

All this, just so I can sleep at night.

Here's a picture of the original 1983 drawing sent to me by the good folks at Catalina Yachts.  If you want to know how they do it, it's worth a look.

Here's what I did.

The Garbage:  To remove the old plastic thru-hull fittings you have a few choices.  Depending on the location.  I used all of them. 

1st Method:  Remove hose, remove valve, remove nut, beat the living hell out of it until it falls out and lands under the boat.

2nd Method:  Remove hose, remove valve, Take your rotary cutting tool (Dremmel) and cut the nut in half, beat the living hell out of it until it falls out and lands under the boat.

3rd Method:  from the outside, take your rotary cutting tool, cut around the inside of the thru-hull, pry the external portion out with a screw driver, then beat the living hell out of what's left of it into the interior of the boat.

4th Method:  A man with a Dremmel, screw driver, and a hammer should be able to come up with at least one more way to do this, I'll let you use your imagination.

The Holes:  Don't put that Dremmel away yet.  Clean the holes up, get all the old bedding material out.  Make sure that (if it is installed) the wood backing is in good shape.  I was fortunate.  Catalina did a good job putting this together.  Everything cleaned up like it was brand new.  Hopefully this isn't where you discover that the previous owner used 3M 5200 caulking.

New Thru-Hull Fittings: Oh, joy!  Here's the three sizes below the water line on my particular boat.  It changes by year and model.  My boat had two 1/2", three 3/4", and one 1-1/2" installed below the waterline.  Above the water line there were four 1-1/2", one 1", and three 3/4" fittings.  Below the waterline I used bronze, above the waterline everything is stainless steel. I chose stainless just for the looks, bronze will work there too.  Here you see the new Groco stuff sitting next to the original.  Which would you trust more to keep water out of your boat?

Installation:  The hardest part about the installation is reaching all of the thru-hull locations.  Unlike removing them, there are no choices.  You must lay hands on both sides. 

There's the galley sink drain thru-hull, right between the refrigeration unit, and the hot water tank, directly below the fresh water tank isolation valve.  Has anyone designed a wrench that will fit in here?  The correct answer is "no".   And apparently God hasn't designed an arm or hand that will either.  These little facts must've slipped the mind of the guy designing this thing.  At least it wasn't installed under something that would've required the boat be cut in half to reach, as is the Navy's standard operating procedure.

Anyway, enough of that.

Here's a view of an installed thru-hull from the outside, the next is a view from the inside.  A nice even bead of caulking around the edge in both cases.  Once again, more is better than not enough.

Clean the area well, inside and out you want the bedding material to adhere as tightly as possible.  Catalina's drawing calls for a urethane bedding material.  I had one fella in the boat yard who swore by 3M 5200.  I'm sure that would've been very effective, however, 5200 is as close to forever as you are likely to get in a tube.  The next time the thru-hull is removed (if ever) the gelcoat is coming with it.  So if you seriously never intend to remove these again, or you just want to screw with a future owner, use 3M 5200.

I personally like having the the option of being able to remove these someday, if necessary, without causing any damage.  I chose to use 3M 4200.  It is approximately 1/2 the strength of 5200.  It is much more similar to the product I found in the original manufacturer's installation that had lasted and remained resilient for 20 years.

Let the sealant cure for a couple of days, then give each fitting a good pull & push.  They shouldn't move.  If one does...  You can try tightening it up, but there is no room for error below the water line.  I'd recommend starting over and getting it right. 

Now it's time to install the new valves, and fittings.  Ensure you use Teflon tape or some other product on the threads.  I found a high quality plumbers dope that could be brushed on at Lowes.  It has a temperature range of 0 to 160 degrees Fahrenheit, is effective on systems with pressures up to 10,000 psi, is thick & gooey and claims it will not dry out.  Oh yeah, and it's safe for potable water systems.  I wish I could remember its name and manufacturer.

Note on installing the valves:  Make sure, after the valve is tightened up, that the lever can be moved in its full range of operation.  Most high quality valves have set screws that can be repositioned to change which direction the handle can be rotated.  It doesn't do any good to have a valve installed if you can't open it or close it.

Secondly, if you are installing a check valve, pressure metering valve or other valve that requires fluid to pass through it in a certain direction, ensure it is installed with the direction of flow arrow, that is cast into the valve body, pointing in the correct direction.

Side Project:  The original plumbing had the shower pan draining into the holding tank.  The sinks both drain directly through the hull into the water.  The same stuff that's going in the head sink, is the same as the stuff going through the shower drain.  Soap and water basically... So why am I filling my holding tank every time I take a shower?  The answer is I'm not... anymore.  If you look at the last picture you will see a 'T' fitting installed, so when the shower drain pump is turned on the water exits the boat through the sink drain thru-hull fitting.  I also installed a check valve above the 'T' fitting to keep the waste water from being pumped up into the sink.  No more peeing in the shower; small sacrifice to make if it keeps the pump cart away from my boat.  You might want to check your local environmental laws before you make a modification like this.

Back to Projects