Sunday, January 18, 2015

Thru-Hull Replacement

Holding Tank Drain with Signs of Leakage
One of the most important items on our summer refit list was replacing the thru-hulls that we had not already replaced. LUX has four thru-hulls below the water line in the hulls, plus one built into each saildrive in the engine compartments. The port hull water intake had been replaced a year ago, increasing its size from 3/4 inch to 1.5 inch. It feeds a Groco manifold that supplies raw water to the toilet, air conditioner, and genset. We really wanted to replace the holding tank gravity drain fittings, which were showing signs of leakage. Other Leopard owners had reported decay of their thru-hulls, making us nervous.

Thru-Hull After Removing the Mushroom Head

One of the thru-hulls showed signs of decay through about 1/2 the thickness of the metal.

We had been planning to install a backing plate on the inside of the thru-hulls to strengthen the hull, however, we found that the hull in the area of the holding tank drains is 1-7/32 inch thick. There's plenty of strength there with a solid layup.
Holding Tank Drain Hull Thickness

Toilet Water Intake Hull Thickness

The bottom of the hull where the toilet water intake is located was much thinner, about 1/4 inch thick. A G10 board backing plate was used for that thru-hull.

One of our concerns was that the thru-hull fitting was NPS (National Pipe Straight), which doesn't thread more than a few threads into a NPT (National Pipe Tapered) fitting. We took care of this by running an NPT tap over the end of the thru-hull fitting, giving it a tapered thread. The resulting tapered thread seated nicely in the full depth of the NPT bronze elbow.

Final Installation

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