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August 2005

A Careful Look at Seacocks and Through Hull Fittings

Marty Chin, who manages Bay Marine Diesels in San Francisco, sent us the following letter, which we feel is worth sharing. The Groco seacocks he describes are a different model than we have on Taleisin. The ones we use on Taleisin were made by Groco, but instead of having a stainless ball and Teflon seating, they have expandable rubber cones. We added grease cups which we tighten down twice a year to keep the cone and bronze seat lubricated. After 23 years they are still in fine condition.

Thank you to Marty for permission to share this info -

We recently hauled our BCC Shamrock and took a look at the Spartan seacocks in our boat, current production Bristol Channel Cutters use Groco. Our original plan was to replace them with Groco, which seem to be some of the better through bolted seacocks on the market.

The Groco seacocks with the stainless steel ball and teflon seat seems to give a good clean seal, the teflon act as a wiper, cleaning the ball if the valves are cycled open/close often. We did note as with most teflon/ss or chrome plated ball type valve, if left closed for prolonged periods of time, the ball became pitted or encrusted with mineral deposits, when the valve was cycled the deposits/pitting tended to score the teflon seat causing the seacock to leak internally around the ball; if the hose failed, closing the valve slowed but failed to stop the leak.

Our severely neglected Spartan seacocks suffered the same fate of leakage around the bronze tapered plug. We lapped 4 of the 1-1/2 and restored them to new condition; the 3/4" seacocks were not salvageable due to long-term neglect. We later removed the mushroom thru-hull fittings and found they had been cut to short, only 2-4 treads engagement, the majority of the threads were exposed to the sea and subsequently were lost to electrolysis.

It was a tough choice, but we decided to replace all the seacocks with Spartan seacocks to keep it simple, allowing us to disassemble, clean, lubricate or lap if necessary at each haulout. This time around we measured the hull thickness, backing block thickness and total thread depth of the seacock and cut the mushroom thru-hull fittings 1/16" short to get maximum thread grip inside the seacocks, in addition to the 5/16" bronze thru-bolts. We also added a little Sikaflex 291 to the threads of the thru-hull to prevent water from migrating along the threads, same sealant we used to bed the thru-hull fittings and seacocks.

We were impressed with the massive construction of the Spartan seacocks, the handles are pinned with a 1/4-20 SS allen screws threaded through the handle and pass through a large rectangular lug on the plug, we still have 6 used handles in new condition, I swear the handles last forever. We purchased Groco thru-hull fittings, they are CNC machines, no crude castings, threads are cleanly cut not rolled and the price from local distributor was the lowest on the market. The Spartan website: http://www.spartanmarine.com/

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