PS Advisor 01/15/01

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Rigid PVC Plumbing
I purchased a 1975 Islander 36 with a 6-gallon holding tank designed to be discharged when beyond the 3-mile limit. On Lake Superior the discharge thing doesn’t work so Im in the process of upgrading the size of the tank to 23 gallons. The new location of the tank will be about 4 feet from the head.

My question is this: Would it work to use rigid PVC to connect the new holding tank as it is clear from your September test that everything else will fail given enough time? Im aware that the PVC must be supported very well to avoid breaking in rough seas. What problems might one have?

Dale Mackereth
Via email


We used rigid PVC to replumb much of our Tartans holding tank/toilet system and never had a problem, but the runs were short. No odors, period. Some marine sanitation experts warn against too much rigid PVC due to possibility of joints cracking with boat working in a seaway, but if you support it well, hopefully there will be no problems. Rigid PVC is tough stuff, including the glue joints, so we would proceed using only common sense in laying out the pipes.


Loose Hull/Deck Thru-bolts
My 1976 Scampi 30 had some minor leaks at the hull/deck joint. When I checked the bolts securing the deck I found about 25% of them were very loose at various points around the boat. Most of the rest needed at least some tightening.

The hull has an inward-turning flange that the deck rests on and there is an aluminum toe rail. The joint is secured with a non-setting compound and bolts with nuts and washers on 6″ centers.

When I tightened the first bolt the fiberglass began to crack before the nut was very tight. After that I just snugged up the rest of the bolts.

My questions are how tight should these bolts be and how often should they be checked?

Also, should I be concerned that this is indicative of a larger problem?

Neil Donovan
Chicago, Illinois


Perhaps some of the compound used between the hull and deck has squeezed out over the years, eliminating the cushion for the bolt and nut. Now when you tighten, the bolt head and nut exert all the load directly on the gelcoat/glass and cause it to crack-not good. We wouldnt overtighten any of the others…you were right not to.

But we don’t like the idea of the bolts being loose either. Getting new compound (like 3M 5200 or a rubber gasket material) into the joint would require lifting the deck-a lot of work. So, what you might try instead would be to seat the bolt head and/or nut on soft washers-nylon, rubber, etc. with the hope that you can tighten the nut without cracking the glass. (If you still can’t tighten the nuts without cracking the glass, use Nylock nuts that wont unthread.) This doesn’t solve the problem of the two hard glass surfaces on the inside joint touching, but it may be the best you can do.

We do not think the loose bolts are indicative of a larger problem, but you should address the situation because the hull-deck joint is critical.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at practicalsailor@belvoir.com.