PS Advisor 07/15/99
Holding Tanks and Hoses
My brother-in-law and I are planning to install a holding tank in our 1970 Morgan 28. Iíve tried to research the best option, from hard copper pipes to stainless steel tanks to PVC hose and inflatable holding tanks. In his Offshore Log, Nick Nicholson only mentioned PVC, but referred to on-going PS tests.
We primarily sail in the Great South Bay, but every year sail east and visit Shelter Island, Block Island, and Newport, Rhode Island. With the spread of ďNo DischargeĒ harbors, please advise.
Weíd use polyethylene for the holding tank. If they have a size that fits, SeaLandís tanks are thicker-walled than the others. And SeaLandís Odor Safe PVC hose is the best of the white sanitation hoses for containing odors. We have tested it but not reported the results yet. The only thing better is rigid PVC pipe, bought from a home supply store. No odors can get through it, but routing rigid PVC is more difficult than semi-flexible sanitation hose. We replumbed our test boat with as much rigid PVC as possible and it made a huge difference. We also have a SeaLand discharge pump for emptying the tank outside the 3-mile limit, which is what we usually do. Itís nice not to have to depend on pump-out facilities, which is what we do, of course, when needing a pump-out in the harbor.
We own a 1972 Newport 41. A Newport 41 is a West Coast-built version of a C&C 41 of the same vintage.
We would like to maximize speed under power and maintain the boatís excellent sailing characteristics. It appears that a 3-blade feathering prop would be the best solution to our propeller needs. However, we have no idea which prop would be best for us. Do you have a recommendation?
Corona Del Mar, California
We published results of tests conducted at the Massachusetts Institute of Technology in the October 1, 1993 and January 1, 1995 issues. The latter is available from our publisherís Back Issues Department by calling 800/424-7887 or sending an e-mail to: firstname.lastname@example.org.
A feathering prop has less drag than a fixed prop, but a bit more than a folding prop. A feathering prop such as the Max-Prop, however, has better performance in reverse, which may be important if you keep your boat in a marina. The Max-Propís efficiency in forward isnít quite as good as a fixed or folding prop because its blades are flat; the solution is to apply more throttleÖif the horses are available. Nonetheless, the Max-Prop is an excellent, all-around choice, albeit an expensive one.
We keep our test boat on a mooring and so can get by with a folding prop, which does just fine motoring. But when we have to bring the boat into a marina, we go very, very slowly! The makers of the Martec folding prop, however, insist that a boat with a folding prop can stop quickly enough, and that the secret is in applying lots of revs to the engine. We do, and itís still nerve-wracking.
Fixed props are the least expensive and are probably the most efficient for motoring. But the drag, which varies by boat but probably costs .3 to .8 knot on the average, is a serious drawback for one who likes to sail as fast as possible.
Yet another choice is the self-pitching Autoprop, an unusual design that automatically changes pitch to match loads. It, too, feathers under sail. Cost is about the same as a Max-Prop.
As boat owners are wont to say, itís another case of trading off one attribute for another.