C&C 27 Association – Hose Clamps

Hose clamps are simple devices, but they take some care in installation if they're going to do their job, which is to contain water or the engine's potentially lethal exhaust gasses.

For safety and security, bear in mind the following:

  • Hose clamps must be 100% stainless steel, which means those sold as marine-grade or underground-use. The automotive clamp business is a least-cost dogfight, so automotive clamps may have a stainless band and a mild-steel knuckle, a plated band and a stainless screw with plated clamp or any combination of the preceding that happens to be on the shop floor that day (seriously). The band should be cut through for the screw threads to engage; bands with threads that are just pressed in are insecure. Many of the original hose clamps on an Atomic 4 are crimp-on or mild steel; replace them.
  • Practical Sailor magazine recommends that a strong magnet is a quick and easy guide to quality. They advise that clamps made with a 400-series stainless or other metals (very bad) will be very attracted to the magnet. Better-quality clamps made from 300-series stainless will be non-magnetic or nearly so. The best clamps will be 316 stainless and utterly non-magnetic.
  • Hose clamps should be doubled on both ends of any hose that ends near or below the waterline, or that is associated with your engine and its exhaust.
  • Clamps need to be tight, but not over-tight. Note on the accompanying pictures that the stainless band bears directly and firmly on the hose but does not dig into it.
  • Properly installed, clamps lie in opposition, with the knuckles (the screw and its enclosure) on opposite sides.
  • Dealing with hose clamps is much easier if you have a 5/16" nut-driver or socket to grip the hex head; trying to keep a flat-blade screwdriver centred while reaching under the cockpit is a waste of time and the flesh on your knuckles.
improper clamping

"The purpose of double clamping is to provide a "secure, liquid and vapor-tight joint." Placing the "knuckle" of each clamp on the same side technically meets the requirement of double clamping but misses the purpose. A hose clamp provides the most tightening from the centerline toward the knuckle. It is best to place the knuckles on opposing sides, thus providing the most tightening force equally on both sides of the clamped hose. I have been involved in cases of carbon monoxide migration, caused by back pressure, through improper clamping. Since you’re putting two clamps on anyway, why not do it right?" – Scott Schoeler, MKIII, Scot-Free

Accordingly the first photo, of an Atomic 4's waterlift muffler, is wrong and should be changed. The second photo shows a correct installation.

correct clamping


Mk I