The watertight integrity of a vessel often relies on something as simple and mundane as a hose clamp, some of which cost less than a couple of dollars. Who gives any thought to the lowly hose clamp? As long as it’s made of stainless steel, isn’t one the same as the next. No way, and thinking like that can sink one’s boat.
Then there are all the important hoses that hose clamps secure: fuel, potable water, bilge pump and sanitation. Clamps that fail or are improperly used in these applications can lead to a host of failures that range from the merely inconvenient to the truly catastrophic. Inspecting a boat’s hose clamps annually will go a long way toward preventing failures.
The most common style of clamp, wormgear driven, has been around since just after World War I when inventor Cmdr. Lumley Robinson, a retired Royal Navy officer, patented the first design in 1921. He called it a Jubilee Clip. Worm-gear clamps utilize embossed threads and have a smooth, lined underside that reduces intrusion.
Inexpensive clamps have bands with stamped-out slots, the edges of which dig in and drag against the hose, holding that part of the band in place, while the non-perforated part of the band moves easily, so it’s pulled in more. The result is less clamp force under the slots and too much where the band is smooth. The best clamps have embossed slots that keep the underside smooth. In addition, the band under the worm gear should be rounded — not flat — to match the arc of the hose, so it moves easily.
The common perception is that it’s best to crank down hard when tightening a clamp, but that can cause a blowout by squeezing the hose material too hard and reducing the thickness of the hose. All they require is 35 inch/pounds of torque at the screw head. That’s about as much as most people can apply with a screwdriver without grunting. Too much force can lock up the screw and destroy the hose. Hoses adjust to pressure and slowly give where it is applied — a good reason to regularly check clamp tightness.
One of the most important aspects of selecting a hose clamp is ensuring that the clamp size is properly matched to the hose that’s being secured. If the clamp is too small for a given application — if the band width is too narrow — it may not impinge on the hose.
Using a two-inch clamp on a one-inch hose results in excess threads once the clamp is tightened. Not only is that inefficient but a sharp, lengthy tag end remains that can injure someone working on the boat. Also, in extreme cases, it may bottom out, fooling the installer into thinking it’s properly tightened when in fact it has run out of usable thread.
The other style of hose clamp is the T-bolt clamp, which uses a bolt and nut to tighten the band. This design is used for larger-diameter hoses and hoses in high-vibration areas, such as exhaust and turbocharger hoses. Usually, they are installed using a ratchet and socket, and the nut includes a nylon insert that can resist vibration-induced loosening.
T-bolt clamps have their weaknesses. Because the bolt and nut are both made of stainless steel, they are prone to galling, or thread damage caused by localized friction-induced heating. This can be avoided by torqueing the clamp slowly and by adding a small amount of light lubricant to the threads prior to installation. In addition, some T-bolt clamps are manufactured using a folded section of tack-welded stainless steel and are, under certain circumstances, susceptible to crevice corrosion. A good T-bolt clamp uses interlocking rather than folded and spot-welded bands, virtually eliminating the water-trapping fold and the corrosion to which it so often leads. These clamps are well suited to wet locations without concern for such failures. When it comes to selecting hose clamps, don’t skimp on the important component. Clamps must be all stainless steel — 304 for dry applications and 316 for wet — with solid, embossed-thread bands.