Next to pumps, V-belts cause the most annoying maintenance problems when cruising. If they are the right design for the job, properly installed, and correctly tensioned, they will give you thousands of hours of trouble free life.

But since this is not typically the case, be prepared with lots of spare belts!

How They Work

V-belts transmit power with their sides, not their bottom. They depend upon a certain amount of contact area with the pulleys to get the job done. This brings into play several factors.

The first is belt wrap. Under ideal conditions, with a 1-to-1 pulley ratio, each belt will wrap around 180 degrees of pulley. However, with a stepped-up system, as we normally use on boats, the belt wrap will be greater on the drive pulley and less on the accessory pulley. This degrades the performance of the belt. One way to mitigate the belt-wrap problem with the smaller pulley is to move the two pulleys further apart, as this reduces angular change between the two.

Another way to make the belts more efficient is to increase the size of both pulleys. There are, of course, some practical limits with drive-pulley size and weight. Also, check on maximum allowable belt speed. Belt speed is a function of engine rpm and pulley circumference. For a given rpm, as diameter and circumference increase, so does belt speed.

Types of Belts

There are literally dozens of types of V-belts -- all sorts of designs, constructions, power ratings, and configurations. Two similar-looking belts may have vastly different power ratings.

The typical automotive belt, which you'd buy in an auto parts shop, may be able to handle 3 horsepower. If you step up a grade and go to an industrial belt, such as the Gates High Power II, for a couple of dollars more, you'll double that rating. It's usually necessary to visit an industrial belt distributor in order to obtain higher rated industrial belts.

Belts are typically sold in cogged and smooth designs. Cogged belts generally have higher power ratings and grip the pulleys better.

You can also buy adjustable belting, which can be used at any required length. This works great in a pinch, but only for low-power applications.

Horsepower Ratings

If you consult an industrial belt engineer about your application, he'll run your system through a computer program. He'll want to know the rpm at which the belt is expected to operate, required power, pulley diameter, and the distance between the pulleys.

The engineer will then specify several belt types, In the process, he'll predict how many hours of operation to expect.

It is amazing just how much power you can transmit. With high-quality cogged belts, using a 2-to-1 pulley ratio and belt life of around 1,000 hours, a single belt will handle close to eight horsepower. However, to do this, belt tension and alignment must be exact! We've found (the hard way) that for most people, this situation is too aggressive, and it is better to de-rate the belts down to the 4-horsepower range.

Belt Tension

We've now mentioned belt tension, which is critical to long life, a couple of times. The problem comes in determining the correct tension. Your engine manuals may indicate tension requirements. Belt engineers can also offer figures.

Our experience with large alternators and their high power requirements has been that a new belt should start life at around 75 to 80 pounds (34 to 36 kg) of tension. After the initial break-in period where the belt is stretching, this tension should drop to the 50-to-60-pound (23 to 27 kg) range. Most industrial belt suppliers have inexpensive and easy-to-use devices for measuring belt tension.

Before we leave this subject, be aware that overtightening can also be a problem, leading to premature bearing failure.

Dusting

All belts make a certain amount of dust when running. However, if the correct belt is being used, if it is set at the proper tension, and if pulleys are correctly aligned, dusting should be minimal. More than a small amount of dust is cause to investigate.

One Belt or Two?

If you have a minimum of accessories, it makes sense to transfer power with dual belts. Thus loads are split, and most of the time, belts can loaf along.

With multiple accessories, however, using dual belts makes for a large, heavy drive pulley. This puts more load on the engine PTO, front bearing, and front oil seal. Over the years we've found that with multiple accessories, it's better to work hard to make the single-belt systems efficient, thereby reducing PTO loading.

Multi-Belt Systems

Odds are you'll have a bunch of belts on the front end of the engine. When the time comes to change a belt, Murphy will make sure it is the innermost belt -- meaning you have to remove all the outer belts to get to that inner belt! The one way around this is to put on an extra set of inner belts. Tie them out of the way so they are available when needed.

Dealing with the Unexpected

Over the course of cruising, all sorts of problems may crop off with your V-belts and related accessories. It may be that you cannot find the correct length of replacement belt, or that your own belts are on their last legs. Perhaps the bearings are going out on one of the accessories.

There are a variety of things you can do to keep going. One is to carry some Òbelt dressing.Ó Available in solid and spray form, it increases the friction between belts and pulleys. If a belt has stretched too far to tighten properly, sometimes a little belt dressing is just enough to get the job done -- but do not make a steady habit of using it.

If a bearing is going, reducing belt tension will often help delay the point of total demise.

You can also reduce the power requirements of your accessories by reducing output. With alternators, cutting back on the regulator reduces the load on bearings and belts at the same time.