Fighting friction

Buying the best gear can be expensive. But sometimes any savings have to be repaid by increased effort.

Disappointed with your deck hardware? Join the club. It’s both ironic and illogical that racing yachts are lavished with all sorts of fancy deck hardware while their plodding cruising cousins get the penny-pinching bits of gear. And it makes no sense. Race boats tend to be manned by large crews of a relatively muscular disposition while the more sedate of the species are often crewed by ‘him and her’ couples, often getting on a bit in years. It’s usually the latter that need all the help they can get and – if there was such a thing as natural justice – they should be the beneficiaries of the very best that mechanical engineering can devise.

There are many examples but, to illustrate the point, let’s look at a typical mainsheet arrangement. In order to keep the cockpit clear, the modern trend is to have the mainsheet track and car located forward of the companionway, approximately at half-length along the boom – frequently for no better reason than it avoids cluttering the cockpit and allows a nice shady awning to be rigged. Unfortunately, it also makes the load on the mainsheet much higher than if it was attached at the boom’s after extremity. It’s all a matter of leverage.

To overcome this disadvantage, a 4:1 tackle might be used, with the sheet being led forward to the gooseneck, downward to a swivel block at the foot of the mast, onward through a deck organiser block and finally to a winch on the coachroof. I’ll save you the trouble of following this route in detail by telling you that the sheet passes over a total of seven sheaves.

Now, the property that distinguishes a good block from a mediocre one is its ability to run freely under load. Good quality blocks with ball-bearing or roller-bearing sheaves might have less than 2% friction (100% of effort in, 98% out) but budget blocks with plain plastic sheaves take a higher toll – let’s say 6% from the output, since this isn’t unusual.

Let’s also assume a mainsheet load of 1000lb (454kg). Given our 4:1 mechanical advantage, we would expect the load at the winch to be 250lb (114kg) if it wasn’t for friction.  But, of course, there’s no such luck. As the mainsheet snakes its way from its dead-end to the winch, every sheave will add its friction loss to that of the sheaves that went before.

Again, I’ll spare you the arithmetic and simply tell you that the cumulative effect will be such that the winch will need to exert a pull of just under 400lb (182kg) – over half as much again as the theoretical requirement.  That’s 60% more effort for a possibly already overtaxed crew.

Now let’s consider the reverse case – easing the mainsheet against the blocks which are now working to disadvantage. With no load on the fall, it’s only the friction that prevents the sheet running out. And which of us hasn’t had to push the boom outboard, usually in a series of jerks, just to get the mainsheet to run out?

All of which means that when it comes to critical applications, you should fit the best blocks you can afford if you want a less arduous life.

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