## Deviation

The other major factor affecting a compass is deviation. This is an error originating from within the boat. Any ferrous metal affects a compass to a certain extent. If it is too close (say, either 4 or 5 ft in a horizontal direction) the results will be noticeable.

Deviation, unlike variation, is not only undesirable, it can be minimised by your own efforts. Site the steering compass intelligently and don't leave screwdrivers, battery driven appliances, radio speakers and other magnetically active bric-à-brac scattered around it. If you've done this successfully on a GRP production cruiser you may end up with little discernible deviation. On other craft, though, you'll have some left for sure. If your yacht is steel, or ferrocement, there will be plenty.

The first thing to do about deviation is to try to get rid of it. This is achieved by employing the services of a compass adjuster. He will come along with his magic toolbag and work his miracles with compensating magnets. If you want to try this for yourself, buy a book on the subject or go to college, but don't ask me to help. It's a very skilled and specialised job.

The compass adjuster will leave you a deviation card which shows how you can now expect your compass to perform (Fig 16.2). Look at this and you'll see that, unlike variation, deviation varies with the yacht's heading. This makes sense when you realise that since the boat is effectively turning round under a stationary compass card, the relationship between the 'north pointer' and the boat's ironwork will vary.

Deviation is expressed in degrees E or W of the vessel's magnetic heading. Thus, if you dial up your course in degrees true you must convert this to magnetic before consulting your deviation card for the final adjustment to compass. If you are correcting the

Fig 16.2 A deviation card.

other way, the opposite process is required, again with magnetic in the middle.

A true heading to which variation and deviation have been applied is called a compass beading.

In practice, all this is simple to deal with, so don't be daunted. There's a wonderful mnemonic, beloved of all sailors, which goes like this:

True = True

Virgins apply Variation (error west, compass best etc)

Make gives Magnetic

Dull apply Deviation

### Companions gives Compass

If you are converting from compass through to true and you happen to be British, 'Cadbury's Dairy Milk Very Tasty' will stand you in good stead. If you arc not a native of Blighty you will never have heard of this noble confection, so you'll cither have to come up with something else, or reverse your True Virgins.

## How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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