SpearFish 520 on test

What's the point of the ‘long and thin' as opposed to the normal 'short and fat' with a small inflatable? David Harding finds out

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With boats, as with most things, form follows function: a boat's shape reflects what it's designed to do.

In many cases, that means you can get a pretty good idea of a boat's likely performance and handling qualities from a cursory glance, though, of course, there may be hidden secrets below the waterline.

Sailing yachts with narrow hulls are often more easily driven, smoother to sail, better balanced, more tolerant, more predictable and better able to handle extreme conditions than wide-bodied alternatives. Much of the time, they are also faster.

Their principal drawbacks are that they can be wetter to sail-more prone to going through the waves than over them-and less roomy below decks.

In these days of pressure to maximise volume for any given length, it's sad that the long and slim (and often elegant) has become something of an indulgence, whether you own a classic yacht or one of the small number of current designs in a similar vein.

It's much the same story with motorboats as with sail. A more comfortable motion into a seaway and the need for less power are among the plus points of a narrower hull, at the expense of greater tendency to roll in a beam sea and, inevitably, less space.

So, where does that leave very small boats, including ones that you can deflate and put in the boot of your car? Well, in broad terms-so to speak-the same applies. Have you ever seen a wide kayak or canoe? They're narrow for a reason, and sea kayaks are long for a reason.

Tenders and small, multipurpose inflatables have always tended to be on the short and squat side, again to maximise carrying capacity for any given length. If you're going to carry an inflatable fully inflated on deck, across the transom or, perhaps, in davits, length does matter-not that that necessarily means buying the shortest tender that will carry what you need.