1 BOATS AND THEIR BITS Heavy displacement
The word ‘displacement’ refers to the amount of water displaced by the hull – the weight of which is equal to the boat’s weight at any moment in time. This might seem a rather roundabout way of defining how heavy a boat is but it actually works very handily, since it includes factors like the number of people on board, fuel levels and − naturally − the colossal weight of your catch after a good day’s fishing. Oddly, with this type the displacement has almost no affect on maximum speed, for reasons that will be explained on page 9. Heavy displacement boats have an easy, comfortable motion when under way but can roll abominably when anchored. They are usually powered by inboard engines.
Fig 1:3 Planing hulls Fig 1:4
Whereas heavy displacement vessels plough through the water, planing boats skim along the surface, relying on the same hydrodynamic forces that prevent water skiers from sinking. There are various hull forms but the most common for offshore use have ‘V’ shaped underwater sections with a number of longitudinal spray rails to help lift the boat ‘onto the plane’. V-hulled boats perform poorly at low speeds
but become very efficient once planing. Their veed bows allow them to slice through the waves making them particularly able performers in rough conditions. The ‘fast fisher’ type designs are good examples of this increasingly popular category.
Dories
The original fishing dories were flat bottomed but the modern equivalent have more complicated sections − typically being flat aft and veed towards the bow, with prominent spray rails almost at full beam that help force the waterflow under the hull and create a partial air cushion effect. They plane even more readily than V-sectioned hulls but their flatter profiles make them prone to slamming in waves. Hardly surprisingly, this makes them better suited to protected waters, where there’s usually only slight wave action − though there’s no reason why they shouldn’t venture offshore in calm weather. Dories are nearly always powered by outboard motors.
Fig 1:5 Catamarans Fig 1:6
The word comes from the Tamil kattu-maram meaning tied wood, and describes a craft with a pair of narrow hulls joined by some form of deck structure. Since their hulls are very fine, the water doesn’t have to be shouldered aside very far, so catamarans can achieve
their intended design speeds with relatively less powerful engines. The twin-hulled approach inevitably brings greater than average beam, so they are exceptionally stable. At anchor they roll less than single hulled boats but their action can be rather twitchy, which some people find uncomfortable. Their wide deck usually means lots of space for anglers.
8 RYA Seamanship for Sea Anglers
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