HOW TO MANEUVRE A SHAFT-DRIVE BOAT

One of the joys of boating is the wide variety of different craft on offer. Whereas the vast majority of cars have four wheels and one engine and therefore drive in roughly the same way, boats are much more varied in terms of size, style, hull design and means of propulsion. As a result they tend to handle very differently too, so making the switch from something like a single-engined planing sports-boat to a twin-engined semi-displacement cruiser requires a certain amount of readjustment from the skipper too. So how do you go about doing that? For me, having a clear understanding of what’s happening when and why is vital to grasping what steering and throttle inputs are needed.

This particular boat is a perfect example. It’s a brand new Dale Classic 37 with a semi-displacement hull driven by twin Volvo engines on shafts and rudders. There’s a shallow keel running the length of the hull, which gives it slightly better grip on the water than a full- planing hull, but the tall bow means it’s likely to have a reasonable amount of windage too. The drive system’s power delivery to the water and how to use it can be split roughly into thirds.

Both propellers turn outward in ahead gear and inwards in astern. However the positioning of the propellers, offset to either side of the centre line, gives one third of the turning ability; put port ahead and it will induce a turn to starboard and vice versa, with a pivot point about a third of the way back from the bow. Putting that same port engine in astern will produce a similar turning motion by pulling the stern to starboard but this time with a pivot point closer to the stern. It’s a bit like pulling or pushing on one side of a shopping trolley’s handle.