Boat Wandering at Low Speeds

 The topic comes up in conversation now and then regarding the tendency of a boat to wander a bit at low speeds. With the increase in no wake zones where we typically boat it is more concerning than ever. So why does a boat wander at low speed? Is this a problem that can be corrected? Before much time is dedicated to the cure, let's discuss the cause. 

Boat hulls vary dramatically sometimes from one to another but almost all of them can be easily divided between planing hulls, and non planing hulls. An excellent example of a non planing hull would be a sailboat. Others would be tugs, ships, canoes, and so on. Planing hulls are most recreational power boats these days, where the hull climbs on top of the water with sufficient speed where the tension of the water supports the weight of the boat rather than the hull displacing the weight of the boat with an equal weight of water. We could go into much deeper detail but I think this description of a planing versus non planing hulls is sufficient to the conversation. 

Most non planing hulls, or displacement hulls, operate at relative low speeds, and to maintain directional stability they will have hull features such as a keel and a rather large rudder. With the considerable surface area provided by these parts of the hull they together provide the pressure needed to direct the boat along the chosen path. A planing hull in contrast has very little if any keel, and the only rudder on most is the gear case of the engine. The gear case is only as large as it needs to be to house the mechanicals of the assembly, and is only a rudder by default which renders it all but ineffective at lower speeds as a rudder. It does offer directional suggestion though through the force of the prop turning when it is in gear. 

Basically the non planing hull is all but adrift at low speeds, while the engine is doing a poor job of telling it where to go, no matter what the captain does with the steering wheel. So how to handle the inevitable low speed operation in these boats? The best approach I've found is to find a target on the horizon for reference, and maybe to aim towards, then align the point of the bow with that target. With these two aiming points I can quickly see when the hull wanders off course. The reaction to the wandering is key. Do not over react. Small corrections are best, and then patience. Wait to see how the hull reacts. If it's still wandering off in the same direction add a bit more correction, and if it's coming back too quick, ease up a bit on the correction. It's best to get a feel for this in relatively calm conditions before tackling low speed handling with wind, current, and heavy boat traffic. 

I like to point out that water is what I call an imperfect support system. It's great fun to play on and in, but it's dramatically different from riding on a solid. A boat is more susceptible to misbehaving because of this, but to me it's all part of the fun in owning and operating a boat.