Yacht Weigh-ln

How weight and its location influence your yacht s speed and handling.
Medical experts agree that itnot just how much you weigh, but where you carry that weight, that figures into your likelihood of having health issues. For some reason, particularly if you are prone to being overweight, an apple-shape physique is far more dangerous than a pear-shape one. Armchair naval architects take notice; there is a close analogy in yacht performance.
Carrying a lot of extra weight aboard your vessel not only wastes fuel and money, but it also can be the death of good performance. Itbad enough for displacement craft, where the relationship between weight and fuel economy is roughly linear, but for planing craft too much extra weight can prevent the boat from planing at all. You could end up with a yacht that, instead of dancing across the water at 30 knots, lumbers through it at 15 knots with all the grace of a hippo.
Where that extra weight is carried is also critical. Like an overweight person, carrying the additional pounds out front and higher up poses more risks than farther aft and lower down. In technical terms, designers refer to the vertical center of gravity (VCG) and longitudinal center of gravity (LCG) to put a specific value on these locations.
A high VCG can pose a number of risks, the primary one usually being a reduction in transverse stability. This is a double-edge sword too, for not only will the vessel roll more easily and to greater angles in a given sea state, but it will also have a smaller range of positive stability meaning it is more prone to capsizing at lower rolling angles. The longitudinal stability, often overlooked, will also be reduced, so that pitching is exaggerated beyond what it should be. Likewise, the tendency toward broaching or pitchpoling increases. Even if the problem never lises to the level of a capsize or broach, you will still get a lot less enjoyment out of your yacht and will finish a dayrun beat up from motions that are considerably worse than they need to be.
Yacht Weigh-lnAn LCG that is too far aft results in a bow-up running attitude and, in the extreme, may prevent planing. Weall experienced this in an underpowered, overloaded skiff that struggles along with the bow in the sky until someone moves to a forward thwart. Suddenly, the craft rides over the hump, levels out and doubles its speed. The same is true of large vessels, and the solution is basically the same: move weight forward to shift the LCG.
An LCG that is too far forward has its disadvantages as well. A bow-down running attitude is unattractive for sure, but more important, the boat will tend to be wet, shipping lots of spray across the windshield and bridge. In severe cases, the effects of dynamic instability loss of directional control, laying to one side, bow diving, chine walking (transverse oscillation) and others will become evident. Like a high VCG, a forward-biased LCG can also increase the tendency to broach.
Now that we know the problems of weight and location, and how to spot them, ittime to consider what can be done to avoid or cure them. First and foremost, try to keep the weight off. Put your yacht on a diet. As part of your spring commissioning this month, get rid of all the clutter that has accumulated over the course of the past season or two. If you wonuse it for your next cruise, donput it aboard, and that includes extra fuel and water. If you must cany an extra something or other, stow it below rather than on deck whenever possible, helping to keep your VCG in check. And keep a watch on your longitudinal trim, selectively burning off fuel and using water from different tanks as appropriate, and relocating equipment and spares, to avoid an LCG thattoo far forward or too far aft. Ita bit of effort, but your yacht will reward you with better performance.