>Leonard Stern of Indifference wrote: >The design should also include as much ballast as practical. This last >statement is made because some passagemakers being built do not >actually have real >ballast and depend only the weight of the boat. Leonard and others-- Why is ballast important for a passagemaker? --Georgs

Ballast allows you to maintain your boat's designed trim and stability. It maintains the vessel's original center of gravity. I just finished rereading "Typhoon" about ADM Halsey's fleet encountering two typhoons owing to errors. He lost three destroyers, two of a class know for their poor stability - they called it metacentric point. The third destroyer was a more stable design, but the captain failed to replace the ballast lost by his low fuel state with water and over the ship went. Ron Rogers ----- Original Message ----- From: "Georgs Kolesnikovs" <georgs@trawlering.com> | | Leonard and others-- | | Why is ballast important for a passagemaker?

At 08:41 AM 1/9/05 -0500, you wrote: >Why is ballast important for a passagemaker? > >--Georgs Ballast is weight. Calling weight ballast implies some special characteristic about that kind of weight. The word ballast is used in several different contexts, the difference of which is quite important. In a vessel for which the principal activity is the carrying of cargo, where the vessel has been maximized for the carrying of such cargo, ballast is the weight needed to replace the "cargo" not carried. The amount required may not be as much as the cargo normally hauled, but the amount needed is that necessary to maintain an adequate amount of stability when the vessel is at sea. In that regard, perhaps only 1/2 of the weight of cargo might be required, especially if the weight is concentrated low down in the hull. Using more ballast weight than necessary for stability will generally result in a lowered cruising speed and additional fuel consumption. Both of which are undesirable. In a commercial operation today, the ballast weight and it's distribution within the hull are very carefully calculated. These principles apply to even a small vessel, but generally due to lack of education the principles are muddied and the calculations are done offhand. The results of such seat of the pants estimates can and have been fatal. In the case of a sailboat the amount of ballast is calculated as the weight that can be concentrated at the end of the keel such as to improve the righting arm, make the boat stand up in order to carry sail. Obviously, if you could use the ultimately dense ballast it would occupy no space whatsoever and you could place it at the farthest point from the center of gravity and it would be that mass which would resist the boat inclining from the force generally of the wind upon the sails. In the case of a small powerboat, the wind force is relatively small compared to that of the sailboat, the ballast is generally to bring the waterline up, the hull down in the water and to provide inertial resistance to the boat rolling. There are 2 forces now at work, for which we are mostly concerned with. There is the resistance to inclining, which is important for itself and there is the inertial resistance which we desire in order for the boat to improve dynamic stability. The static inclining part can generally be improved by the placing weight in the boat, as far below the center of gravity as possible. However, in order to improve dynamic stability this weight must be distributed, for instance by placing equal parts, equally spaced, as far as possible from the CG. If the desired effect is to improve side to side roll, then the placement must be around this center of ROLL (not just CG). On the other hand if you want to effect the roll/pitch from bow to stern, then the weights must be placed as far as practical from the center of the longitudinal(fore/aft) pivot point. It is not generally desirable to try to effect the longitudinal pitching by the use of ballast. What is true is that many boaters do this accidently by placing heavy weights like the anchor and chain at the ends of the boat. Remember the comment about using 1/2 the not carried cargo weight as ballast for a big ship? This rough estimate of necessity can be applied to the small vessel. For instance, one might carry about 1/2 the weight of usable stores, fuel, food, etc. as ballast in order to partially negate the effects of using up these stores. Keeping in mind that any such ballast should be distributed in such a way as to maximize it's beneficial effects on boat motion and stability. The actual ratio that would be desirable may not be 1/2, but you get the idea. Time for Bob A. or someone else to weigh in. Mike Capt. Mike Maurice Tualatin(Portland), Oregon