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Angle of Loll





Angle of Loll


The term loll describes the state of a vessel which is unstable when in an upright position and therefore floats at an angle to one side or the other. If disturbed by some external force, caused by wind or waves, the vessel may lurch to the same angle of loll on the opposite side. Loll is quite different from list, being caused by different circumstances and requiring different counter measures to correct it and it is therefore most important that the mariners should be able to distinguish between the two.

Fig 4.10 shows how an unstable vessel takes up an angle of loll. Note that M is not on the centre line when the vessel is in the lolled position.

To correct for loll the following procedure should be observed.

First verify that it is loll and not list. Lists are caused by shifting of cargo or uneven distribution of fuel, water or cargo. If none of your cargo has shifted and your fuel and water tanks are more or less even on both sides, then you should suspect that your vessel has loll. You must lower the centre of gravity. There are two options open to you






















Figure 4.10


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(i)         You can take ballast. If you do so, (and if your vessel has ballast tanks that you can fill) then you should begin by pressing up tanks on the low side first. This will initially make your angle of loll worse because you are adding weight on the side to which the vessel is leaning and you are introducing a free surface (if you are ballasting on an empty tank). This is still safer than ballasting the high side first, because that could cause the vessel to flop-over to the other side, and possibly capsize. By introducing ballast you lower the centre of gravity. If you are pressing up half-filled tanks, you are still lowering the CG and removing the free surface. The only negative effect of adding ballast is that it will increase your draft, reduce your freeboard and reserve buoyancy wit the result that your vessel will ship water at a much smaller angle of heel.

(ii)        The second option open to you is to remove the cause. A loll does not suddenly occur. It is a result of decreasing stability which is caused by the progressive raising of the centre of gravity of the vessel. This can only occur if you are loading weights on deck, and using fuel or water from low down in the hull (where most tanks are located anyway). You would have felt the vessel becoming progressively more tender and the roll period, and angle of roll steadily increasing. You may have been catching a load of fish - your brine tanks full and a large load of fish on deck. Too much weight high up. In these circumstances you may have to jettison cargo. This may be a painful decision, but the cargo is no use to you when your vessel is upside down!

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