The greater all these three magnitudes are, the greater the stability of the canoes. A shallow canoe, without much freeboard, will be easily forced into the water; moreover, if sailed in rough weather, waves will break over it, and fill it with water.
(i) The volume of the dug-out log naturally depends upon the length, and thickness of the log. Fairly stable canoes are made of simply scooped-out logs. There are limits, however, to the capacity of these, which are very soon reached. But by building out the side, by adding one or several planks to them, as shown in Figure I (4) the volume and the depth can be greatly increased without much increase in weight. So that such a canoe has a good deal of freeboard to prevent water from breaking in. The longitudinal boards in Kiriwinian canoes are closed in at each end by transversal prow-boards, which are also carved with more or less perfection (see Plates XXIV c, XLVII).
(ii) The greater the distance B—C between dug-out and outrigger float, the greater the stability of the canoe. Since the momentum of rotation is the product of B—C (Fig. I), and the weight of the log C, it is clear, therefore, that the greater the distance, the greater will be the momentum. Too great a distance, however, would interfere with the wieldiness of the canoe. Any force acting on the log would easily tip the canoe, and as the natives, in order to manage the craft, have to walk upon the outrigger, the distance B—C must not be too great. In the Trobriands the distance B—C is about one-quarter, or less, of the total length of the canoe. In the big, sea-going canoes, it is always covered with a platform. In certain other districts, the distance is much bigger, and the canoes have another type of rigging.
(iii) The size of the log (C) of which the float is formed. This, in sea-going canoes, is usually of considerable dimensions. But, as a solid piece of wood becomes heavy if soaked by water, too thick a log would not be good.