Keelson scarfs are proportioned by the same rules that already have been given for keel scarfs. However, the lower nib, when falling against a floor where it is concealed, is frequently made only one inch deep instead of the rule depth of possibly several times this. The locations of the various scarfs are usually shown on the plans. They should be arranged so as to use the longest available timbers and should be properly shifted in the various strakes. No fixed rule can be given for the shifting of keelson scarfs. They should be kept as far apart as possible and in no case should any part of a scarf in one strake overlap any part of a scarf in another strake unless the number of keelson strakes is greater than eight. Scarfs in adjoining strakes should have from six to eight frame bays between them if possible.

All keelson scarfs are commonly made flat, that is, with the flat of the nib resting on the floors, or keelson strake underneath. It is common to speak of keelson scarfs as flat when they are in this position, even where occurring in a keelson having greater molding than siding, when, according to rule, the scarf would be an edge scarf. It is good practice to so face the scarfs as to permit the placing of the midship lengths of the main keelson first, thus permitting this work to be done as soon as enough of the square frames are up to receive a full timber length. There will then be no time lost in getting the main keelson ends down after the square frame has been completed.

The sister keelsons are generally run in beginning at the bow and working to the stern. The ends of the sister keelsons forward and aft are sniped off to fay to the edges of the ceiling coming in contact with them at that point. This is accomplished in the manner shown in Fig. 86. The ends of the sister keelsons may be worked out from offsets furnished from the loft, these being carefully checked from the ship before cutting the timbers to exact size.

Figure 86. Keelson Ends.

Where there is more than one set of sister keelsons, as in Fig. 83, each keelson strake would be run straight fore and aft, or parallel with the keel, and the ceiling would run across the ends of the keelsons as indicated for the one strake in Fig. 86. Thus it will be noted that, before the final shape of the ends of assistant keelsons can be laid out, the ceiling line crossing them must be run in. This line is sometimes that of the lower edge of the thick bilge ceiling as is described further on in this chapter.

In some cases the sister keelsons are cut off square a short distance from their natural endings, and "thick strakes" are fitted, these being about the same shape as the keelson ends would have been if extended as shown in the figure. These short timbers are easier to handle and fit, and that is the principal object in using them.