Sec. 76.8 



DESIGN OF SPECIAL-PURPOSE CRAFT 



767 



(12) Project the point D in the profile downward 

 to the latter generatrix FT, intersecting it at D. 

 This is one point in the plan view of the deck 

 edge at the side. FD in the profile and FD in the 

 plan view are two projections of the same straight 

 line in the side of the boat at the forward quarter. 



(13) Starting similarly with points P, N, and Z in 

 the chine profile, find the plan contour of the 

 deck edge at the side abaft the point D in the plan. 



(14) To get the fullness of side required at the 

 bow a shorter and fuller cone is used. This tran- 

 sition is made by having the first element of the 

 new cone coincide with the last element of the 

 old cone; for example, FDU and FDS in the 

 profile. This means that the apex U in the profile 

 ■must lie on the generatrix FDS. Apex V is laid 

 down on the generatrix FDT opposite apex U. 



(15) From a selected point H in the chine profile 

 forward, draw HJ on a straight generatrix 

 toward the bow-profile apex U. This straight line 

 intersects the sheer Une at J in the profile. 



(16) From the point H on the chine in the plan 

 view, opposite H in the profile, draw a straight 

 line to apex V 



(17) Project J in the profile downward to the 

 generatrix HV, which it intersects at J in the 

 plan view. This is another point along the deck 

 edge in the plan. 



(18) Continue in this manner until sufficient 

 points in the forward deck edge are available to 

 permit drawing this line for the entire length 



(19) As an aid in dehneating the deck edge aft 

 in the plan view a waterline WLi is drawn 

 through the hull in the profile, parallel to the 

 baseline. By estabUshing the approximate outline 

 of the transom, half of which is indicated in the 

 body plan, it is possible to lay down the point E 

 on the plan view and to determine another point 

 along the deck edge aft, lying on the generatrix 

 ET. Another way to do this is to extend the 

 chine for a station or two abaft the transom and 

 follow the regular procedure. 



(20) To determine the keel profile, first draw a 

 line in the plan view from F on the chine to apex 

 B in the plan, intersecting the centerHne at K 



(21) In the profile, draw a line from F on the 

 chine to apex A. Project K in the plan upward 

 to its intersection K in the profile with the 

 generatrix FA. Point K is one point on the keel 

 profile. 



(22) Draw a line from another point H on the 

 chine in the plan view to apex B; it intersects 

 the centerline at the point M 



(23) Draw a line from H on the chine in the 

 profile to apex A. Project the point M in the plan 

 upward until it intersects the generatrix HA at 

 M in the profile. This is another point on the 

 keel profile. Continue in this manner until all 

 points along the keel profile are determined. 



(24) To assist in delineating the after portion of 

 the bottom and to help in preparing the lines 

 drawing later, draw a buttock Bj at about 0.4 

 times the half-chine beam Bc/2 (or draw several 

 of them). Then draw the generatrix QB and 

 proceed as before. 



To draw the buttock B, in the profile: 



(25) The generatrix PYB in the plan view inter- 

 sects the buttock Bi at the point W. Project this 

 point upward, intersecting the (same) generatrix 

 PYA in the profile at W. This is one point on the 

 desired buttock. The remaining points are drawn 

 in the same manner. 



(26) To draw the waterline WLi in the plan 

 view, the generatrix FDS in the profile intersects 

 this waterfine at the point R. Project R downward 

 until it intersects the (same) generatrix FDT in 

 the point R of the plan view. This is one point on 

 the desired waterline. Continue in the same 

 manner to find remaining points. 



(27) To draw the customary body plan, it is 

 possible to lay down the projections of the deck 

 edge, the chine, and the keel on a transverse 

 plane, using the station offsets of the other two 

 views 



(28) Draw apex on the body plan, using the 

 transverse offset of apex B in the plan and the 

 vertical height of apex A in the profile. The 

 transverse projections of the two apexes for the 

 side are drawn in the same manner but they are 

 not shown in Fig. 76.D. 



(29) From the known point F on the body plan, 

 where the chine crosses Sta. 1, draw a generatrix 

 to the apex 0. The point G where this generatrix 

 FGO crosses the section line for Sta. 0.5 is then 

 found by stepping off (1) the offset from G in the 

 plan view to the centerline or (2) the height from 

 the basehne to G in the profile, along the fine 

 FGO. Sufficient points for drawing this and all 

 the other section lines are found by continuing 

 this operation. The section fines, when drawn, 

 are found to have the usual shape for a develop- 

 able surface, slightly convex outward. 



When the process is finished the boat may not 

 have the shape that the designer intended. He 



