Sec. 7r,.J5 



DESIGN OF SPECIAL PURPOSE CRAFT 



775 



that they are neither too small nor too heavily 



loaded when running free. 



(h) Too much attention need not be paid to a 



hull of minimum free-running resistance, if other 



more important features are thereby improved. 



As a rule, the pumping requirements call for 



plenty of power so that a not-too-high hull drag 



may be accepted if it leads to a better all-around 



firefighting craft. 



(i) Harbor icebreaking features, if called for; see 



Sec. 76.26 following. 



To achieve maneuverability and handiness in 

 and around scenes of possible fires: 



(1) The craft should not be too large. Depending 

 upon the pumping capacity required, lengths of 

 70 to 80 to 90 ft are adequate. Lengths of 110 

 and 120 ft are approaching the extreme; 125 ft 

 is possibly the maximum [Parsons, H. de B., 

 SNAME, 1896, p. 49]. 



(2) The length-beam ratio should not exceed 5.0. 

 Preferably it should lie between 4.0 and 4.5. 



(3) The sides should have continuous curvature, 

 as for a tug, to enable the heading to be changed 

 readily when the vessel is alongside a pier or 

 another ship. The ends should be well rounded. 



to prevent the craft from jamming itself between 

 piles and the hke. 



(4) The draft should be a minimum consistent 

 with other characteristics 



(5) There should be no excessive keel drag or 

 filling out of the lateral plane at either end 



(6) The rudders should always be so placed as 

 to lie in the propeller outflow jets. 



The reaction forces at the discharge nozzles or 

 monitors, illustrated pictorially in Fig. 76. H and 

 indicated numerically by the example given later 

 in this section, can be very large. They are 

 counteracted by one or more of the following 

 procedures or devices: 



(7) Constantly moving the fireboat or holding it 

 on a certain heading with its propulsion device (s) 

 turning over. This may involve a corresponding 

 shift of the water streams to keep them playing 

 on a desired spot of the fire. 



(8) Passive drift-resisting keels, described in 

 Sec. 36.15, or the equivalent. These are a help 

 at times but they are not adequate for all possible 

 situations. 



(9) The provision of one or more swinging or 

 rotating-blade propellers. This method, however, 



Fig. 7b. H Honolulu Fireboat Abner T. Lunyley With Jeis in Action 

 Photograph by Lawrence Barber, Portland, Oregon 



