Ventilation. 43 



canvas sheet or other suitable material will 

 often greatly help them in performing this 

 dual office. 



The chief mechanical means by which ven- 

 tilation on board ship is facilitated, are : 

 Windsails, air-scoops, ordinary cowl ventila- 

 tors, steam ventilators, and electric ventilators. 

 Windsails and cowl ventilators are shown in 

 Fig. 2. As a rule, a windsail is only an 

 inlet, and should therefore be kept trimmed 

 towards the wind. It is generally used to 

 ventilate hatchways. Its diameter should not 

 be less than 30 inches, and its lower end 

 should be kept at about a foot above the 

 deck it is supposed to ventilate. When a 

 horse which is standing on or near a hatch, 

 requires more fresh air than he is getting, a 

 windsail or two may be trimmed on him. 



