logoman....in lay terms....we need to understand the purpose of the ventilators
1) to provide an exchange of air
2) to provide a method of heat removal
3) to provide a higher air pressure [over atmosphere] for the purpose to aid combustion
4) ventilators usually had a worm & worm wheel so they could be aligned at the prevailing breeze or wind direction irrespective of the vessels path or direction
5) even if the vessel is stationary the velocity of 'air' is captured in the funnel like structure admits the air to where the lower pipe work is located
Dependent on the velocity of the breeze.....this admission of air to a closed chamber would increase the air pressure by say 2 PSI above atmosphere....but this serves no purpose unless we can allow spent or hot air to escape....hence having the engine skylight vents open & hence a continual convection of changing air flow
So for boiler rooms the ventilators were to aid combustion, but engine room ventilators were to expell hot air
In addition to conventional ventilators as shown, venturi type vents were also used.....the attachment is self explanatory as the same breeze is harnessed to 'suck' spent or hot air out of the enclosed space...........Derek
