A funnel is the smokestack or chimney on a ship used to expel boiler steam and smoke or engine exhaust. They are also commonly referred to as stacks. The primary purpose of a ship’s funnel(s) is to lift the exhaust gases clear of the deck, in order not to foul the ship’s structure or decks, and to avoid impairing the ability of the crew to carry out their duties. In steam ships the funnels also served to help induce a convection draught through the boilers.
Note: YES. I am playing with numbers here for my amusement. I am a modeler not an engineer so this is just for fun.
Funnel area – The required funnel cross-sectional area is determined by the volume of exhaust gases produced by the propulsion plant.
From “The Steamboating Forum” there was a discussion on “Funnel Diameter to Grate area ratio“. Mention of the flue inside the stack .. “The Tug’s boiler has a six inch diameter flue (inside the 12″ stack)” … ok. I can then say .. “The flue is half the dia of the stack”. The conversation continues with “Cross sectional area of 6″ flue is 28″ using the 1:15 that would be 420 square inch grate, around 15 X 30 grate.”
So. I have a 14″ length of Acrylic tubing measuring a 35mm OD and 31mm ID. I am going to ignore the ID .. can hide the oversize thickness of the tubing. If I follow the bit about the flue being 1/2 the diameter of the stack, then I have a flue 17.5mm OD. That is 0.689″ .. in O scale that would be 33″ OD full size. From that we get a flue with a cross-sectional area 855 in.sq. Finally that gives a 12,825 sq.in. grate (855 x 15) or 89 sq.ft.
AI Overview – “For hand-fired coal boilers, a practical guideline is roughly 1 sq.ft. of grate area per 5-10 BHP, depending on coal quality and firing rate. Generally, 1 PHP equals 34.5 lbs of steam per hour.” For the 89 sq.ft. of grate we would have 445 to 890 BHP. Since this is an older 1890’ish boat I will say … ok .. 450 bhp. On the page about the steam engine on the Grazyna I calculated it to put out 513 H.P.
I think that is … “Close Nuff”