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”
Funnel Base – I’ve had a liking for “Steam Punk” for a while now. That is in part I think why I like modeling the later 1800’s and early 1900’s .. that was a time when Engineers would just .. try it .. very my Steam Punky to me. The Grazyna’s funnel is out in the open so I decided it needed a “base”. The design has evolved into something very much so … Steam Punk.
This is in two parts … you can see the seam between them. In reality there is in the design a place for rare earth magnets which will hold these two together but allow them to be taken apart if needed. I originally put in sockets for magnets for the lower part but now thinking that is a bit much. The plan now is for that lower base to be glued solidly to the boat. The stack will be glued into the upper part of the base.
Upper and Lower parts – the reason for this as I said is that the lower section will be glued to the deck. The funnel will be glued into the socket on the top section. Rare Earth Magnets will hold the two together.
Top section – From above. The socket for the acrylic tube I enlarged by 0.1mm – hopefully this will allow the tube to slip in.
Top section – From below. There are four locating tabs that fit into pockets on the bottom section. The battery pocket is made for Rare Earth Magnets from Harbor Freight, 5/16″ x 1/8″.
Bottom Section – Here you can see the pockets for the locating tabs on the Upper Section. The batter pocket is the same as the other one. It is these two magnets that will “grab” each other to hold the Upper and Lower section securely together. Finally the upper edge is recessed .3mm x .3mm to give a visual simulation to indicate a slight gab between the two. This is massively oversized .. a 0.3mm gap in O scale is ~1/2″ full sized. Thing is .. like nail holes in buildings the brain accepts this .. IMO .. adding a bit of added interest and yes .. realism.
The red arrow is simply for me as it indicates the direction of the bow.
Intermission: Goldie Locks tried porridge three times to get it “just right”. Last night ran a test print on the upper and lower base sections.
– That first print failed .. I used light supports in Chitubox.
– I then used heavy supports .. and it printed fine .. BUT .. supports were so dense and heavy that the print was useless. Now .. I am hoping that lowering the density of the supports from 85% to 50% and using Medium supports .. it will be “just right”.
…… and ….. CALL ME GOLDIE LOCKS!! Success!!
A look at the undersides of the upper and lower sections.
On the left is the upper section. You can see the four locating tabs. In the center is a Rare Earth Magnet from Harbor Freight.
On the right is the lower section. There are four pockets for the locating tabs so I suppose that I could call them locating pockets. In the center is another magnet, aligned so the two magnets attract each other.
I painted and weathered the funnel base . Poor thing .. has had a rough life.