|What are they?|
For a long time the most common ventilator was the cowl ventilator until the advent of forced ventilation using power-driven fans. Used on all types of vessels it was used to supply fresh air and remove foul. The ventilator could be rotated to face forward to gather fresh air and rotated to face to the stern to extract bad air.
The diagram to the left1 gives some basic (relative) dimensions of a Cowl Ventilator.
The Boiler Room is fitted with two cowl ventilators, of larger diameter than those in the Engine Room. They are fitted in the two forward corners of the boiler hatch and stand above the Fidley Hatch to have a good draft. The cowl hood of all these ventilators is built separate from the ventilation trunk pipe (which is round in section) and rests on top of the trunk as a guide, so the cowl can revolve. On the outside of the cowl, below the throat and just above the trunk a gear rack is fitted to engage with a pinion gear wheel. (operated from Engine or Boiler Room). The ventilators in the Boiler Room are made larger in diameter as they are also used as elevator shafts. The Boiler Room has ash buckets which are used to raise and dump ashes over the side into the dump scows while in harbor, if the steamer is a coal burner.2
The above shows how I could use a number of ventilators – 4ea of one size and 2ea larger versions.
|Follow me and Curves|
One of the most useful tools in Sketchup is the ‘Follow Me’ too. You can create a path .. a straight line or a series of joined curves and pull a shape through that path. You can make molding follow a wall .. the handrail of a curving staircase .. or a pipe elbow. Once you understand how it works it isn’t that hard.
Using the pipe elbow as an example – you create a curve and then use the Follow Me tool to push a ring along that curve to create the elbow. That curve by the way isn’t necessarily 90° even when you want a right angle elbow. The reason is that when you look closely at the curve it is a series of straight lines. The greater the segments the smoother the curve. If you think about it a second you can see that depending on the way the software creates this curve a curve might not end exactly at 90°. The best way I think to understand this is to think .. if you tell the software to draw a circle .. with three sides it is a triangle. If you tell it to use five segments to draw a circle then it is a pentagon. I normally use at least 60 segments for a circle – depending on the size of the object we are wanting to print in 3D .. if the segmentation is less then the resolution of the printer then there is no need to increase that segmentation.
This is I suppose useful information to anyone wishing to use Sketchup but if I try to create a reducing elbow – which is really what the cowl ventilator is at a basic level, we have a problem. Sketchup’s native Follow Me tool won’t do that .. so we need a plugin.
Enter .. Crviloft