The duration is dependant upon a number of things such as boiler water capacity, gas tank capacity, seperator tank capacity and lubricator capacity.
I have been working on a number of these to improve duration. The gas tank I have improved by fitting a valve system that allows steam pressure to be raised on the bank from an external gas tank. This also helps to reduce the cooling of the on board gas tank during this time. When the boiler is up to pressure I change over to the on board tank. The gas control valve also dramatically improves the life of the gas tank as it turns the burner up and down according to the boiler pressure.
Water in the boiler of course is used and dumped straight to atmosphere after the seperator tank so that is also a limiting factor. A big improvement here is fitting an on board feed tank in the bow so that I can top up ther boiler at the bank without having to vent the boiler and repressurise. You can actually get an automatic system that uses an engine driven pump, a three way valve and a level sensor. I decided to draw the line at that!!
After the trials I have had I find the limiting factor is the boiler water level which should give about 20-30 minutes of average use. Then I bring it in, top up the boiler from the feed tank and empty the seperator with a large syringe. I also top up the gas tank and it should be good for another 20-30 minutes.
I agree it is a vast differrence in preparation required to get one of these on the water but that is actually part of the enjoyment of the model, not just sit it on the water and go. I particularly want to use this as much as possible which is why everything has been geared up to making life as user freindly as possible.
The angled funnel makes me smile every time I think of it. I was walking around one of the scrap metal stores on the ship one day toying with ideas when I knew I needed to look into the possibilities of what I could do with the funnel. I had brought the brass ring from the boiler top with me so I had an internal diameter. I noticed a peice of old refrigeration copper pipe, which fit but that had been used as a paint stirrer so I thought I would have a play.
I designed the cuts I thought I would need to generate the offset I wanted whilst maintaining matching surface areas for silver soldering and a resultant vertical funnel with a 1 cm offset. I cleaned up the pipe, cut it, silver soldered it and polished up the final peice. At the end of that trip I took it home to see how it would do and was absolutely amazed to find that my 'test' piece fit perfectly as regards amount of offset and the height of the offset.
I also noticed that the offset gave me the perfect opportunity to fit the exhaust pipe from the seperator which I particularly wanted to run up the inside of the funnel rather than outside as is more normal. The engine exhaust then comes out of the funnel which looks a lot more realistic and the exhaust from the seperator is heated by the exhaust from the boiler which helps to prevent it condensing and spraying dirty water on the model. So I took the funnel back to the ship the next time and made the exhaust pipe and fitted it inside the funnel. These will both need cutting to length when the model funnel is finally fitted.
So the funnel evolved from a scrap test peice of copper pipe that had been used to stir paint!!