Mike one thing i have learned from the good folk on this forum is that the burner and boiler dictate the performance, so if your boiler makes x amount of steam then that steam is all you have got, then it s then used to turn the engine, so the choice of two or three cylinders is crucial - you will need 50% more steam to turn the 3 cylinder Saito compared to the two cylinder (dependent on which 2 cyl version of the Saito) check out the cc of each engine - the 2 cylinder is 5.4cc and the 3 cylinder 9cc, so if you have 100cc of steam it will turn the 3 cylinder engine 11 times however it will turn the 2 cylinder engine 16 times. this is important since that is how many times your prop will rotate and will affect your speed and duration. So the next thing to do is to fit the largest prop the engine will drive with the steepest pitch you can. This will make the boat go further, faster and use a lot less steam, therefore extending your run times. I am sure others will explain this better than I since I am still learning. I have looked into this and am learning about it for a build that I am collecting parts for, it will use two twin cylinder Saitos, so wish you well with your build.