Hi Ian,
That's very interesting on the gland, if you did find that there was too much let-by or you had to have it too tight and caused too much friction you might wish to try PTFE tape- it's worked perfectly for me in glands of 'tight' persuasion in the past.
I see the brass collar now you point it out.
Re. the hogging issue- first off, Vital Byte's inherent flaw is that she is flat bottomed, fixing anything to the hull along the centreline simply creates a 'bi-metallic' strip (but one half being of wood!), and the further away from the stress you get along the keel, the more exaggerated the issue becomes at the extremes of the boat- so the prop shaft binds and seizes and cracks can appear at the base of the stem.
Full size boats are, as you assume, no different. And the problem is tenfold as the exaggeration of the curve is across a so much longer length, however, as with your Edwardian hull, the subtle curves of a well designed hull do far more than provide a hole in the water to put a steam plant in (and throw money down, of course). Launches typically have straight keels- this is great for a boat with a straight shaft and reduces deadwood and amount of timber that has to be bored to receive the sterntube. However, this in itself creates problems, as the boat relies on the keel keeping it's line to perform properly. In boats such as this a number of methods are employed to tie the keel in as rigid a position as possible;
Floors; bulkheads that go over the keel- very much in the manner yours do in your model- however they are each one through bolted through the hog and keel. They rise up from the keel, fitted to each plank- with a limber hole either side of the keel- for around 4-5 planks up.
Stringer; self explanatory, much used in both models and full size- however in full size it is important they are tied properly to the grown frames...
Grown frames- these are traditionally sawn from curved grown oak, these span over the keel and up each side to the gunwhales. They are through bolted or rivetted to each plank. The grown frames on a larger launch- say a 35-40ft version of your launch- would have grown frames at every 4ft station along the hull. In modern launches the grown frames are now often laminated. In between the grown frames are...
Steamed frames; the main structural component in any traditional boat from a 10ft pram to a 120ft yacht, and I'm sure you're well aware of their use.
Bearers; over the top, and often let into the floor timbers, are bearers which carry the boiler and engine- these are very important as they cancel the 'bending moment' caused by differential expansion- in boats with a flat run aft these bearers can run all the way to the shaft log.
Shaft log; as in a model really, except in large launches it can be made box section- similar to a hollow box mast construction- this produces a much stronger more rigid frame for the sterntube.
Another point that is overlooked often is the shaft itself, in a solid shaft of, say, 2.5" dia., over a 16-18ft length it will put up with a surprising amount of flexing. A good thrust bearing- either engine mounted or inline is a must.
Greg
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Topic: Edwardian Steam Launch build (Read 28455 times)