On Fri, Nov 7, 2008 at 6:18 PM, Brian J Goggin <[EMAIL PROTECTED]> wrote: > Any propeller experts around?
Everyone's an expert on this list! :-) Re: Prop size, first I'd say, choose an engine size. You say people have said the barge is underproped (and looking at the pictures I'd say so!), however does the engine get up to maximum revs in forward gear? I'm guessing so, and so not only is the barge underproped but the prop is mismatched to the engine (or vice versa). What are you impressions of the current setup with regards to speed, and maneuvering? Is the boat fast enough? Does she stop within a suitable distance? It may be possible to work out from the revs that you usually use (and the engines power output at said revs) to work out what size engine you may need. If you are always using full throttle then the current prop is too small (or your hand is too heavy! :-) Once you've decided on the engine you have a few choices with the prop some already mentioned here, though I think personally I would bite the bullet and put the prop nearer the center of the available gap (is the original prop shaft hole still there, or has it been completely filled?). With regard to the prop size, I would then call the very helpful Crowther Marine in Oldham: http://www.crowthermarine.co.uk/ Tell them what size of engine, type and size of boat, prop shaft size and type, size available to swing, and they will tell you what sort of prop you need. We have the opposite problem to yourself (prop shaft to high), and so we are now swinging a smaller prop but with more blade area (a so called high efficiency prop) which works really well. If you can't move the prop shaft this may be the only option. Crowthers will probably also be able to help with engine size if you are unsure yourself. Once you've chosen engine and prop you will need to think about a gearbox (or hydraulic motor ratios), the ratio will be chosen by your engine/prop config (though I'm sure Crowthers will let you know what they recommend). Re: Vibration, I think because the close limit is near the skeg and not something more substatial like our proplem (counter, and uxterplate) you could push the limits of closeness a little more than normal, I don't think you would notice the difference between 2" and 1.5" in this case anyway. Most of the vibration is probably coming from the engine if it's on hard mounts. Thats my tuppence worth, Mike -- Michael Askin http://shoestring_DOT_zapto_DOT_org/
