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Posted: Tue Feb 22, 2011 9:42am

Post Subject: Engine & Prop Shaft

Heres my problem. I am having a large barge built with an approx final displacement of 50-54 tons. It has a slight v and is 70ft long and 15ft wide with an upper wheelhouse of 12x20ft. I will be using it for a full residential home and am having problems with the selection and cost of the stern gear as the builder is wanting to launch the boat quite soon. The max prop size is approx 28inch. What i need to know is can i fit a generic prop,prop shaft and stuffing box so that at a later date i have a wider choice of engine. Everybody is telling me that they have to match perfectly, meaning i will have to ultimatly buy a new engine so that i am sure i can get that model one at a later date. Which i believe will need to be approx 120hp. I would prefer to have a choice, so that i could possibly save a lot of money and get a recon engine


Posted: Tue Feb 22, 2011 10:05am

Post Subject: Engine & Prop Shaft

I think there are misunderstandings here. The engien and shaft do have to be as near perfectly aligned as possible but that is alignment NOT matching. If you have enough space between the front of the shaft and the gearbox coupling you could fit a jack shaft with two universal joints in it (like a rear wheel drive car's propeller shaft) or an Aquadrive/Pythondrive and then the shaft alignment becomes all but irrelevant. What you have to do is to ensure the shaft is strong enough to accept the engine power and this is important so specify your shaft diameter, coupling etc for your planned 120bhp and then a lower powered engien will be fine. The other thing that needs matching is the propeller to the engine power & gearbox ratio. If you are fitting a smaller engine at this time it will need a different propeller and you may find that your shaft is too large for the standard hole. In this case simply specify the shaft size and the supplier should be able to oblige. You may also find that the shaft to gearbox coupling does not match with a low power engien driving a large diameter shaft but again a simple adaptor plate can be used it required. Why you builder does not know this and advise you along theses lines is beyond me - unless he has a piles of sterngears he wants to shift. Tony Brooks

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