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>>Thanks, Robin. That's really clear. Having talked >>and thought it through since Friday, I'm now moving >>away from the idea of replacing the engine. At least, >>not now. We've a lot to do, still, to get the boat >>shipshape inside and out and, although it's a bit slow >>for the tidal Thames, it's fine for mid-Thames, where >>we're based. >> >>We have checked speed with a gps and averaged out >>upstream and downstream speeds to give us a >>black-smoke-free speed of 6mph. With a bit of black >>smoke, she'll do 6.5. I'm starting to think that for >>a 45-year-old, 40hp diesel, that's not bad. >> >>Next time we're out in her, we'll check the revs with >>a tachometer while the engine's under load to get a >>more accurate understanding of the power being >>delivered. >> >>Thanks again to Robin and Ian > >Alan >I got a bit confused with the 6mph to knots, its 5.2 >Knts not 4.5, we're on the broads and the limits are 5 >and 6mph and my log and plotter is in knots so I >should know. At 6.5 mph, you're getting towards 6 >knots and the hull speed is 6.5 so there's not a lot >to be gained. As like mine you have a 1 to 1 box you >also need to consider the shaft speed, with a bundle >of revs you will exceed the design speed of the shaft >and get increased wear. Mine is proped to run at a max >of 2200 with a 12 by 8 prop. We have some quite strong >tides here, I've seen 3.5 knots on the log with the >boat stopped and ballanced on the tide and our boat >will pull like a train against the tide using the >torque of the engine. If you are producing black smoke >its either over fueling or pulling a bundle of revs, I >think you need to look at the prop, is it too short a >pitch or worn. have fun. >Best regards >Robin

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