ianc1200
Well-known member
I apologise as I've asked too many questions lately, and do realise most will feel this is sacrilege to even think about this, but just playing with an idea.... I've bought an Aquastar 38 with twin Cummins 250hp. The boat cruises really nicely at 12-13 knots, and probably a lot more than this. But it idles in gear at about 7.5 knots, and on one engine 4.5 knots. It's not happy idling for long periods, I've been told the Nippondenso EP9 fuel pumps are industrial but don't like to idle. I'm based in NE Essex, and the plans are to take her to the Upper Thames, Broads, and eventually France/Holland Belgium etc. Some of the canals I'd like to visit (eg the Canal de la Marne au Rhin) you can barely go a walking pace, and are very weedy. The boat has not got a generator, and there's plenty of room between the two Cummins for a third small engine. So my fantasy - which I'm sure will never happen - is why not put a third engine between the two Cummins, keel cooled, even perhaps a folding prop, so it could be used for both propulsion on slow weedy canals and a generator. I'd not have a third rudder - the boat has two very small rudders but steers more effectively, certainly close handling, by throttle control, but would then have to have bow and stern thrusters. My question is not whether this is a stupid idea, or I've bought the wrong boat, but how much hp would I need to push the boat along at say 4 knots, plus stopping power at that speed. We do have two other boats - a wooden estuary cruiser, about 5.5 tons dead weight, 30' long, which has a Yanmar 1GM 10hp wing engine and can get 5 knots in still water. Our 26' 1910 gaff cutter, about 3.5 tons, with a 20hp Beta, gives us about 6 knots. So I'm thinking, a 38' semi displacement, much wider and 9.5 tons, could be OK with a similar Beta 20.
