darkside 61 Posted November 6, 2019 Share Posted November 6, 2019 A diesel engine is designed to bypass fuel not required back to the tank. Because of this feature fuel burn is only loosely related to revs. It's load that matters. If you want to get really flash you get a variable pitch prop and load the engine to the correct exhaust temperature. But at 3.1l/h who cares? 1 Quote Link to post Share on other sites
Guest 000 Posted November 6, 2019 Share Posted November 6, 2019 I think probably under pitched. I feel a bit of a goat not knowing the prop details other than it's a 4 bladed prop with a lot of blade area on a 2.8 : 1 reduction. I'll see exactly what it is when we return next year. We pushed the engine to 3550 rpm once and it was just starting to make a wisp of black smoke but was not labouring. So I would say that our good fuel economy and slowly increasing speed when we open the throttle would confirm underpitched. For us this is no problem due to the speed restrictions on the canals but probably not so fine for the engine since diesels like to work. But I can live and die with it. The engine has 592 hours on it. We average 300 hours per season. I'm 75, perhaps another 4 or 5 seasons left in me, so 2000hours on it when I'm done. The engine should do that ok. We look after it well and according to the manual. Quote Link to post Share on other sites
Frank 157 Posted November 6, 2019 Share Posted November 6, 2019 The whole canal boating thing sounds cool, is there a risk you just go from pub to pub ? Quote Link to post Share on other sites
wheels 543 Posted November 6, 2019 Share Posted November 6, 2019 Pitch is pure and simply, the distance the prop wants to move through the water per rev. It is like a gear ratio. It is diameter and blade area that equates to the props efficiency at being able to push the boat forward with less slip.Blade efficiency and Engine RPM are not related. Meeting engine RPM is all about loading on the engine and there are many points that are essential if you want the best life from the engine.If you take a look at the graph, the fuel curve is just that. A curve and it is concave, or droops down in the middle. So, if my memory is correct, the most economical point in the engine RPM is around 2300RPM ?? I think. The curve works s mcp stated above. grams of fuel used per Kw of engine. So you look at the revs, the Kw being produced at those revs and the fuel consumption multiplied by the Kw figure. The grams per Kw is at the greatest at both ends of the RPM range. Quote Link to post Share on other sites
mcp 32 Posted November 7, 2019 Share Posted November 7, 2019 I think probably under pitched. I did a rough calculation and your pitch will be about 12 - 13 inch based on the information you have provided above. Which would be about right for 9 knots, in a displacement hull with limited weather and current effecting you. Quote Link to post Share on other sites
mcp 32 Posted November 7, 2019 Share Posted November 7, 2019 I did a rough calculation and your pitch will be about 12 - 13 inch based on the information you have provided above. Which would be about right for 9 knots, in a displacement hull with limited weather and current effecting you. And when I say I did a rough calculation, I did it using an online prop calculator I used for sizing the prop for my dinghy. http://www.csgnetwork.com/marinepropcalc.html Quote Link to post Share on other sites
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