Guest 000 Posted July 26, 2018 Share Posted July 26, 2018 The engine we have in our canal boat is a Lombardini 4 cylinder, 60hp, 3600 maximum RPM. The 'sweet spot' is 21 - 2200rpm. We have kept good records for long enough now to know that at this rpm we burn 2.55 litres per hour. Does this sound right? Engines are a popular topic of conversation when canal boaters congregate in the evening to tell lies to each other, and what I frequently hear is owners saying their 60, 70, 80, even 100hp engines running at 2 litres/hour. Porkies, or is my engine a bit greedy? Quote Link to post Share on other sites
Jon 360 Posted July 26, 2018 Share Posted July 26, 2018 Our 110 hp VP uses 2.66ltr per hour at 1550 rpm doing 6kts However at 2000rpm we are doing 7.5kts and using over 4 At 2500rpm which is a nice comfortable fast cruising we are doing 8-8.5 but burning more like 7 plus ltrs At WOT we are doing 9 plus and must burn over 10 It’s a steep curve so it’s all about speed verses economy If we are away for a few days the extra fuel is cheap so run at 8.5 kts If we are on a long passage we run at 6kts if no wind and then have enough fuel to motor from AKL to Fiji with a bit to spare but at 8 kts wouldn’t get halfway I’d think a canal boat would possibly have a flatter curve as it wouldn’t squat as much as you increase power being a flat bottom girl ? Quote Link to post Share on other sites
Tillsbury 5 Posted July 26, 2018 Share Posted July 26, 2018 Also, rough water makes a huge difference. I have the 105hp VP and can really chew through diesel when motoring through decent sized waves at 7-7.5kts. Canal boats are usually idling at 3-4 knots on perfectly flat water, and I can believe that 2l/hr is no problem then. See the dotted line below showing expected fuel consumption at various rpm. Quote Link to post Share on other sites
Fish 0 Posted July 27, 2018 Share Posted July 27, 2018 Hi Chris, I reckon your consumption sounds correct for your revs. There are so many variables with engines, like the revs others are running at, gearbox ratios and how good / efficient their props are. As already commented, consumption increases rapidly with increasing revs. At a theoretical level, the energy required to move the boat comes from the fuel burnt, so the engine size (in Hp rating) is not a primary factor. Speed and displacement are. The short story is a 100 Hp engine at a tad more than and idle could probably achieve the same speed as you when you run 2,100 rpm. A 100 Hp engine may well use 2 l/hr at an idle, so they may be about right. I wouldn't think your engine is 'thirsty', but getting to two decimal places in your fuel consumption sounds very accurate (i.e. suspiciously accurate). I'd probably question the level of 'precision' of a lot of those fuel consumption numbers. Remember 2.44 l/hr rounds down to 2 l/s when expressed as a single digit, so those other engines could be much closer to yours in consumption, and its just a bit of smoke and mirrors in the details... Quote Link to post Share on other sites
marinheiro 352 Posted July 27, 2018 Share Posted July 27, 2018 Here are a couple of sets of fuel consumption figures to provide an idea of speed vs fuel burn https://www.hallberg-rassy.com/fileadmin/user_upload/pdfs/boats_pdfs/HR40propellerFlexofold.pdf https://www.hallberg-rassy.com/fileadmin/user_upload/pdfs/boats_pdfs/HR48propeller.pdf In both case the yachts are slightly underpropped, the Yanmar should be burning about 12lph at full revs, the Volvo should burn about 25lph, but the 2 speed Gori prop probably blurs the issue. When a boat is travelling at sq root LWL in ft (I could not find the symbol) fuel consumption is very low. Above that fuel consumption typically doubles for evey 1 knot increase until you hit the "wall" of hull speed - 1.34 root LWL My 4JH4 Yanmar in 14.5m yacht averages all up ~2.5l/hr as well. The important thing to remember is engines at these fuel figures are running seriously underloaded and need to be run up to near full revs quite frequently, especially turbo charged motors. Yanmar even provides a procedure in its manual. https://www.proboat.com/2015/02/why-you-shouldn-t-go-easy-on-a-diesel/ Quote Link to post Share on other sites
Crazyhorse 47 Posted July 27, 2018 Share Posted July 27, 2018 I hope everyone is changing load (revolutions). My own experience is staying in the 'sweet spot' for hours can cause coaking, the engine doesn't get warm enough, injectors clog. I did once took a mack 230hp tractor unit from Mingle Wells to Port Headland on emptying tanks after forgetting to fill up. Not enough fuel to get back so kept going, praying and vertually just above idling in top. Made it! Quote Link to post Share on other sites
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