AHoy Posted June 11, 2007 Report Share Posted June 11, 2007 At the last club meeting got to talking about fuel consumption figures for boats but hadn't checked my boats figures recently, so couldn't confirm my "2 gallons an hour" guesstimate. I have a Quicksilver 640 fitted with a Mariner 80hp 4-stroke engine. I decided not to fit the more common 100hp engine as it gave me a better price package and I felt that the 80hp would be "adequate" for my use. As far as load is concerned, it is equipped with the normal domestic/live aboard gubbins and standard coastal boat equipment, with a crew of 1 (me single-handed) for about half its use and 2 or 3 crew for the remainder of the trips. Usual personal gear, nav/electronics and fishing kit carried back and forth as needed for each trip, typically a trolley load! Usage figures from February this year to date are:- log distance: 279 NM engine hours: 33 fuel used: 251 litres litres/mile = 0.9 litres/hour = 7.5 to 8.1 gallons/hour = 1.7 to 1.8 These figures were obtained travelling at the prevailing Poole harbour speed limit or 16 to 24 knots as appropriate in open waters in generally slight sea conditions. Working area has been between Christchurch ledge and the Peveril marks for fishing plus some general "motorboat" blasts in company with my sons sport-cruiser boat. I obviously expect worse figures on more extended high speed runs (if conditions ever allow it) and in more adverse conditions. Also the engine is a bit "over-propped", it is relatively slow onto the plane and has not achieved the expected top speed of around 28 knots. Correcting this will probably result in slightly higher fuel consumption if it happens. Overall I am satisfied with the fuel consumption achieved so far but have no idea how it compares with others. BTW, with a fuel capacity of 135 litres I quote a range of 7 hours on my CG66 to allow for worst case motoring. AHoy. Quote Link to comment Share on other sites More sharing options...
TomBettle Posted June 11, 2007 Report Share Posted June 11, 2007 HI Ahoy It was nice meeting you at the meeting. If mymaths are correct then your average speed over 33 hours is just under 8.5knots. This is fairly slow as an average, but would take into account a fair bit of pottering around, getting in and out of somewhere like Cobbs Quay. Based on an average of 8.5 knots, I'd say that your fuel figures are close to spot on, but expect that to increase quite markedly as you start to open her up a little. You may well find that at the typical 20 knot cruising speed you are using somewhat more fuel than someone with a 115 for example. This will simply be because your engine is working a fair bit harder to maintain the speed than a more powerful lump. That said, at harbour speeds and cruising on or just beyond your slower planning speed (12 to 16 knots?) you should find yours is fractionally more economical. Tom Quote Link to comment Share on other sites More sharing options...
duncan Posted June 11, 2007 Report Share Posted June 11, 2007 these figures are almost identiacal to Phaeton's. The gph is more a function of Poole Harbour boating than anything else though and, whilst a practical guide for people doing similar boating, would be misleading in most circumstances. I prefer to think in terms of 4 gph which is my 'up and running' consumption rate..........or statistically looked at it a completely different way the more engine hours I log the better value I am getting out of moorings, maintennace and the capital cost of the boat! Quote Link to comment Share on other sites More sharing options...
Afishionado Posted June 11, 2007 Report Share Posted June 11, 2007 Quote from Tom...You may well find that at the typical 20 knot cruising speed you are using somewhat more fuel than someone with a 115 for example. I have to back this up from my own experience on Pride of Morpork. Initialy befor we bought the Jeanneau (115 Suzuki 4 stroke) we had worked on our fuel costs being slightly more than with the prevous boat and its 60hp 2stroke Tohatsu. This estimate was based on the Janneau being twice the size of PoM 1 and the engine being very nearly twice the hp. However now the Suzi' is past her running in stage and has lost the brand spanking new tightness we have been delighted to find that our fuel costs are actually LOWER! than before. The 4 stroke economy is fantastic and as the engine is so well matched to the boat we can cruise at 22knts or more depending on the day, at only 4000rpm. Full throttle takes her up to 30 knots at a bit over 5200rpm but one can almost feel the petrol being sucked out of the tank. Duncan has a very very good point about usage, and one both Mark and I are very conscious, the more we use her the less overall per day/trip/season will cost on the terms of value for money. We see some very flash large cruisers at Cobb that haven't moved at all this season they must be costing a fortune in the terms of cost Vs use. Mad Mike Quote Link to comment Share on other sites More sharing options...
spNOam Posted June 11, 2007 Report Share Posted June 11, 2007 I am running the Mariner 90 fourstroke (carb model) on a similar type of boat, The ally prop supplied was a 19" pitch which I also found to be a bit slow pusing the boat out of the hole with the boat fully loaded with 80ltrs of fuel & three burly people on board (however not really a slouch either) Max RPM (WOT) with this prop 5400rpm. A swap to an 18" pitch SS prop gets the boat (same loading) on the plane quickly & easily. Max RPM (WOT) 6000rpm (as per the manual) Max speed (gps) 39mph. Hope this has been of some help Quote Link to comment Share on other sites More sharing options...
AHoy Posted June 16, 2007 Author Report Share Posted June 16, 2007 Thanks for all the feedback guys. I have a few longer runs coming up soon (Solent area, old haunts at Cowes/Folly) so will take your predicted fuel consumption into my planning. I still have to check prop sizing and options. Will post an update at some stage. AHoy. Quote Link to comment Share on other sites More sharing options...
great white Posted June 18, 2007 Report Share Posted June 18, 2007 I think Duncan has hit the nail on the head with this one Its down to overall costs during a season. mooring, depreciation, equipment and boat maintenance, fuel, bait etc. I once started to work it all out and realised that its cheaper to just use charter boats, but our way is more fun and you get more satisfaction when the plans work as Ahoy said at the start the engine boat package costs were a consideration as they are with all of us. I was wondering if the engine hours used are off your instruments or from a log? If they are from the instruments they will include all idling and it is surprizing how much of that we do, stopping to drift for bait, talk to other boats, stow or prepare lines and tackle etc Of course the idling is at minimum fuel consumption and may be why the average speed and fuel consumption is so low Charlie Quote Link to comment Share on other sites More sharing options...
AHoy Posted June 18, 2007 Author Report Share Posted June 18, 2007 The engine hours quoted are from the engine hour meter and the distance log from the integrated fishfinder/data unit (it compares fairly well with the GPS log). As mentioned this record includes the idle time etc. but from my perspective reflects the overall use of the engine and helps with planning trips and the overall boat budget. For passage making and long distance marks then the cruising consumption becomes the critical figure and is the one subject to most variation. This is where a fuel flow meter would be handy - if it wasn't the price of a lot of fuel! That is why the answers here have been useful. I also follow the "more use = better value" theory as the majority of boat owning costs are fixed, it is only engine/transmission servicing and fuel that are usage dependant. My engine unit requires a service annually or every 100 hours, so anything less than 100 hours per year increases the per hour cost; 35 hrs in 4.5 months is on target Similarly, marina costs are high but looked at as a daily charge of around Quote Link to comment Share on other sites More sharing options...
Adam F Posted June 19, 2007 Report Share Posted June 19, 2007 This is where a fuel flow meter would be handy - if it wasn't the price of a lot of fuel! As the post elsewhere on the forum says, I have just fitted one of these to OotB, sure the initial outlay as expensive ( Quote Link to comment Share on other sites More sharing options...
cascars Posted July 12, 2007 Report Share Posted July 12, 2007 My 640 is fitted with the Mariner 100hp. It is based at Newhaven so I do not have much slow speed pottering, apart from when wreck searching, but my average consumption with myself and (usually)3 crew is around 1 1/2 ltrs per mile (3mpg) Quote Link to comment Share on other sites More sharing options...
AHoy Posted July 20, 2007 Author Report Share Posted July 20, 2007 As a trial I have replaced the original 19in prop with a "TurningPoint" Hustler 17in prop (intended to be my spare). I have not been able to do a WOT test yet but under fairly good sea conditions with self and 1 crew got 21 knots (GPS) at 4,600 rpm with plenty of throttle left so should comfortably get 5,000+ rpm at WOT. As the boat has been afloat for the past six months I expect a couple of knots are being lost to a "dirty bottom". As expected, manoeuvring "kick" was down a little but this was made up for with a better cruising rpm at harbour speed and quicker acceleration onto the plane. The 80 hp motor seems to have plenty in reserve at a typical 20 knot cruising speed so I will probably stay with a 17in prop and just have to put up with second choice on the marks when I lose the drag races with you guys Quote Link to comment Share on other sites More sharing options...
TomBettle Posted July 20, 2007 Report Share Posted July 20, 2007 ...don't worry I'll arrive half an hour later and snuggle in amongst the rest of you. Quote Link to comment Share on other sites More sharing options...
AHoy Posted July 20, 2007 Author Report Share Posted July 20, 2007 (edited) Tom, You can make that little rubber dinghy go THAT fast! Edited July 20, 2007 by AHoy Quote Link to comment Share on other sites More sharing options...
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