If ( big IF) there is a saving in fuel consumption then with 30% engine use that should be considered in the equation, as should a greater top speed for no increase in RPM. So it is not quite as simple as you might suggest
I have had the Brunton Auto prop for circa 3500 engine hours. I needed a service for new bearings & rubber bush etc a few years ago (forget how long ago) It hit my pocket to the tune of circa £325-00 . I do service it every season. They did say that the rubber bush can deteriorate over some time, so it is not just bearings. They rebalanced the blades as part of the service. I seem to catch an awful lot of weed with my prop. I cruise the Channel Islands & the weed can be long strong roots. As well as this there is a lot of discarded net. Similar in the Dover Straits. In the future I would go for a folder to reduce the likelyhood of snagging when sailing, not under power.
Plus another for Maxprop.
The fuel saving is an illusion. While a Bruntons may reduce the engine revs for a given cruising speed the power used is exactly the same. As fuel burn is a function of power there is no measurable reduction in fuel consumed either per hour or per mile. So it is a simple as I suggest. Of course people claim reduced consumption because the engine is running at lower revs, but that does not change the physics!
Also, if one considers consumption as liters/miles, it will be the lower the lower boat speed is, having a propeller which tends to give consistently higher boat speeds, tends to reduce mileage per liter.
Thanks for the heads up on that. We sail mainly in France but get there from the Dart usually via the CI. We have never been aware of anything getting caught on the prop until this year. Mostly, it just slips off when sailing. This year late on, probably Falmouth, we did pick up a fairly thick, short length of rope.
I sail from the east coast via the French coast & apart from weed, there are lots of pots in some well known areas. Boulogne/Cap griz nez. Just West of Dieppe & le Havre. West Of Cherbourg . I have had quite a few hook ups over the years along that coast.
Actually I made the comment because the manufacturer claims a saving. On top of that I have seen reviews of some propeller suppliers claiming savings. I was not going to mention it but now I will. The fuel consumption of my autoprop is significantly higher than with the volvo fixed prop. Up from 1.7 litres per hour to 1.9 litres per hour when running at about 1900 RPM in ( I have to rev much higher in rough water & it rises to 2.3 litre per hour at 2300 RPM.) That is taken over many hours cruising both heavy weather to Dutch canals. I religiously keep fuel records so I know it is accurate.
A more useful measure would be fuel per nautical mile. Fuel per unit time is shaft power. Power converted to thrust via the prop so " thrust specific fuel consumption" would be the correct measure to compare different props on the same hull.
If your next boat needs a different sized/pitched prop then your Brunton may not be suitable
But that depends on sea conditions and wind. For comparison reasons you could only do it in flat water and no wind otherwise it would be hard to compare.
That is the whole point - with a fixed pitch prop at 1900rpm the prop will be demanding less power. at the same revs the Bruntons will demand more power and you will be travelling faster. As suggested it is consumption against speed that is the measure, not at engine RPM. Assuming comparable prop efficiency the power requirement is the same, just that the Bruntons will mean lower revs because it will repitch to fully load the engine.
i will contradict you there
