Fuel consumption expected

[Leland]

As of yet, we have no running time with this boat (58’ Yachtfish). Anyone have an educated guess as to GPH at around 1200-1300 RPMs. I’m anticipating about 10kts at this RPM.Bob

[Briankinley2004]

What engines? 1200-1300 sounds a little high on RPM's for economy

[Pascal]

It s not about RPM it s about hull speed. On the 58, it s about 9.5 kts. At that speed you should burn about 10gph. If you go just an extra knot over that your fuel flow will almost double.

Depending on your engine and most importantly prop 9.5kts should be between 1200 and 1400

[Leland]

Thanks. I was hoping for a little better - don’t we all. My 50’ Grandbanks (which is a little heavier) burns 7gph at 8.5knts at about 1600RPM with Cat 3160s. 10gph isn’t bad though. Considering a trip next summer to SE Alaska which will be about 1800 miles round trip and trying to cost it out. It’ll probably put us on the water for at least 6 weeks.Bob

[Pascal]

Throttle back to 8.5 kts and you will probably bring fuel down to between 7 and 8 GPH. The longer waterline of the 58 should offset the DD higher fuel burn.

You don’t realize the impact of speed until you ve used flow meters. True of all boats. Half a knot makes a huge difference. As long as the DDs remain at operating temp they ll be fine just run them up briefly every few hours

[oscarvan]

You don’t realize the impact of speed until you ve used flow meters. True of all boats.

So how does one install them on the DD....fuel circulates around the engine until right before the injectors... You'd have to put a flow meter on every lateral no? Or are there meters that measure supply and return and calculate the difference?

[Walter P]

I've had flowscans on a couple of boats and they do work.......usually. The do work by calculating the
difference between the supply and the return. If they are calibrated correctly they work fine.

Walt

[Pascal]

Yes on diesels flow meters have two sensors, one on feed and one on return.

I didn’t mean to say that they are really needed, my point is that speed is the most important factor in fuel economy. Not weight or engine size and brand. Beam is probably the second factor behind speed.... obviously hull shape as well.

On long trips running at set RPM you can quickly establish real fuel flow numbers when refueling. Also, when refueling from low tanks, say under 1/4 full, take the time just once to calibrate dipsticks in 50 gallons increments. On the 1510s it’s pretty easy to access the fuel tank to stick them.