An original Trojan spec sheet that I got some information from for the F32 with twin 318's suggests that the fuel consumption once on plane remains fairly flat till the 4 barrels switch in above 3000 rpm.jordan wrote:I would figure more like a gallon per mile with twin 318's and not at 18 knots. My F- 32 with 318's, I plan on 1 gallon per mile at 7-8 knots, 1600 rpm and not planning or 1 gallon at 12- 13 knots at 2300 rpm at a slow plane. Any thing more than that it is all down hill so to speak.Jim
What I get with mine seems to confirm this... though it is by best guess calculation as I do not have fuel flow meters which I don't consider worth the expense as the Trojan's fuel burn is so flat once on plane till the 4 barrels hit.
Trojan calls 2500 rpm slow cruise and 3000 rpm max cruise and 4000rpm max: speed in that data sheet. Here is the information I saw:
RPM.............MPH.........calc Knots........GPH................calculated mpg
2500............15.0..........13.04.............15.6.................0.96
3000............21.3..........18.50.............22.5.................0.95
4000............32.3..........28.07.............40.5.................0.80
Based on the above data I made the decision to tend towards the max: cruise level so try to maintain 3000rpm most of the time. Have you evaluated what your boat does up nearer 3000rpm?
I tested and concluded that the extra speed of max: cruise was worth the 1% mpg penalty as my run time was reduced nearer 30%.
Looking at your numbers I have one other question... the 7-8 knot speed at 1600 rpm can you get the same speed with lower revs?
I seem to get that speed with lower revs... no trim tab. I find that the rpm range is quite large for little speed increase at that low displacement running speed.... so am suggesting maybe you can throttle back, push less water and still maintain the speed. I do carry a dinghy on the swim platform and that could be a key difference at non plane speeds.