[cdavisdb]

Well, I finally got my new (to me) boat back from the mechanic. Looks like the work was done well, but it took a loooonnnggg time. First time out today and I did a bunch of performance testing, results below. You guys who are familiar with vacuum gauges, please look at my results and tell me what you think. I'm particularly interested in using it to help establish the most efficient cruising speed. (sorry for the rough tables, I can't get this program to work quite right)

The boat is a near original 1972 25 seafari with a 1998 fuel injected 5.7GSI volvo/volvo sx duoprop. aluminum D2 props that were somewhat nicked when I started and are a lot nicked now. Somebody put a sand bar where it wasn't supposed to be. The grounding only affected the fuel economy estimate and probably not much of that.

I suspected the boat was underproped. It is. max rpm is 5100, 100 over the max. My old Seabird 24, about the same weight,carborated 5.7/290 duoprop with F5 stainless props, was right on red line for that engine, 4600 rpm. This engine has a 4600-5000 max rpm range. If I go to stainless props that drop the rpm to 4800, do you think I will gain a knot or two and fuel economy to get near 2.9 npg from the current 2.6?

Conditions, 15 knots out of the NW, long fetch in a shallow bay and a short, breaking 1-2 ft chop, the kind I like to call "washboard" Not a major test for the hull, but I could run straight into it at 28 knots and still be comfortable. No pounding, the hull just got jittery sometimes. My old seabird would have been rattling my teeth at anywhere near that speed.

General impression: I'm going to like this boat. It obviously is going to live up to its rep as a sea boat. Its tippy, much more so that my seabird, but no worse than a formula 23. It is very lively at rest, I think more weight will help that as it settles down on its lines. Did not see a snap roll like a formula, but the conditions were not a fair test. Too early to tell on roll.
Just looking at the hull, it doesn't have the appearance of a dry boat, but I ran around for 3 hours on a day that should have produced a fair amount of spray and had almost entirely dry decks and very little spray on the windshield, not a complete test, but looks good.

24 mile economy run, 2.6 npg Half way through, props very nicked. One person, full load of fuel, 3300 rpm. Can anyone tell me what is the most efficient rpm for a fuel injected engine?

hole shot: just over 2 seconds

All other speed/vacuum data taken with one person, 1/2 load of fuel

NO LOAD, OUT OF GEAR, WARMING UP
RPM Vacuum
500 13
1000 16
1500 19.5
2000 20
2500 20
3000 11
3200 9
3600
3800 6
4000 4

Under LOAD

falls off a plane below 2400 if tabs and drive are not down. Minimum planing speed, 12 knots at 2200..

RPM Speed Vacuum
2200 2200 --12.2, tabs down
2400 --14.4 tabs down
2400 --13.2 tabs up
2600 --15.7
2800 --18.3
3000 --21 --12
3200 --23.6 --10.5
3400 --26 --9
3600 --28.2 --9
3800 --30.2
3900 -------7
4000 -------6
4200 -------5
4350 -------4