1990 Carver 38 Aft Cabin Performance?

For that trip you might want to move toward diesels. That boat cruises at about 14-17kts and has a range of a little over 100nm. Slowing to idle will certainly give you better gph, but it won't affect overall range by much. Ran one down to Miami a few years ago and couldn't even make Coinjock to Beaufort (150sm) which meant grabbing gas at a commercial fishing dock that rarely pushes anything but diesel. The alternative was to lose a couple of hours leaving the ICW. It's also not the most seaworthy boat, more of a weekend party boat. If you're looking to do that trip and speed is not a big concern I'd look toward a trawler.

I bought a 1988 3807 AFt Cabin with 454s in Apr this year. I don't have a real accurate GPH rate, but I am guessing it's about 20 GPH. I have a dirty bottom and I am only cruising about 11-12 MPH right now. I had it up to 19MPH after a haul out. I would guess the range is about 150 or so. Again, these are rough guesses. Love the boat! Good luck. I notice there wasn't much difference in speed between 2300 and 2800 RPMs, only about 1-1.5 MPH. So find you an efficient speed to cruise.

there may not be a big difference in speed bet. 2300 adn 2800 but you can bet there is a hige difference in fuel burn.

as soon as you exceed hull speed (roughly 7 to 7.5kts on a 40ish foot boat), fuel burn increases much faster than speed. typically, just an extra knot of speed, may cost you 30% more fuel or more.

you either need to run full settled in the water, at or below hull speed, or fully on plane. halfway in between, you will burn as much fuel as if on place but go much smaller, throw a large wake and lug the engines.

also, trim tabs are often critical to get those stern heavy boats on plane, make sure they work

Pascal is correct about the trim tabs. My 31 Chris Craft with 454 Merc's is hateful with the tabs not working. The ability to trim the boat for changing conditions is essential.