' 67 sea ray electric shift w/ '78 chevy 305 fuel consumption question

okay so i took her out for the long awaited maiden voyage yesterday in our local lake. we stayed close to the 5 mph zone in case of mechanical failure and drove around for about half an hour. gaining confidence , i decided to go for a cruise and headed across the lake at about half throttle , not wanting to push her too hard .we went roughly two miles or so and without warning she just quit on me . i began the process of elimination starting with fuel . i pulled the fuel line that feeds the carb and had the wife crank her over...no fuel. i inspected the water fuel separator . empty and clean ,then i pulled the fuel line from the tank to the separator and not a drop of fuel. so i pulled the drain plug at the bottom of the fuel tank and it was bone dry. we never smelled even a hint of gas so i dont believe there is a leak . the question is ...would it be normal for the chevy 305 2bbl to burn 5 gal of fuel in two miles at half throttle ? thanks in advance.....dimitri

This a external tank ?

Never in my life ever saw a bottom drain plug in any kind of tank.

The portable ones i have a bunch like a outboard one.

Metal inboard ones i never saw a bottom drain plug ever.

most runabouts get between 2mpg and 6mpg running at cruise on plane. so, no not normal. 1/2 throttle might be an inefficient speed for your hull....were you plowing/struggling to plane?

yes hystat we never got up on plane , we went between 6 and 14 mph the whole way...not stuggling just not wanting to push the engine...first boat trip , i was kinda scared to hammer down

at that speed, you are probably pushing the engine nearly as hard as you could...(wide open throttle excepted), but it still can't drink 5 gallons in 2 miles of that... you only went for 10 minutes based on your reported speed... a 307 2 barrel can't drink 50 gallons per hour..... at WOT full load, the max it can drink is 18 US Gallons per hour.
sounds like you have a leak somewhere.