Feathering Prop for Fuel Savings?

The drive system(shaft and props) would be fine with slower speeds.Although the prop may need repitching.

You might contemplating selling the large engines and installing 2 MUCH smaller engines with a very deep reduction gear.
6-1 or so.

AS a start I would remove both props and get someone to tow the boat at speeds from 3K on up in half K intervals.
Find an accurate way to measure the drag , simplest is a block and 55g drums filled with water.

When you have the drag curve at the all speeds you can tow the boat , someone on this board will be able to size the new engines for best cruise.

Cheapest will probably be at the Sq rt of the LWL in Knots. Not faster, 8K is OUT! But 7K might be OK.

If you can live with that speed , and not a lot of reserve power for 30K headwinds, you can probably triple your range with the existing tanks.

FF

 

Or you might get one of these and just coast downwind.

http://www.youtube.com/watch?v=Z6pPYwmu32w