[Sailor Steve]

One of the problems with maximum speed is that there is an optimum max to any hull design, and once you reach it you will need to double the horsepower for an increase of half the speed, and doubling it again gets you half of that.

I used to have a Ford Escort wagon that could make 90 mpg on 88 horsepower. A Grand Prix car with 800 horsepower barely makes 200 mph.

The North Carolina Class battleships made 28 knots on 120,000 horsepower, at a full-load displacement of 46,000 tons. The South Dakota class increased that power to 130,000 on the same displacement, and gained one knot for a max speed of 28. The Iowa class had a massive jump to 212,000 horspower, and this gave them 33 knots. On the downside their full-load displacement was much higher at 57,000 tons; but on the other hand they were more than 100 feet longer which gave them a better fineness ratio. The exact effect is arguable, but you can see the point.

And the point is that a Type VIIa u-boat without supercharging displaced 626 tons and made 2310 horsepower for 17 knots. A Type VIIb with supercharging displaced 753 tons and made 3200 hp for 17.9 knots. A Type VIIc with the same setup but an increase in displacement to 769 tons (an increase of 2%) reduced the speed to 7.7 knots.

To get even 18 knots out of a VIIc is going to take a lot more than just a little tweaking by the LI.

On the other hand the speed should increase slightly as the patrol goes on, due to the reduction in weight from using both fuel and food.