Adding some numbers. A smallish supertanker, one you are more likely to find available for scrap, carried in its day 500,000 barrels of oil. That weighs ~79,00

Adding some numbers. A smallish supertanker, one you are more likely to find available for scrap, carried in its day 500,000 barrels of oil. That weighs ~79,000 tonnes. So if you use 5000 tonne weights, it has capacity for only about 16 of them. The biggest tankers in use now would handle 32. This is a smaller number than I would have guessed. So, maybe you use 1000 tonne weights instead, and put 80 of them aboard, with 80 cables, reels, and clutches, and maybe five shafts. If you don't want to build a "moon pool" for each cable through the bottom of the ship, you can run balanced pairs of them over pulleys on opposite gunwales.