Assuming 40 slips, the asking price is $62,500 per slip.
Key word, Asking Price. Two things. First you don't invest in a marina at the individual slip price. Assuming someone wanted to sell the slips and $62,500 was reasonable. Then for the marina, half of that would be reasonable. By the time you held slips, did all the legal work necessary to sell membership interests, and marketed then you could have a decent profit. Selling the slips limits you to a one time profit.
Second, I don't believe slips in that area would sell for that. Too many marinas with slips available and still not the prime Annapolis area. This isn't the only marina in that area to be on the market in the past couple of years.
I don't know if Pleasure Cove is still for sale or not. But looking at asking prices of some other Maryland marinas with comparable locations, here are some examples. 24 slips, $720,000. 136 slips, $1.7 million. 84 slips, $3.5 million. 70 slips, $2.9 million, 21 slips, $825,000. 64 slips, $2.7 million. 106 slips, $2.5 million. 59 slips, $350,000 (ok, bad shape). 74 slips, $2.3 million. 180 slips (+100 dry rack) $7.2 million, 200 slips, $7 million.