Ran this for my OD&D group, levels 3, 4, 5, 6, 6. It was a fairly challenging adventure for this group despite having 2 clerics and most of the party having magic weapons. I think the recommended group of two to four lvl 3-5 characters would TPK, or best case scenario would have to avoid most of the adventure content to focus on getting off the ship alive. My group managed to finish it in one session, but they basically ignored the lower deck. It might take 2 sessions for a more thorough group. Overall it was a positive experience. Here are my notes:

1. Area 1 is not marked correctly on the keyed map. Based on the description it should be the small room labeled A, not a spot on the deck.
2. The color map scale is listed as 5 ft squares, but the adventure was clearly written for 10 ft squares (and the main deck combat map also uses 10 ft squares). Combats will be very cramped if you have 5 ft squares, with the monsters taking up most of the rooms and the party having to be crowded out in the hallway.
3. I don't love that you can accidentally fall through the floor right into the final objective of the dungeon (hazard E); I changed this to drop you into room 11 and made that door into area 13 inaccessible. Otherwise my party would have finished the adventure 20 minutes after getting on the ship and missed most of the content.
4. The issue of needing to kill less than 20 undead in order to avoid becoming part of the crew is not that well telegraphed, so you will probably need to have an NPC refer to it more clearly. It's an interesting additional challenge, but only if the PCs know about it.
5. Almost all of the treasure is in one room on the lower deck with nothing indicating it is special. There's only a few hundred gold worth of treasure (plus a couple consumables they will probably use this session) scattered around the rest of the ship. My players skipped the lower deck, because they figured the captain's quarters would be above and would have the good treasure. If your players miss this one room the treasure for the adventure will be pretty paltry for its difficulty level. I would recommend either distributing this hoard around the ship or swapping the contents of this room with the captain's quarters.
6. I changed the mummies on the deck into ghasts because I felt that a mummy should be a consequential encounter and not a throwaway mob; this way the captain stands out as the most important undead.
7. The intended method of finding the astrolabe in room 13 by searching 3 times--even after the DM has told you "there's nothing in this room"--is stupid. It's also not clear what you need to do when you find the astrolabe. Adjust this according to how you have fit the adventure into your campaign.

With these simple changes the adventure should run pretty smoothly. If you have more time you could tighten up the narrative a bit (for example, what is the purpose of the woman in room 22? why have the crew's weapons been confiscated?) but it's not mandatory.