Just as the title says,
I have only seen this on sloops as I have not been able to test it on other ships yet. When the ship's anchor is deployed; the ladder that comes already attached to the sloop is not usable. When clicking "E" on the ladder, the character goes into the climbing ladder pose; however, when you press "W" to ascend the ladder your character runs into the structure of the ships and falls off. This makes the ships impossible to get on without attaching a built ladder. This only seems to happen when the anchor is deployed.