This makes no sense.
It could be birthmarks.
If a vessel is unpaired, it typically means that it is not part of a paired set with another vessel. This could refer to blood vessels, nerves, or similar anatomical structures that are normally found in pairs. In certain contexts, it could also mean that the vessel is not connected or associated with another vessel in a functional or anatomical manner.
This is a case where the sailing vessel does not have the right of way. The overtaking vessel must stay clear of the vessel being overtaken. The best thing you could do would me to keep a steady course, or make any changes obvious so the overtaking sailboat knows what you are doing.
Cholesterol, blood clots, fat embolism', even plastic from a hypodermic needle that has broken off can block blood vessles.
A hyperextended blood vessel could cause a stroke
Nitrogen by itself does not support combustion. But if pressuring a vessel with nitrogen and allowing it to overpressure (beyond vessel limits) a vessel can explode by fatigue. Under pressure, for example when scuba diving, yes, but otherwise, I don't think so.
the PWC
Wind could knock you over or blow your vessel into a submerged (unseen) obstruction.
That could be either a ketch or a yawl, depending on location of the wheelhouse.
Could be your diet. Do you use tobacco?
No, a vessel could be a number of things, such as a containment pod or space shuttel.
A place where a child could rest there head