Sounds like you are talking about a baby stay.
Does your boat have forward lowers ? If not then yes,definitely a baby stay, particularly as you say its attached to the (I presume you meant to say cabin top not sole) just aft of the hatch.
Here's another thread...
“Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life.” Terry Pratchett