You might be thinking of Argo Navis, which was a large and ancient constellation representing the ship of Jason and the Argonauts. However, Argo Navis was so large that it was divided into three smaller constellations:

* Carina (the keel)

* Puppis (the stern)

* Vela (the sails)

So, Vela represents the sails of the mythological ship Argo Navis.