I can't see what sort of connector that thing has so I have no idea what sort of coax you can use. I was thinking along the lines of LMR400 but there are unanswered questions.
Eh, the antenna leaves much to be desired and Jimmy's general rule doesn't apply to 1/4 wave ground planes. Mounted on some metal structure of a boat it would have a crude planing surface but mast mounted as a base antenna it's only half an antenna system. You may drill holes in the corners of the horizontal part of the mounting angle bracket and mount 4 38" lengths of 1/16" diameter brazing rod as radials, that will surely improve things but don't expect miracles. Stainless steel bolts, nuts and split ring lock washers will do the trick nicely, don't use cad plated crap hardware outdoors that will turn to rust in short order. Don't use copper wire for the radials either, it's soft and will turn into a pretzel in the wind. Brass is stiff and short lengths will withstand a hurricane.
You have another option, a good and proper marine antenna that doesn't require a ground. They have a bit of dB gain to them while a ground plane has unity gain, nil. In any case consider the coax, on a boat it's a short run so a bit of signal loss is tolerable. For a longer run such as you have loss becomes a consideration, essentially you need better coax than what came with the antenna.