Loss is not ordinarily a factor for short runs at HF. You would choose a cable that is:
* Readily available, including suitable connectors
* Durable in a marine environment
* 50 ohms characteristic impedance
* Able to handle the power.
Ordinarily RG8 or RG213 would be used. They are reasonably flexible (though not as flexible as RG58 or RG8X) and perform well in a variety of environments. They're inexpensive. PL259 connectors for them are readily available. There is little difference between RG8 and RG213 at HF.
RG58 is marginal for the amount of power involved but will probably work
OK as long as your tuner, antenna
, and ground are good. Intermittent connections in these systems can reflect enough instantaneous power back towards the transmitter to damage RG58 though.
I wouldn't use LMR400 for several reasons. It has an aluminum
foil inner shield that is more prone to corrosion
than braid in marine environments. It also uses a foam dielectric that can lose its shape in high-temperature environments where there are tight bends or pressure on the cable.
RG8X has a foam dielectric also though the shield is copper braid. No real benefit for a short run where there's plenty of room -- the advantage over RG8 is that it's small and light.