Larry is correct. 40' of rg58 with a matched antenna will have about
2db of loss on the marine band. This is nothing to be concerned about.
Nobody can tell, with there ears, the difference between the rg58 vice
LMR400. Use the rg58 and use BNC connectors. You can cut the antenna
cable as short as you want because you are adding another 40' length of
cable. Most laymen just don't understand the relationship between power
output and field strength.

Eric