The SWR meter has a label stating the usable frequency range. You want one to go up to 200 MHz at least (many CB versions are okay).
For power you need a way to calibrate it on the used frequency. Many cheap
CB meters can't do that so the value shown on the meter is not usable to determine power level... but you can use it to find differences along the line (cable). Most have a switch to change the range; it should have a usable setting.
Lincolnshire.... yes you should pick up transmissions 20 miles away but there must be those transmissions to start with... I haven't sailed in the UK for 10 years but it was pretty quiet on the VHF then... unlike in the USA.