Glad to help!
"I will have to take to my sons and try out away from home"
That's gonna be a pain in the neck if you have to do that whenever you want to test a setup☹️
" if I try to sail round the islands in the lake I will lose contact. "
Alas alack at VHF (30 - 300 MHz) and above transmissions are Line of Sight (LOS).
I.e. if you can't see the model neither can your receiver 'see' the TX
Do the islands have trees and bushes? They will also absorb some 2.4Gig RF power as well.
As far as range is concerned: If you can always see the model you should be OK for several hundred metres. Take your binos with you👍
Tips for maximum range with 2.4Gig RC sets!
Most RXs have two short wire antennas, ca 12cm. Approx one wavelength in the 2.4G band.
Make sure that they are installed in the boat at 90° to each other.
That means one vertical and one horizontal, NOT both horizontal!
Why? Two antennas means 'Antenna diversity'. Vertical or horizontal polarisation.
Analogy: Waves in the sea roll into shore horizontally, how else you cry!?😁 That's Horizontal Polarisation'. But imagine if you could turn the seabed through 90° to the vertical and the waves turned with it! That would be Vertical Polarisation.
The RX constantly checks which signal from your TX (H or V) is strongest and has the least errors and uses that to control your systems.
Most 2.4Gig TXs have two antennas; one vertical sticking out the top (stub antenna) and one horizontal built into the handle. (Silly pistol grip and wheel TXs excluded)
Maximum signal from the antennas comes from the middle NOT from the end.
Same applies for any frequency BTW! Unless you use a Yagi antenna! Another story!
For the handle antenna that's not important, however you hold the TX it's still horizontal (unless you're lying down😴😁).
For the vertical antenna it is important.
DO NOT hold the TX flat and point the stub antenna at the model. That is the weakest signal, almost null.👎
Hold the TX upright so that the stub is always vertical for maximum signal to the model.👍
Cheers, Doug 😎