Quite right Rod👍
Also they should preferably be Schottky diodes.
Stephen; These have a much lower forward voltage drop, ca 150 - 450mV as opposed to 600-700mV for general purpose silicon p-n diodes. Such as the 1Nxxxx series.
The lower forward drop means, apart from saving energy, they can switch off much faster when presented with a reverse current flow, as in 'back charging' of one battery by the other.
Such 'back charging' can create high current which can cause wiring to overheat and maybe catch fire and the loss of the model.🔥😭 You have been warned!
To minimise this risk both batteries should be as identical as possible; same brand, type, voltage, capacity (mAh) and especially state of charge. If in doubt about the state of charge run them both through a discharge - charge cycle before sailing.
Stay safe Stephen and enjoy the fruits of your labours🤞