OK so everything can now be seen to have 40MHz labels, TX, RX and crystals. Assuming that the crystal in the TX is appropriate for the TX, and same for the one in the RX. They won't be the same actual frequency because of how radios work, BUT they might carry the same frequency on the label along with a mark for transmitter or receiver just to indicate what channel they belong to. Different manufacturers have different ideas of what that offset should be. There is also a different offset between AM and FM, and a yet different offset between single and double conversion on FM sets. When dealing with these, having the right crystal at each end is vital. The transmitter needs a crystal from its own manufacturer, the receiver similarly needs one from its own manufacturer.
Ideally, at the moment, the parts that can be taken out need to be hooked up out of the boat to a known working battery. Only after that can serious fault finding begin. There might be more than one problem (most faulting manuals assume only one), but this is the real world, so things might need to happen step by step.
First things, know the voltage of the battery under load, then find the voltage on the receiver power pins.
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