Not even with a pressure-reducing valve. This is an invitation to sink your boat. All you need is for one of those hose clamps to quit, or a flexible section to rupture and there is an unlimited supply of water to fill your boat. Far better to fill your water tank periodically using a hose and using the onboard water pressure pump to supply your requirements. Keeping your pressure pump working on a regular basis is also better for it.
Nothing kills pumps quicker than being idle for long periods.
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