The valve WATTS Relief Valve, 1/2 In, Brass, M x FNPT - Relief Valves - 1X624|530-1/2 - Grainger Industrial Supply should blow before a clamped hose comes off I assume! So I would just T it into the line from the hot water tank, drain to the bilge.
Have to scout out on the boat where I can put the tank ProFlo Thermal Expansion Tank 2 Gallon - FreshWaterSystems.com on the boat.
what pressure should the tank be set at?
[EDIT] Sorry, took out the valve reference, the model quoted is better suited for the task and a little harder to find[/EDIT]
Can you measure the pressure on your water
system when it is running normally? That should be the tank setting. If you can't measure, you might be able to see pressure settings on the pump controller. Failing all of that, IME most boat systems are relatively low pressure, 20-30 psig.