It depends upon whether you want to carry the whole aircraft with you on your boat and obviously how big your boat is.
A flexwing trike on floats might appear to be the best solution, if you have a big enough boat, but the leading edge booms do not break down nor its long floats. They will certainly not fit in your front boat locker unless you have a really big boat. The Airborne trike shown below is suspended across the stern of a big beamy boat, but you still need lots of room around it to rig its folding wings when it is on the water. Best to tow it ashore and rig it.
My 92hp 4-stroke D-motor powered Fly Synthesis Catalina NG 2-seater flying boat ‘Ding’ is heavier (320kg basic empty weight BEW and 545kg maximum takeoff weight MTOW) with folding 9.5m wings and 6.3m total length (see my Avatar). It cannot be rigged on water, so it needs a much bigger boat with sufficient deck space around the flying boat hull (3.6m long with 1.64m beam) and use of a telescopic deck davit to lower it onto the water after rigging. Its hull is based upon the Ramphos folding flexwing amphibious trike, but you have the same on-water rigging problem with the Ramphos.
The Polaris Motor 11.2m folding flexwing amphibious trike is based upon an inflatable boat hull and another boat-based solution with a BEW of 216kg and maximum takeoff weight MTOW of 406kg, but still the same on-water rigging problem.
A lighter, more compact, though high risk and operationally complex boat-based solution might be a 64hp 2-stroke Rotax 582 powered 2-seater Aerochute fitted with inflatable floats on its 100kg three wheeled frame. It has a 300kg MTOW. You would need sufficient deck room like a catamaran to secure it on the stern of your boat.
Climb aboard with your passenger, steer your boat directly into wind, release and inflate the chute above the water like they do to launch towed parasailers. Then start the Aerochute engine when risers and lines are clear, apply power to match boat speed, unlock the Aerochute from the deck and allow the weak link-protected tow line to slowly reel out, then release it from the boat end. Reel in the tow rope to the Aerochute after release.
It would be messy to retrieve that 10.7m span 34sqm salt water-soaked chute on a full-stop water landing upon your return to your boat. Lowering the tow rope from the Aerochute over the boat for an aerial hook-up to the boat stern while it is underway again could be achieved after lots of practice. Then you could be slowly winched in without getting your chute or your feet wet and locked down again. Two-way radio communications would be essential. Approval from the manufacturer (and no doubt CASA who certified it in its standard land configuration) for float installation and complex high risk water launch/recovery operations demanding highly competent boat and aircrew would be involved. You would also use up lots of boat fuel.
A safer and less complex aircraft and operations in the Experimental Category might be to combine a Polaris-like amphibious hull with its Rotax 582 engine, propeller and seating inside a roll cage that is necessary for chute operations, together with a larger chute than the Aerochute to carry the extra weight. You could use the inflatable hull as an airboat tender without deploying the chute. You could motor ashore for a safer beach takeoff and landing if one is nearby, but more trouble logistics-wise. Otherwise, you could revert to the high risk deck launch and retrieval method for the Aerochute if you have the rear deck room. I could imagine such a configuration would be difficult to control under the chute due to large hull windage, especially in gusty wind conditions.
As an avid angling aviator, I far prefer my Catalina NG fun fishing flying boat to quickly get to my favourite fishing spots safely and directly or go long distance touring. With minimalist camping gear, I can sleep aboard in my net-covered hammock suspended between the wing struts under the wing. And I do not have to waste my time dragging a boat long distance behind my car on a trailer to and fro.
It all depends upon whether your focus is on family boating with a dash of fun flying or fun flying and touring with a dash of boating and fishing.
In the latter case, you can operate independently if you have sufficient competent boat crew, and just meet up later at a suitable anchorage point and take everyone flying anyway. At the end of the day, you can tie up the flying boat to your boat in protected waters, enjoy everyone’s company and sleep aboard your boat in luxury.
Cheers
Dale