Also, if the shallow ramps are near you, and if they don't just stay shallow but gradually drop off beyond car + trailer range, you could try the launching method where you uncouple the trailer up on the flat near the top of the ramp, attach it to your vehicle with a 25' or longer cable or strap, gently tension that at full length to your car, then slowly let the trailer down the ramp (probably need a push from several people or from another vehicle to get it going down the ramp). Then, slowly backing your car down the ramp, let the trailer roll itself all the way out as far as it will go underwater, thus reaching the deep water
25' further out.
Full disclosure: never done it myself! But I recall
Phil Bolger recommended back about 10 years ago when he was still alive and writing.
For getting the boat back on, I assume you would need some trailer "goalposts" or other method to get it aligned properly while out farther.