SFKjeld and others were looking for ways to remove some ballast to float the boat higher making retrieval onto the trailer easier. If you have 200 gallons of water in your bilge you are going to need a "bucket list" and maybe the portable genset mentioned as a possibility for powering a sump pump. My simple solution for removing water from the bilge works for me. I presume most people already have a cordless drill. They are cheap and usually come with two batteries and sometimes other devices like a powerful flash light. This I find useful for checking navigation marker numbers or the windex when sailing at night. For ten bucks I make that cordless drill even more useful and you can too. I am not advocating using a drill pump to empty the ballast tank but water in the bilge or in a ballast tank can be transferred using this simple pump in a cordless drill chuck.
And about emptying the ballast tank on these water ballast boats; the prohibition from the manufacturer is in attempting to move the boat under sail or power without ballast. Granted these unballasted boats are tender but tied to the dock it is not going to tip over. If they were so inherently unstable it would be necessary to add water prior to launching. These boats are launched empty then fill up with water. Why would blowing the ballast, in the exact same location it was taken on, be more unstable? Partially blowing the ballast prior to retrieving the boat makes good sense if the ramp is steep. You can also make retrieving the boat easier by removing the rudder assembly, motor, fuel and battery from the transom area and placing them in the center of the boat (or better yet into your truck). Of course you want to do all that prior to blowing the ballast.
It is the angle of the ramp relative to the way the boat floats in the water that makes it hard to retrieve in some places. Getting the weight out of the stern and blowing the ballast means the boat can be retrieved with the trailer at nearly the same point it was launched. The stern is the first to enter the water when launching and the last to leave when retrieving. When launching, the water supports all that weight in the stern and eventually the boat nose floats free as you back into deeper water. Reversing the process you pull the boat up the ramp and the nose is the first contact with the trailer. Visualize it from the fish eye lense and you can see the angle of the boat relative to the ramp is altered the further forward you pull the boat. The bow lifts and the stern sinks but the trailer is still at the same angle. When the stern contacts the trailer and you pull the boat out you find the vessel is a bit further back on the trailer than when you launched. Hence the parking lot bump. Reducing weight in the stern prior to retrieval will help maintain a better angle relative to the trailer. Blowing some or all of the ballast can help the retrieval process. The boat floats off the trailer, unballasted, at a shallower point on the ramp than can be achieved with the ballast (and weight of fuel, motor and rudder) in the stern at retrieval.
Until someone suggests a better way of moving a quantity of water, driving screws, drilling a hole, cutting through metal in an emergency (a cutting wheel in the drill to sever a shroud if dismasted) powering a winch, illuminating nav markers or checking the windex while sailing at night and possibly a means of propulsion, all with the same light weight tool, a couple of batteries and equally light weight attachments, I will continue to use what I have and hopefully discover other uses as well. I see there is already a much improved version of my repurposed weed eater outboard motor. As we are prohibited from posting items for sale here, try searching for a drill powered propeller. Wal-Mart has one for about $30. I will give it a try and post my findings.