Hello emmott,
Just an observation from me before you attempt to launch your boat using the long extension......
There seems to be far too little contact between the extension and the solid part of the trailer. Leaving the trailer jack wheel on the pavement will grind the wheel to smitherines in a short time. I know that because my wife and I drag our Celebrity (800 pounds) about 30 feet across a level macadam parking lot to launch using a crane. Our wheel is "toast" after one season. Second, without support of a wheel the long tongue is suspect. It might bend sideways, not support the weight of the boat on the tongue due to the long distance from trailer wheels to the ball hitch, or the U bolts might not hold the weight. Push the extension back into the larger tube far enough to pin the tubes together using the holes in each of the tubes. Picture #1 and #2 look scary! That is a big boat.
I would like a tongue extension on the trailer for our CD Typhoon, but the design you show is not how I would expect it to work safely even though our boat is much lighter.
A note added later: I did not read all the responses prior to giving my thoughts or in this case "airing my laundry". I read that my concerns were not founded in fact.