I had 2 out of 3 attempts at the featured "Lego" balloon boat leak air so much that you couldn't blow up the balloon (https://www.thingiverse.com/thing:2783012). So searched for other models and found this one (https://www.thingiverse.com/thing:2347730). Big thanks to the original designer as the shape of the Hull is awesome!
I was also inspired by a previous remix that split it into more pieces (https://www.thingiverse.com/thing:2452678), but had problems printing it with the hull being very thin on the sides towards the rear. I also wanted to mount the balloon more towards the rear to move weight and help balance the boat and keep the jet in the water, so used Tinkercad to create this remix.
I print the "Jet" at .12 100% infill to prevent any leaks and they always come out air tight, the "Deck" at .2 30%, and the "Hull" at .28 100% infill, rotated 180 degrees "upside down" and it did not require supports on the several that I made.
To assemble, I put the Jet thru the hole in the Hull and the use the Deck to get in the right spot, then "tack" it to the bottom of the Hull with a drop of superglue. After that dries, I pull off the Deck and put a bead of superglue on each side of the Jet where it touches the bottom of the Hull, then also a big drop ("runny" superglue works better than gel) on the top of the Jet where it goes thru the inside of the and tip it to the side so it runs down to the bottom to create a seal. Then do another drop tipping it the other direction to get both sides. Then I put a bead of superglue around the top edge of the Hull and drop the deck into position and let that dry. Then I put a good fillet of superglue around the inside of the balloon neck where the top of the Jet comes and let that run down to seal there, let it dry and do it again to be sure it is air tight there.