Started a new scratch build after getting interested in waterjet propulsion from articles by JBKiwi and Rowen. Didn't initially have a specific boat in mind at the start, just wanted to see if I can make the thing work. After looking at different hull designs, I elected to go with the Cresta which is on the KKEezebilt boat web site.
I know, I know, egg crate construction! not exactly the best, however, after getting into it, this has created quite a bit of room inside for the water thruster, and it also has a very flat "V" shape to center mount it . It also turned into a very easy build up to this point. The boat frame is made of 3/32" basswood, with 1/32" sides and bottom. There is also 1/32" ply for the thruster intake, and the exhaust nozzle in the transom. The chine is reinforced with basswood strips.

After downloading the Cresta Plans, I scaled up the prints to the length of 23", this seemed to be the best fit for the 16mm thruster purchased from Amazon. I initially purchased a 26mm unit complete with reversing bucket, however this one was way to big. Unfortunately, the 16mm unit does not have a reversing bucket, so it is forward only. (My ESC is a bidirectional unit which will reverse the brushless motor, so maybe it will have some sort of reverse🤞!)

Modifications to the Cresta plans include adding extra angle bracing between the floor and the bottom, modifying the transom, and cutting down the beam for the thruster unit. I also made the top removable to access the internals. The cabin area cutout will have a fake bottom to allow for wiring and connections on the subfloor. Once I get the whole boat covered in fiberglass, a float test will determine the placement of the batteries and electronics, as well as look for leaks😐.

The first picture shows the water jet as purchased. I measured the gap between the exit nozzle and the input grill and the main body of the jet which came out to be about 0.040". This determined the 0.032" plywood to be used as the mounting sheet for the unit. This will also allow for a sealing gasket to be used between these parts.

With the exhaust nozzle, prop shaft, and input grill removed, I placed the main body of the unit on the rear inside floor centerline, and drew around the body for the cutout. I also added a portion more to allow for the motor mounting. I cut this portion away and prepped the plywood for the input cutout by first drawing the same footprint of the body on paper, and cutting the input hole to use as a template. Once the plywood was cut, I glued it in place to the bottom of the floor.

I tack glued the cockpit sides to the floor, and when dry, held the transom rear brace in place on the rear. I then place the body of the water thruster in place and traced around the rear for the cutout on the transom brace. Once glued in place, the waterjet housing fit firmly in place flush with the rear of the transom brace. The actual transom is made from 0.032" plywood, and then fits up against the brace. To determine where the hole cutout should be, I put a dab of graphite on the end of the prop shaft, which made a nice center mark for the hole. Using a hole template, I centered the dot and drew the hole cutout. The mounting holes were then drilled by marking the centerline of the exhaust nozzle on the centerline of the hole. To glue the transom in place, I mounted the waterjet body in place with the input screws, and placed the transom on the model and held it in place with the exhaust nozzle and a few screws. Once dried, the thicker transom piece was cut and fitted in a similar fashion. Glued and screwed for proper alignment.

I fitted the out-runner brushless motor to the waterjet unit using the standard
motor mounts. The two holes on the waterjet aligned with two of the holes on the mount. I fastened them with 3mm screws and locking nuts. The picture shows the modification to the metal mount for the bottom of the jet unit. I then mounted the motor to the mount in a similar fashion with 3 mm flat head screws. Again cutting the lower portion of the mount.

Coupling the motor with the jet unit was accomplished with 3 - 45mm long 3mm screws. The motor can then be slid in place and fastened to the coupler. The nuts at the water jet mount can then be tightened. The locking nuts at the motor end have a slight gap to allow the motor to move laterally back and forth a bit.

Initially I was undecided about paint scheme. Looking at different items on the internet, I came across vinyl wrap items for pinewood derby cars. This gave me the inspiration for a vinyl wrap flag scheme. The long flat surface of the top hull made this the ideal candidate for this procedure.
I ordered the vinyl from an internet vendor off of Etsy. Fairly inexpensive, only $8 for a 24"x12" sheet of peal and stick.

The whole model was painted with several coats of a dark navy blue, and when dry was then sprayed with several coats of gloss clear coat. I made a paper pattern of the top hull, adding extra for the curve down on the sides. i also made a cutout for the engine cover at the rear of the hull so this could be cut out in the correct position on the vinyl. With the paper pattern complete and fitted the way I wanted, the pattern was then drawn on the rear paper backing of the vinyl with the top down so that the top of the vinyl would be correctly positioned. After cutting out the hull shape and the engine cover, I peeled the paper backing from the rear to first expose the part for the engine cover and cut the backing so that I could position only the stern portion over the motor housing correctly. Once this was positioned correctly, I then slowly peal the backing and work my way to the bow working out any air bubbles along the way. The last was to slowly work the curve around the hull and trim off the excess.

I trimmed the cockpit with navy blue felt on the floor and around the sides to simulate waterproof carpeting. The seats were painted navy blue, and the seat portion covered with matching areas of vinyl, and glued down along with the dashboard, windshield combination.

The final step was to spray the top of the vinyl with several coats of clear for protection.