Scratch built Jet Sprint Boat

[makaveliks]

Hi, Just finished building a jet boat from nothing, though I would post it here as it was very hard for me to find info to build it. It was a fun project, and turned out to be a fun boat as well.

Here's a video of the finished boat, and the info on how I got there is below!


Here's the parts and materials I started with.


I cured a flat sheet of fiberglass 2 plys thick. Then while this was curing I used thick cardboard like paper to make templates for all my hull pieces. Once the fiberglass cured, I traced the pieces and cut them out. Tomorrow I will make a temp frame that will only be there to hold the parts in place while they cure together then I will bond all my parts together with fiberglass. This way I should be able to build the hull without a mold. Here is a picture of my parts, and some extra fiberglass sheet I bonded. The 16oz water bottle is in the pic for a size reference.


Well I made the basic jet drive that I plan on using, and started glassing the hull together. Here's some pictures of the hull.




Now for the Jet drive. I decided since this is small and does not pack too much power I can hopefully get away with a combo of wood, resin and fiberglass. So I quickly made what will be my drive housing and impeller from wood. They still need a bunch of fine touches that I will do my hand to smooth and finish them. I am trying to use a screw type design for my impeller. I have no clue how it will work, but why not... The impeller is 1/2" diameter by 3/4" length. My shaft is 1/8 helicopter shaft. Once finished the inside of the housing and impeller will be sealed with fiberglass resin to waterproof. I will make a fiberglass grate, nozzle, stator, and a duct to fit over it that will be used for steering. The housing will have an aluminum stuffing tube, which I had that perfectly fits my shaft. It was going to be my new tail shaft for the helicopter. If this impeller does not work well I will make another differently and try that out... The housing will also be trimmed down considerably. Well here's the pics:
This is my radio, reciever/esc, steering servo, motor, jet drive. Tiny!

[makaveliks]

I didn't do any details like roll cage, driver, and motor, they will come after I make sure the whole thing works! I got it all smoothed out, primed, hatch made, and body posts for attaching hatch. I'm going for sprint boat looks, but I think I got a little angle on the V, looks good overall I think.




Here's a pic of the other parts I made.


I remade Impeller. After searching the net some more I found out screws are not that good for jet drives. So I made a 4 blade impeller with less angle on it to hopefully be better at compression. I cut 4 pieces of .020 aluminum then JB Welded them to an aluminum tube hub, which I then JB Welded to a shaft. The package says JB Weld can fix a cracked motor and it seems really strong. We will see how it hold up as I used it alot making these parts.

[makaveliks]

Here's the nozzle. I rolled some .020 aluminum into a cone shape, then used Jb weld to hold the seam and make a flange to attach noozzle. Then I drilled a 5/32" hole and inserted a 5/32" Aluminum tube into it to use for cooling motor. On the back of nozzle I rolled another cone from .020 aluminum, used 2 small screws as hinges which are JB Welded to the turn nozzle, along with an arm that will be attached to the steering linkage.



Now the water cooling jacket. Again rolled .020 aluminum to fit motor, then cut .020 aluminum rings to fit around this, about 1/8 wide all around. JB Welded to rolled aluminum, then rolled more .020 aluminum around the rings. Once this jb welded on and sealed then I drilled 2 5/32" holes and inserted 5/32" tubing to attach water cooling lines. I will use thermal paste to attach to motor to ensure best heat transfer.


For my housing, to help keep the metal prop from messing up the wood housing, I rolled .020 aluminum and bonded into housing. I then sealed and smoothed the housing with JB Weld(of course). Also bonded .020 aluminum sheet to the aft of housing. I don't know why, but It seemed like a good idea at the time. I was tired. lol.

[makaveliks]

Here's a picture of everything I made painted and ready for install. This includes hull, motor mount, servo bracket, motor cooling jacket, jet housing, impeller (in housing) intake grate, nozzle, steering nozzle, and trim tab/jet guard. I have also made a cage! It just didn't look like a sprint boat without it.

[makaveliks]

Here's the trailer... All functional, just needs some details and paint. Need to make a hitch, jack for the front, and some maker posts for when trailer is under water, but it's probably too high to actually launch depending on steep the waterline is. Everything was made from flat .025" aluminum that I cut and bent.

[makaveliks]

Well, anyone reading this thread should realize by now that I am not one to leave well enough alone... I thought up and idea to easily add strakes to the boat without adding much weight. First I started with a block of balsa wood, I cut wedge shaped strips out of this block. Then I used shoe-goo to glue these to the hull. After this I coated with fiberglass resin to stiffen up. Then used bondo to smooth onto hull and repainted bottom! Done! I really should make a mold of this so I can remake it lighter using only 1 or 2 plies of fiberglass cloth... This would more than cut the weight of boat down by half. If I did this, I would build that one right... More powerful brushless motor with a considerably larger jet., and probably when grafting deck to hull I would cut down hull more for lower profile. Right now from starting with 2 plies, grafting them together, smoothing with bondo, adding strakes it's made the hull the heaviest part of the boat. I don't have a scale to measure small weights though for exact numbers.

[makaveliks]

Here's a video of it with my homemade jet... Worked great, but not enough volume to power the boat. Needs to be bigger



I tore out the old stuff, re-cut the intake and outlet in hull, bonded in the mini jet, mounted new motor and touch up painted the exterior. This is my new jet as it is with the Trinity 19T 540 motor from my Slash before i went brushless! I glassed in the jet using chopped fibers. It's Glassed in pretty well, I think it should hold it good. It's messy looking as I had to use a stick to get fiberglass in that tiny area(my fingers wouldn't fit). Also glassed over holes no longer needed with chopped fibers. Still need to attach steering servo, mount nozzle, ESC, and split a 8.4V stick pack to straddle the jet. Otherwise it only fits directly on top of motor... Gonna try and run without motor/esc cooling and watch the temps. I can't imagine that big motor getting hot turning that lil jet, but we'll see. Then Id have to figure something out as there is no room for water jacket.

[makaveliks]

My wires came, I split a 8.4V 3300mah NiMH and a 3000mah NiMH so I have a couple batt's to run. Got my velcro glued in to hold batteries, now It's ready to try in some water. Here's the pics of the hull ready to go!



Alright, here's a better video of the boat. I used a stick battery sideways in front of motor to move center of gravity right up to 50%. This seems right on for this boat. It moves pretty good. I didn't tape the hatch this time and the big waves were coming over the top when i slowed down so it slowly filled with water and slowed the boat down. I think this boat would really move with a 380 9xl brushless motor and 3s lipo. Cut down the weight, add power and rpms. Here it is:



It seems the hull is very stable. Lucky because I didn't think it woujld be jumping waves like that and didn't bring anything to fetch a flipped boat.

[damfurst]

Good job on the jet sprint. Puts all of us to shame that took the easy route and bought a Nqd jet sprint.

[makaveliks]

Thanks, it's not perfect being I didn't make a mold, but It works great. The hull is not quite as flat as it should be, but it's always windy here and you can see the waves in the video. The deeper vee on it doesn't take too much from the looks, but it makes it really handle the waves nice. That's normal here in ND. LOL.

I think I may make a mold of it so I can make it with only 1 or 2 layers of fiberglass instead of all the 2 layer pieces glasses together(makes 4 layers) that I made it with this time. That way with a mold I can make it without any bondo and the strakes would be one piece with the hull also. I think it would be a lot lighter then. Also, then I can make more for my buddies. lol. I'm working on a full size boat right now too, so I think when thats done I'm going to mold this and make another plug for a more to scale jet sprint. I think I'm acually gonna go smaller with the next one I make and use a 380 to power it... Either that or go slightly bigger and use a larger jet. This hull seems like it may be a little big for the jet in it, and a little small for the next size jet. It's the Graupner Mini jet that has a I believe a 19mm impeller.

[J.M.Fangio]

Nice Job !

[makaveliks]

new video

Here's a video of it running on smooth water. Battery was almost dead. I forgot to hit record until almost dead. I'm going to try to get my VXL 3500kv brushless motor in here. The shaft is waay to long though, I may have to either cut it down, or find really long screws and spacers for the motor mount. Hopefully tomorrow weather permitting I'll have a video of it with the VXL.

[makaveliks]

Here it is running with a VXL 3500KV motor on 8.4V NiMh. Water was not so smooth today.



I do not know why the sound doesn't match... It does on my computer but once on youtube it no longer matches?

[makaveliks]

Added Drivers!

Added drivers, now I need my motor!




A piece of styrofoam blew up to my door(literally) so I used a box cutter and cut the shape out, I then completly covered this to smooth with a thin layer of bondo. I sanded, then painted! using the bondo and not completely sanding it allowed the bodies to have a wrinkled look like they are actually wearing suits. Took 4 hours from start untill painted and glued to hatch. Nice and light and free! Plus since there hand made, there not identical and look more realistic!

[makaveliks]

Finally made my dummy motor! I think I could have done better, but it'll look great zooming around the lake! I made it from really thin aluminum that I got from soda cans. I cut out the sides and flattened them out, then bent up each part and glued them together with shoe goo. It's extremely light weight. After all said and done, I figured for a little better touch I would add the supercharger pully, belt, oil cap, and 572 markings.