Modifying a Aqua Jet

          Our first change is getting rid of the stock Universal joint. We will replace it with a Flexible Shaft Coupler 4mm-5mm. Below is what the stock setup looks like without the Stock Black Universal joint installed. The screws in the stock coupler are held in with a Loctite or similar type of glue. To remove these you will need a quality allan wrench and a soldering iron. Use the iron to heat the screw for about 30-60 seconds. Than quickly attempt to remove the screw. The stock universal joint is about 1" long, the replacement flex coupler we are going to use is about 2 5/8" long. To make up the extra space there is a really easy solution.

          Below you will see all we had to do is spin the motor mount around (backwards) to make up for the extra room we needed. Before reinstalling the motor mount bend the face plate (were motor attaches to mount) back about 1/4". So that the motor will be angled down at the prop shaft. After you have bent the plate it should be a little less the a 90degree angle. Remount the motor to the mount and install the mount/motor. Check for alignment. The tip of the motor shaft should be pointing at the prop shaft. If not, bend the face plate some more. Be sure to bend the plate outside of the hull, in order not to damage the mounting holes. Reinstall mount, recheck alignment. After installing the flex coupler, bench test the system. It should sound quieter and smoother!

Running on more then The Recommended 12 Cells!

          This hull runs even faster on 14 cells! On 14 cells the boat will run quicker but you will have to check for heat build up in the motor frequently. Water cooling the motor will help this. To test for heat, have an adult give the motor  the 5 second test. Which is, hold your finger on the motor for 5 seconds. If its so hot you can't hold it for 5 seconds, its too hot. Allow to cool fully before running again! 

          With 16cells, water cooling the motor is definitely required to keep the heat down on the motor. The boat is rocket on 16cells! Check for motor over heating often.

          Heat is the only reason these motors burn up. The 775 motor is meant to run maintenance free for a extended periods of time.

          Caution- While running this hull on 12 cells or more, the universal joint needs to be kept well greased! If not the heat will build up in it and snap it in half! Another benefit of the above "flex shaft conversion" is you wont have to worry about this anymore.

Adding a Carbon Propeller!

          One of the most beneficial speed increases are propeller changes. Bigger isn't always better! Testing different props is the best way to figure what works or doesn't work. But that's for a different article. Switching to a quality carbon fiber prop is pretty straight forward. To fit the Graupner carbon propeller on the stock standard shaft a hole needs to be bored into the the back of the prop. If you look in the picture of prop on the shaft, you will see that only half of the prop nut is showing. That's because the rest of it is recessed into the prop. We need to do this because the stock shaft isn't long enough to have the whole nut thread onto the shaft. When putting the lock nut on, put the part with the plastic insert first, so the lock nut gets a good bite onto the shaft.

Click for larger image.
 

Most of the better propellers come in  3/16" shaft sizes. But most Kit boats use a smaller 4mm shafts. To make a shim/sleeve to make up for the extra space, there is a quick & easy fix. Go to the local hobby shop and look for a piece of 3/16th outside diameter, K&S Engineering Brass tubing, stock# 129. The cost about $1-$2 dollars. You can find the on the web at http://www.ksmetals.com/. Cut it to the required length and use it as your sleeve. Since the tubing comes in one foot lengths you will have plenty extra,  so cut a few more while your at it. Incase one gets lost at the pond during a prop change.

OffshoreElectrics.com carries all the above parts