We use a 75mm pipe, of length 20cm to make a mount for the propulsion and steering thrusters. 

Use a strip of paper and wrap it tightly along the circumference of the pipe. Tape the two ends of the paper strip. 

You now have a reference of the pipe circumference. Fold this ring 4 times, to get a total of 8 creases. This provides an accurate measure of 8 parts we divide one end of the pipe in. 

Once you have marked the pipe, cut out 6cm long strips in alternate fashion as shown. 

Use a heat gun to soften the strips, then form it around the end cap of the submarine body.