How to Install a Bob's Nose Cone

Updated April 17, 2017

Based in Tampa, Bob's Machine Shop manufactures a line of motor boat nose cones said to improve engine performance and speed. They may also enhance fuel economy. Although factory installation can be arranged for a fee, you might want to install your nose cone yourself. Nose cone kits come with the necessary hardware; you'll just need the proper tools and paint. Invest a few hours now installing your nose cone and save minutes every time you race your boat.

Remove the boat's lower unit. This makes it much easier to work on. Clamp it upside down in a jig for greater accessibility.

Get an approximate fit. Dust the nose of the lower unit with chalk. Center Bob's nose cone on the lower unit's nose. The chalk will transfer to the nose cone where contact is made.

Carve out the inside of Bob's nose cone with a rotary grinder or file. Wear safety goggles. Continue to fit and grind, checking the chalk until you get a fairly close fit. The fit doesn't need to be perfect because your epoxy resin will help fill gaps. Be patient, as this step can take four to six hours.

Clean the lower unit's nose. Remove all grease and chalk. Sand the paint six to eight inches back from the nose with an orbiting sander

Plug your holes. A lower unit contains several necessary holes. These include the oil drain, water intake and gear case cooling holes, among others. Protect them from epoxy by covering them with wax plugs, modelling clay or another substance you can easily remove. Check the owner's manual to make sure you have found them all.

Etch the nose cone and lower unit with an aluminium etch kit. Begin with a phosphoric acid wash, followed by a chromic acid wash. This process must be done no more than two hours before you are ready to bond.

Glue Bob's nose cone to the lower unit. Add silica to the epoxy until you reach a mayonnaise-like consistency. Apply a thick layer to both the lower unit and the nose cone. Attach the nose cone to the lower unit and press. Excess epoxy should ooze out. Check for alignment on all angles. Clamp it until fully dry.

Mix the epoxy, silica and low density filler until you get a thick paste. Brush this over the nose cone and lower unit, focusing on the seam. Let fully dry and sand. Repeat twice. Remove the plugs from the holes. Sand again.

Cover the new surface with two coats of epoxy. Let dry. Wash with water and a sponge. Sand with 180-grit sandpaper. Paint with marine outboard paint.


Contact your boat dealer before installing a nose cone. Installation may void your factory warranty. For additional technical support, contact Bob's Machine Shop. 800-966-3493. Be sure you're choosing the right size nose cone. If your boat is too heavy, a nose cone could cause you to lose speed rather than gain it.

Things You'll Need

  • Chalk
  • Safety goggles
  • Rotary grinder
  • Orbiting sander
  • Aluminium etch kit
  • Epoxy primer
  • Colloidal silica
  • Low-density filler
  • 180 grit sandpaper
  • Paint
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About the Author

Roberta Dunn began her writing career in 1997. Her short films have screened at the Silver Lake Film Festival and L.A. Shorts Fest, and her short fiction has been recognized by "The Atlantic Monthly" and "Glimmer Train." The recipient of an Elizabeth George Foundation grant, Dunn holds a Master of Fine Arts in fiction from Warren Wilson College.