How to Measure a Boat Transom

by Will Charpentier
The transom's size is critical to sizing and placement of your outboard.

The transom's size is critical to sizing and placement of your outboard.

The transom is the "back wall" of your boat, the most rearward part of your hull. The rearmost structural member of your boat, it not only distributes the stress of the hull generated by the bow's impact as it cleaves the water, it's the place you hang your outboard motor. Knowing the width, height and depth of your transom allows you to make several important decisions when selecting or purchasing a new outboard.

Ask a friend to hold one end of a measuring tape at the extreme outer edge of the top of the transom while you pull the tape across its width to the opposite outer edge to measure the "length of the taffrail," which is the width of the boat across the top edge of the stern. The center is the point where your outboard motor is (ideally) located.

Hold the tape on the top, center of the taffrail and measure straight down to the point, usually a sharp angle, where the transom joins the bottom of the boat. This is the dimension you'll need to know when deciding between a short shaft, long shaft or extra long shaft for your outboard motor.

Set the end of the tape on the outside edge of the taffrail at the center and measure inward to the inside edge of the taffrail. This is the dimension you'll need when selecting a width for your outboard motor's mounting bracket.

Items you will need

  • Assistant
  • Measuring tape
  • Grease pencil

Tip

  • When you measure the width of the stern, mark the center with a grease pencil.

About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.

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