How to measure the shaft length on outboard engines

Written by karen cotton
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How to measure the shaft length on outboard engines
The right outboard engine keeps your boat running smoothly. (Wooden Boat image by Pearsoc from Fotolia.com)

Outboard engines come in a range of sizes to meet the needs of different boats and sailing conditions. Starting at 15 inches in length, short shaft outboard engines suit smaller craft, such as canoes and inflatables. Pontoon and most other sailboats require a long shaft engine, while larger vessels, such as barges in need of high thrusting power, require an extra long shaft outboard.

Skill level:
Easy

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Things you need

  • Measuring tape
  • Paper
  • Pencil
  • Yardstick

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Instructions

    Measure Engine Shaft Length

  1. 1

    Lay the outboard engine on the ground.

    How to measure the shaft length on outboard engines
    You may also prop the engine on the back of a chair. (chair image by inacio pires from Fotolia.com)
  2. 2

    Identify the outboard engine's shaft length. This runs on the side opposite the tiller. It extends from the top of the mounting clamp bracket to the cavitation plate.

    How to measure the shaft length on outboard engines
    The transom is located on the right side of this motor. (toy outboard motor image by pearlguy from Fotolia.com)
  3. 3

    Using a measuring tape, measure the outboard engine's shaft length. Record this in inches.

    How to measure the shaft length on outboard engines
    Outboard lengths are measured in inches. (feet and inches image by John Sfondilias from Fotolia.com)

    Measure Your Boat

  1. 1

    Identify your boat's transom, which is at the stern. It comprises the panels at the back of the boat that remain out of the water during operation.

    How to measure the shaft length on outboard engines
    You can find an approximate shaft length by measuring your boat. (yacht wake image by Xavier MARCHANT from Fotolia.com)
  2. 2

    Use a yardstick to measure down on a vertical plane from the top centre of the transom to the boat's hull. This will give you an approximate shaft length that is within an inch. Transoms are rarely vertical, so do not measure a sloped or angled transom. Just draw an imaginary vertical line down from the transom.

    How to measure the shaft length on outboard engines
    A yardstick lets you take an accurate measurement. (measure image by Stanisa Martinovic from Fotolia.com)
  3. 3

    Use the approximate shaft length to determine what type of outboard engine you'll need. If it's between 15 and 17 inches, choose a short shaft outboard engine. Boats measuring 18 to 21 inches require a long shaft, and vessels up to 27 inches can use an extra long shaft.

    How to measure the shaft length on outboard engines
    Barges normally need an extra long shaft. (barge image by Dubravko Grakalic from Fotolia.com)

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