Choosing a Short, Long or Extra Long Shaft
Determine the size of the shaft of your next outboard motor. Choose either a short shaft, long shaft or extra long shaft. Take the boat out of the water, set it on level ground and measure the shaft length. Measure from the top of the transom (where you clamp the motor) to the bottom of the boat. You should get around 15", 20" or 25". These correspond to short, long or extra long.
When purchasing an outboard motor one of the most important factors to consider is whether or not you need a short, long or extra long shaft outboard motor. The information on this page will narrow down the importance of shaft length and will give you an idea of what type of motor you should buy for your boating application.
First off lets display how the shaft length is measured:
As you can tell from the diagram and photo the shaft length is from the top of the mounting clamp bracket to the bottom of the cavatation plate. THE SHAFT LENGTH IS NOT FROM THE BOTTOM OF THE POWERHEAD ALL THE WAY TO THE BOTTOM OF THE SKEG, THAT MEASUREMENT IS USELESS! This measurement should equal the aft transom of your boat (give or take an inch). When the boat is on plane, the boat is completely out of the water from the bottom of the boat transom. The motor is out of the water from the bottom of the cavitation plate. Please study the diagram to familiarize yourself with engine and boat terms.
Examples of shaft lengths:
1984 Johnson 15 hp
Short Shaft
15"
*
For Small Jon Boats
* Sailboats with movable brackets
* Small Sailboats
*
Inflatables
*
Kicker Motors
*
Trolling Motors
*
Gheenoes
*
Canoes
*
Most Small Boats that Have a 15-17" Aft Transom
1979 Johnson 9.9 hp
Long Shaft
20"
*
For Small Jon Boats
*
Sailboats
*
Kicker Motors
*
Lake Trolling Motors
*
Pontoons
*
Some Carolina Skiffs
*
Most Small Boats that Have a 18-21" Aft Transom
1989 Evinrude Sail Master 9.9 hp
Extra Long Shaft
25"
*
Sailboats
* Kicker Motors
* Lake Trolling Motors
* Large Barges that require high thrust
* High Transoms
* Any Water Vessel that has a 21-27" Aft Transom
FAQ.
Q. Can I use a long shaft motor on a boat that is rated for a short shaft?
A. Yes, it will work but you will notice a little more drag and a little less top end performance, but it is ok to do this and it will work fine. You may not want to do this if you are operating in shallow water.
Q. My sailboat has an adjustable bracket can I put a short shaft motor on it?
A. Yes, but make sure that you are comfortable with the position of the motor and make sure that the motor bracket allows the engine to be positioned correctly.
Q. When I'm running my boat the motor seems to cavitate or come out of the water often, do I have the incorrect shaft length?
A. Possibly. Your motor should not be doing this unless you are in very high seas. It could be that your motor tilt pin is not far enough, check that first before anything.
Q. Can I convert my outboard to a short shaft or long shaft?
A. Some outboards you can convert either way very easily, others require more work. Johnson / Evinrudes (OMC) are the easiest to convert shaft length. Others may be more difficult. It is always easier (with regards to kit availability) to convert a short shaft to a long rather than a long to a short.
Choosing a Short, Long, or Extra Long Shaft Outboard Motors
You must measure your transom in order to determine what shaft length motor you need. Keep in mind that the cavitation plate should be flush with the bottom of the boat. You can get away with an inch or two either way but it is wise to keep it close. If you are still unsure of what kind of shaft you need contact your boat manufacturer or look them up on the Internet. We suggest that you review some of the information on this page as a source of knowledge when it comes time to purchase an outboard motor but we are not responsible for purchasing decisions or any influencial information found on this page. Do your own research before buying an outboard boat engine.
