outboard motor shaft leghth

[wyldewal]

This may be a stupid question but I was wondering how to tell how long of a motor I need to buy for my boat. I took a measurement on the transum of the boat. From the top of the transum to the bottom of the boat is 21 inches but I don't know if I am measuring from the right spots, and how do I know what length shaft do I need. 15, 20, and 25 inches seem to be standard motor length but how does the relate to the transum, and where do they take this measurement. Any help would be great. Thanks.

[Satchmo]

If the center of your transom measures 21", then you need a standard 20" long shaft motor. 15" would need a short shaft and 25" needs an extra long shaft motor. You need a long shaft motor.

[Valv]

Satchmo is right. On outboards the shaft is measured from the lower side of the transom clamp to the cavitation plate of motor. There are only 4 sizes

15" (short)

20" (Long)

25" (X Long)

30" (XX Long)

[wyldewal]

Thanks guys, I appreciate the help.