Long shaft or short shaft?

111KAB

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As you may know by now (reading my other posts) my boat knowledge is limited. I assumed I needed a longshaft outboard for my boat .... see http://www.ybw.com/forums/showflat.php/Cat/0/Number/2018138/an/0/page/0#2018138
Anyway I have been offered what looks like a decent (2004) Yamaha but it is a short shaft. What exactly does his mean and what do I need to check on the boat to see if this will suit? Thanks again ~ I'll get there one day!
 

Nick_H

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If i'm not mistaken the shaft length of the outboard is the height between the anti-cavitation plate (the fin like bit above the propeller), and the horizontal face of the u-clamp that sits on top of the transom.

If you measure the height of your transom, at the centreline where the hull is deepest, this will tell you the shaft length you need. The shaft length of the outboard should be somewhere between the same, and 50mm longer, than the height of your transom. If the outboard is more than 50mm longer, you can pack it so it sits higher on the transom. If it is shorter, you will lose performance and there's nothing you can do, short of modifying the transom.
 

111KAB

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[ QUOTE ]
If i'm not mistaken the shaft length of the outboard is the height between the anti-cavitation plate (the fin like bit above the propeller), and the horizontal face of the u-clamp that sits on top of the transom.

If you measure the height of your transom, at the centreline where the hull is deepest, this will tell you the shaft length you need. The shaft length of the outboard should be somewhere between the same, and 50mm longer, than the height of your transom. If the outboard is more than 50mm longer, you can pack it so it sits higher on the transom. If it is shorter, you will lose performance and there's nothing you can do, short of modifying the transom.

[/ QUOTE ]

MANY THANKS - I have measured transom to lowest part of the hull and the dimension is 20" (500mm) so I will TRY and work out whether to have long, medium or short!
 

VicS

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When mounted the cavitation plate above the propeller should in line with the bottom of the transom or up to a maximum of 1" below it, but not above it.

See http://www.smalloutboards.com/shaft.htm.

The quoted shaft length 15" for a short, aka standard, shaft or 20" for a long shaft is in reality a little less than the distance from the inside of the transom bracket to cavitation plate.

Also down load an owners manual for any engine you are interested in and read the section on mounting the engine. Advice varies a little but not by much
 

Tranona

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Yes, your boat was designed for a long shaft motor. A short shaft will be masked by the transom and probably the prop will be out of the water.

Outboards are generally made in the two standard lengths (although some models have extra long, mainly for sailboats) and boats are made to take one or other.
 
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