Does shaft length matter???????

[BAtoo]

We are buying a slightly bigger inflatable tender (2.9m) & larger outboard (6-8HP, not 2) - boys are growing up & I have given in to the nagging - so can I use a long-shaft outboard or do I have to use a short shaft - does it make a difference how far under the surface the propeller is??

 

[Whitelighter]

So...many...smutty...replies...can't...bring...myself..........to...........post.........













My wife seems to think so.








Damnit, really tried hard to resist.

 

[graham]

Better to use a short shaft. In a tight turn if someone blips the throttle wide open the extra leverage of the longer shaft could turn you over. Also more likely to bump the bottom.

Some motors dont like running with the exhaust too deep in the water.

 

[Rum_Pirate]

The best shaft length is one that has the cavitation plate (horizontal plate above the propelllor) of the engine level with the bottom of the transom on the boat.

For more info try:

http://www.smalloutboardengines.com/shaftsizeandhp.html

 

[polwart]

[ QUOTE ]
In a tight turn if someone blips the throttle wide open the extra leverage of the longer shaft could turn you over.

[/ QUOTE ]

I'm not sure I understand the physics of that? We are talking about 5 extra inches anyway - don't think that would be a concern. The main downside of too long a shaft is extra drag - so loss in speed - but not end of the day. I suspect you are asking because you want to use the same engine on the yacht and the dinghy. My experience of using long shaft engines on short transoms is that it will work and is unlikely to be a big problem (although the prop you want for the dinghy and the yacht may not be the same). I have never rolled a powerboat even by doing full throttle hard turns.

 

[cliff]

PAULINE!................Over to you.......... /forums/images/graemlins/blush.gif
--------------------

"Artificial intelligence is no match for natural stupidity"
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[arthur1808]

Not sure I want to contemplate the physics of an extra five inches of shaft, thank you very much!

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif

 

[Kawasaki]

Cos your getting a bigger inflatable toy and a bigger thruster be carefull!
"Can I use a long shaft outboard?"
If your buying another outboard to suit the tender "(we are buying a slightly bigger inflatable tender& A LARGER outboard) .Why don,t you buy the one that suits the tender? /forums/images/graemlins/confused.gif

 

[BAtoo]

I think the outboard does match the boat - it will probably b a 6HP on a 2.9m airdeck inflatable. Beter than the cla**ed out 2HP on the 2.7m we had.
Thanks for the helpful comments - I was sure some would rise above the obvious!!!

 

[Talbot]

I assume you are asking about the long shaft cause you have one as the emergency propulsion for the boat. A long shaft can be used in a tender, but will not be as efficient, more likely to hit the bottom, be a pain when going to the beach, and is somewhat more dangerous in a tight turn. However, there is nothing to stop you adding a bracket to the transom of the tender to raise the motor up somewhat and thus position it a bit better. A lot of people have done this on 13 ft dories.