Long/short shaft...............

sogood

What is the generally accepted standard difference between a long and short shaft outboard. Given that the depth/height of the transom on my Microplus is 20", from top to bottom at its' lowest point, does this automatically make it a long shaft?

Or does the construction and design of the outboard make a difference?

How deep in the water is the best depth for the prop, assuming of course that the water inlet is fully submerged?

Just wondering in the event that I might replace my engine, which is an old Yamaha, long shaft, given that it has an extension on the leg.

Thanks.

fergal.b

Short shaft is 15" long shaft is 20" extra long 25" the cavitation plate of the outboard should be level with the bottom of the boat so it can trim in and out the boat if it is too deep it will not work as well and if too hight up it will not work at all.


.

sogood

fergal.b wrote: »

Short shaft is 15" long shaft is 20" extra long 25" the cavitation plate of the outboard should be level with the bottom of the boat so it can trim in and out the boat if it is too deep it will not work as well and if too hight up it will not work at all.


.

Thanks for that, but what's a cavitation plate? How does trim work and what is "Trim". I assume the 15" and 20" measurement refers to the transom depth/height? FWIW, my outboard has a pair of wings/fins fitted just above the prop. Is this relevant?

Thanks again.

fergal.b

The cavitation plate is the flat bits just above the propeller it works like a fin on a whale or the tail on a bird, by moving the outboard in or out you can adjust how the boats sits on the water "bow up to bow down" on bigger boats the outboards have hydraulic rams that move the engine and on smaller engines you will have a line of holes with a pin to select the right trim setting for your boat.

sogood

Thanks for that Fergal, question answered. I assume the large removable fins attached to my engine are there to accentuate the "bow up/down" effect. My engine has that row of holes with the long pin that sets the angle of the engine in the water, so, the mystery is solved.

Many thanks!

john jameson

How do you select the right trim for your boat is there a general rule some where. Iv a long shaft yamaha 15 hp on lake boat and I keep the engine as close to transom as I can this I assume will cause bow to stay down and cut trough wave. The lake boat transom is low enough I'd be worried with to much or any trim to rise the bow I'd be taking on water over transom.

fergal.b

john jameson wrote: »

How do you select the right trim for your boat is there a general rule some where. Iv a long shaft yamaha 15 hp on lake boat and I keep the engine as close to transom as I can this I assume will cause bow to stay down and cut trough wave. The lake boat transom is low enough I'd be worried with to much or any trim to rise the bow I'd be taking on water over transom.

A basic rule would be to have the engine leg straight down and the boat more or less level when she is just sitting in the water after that with small boats you can adjust how the boat rides by moving people or gear closer to the bow or stern till you find a spot you are happy with.

john jameson

Cheers fergal