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  #11  
Old 07-11-2012
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Re: Tohatsu 6hp Sail-Pro Version

Quote:
Originally Posted by Merit25lovers View Post
I purchased a 6hp Tohatsu 4-stroke with a 25" shaft last season..........and don't lower that cavitation plate too far into the water (easy to do with the 25" shaft!)

Enjoy!
Not sure about the information mentioned above about lowering the cavitation plate too far into the water.

Can anyone explain please?
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  #12  
Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

An extra long shaft engine and high-thrust prop will make a big difference in powering in waves of any size. Just make use you don't have any problems with interference. When I put such an engine on a Pearson 26 many years ago, I had to tilt the engine back slightly to avoid it hitting the rudder under power.
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Re: Tohatsu 6hp Sail-Pro Version

Thanks, good point !! And I'm sure I wont have any problems hitting the rudder unless I swing the motor hard over while pushing the sailboat tiller the other way. My outboard motor will rest in an offset motor well about 15 inches to the left of the keel. Motor well is about 31/2 feet ahead of the stern as well. I know that I will not have any prop wash over the rudder to help steering and will most likely rig up a method to lock the outboard tiller straight anyhow while moving forward. Will probably only use the outboard tiller to help back into the marina slip upon returning. This will be the 1st motor I'll own that has a true reverse gear selector. The others had a spin-it-around-180-degree method the go backwards, was really confusing sometimes.

Really like the idea of the 25" shaft, want that prop down deep in rougher waters. Only drawback is the sail pro motor is 50" tall from the tip of the lower skeg to top of motor cover . YOW , thats over 4 feet of motor!!!

Still not sure about the previous comment about "Cavitation Plate" I have a displacement hull and dont plan on doing any high speed planing as it is...

Again, I appreciate all the great info everyone is providing here. Bruce
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Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

Quote:
Originally Posted by Bruce_L View Post
Not sure about the information mentioned above about lowering the cavitation plate too far into the water.

Can anyone explain please?

From Answers website:

"A cavitation plate is a permanent horizontal plate on the vertical shaft of the outboard right above the propeller. It sits just at the water level when the boat is up on plane (ie: flush with the bottom of the boat, for a planing style hull).
It prevents 'cavitation' of the propeller ie: prevents air from the surface of the water being picked up by the action of the propeller. Cavitation drastically reduces a prop's effectiveness & efficiency; basically a cavitating prop is pushing some air rather that just water. Over-revving can also result."

My outboard is on an adjustable motor mount. All I was referring to was not putting the motor mount too far down such taht the cavitation plate is way below water level...

It just seemed to purr better when it was not so deep in the water!
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Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

"All I was referring to was not putting the motor mount too far down such that the cavitation plate is way below water level..."

If the propeller is low so that the cavitation plate is way below the water level, there will be no cavitation to prevent. But you WILL prevent the prop from coming out of the water when it is rough. On a sailboat, if you do place the cavitation plate at water level the prop will be coming out of the water every time you hit a wave.

In other words, for a sailboat the longest shaft is best - unless it is so long that you're hitting the bottom. Which I doubt.
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Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

At some point of depth it does become difficult for the motor to push out the exhaust gas

Remember even with the sailpro label the shaft lengths main and original purpose is/was different lengths of transoms on plaining hulls
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Re: Tohatsu 6hp Sail-Pro Version

At a depth of 1ft, the water pressure is 1.033 atm. That's 0.47 PSI higher than at sea level, or a reduction in flow through the exhaust of about 3% vs. sea level. Shouldn't matter, it's a small price to pay in terms of power loss if the prop stays in the water.
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Re: Tohatsu 6hp Sail-Pro Version

It matters

All sterndrive boats have idle exhaust relieve ports because the through-prop exhaust is to deep underwater at displacement speed to start correctly

On larger outboards your often are NOT suppose to shut them down when fishing in big swells because the boat can bob deep enough to get the lowest cylinders WET
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Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

Quote:
Originally Posted by MarkSF View Post
At a depth of 1ft, the water pressure is 1.033 atm. That's 0.47 PSI higher than at sea level, or a reduction in flow through the exhaust of about 3% vs. sea level. Shouldn't matter, it's a small price to pay in terms of power loss if the prop stays in the water.
Matters more on a 2 cycle as the whole engine cycle relies on exit of exhaust to draw in next fuel charge. There are no valves to open and close and the fuel only comes in with the rush of exhaust flow. The impact will be notable in top rpm being lower and will not idle as freely. Back pressure is not faborable, but agree you want to avoid cavitation as well.
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Old 07-12-2012
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Re: Tohatsu 6hp Sail-Pro Version

on sailboats the more motor you have in the water the better. I have a 8 hp short shaft i had to put a swing bracket on my boat for the motor to work and the cavition plate is is about 4-6 inchs below the water. good for waves.
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