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Motor Shaft Length

Jack M

Jack M

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What are the measuring points to determine the length of the motor shaft ?

My build calls for a 25" shaft ,a 25" was on the order ,but I think I may have a 20"

I cannot use the trim ,it cavitates immediately .

I made a hard turn going only about 15 mph prop came out of the water ,once again trim all the way down .

 

Thanks .
 
Yamaha does it very simply by model number... What did you get for a motor?
 
Thank You Carl . I am going out shortly and will take a tape .
 
Chris Z said:
Yamaha does it very simply by model number... What did you get for a motor?
Click to expand...
The model on my order does say XL which is the long ( 25") shaft .

I cant find it on the motor .

I have emailed Mercury with the serial number asking them to verify .

I concern is that when I had originally ordered the express package ( 20 ")  the motor did not get changed even though it is on my order .
 
Jack,

I too am experiencing this with the Q that was delivered today...  It's a Elliptical toon so I understand they sit higher in the water, but trim all the way down and i'm barely touching the sand on my dock, and the previous boat I had required me to trim way up to avoid the prop hitting the sand...    

Cwag911 thanks for the link, i'll grab my tape and measure as well...  I'm on the top bolt also so there is nothing to be done about mounting it lower.  

Jack, let us know what you find, i'm interested.
 
I just now ,got off the phone with Mercury .They verified by serial number that I DO have a 25 inch shaft .

I also went out earlier to measure and I got 24 so it is most likely  me on the missing inch .
 
You might have to put a jackplate on that Jack. (no pun)
 
I will mention that to the dealer .Thanks Carl
 
My first prop did that to me Jack. Slight trim and it would ventilate. Changed to the Enertia, and I now have quite a bit of trim range. First prop was a Black Max.

If you have access to another prop, try it.
 
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Kaydano, please educate me; would a prop from two different manufacturers each with the same pitch and diameter really make that much of a difference?  Especially in the scenario that Jack M  is describing that a different prop would cure all?
 
I have an Enerita on it currently .All I know is that is a 15 pitch .

Dealer has another prop on order . ( small dealer he doesn't keep a lot of stainless on hand ) 
 
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I don't think pitch or diameter matters. I think prop design matters.

Think of the thrust coming off the prop. Most of it is directed straight back. Some of that thrust comes off at a slight angle. Even less at a wider angle. And some thrust is wasted coming off the side of the prop, going perpendicular to the shaft of the prop, or coming straight up out of the water.

I think my black max had a lot of this "sideways" prop wash, and it threw a lot of water up through the surface, causing it to ventilate.

I think the Enertia is a much better design, and its much more efficient by not having much sideways prop wash.

Just my theory. I can tell you for a fact there's a huge difference between the two props on my boat though. Not sure if I have the right reason, but it's very plausible in my mind. I have read much about props, and the more I read, the more I realize I don't know, but I have seen diagrams of the cone shape of thrust that comes off a prop, and I know this varies for different props.

It's a fine line. You want the cavitation plate up high enough, but the prop also has to be in the water! I think mine must ride a little high and the prop is too close to the surface. I'm on hole 1 though, so can't lower the motor any more. I love the Enertia, and I think my boat is dialed in just right with it. Jack has the Enertia already, so all this is moot for him.
 
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I take it hole 1 is the bottom hole.  Never paid much attention to it before but this weekend I am going to look at the placement of my motor and with my wife driving I will go back and look at where the cavitation plate rides on the water.

Thanks for sharing your knowledge Kaydano
 
Here is where mine is mounted .

So would that be hole # 1 ?
 
Looks like you are all the way down. Yes, hole#1.
 
Thanks ,

Yes it is all the way down . I have the pic because the dealer asked for it .

kaydano said:
Looks like you are all the way down. Yes, hole#1.
Click to expand...
 
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Sorry Jack, don't know what to tell you about your problem. Investigate the shaft length more...
 
Oops, I see you confirmed that. Carl is right. Jack plate is needed.
 
Are you sure the motor is actually going all the way down when you trim? Might be an obstruction... make sure the motor is pressing up against the transom. Then see your dealer. You shouldn't have to get a Jack plate on a standard boat like this.
 
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