HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

[butteco]

Okay, <br /><br />This is an update to a post I had made a few weeks ago when I noticed my motor spitting up a rooster tail at half all the way up through full throttle. <br /><br />Today I put it at 2/3 throttle and walked back to have a look at the cause... <br /><br />I noticed it was coming up from right behind the lower unit above the anti cavitation plate. It almost looks like my hydrofoil fin is the cause of the problem... <br /><br />Now I want to know if the rooster tail is part of the design or if it isn't supposed to be doing it??? <br /><br />Here are some pictures. As you can see, the water gets compressed between the front of the lower unit and the inside of the hydrofoil and makes its way back and hits the hydrofoil crossmember and as a result is deflected up towards the motor. It almost looks like the rooster tail is planned and is part of the design, as the crossmember is beveled at an angle to shoot the water up??? Anyway here are the pictures. What do you all suggest I do? Besides a little drag/friction, it doesn't really affect my top speed, and the hydrofoil does get me on plane faster... <br /><br />

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[AMD Rules]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

If you like the performance the hydrofoil provides, why not simply cut out the center section that creates the roostertail and have two separate fin pieces, one for each side? <br /><br />Shooting water up in the air is sign of energy being wasted. Excess drag, and actually it means the water is pushing down a bit on the center of the fin. Counter productive.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Cut out that center section? Won't that compromise the structural integrity of the fin itself? Seems like it would bend/flex etc... if that piece gets cut out? Why would the company put it there if it caused a problem???<br /><br />Are there any other possible solutions? (besides removing the fin...)

 

[Mercury140-I6]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

I had one of those on a previous boat, and I filed down that part of the cross member to make is a much more gradual slope. Fixed the roster tale.<br /><br />Hope this helps.<br /><br />Craig

 

[phatmanmike]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

how bot losing the fin altogether.<br /><br />maybe get some tabs instead

 

[roscoe]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

The real problem is that the motor is mounted too low, as evidenced by water being on top of the anti ventilation plate.<br />The plate, and the entire hydrofoil should be above the water when the boat is on plane. If the motor is trimmed at all, and the foil or plate is digging into the water, it is actually pulling the motor down, and slowing the boat.<br /><br />Raise the motor then test run.<br />Then remove the foil and test it again to see if it is needed when the motor is mounted at the right height.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

So I actually want the motor to be higher than it is right now??? here are some shots of the motor height, let me know what you think... <br /><br />

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[LubeDude]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Roscoe has nailed it again !!!!

 

[gss036]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

I am running the same fin on my 200hp Merc and at 40+mph it does not cause a rooster tail. Do you have power trim? Try trimming it up a little bit when running to see if the tail will go away.<br />It does kind of look like your motor is about an inch or so too low, then again that is a good deep V design, should ride good in rough water.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

So I want the anti-cavitation plate to be a little bit above the bottom rear of the hull? As it is currently sits, the A/C plate is pretty close to level with the rear of the hull (hard to tell from the angle of the pictures I took). <br /><br />Okay so I will raise the motor up one notch. I have never removed or lifted an outboard before... What do I retorque the bolts down to? <br /><br />What should I be aware of when lifting or moving an outboard up a notch? Is it just as easy as loosening the 4 bots that hold it to the transom, pulling them out, lifting the motor, and putting the bolts back in?

 

[ondarvr]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

You need to adjust the rollers on the trailer too, the hull needs to be supported at, or near the transom. Your hull is too far forward or the roller too far back. <br /><br />To raise the motor put a wood block under the skeg, loosen the two bolts that are in the slotted holes just enough so it can move, then you will need to remove the other two. Now jack up the front of the trailer, this will lower the transom, the motor is on the block so it won't move down, just keep cranking until it lines up with the next hole. You still have the two bolts in the slotted holes in place while doing this so the motor can't fall off.

 

[ondarvr]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Never mind the roller adjustment, I looked agian it's a bunk trailer with a roller.

 

[roscoe]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Let us know how it works, and if it performs any better.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

So just to make sure I am not wasting effort, it is okay for the motor to be raised up so that the A/V plate is 1 inch ABOVE the bottom of my hull? That is where it will sit if I raise it to the next hole. ALSO, the top of the outboards transom bracket will no longer be resting on the top of the transom, it too will be about 1" above the "rim" of the transom? Is that okay???? <br /><br /><br />AND WHAT DO I TORQUE THE OUTBOARD BRACKET BOLTS BACK DOWN TO ON THE TRANSOM???? DO I USE LOCKTITE OR ANYTHING LIKE THAT?

 

[roscoe]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Its fine for the a/v plate to be above the bottom of the hull.<br />(some motors are raised up 3-5 inches above)<br /><br />Motor does not need to rest on top of transom, most don't.<br />The bolts are whats holding it on.<br /><br />Put a liberal coating of 3M 5200 marine grade sealant on the bolts before pushing them thru. <br />How tight?? I always just make them real tight. Hopefully someone will have a torque spec for you.

 

[gss036]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Butteco, before you go to all that work, try tilting the motor to see if that helps. All you need to do there is place the tilt pin one notch at a time until get results. About the only time my motor is all the way down is when I am running in a no wake zone.<br /> The fin should be riding on top of the water(or very close) when on plane. It works just like a wing on an airplane to give you lift, that is why there is a littledownturn on the back side of the stingray fin.<br />Looking at the picture w/your finger pointing at the fin, it looks like there may be a little bit of a cavity there that might be catching water. Put a thick bead of silicone calk in there to see if that changes anything.

 

[roscoe]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Sorry gss036, have to disagree. An airplane wing provides lift as the air flows over the top of the wing creating a low pressure air pocket, while there is a more dense pile of air beneath the wing, creating lift.<br /><br />The hydrofoil on an outboard should not have water flowing over it except by default from start. The foil provides additional antiventilation effect and a longer planing surface.

 

[gss036]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Ok, bad example, guess that is why they have the vortex generators on top of the wing instead of under them, but stingray does sell a steering type addition to compesate for steering torque.<br />I worked on attack and fighter jets for 7 years so I know what you are saying.<br />Roscoe: What are the flaps for on the wings when they are extended. No, I was not a mechanic, but a safety and surivial tech. Sorry if I offended you in some way, but I was only trying be helpful to someone in need of help. I just hate to see him having to raise the engine if not need. I went out to my boat and looked at my fin, I just don't think one notch will make any difference. The bottom of my fin is about "1" inch higher than his.

 

[roscoe]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

cool, jet mechanic. Talk about having someones life in your hands.

 

[Nos4r2]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ??? ( pictures )

Just a thought Butteco,and if I'm wrong someone please correct me but if you use a cheap "flex gauge"(?) type torque wrench to undo them it'll give you roughly the torque setting to do them up to. At least you'll know you won't strip the threads doing them back up that way.<br /><br />If the threads are rusted ignore this!