HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

[butteco]

Hey all, <br /><br />Sorry for the double post - I realized it wasn't engine related after I posted! <br /><br />I just went out to the lake for the 2nd day. The first day I just putted around 10-15mph for the first tank of gas, since the motor hadn't been run in a while. Today I felt the motor had been sufficiently broken in and so I push the throttle all the way down. <br /><br />GPS said I was going 37mph which is plenty fast for me, but I have a feeling I could get another 2-3mph out of it. the reason being follows:<br /><br />I noticed that at WOT my motor was shooting a large "rooster tail" up out of the water and splashing all over the outboard cowling. It almost looked like something was dragging in the water and pushing the water up and out of the lake. Now while this probably looked cool, I DO NOT LIKE IT!!! I have a feeling this drag is slowing my boat down. <br /><br /><br />I have an 1976 85HP Evinrude w/ the "hydrofoil fin" attached to the cavitation plate. The cavitation plate sits just a hair under the bottom of my boat (about 1-2"). Manual Trim is all the way down on the lowest setting (the setting closest to the transom). <br /><br />I don't see how this water is being kicked up? <br /><br />HOW CAN I FIGURE OUT WHAT THE CAUSE OF THIS DRAG IS?<br /><br />Any advice would really help out! <br /><br />Thanks!

 

[JB]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

You need to raise your engine until the ANTI VENTILATION PLATE is about 1-2" above the bottom, Butteco.<br /><br />Move the trim out until the AV plate is parallel with the bottom or maybe half a hole further than that.<br /><br />Let us know what results are, and good luck.

 

[Moody Blue]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

Without a doubt your motor is mounted too low on the transom. Having the hydrofoil on makes the problem even worse. The anti-ventilation plate should be even with or slightly ABOVE the bottom of the boat and the hydrofoil must never be underwater once on plane. With proper setup you will probably gain more than 2-3 MPH.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

? <br /><br />I am confused? What is the anti ventilation plate?<br /><br />Is that what the hydro-foil fin is attached too? if so, my anti ventilation plate is level with the bottom of the boat, and the little plate above that is about 1-2" above the bottom of the boat. <br /><br />Here are some pictures, am I set up properly??? <br /><br /><br />A picture says a 1000 words, take a look:<br /><br />

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[dajohnson53]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

The "anti ventilation plate" is what you called the cavitation plate. Anti-v is the correct term since what it does is reduce ventilation of the prop. Cavitation and ventilation are two different things, but a lot of people refer to ventilation as cavitation.<br /><br />Great pictures. To me, it looks like your motor is pretty close to being set up OK. Not way off, if at all. The main thing I see is that it is trimmed all the way in (as you said in original post). First thing I'd do is tilt the motor up and lock it up, and move that pin into the center position. I'd also take off the hydrofoil fins and give the boat a try with the trim adjusted in the middle and the fins off. Then, see how it performs all in all. The fins were put there for some reason by a previous owner, but we won't know why (and if there might be a better solution) unless you try it without.<br /><br />RE: the trim pins - boats with electric trim often start out in a way in position (like your motor is now) then adjust to a more tilted out position when underway. For manual trim units like yours, I've found that generally the middle position works best all in all.<br /><br />Give those two things a try, they're easy, and let us know what happens.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

Good to hear thanks for the advice. <br /><br />So you think the trim has something to do with it? When I got the boat the motor was trimmed in the middle position but when I went WOT with it during the "test drive" before I bought it - it almost jumped out of the water, nose went flying up in the air, and the prop was running out of water to push and was sucking down some air. <br /><br />How do you know where to trim the motor at? What is the ideal riding position of the hull, do you want the bow to be riding on water, or out of the water??? <br /><br /><br />BUT - you think that the motor looks to be in the correct position? I don't see why it isn't in the proper place, the previous owner spent $$$ on the boat and had it regularly serviced.

 

[gss036]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

I think the best way to tell if you are trimmed proper is to look at the motor when you are running WOT or close to it, the top of the engine should be level with or on the same plane as the water, not the boat. Then you are trimmed proper. If you push it a little bit more, you may gain another mph or 2. You should also like the sound of the engine, like having that sweet spot.<br />You are getting a rooster tail from something dragging in the water. I have run a fin om my 200 Merc since new and have never had a problem. It just gives you more lift to get up on plane and maybe helps w/porposing(?spelling).

 

[umblecumbuz]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

How do you know where to trim the motor at? What is the ideal riding position of the hull, do you want the bow to be riding on water, or out of the water???

You've nailed the fundamental here, Butteco. Correct trimming has more to do with boat riding characteristics than with theoretical positioning of the motor. If you position your motor according to 'the book', and you end up always riding bow high, then for your boat the theoretical trimming might not be the best.<br /><br />Trial and error will help. Without hydraulic trimming, which can be fine-tuned while on the move, you'll need to experiment with trim pin positions until you get your boat riding as level as possible at varying speeds. Test out the handling at each pin position until you're happy with it.<br /><br />Or fit a pair of trim tabs and cure the whole problem!

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

"I think the best way to tell if you are trimmed proper is to look at the motor when you are running WOT or close to it, the top of the engine should be level with or on the same plane as the water, not the boat. "<br /><br />Sorry, but this is a little confusing; do you mean the "top of the engine" as in the anti Ventilation plate, or do you mean "top of the engine" as in the top of the cowling/engine cover?<br /><br />ALSO - when properly trimmed, will the bow be riding in the water? Or will it be at a slight to moderate angle pointing towards the sky? Seems to me that you would want the bow riding firm in the water because that is where the boat hulls runners/ribs are to catch/cut through the water?(not sure proper terms, but the things on the bottom of the hull to cut through the water and help the boat from sliding) .

 

[dajohnson53]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

He's talking about the top of the engine cowling. This is just a way determining where the thrust of the prop is. Since the prop thrust and the top of the cowling are parallel, if the top of the cowling is paralell with the water, the thrust of the prop is directly on plane with the water, it's most efficient position. This is not likely to be exactly on the same plane as the boat itself because...<br /><br />At WOT, the boat "generally speaking" will be only resting on the rear portion of the hull, not plowing through the water. In my experience, looking at it from the shore or another boat, it will be obviously slightly bow up, but might not feel significant to you in the boat - yes you will probably perceive that it's slightly inclined, but it won't be so much that you have to make an effort to see over the bow.<br /><br />Like the guy said, you just need to experiment. I'd try the pin in all positions, but would guess you'll find one of the middle 3 positions to be the one with best all around performance. YOu'll likely find that a certain position is better for "hole shot" and skiing (acceleration from dead still to plane), another is best for WOT. Another might be best for mellow on-plane cruising through chop (where you might want it to plow a little rather than bounce on top of the waves). But one of the three middle positions is likely to be best all around.<br /><br />Power trim allows you to infinitely adjust this whenever you need it. A very nice feature and one you should consider investing in, but not absolutely essential in most cases.<br /><br />Like I mentioned before, I'd try this without the hydrofoil fin just to see how it works nekkid. Then you can decide if you need it. Who knows, maybe the previous owner had issues that required it that you don't have.

 

[butteco]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

Okay so I did a TON of research last night and found most of my information on "trim tab" websites etc... <br /><br />I understand that the prop thrust needs to be in plane with the surface of water to be most efficient so I will adjust the trim to do so.<br /><br />BUT... <br /><br />My second question is what is the optimum position for the hull? It seems to me that you would want the hull to be flat on plane with the water too??? <br /><br />I assume that since the front of my boat is a "Shallow V" with the "ribs" running from front to back, that it makes more sense for that "V" to be in the water to cut through and help turn etc... Is this wrong?

 

[gss036]

Re: HELP!!! Motor Spits ROOSTER TAIL @ WOT ???

D, good answer. Butteco, normally at planing sppeds, you will be running on the rear 1/3 of the boat. You may have to adjust the bow weight a little when you are running alone. I take you are running about a 16ft boat, the weight distrubition is critical to how it rides. Play with things until you get comfortable. Then you can be like most of us and play (experment) with it to have something to do.