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Author Topic:   A-V Plate Pictures
jimh posted 02-02-2009 10:30 PM ET (US)   Profile for jimh   Send Email to jimh  
Is this anti-ventilation plate running too high, too low, or just right?

jimh posted 02-02-2009 10:33 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is where the engine sits in static trim:

jimh posted 02-02-2009 10:40 PM ET (US)     Profile for jimh  Send Email to jimh     
I mentioned this in another discussion about engine mounting height, trim, and observation of the A-V plate, but I'll throw it in here again:

To experiment with engine trim, have someone else operate the boat from the helm station. Get the boat on plane and at the desired cruising speed. Go to the stern of the boat, and position yourself so you can observe the engine gear case and anti-ventilation plate. Using the engine trim switches on the engine cowling, trim the engine up or down while observing the gear case and anti-ventilation plate. When the engine trim has been adjusted to the desired setting, return to the helm and note the reading on the TRIM gauge.

By using this procedure I found that I needed to trim out my motor further at my usual on-plane cruising speed if I wished to bring the anti-ventilation plate to align with the surface of the water. In any case, it was quite interesting to experiment with trim while being able to see the anti-ventilation plate's position.

Of course, be certain to coordinate with the helmsman so there is no sudden change in speed which could throw you off the boat from your position at the stern.

There is an important refinement to the technique--take some pictures of what you see for reference.

After looking at these pictures, I am beginning to think that raising my engine one-hole might be part of an experiment for next season.

Tom W Clark posted 02-02-2009 11:03 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

It is hard to tell how the motor is trimmed in the first photo, but it appears the arrow you have added does not point to the AV plate at all but rather a point about an inch above the AV plate.

The AV plate appears to be completely buried in the water.

Based on just that photo, I would have to recommend the motor be raised.

number9 posted 02-03-2009 01:33 AM ET (US)     Profile for number9  Send Email to number9     
Looks to me that the motor is trimmed up enough to expose the aft end of AV plate but rest is still buried? Ideal mounting height will allow whole length plate to skim just above the surface when properly trimmed.
glen e posted 02-03-2009 06:39 AM ET (US)     Profile for glen e  Send Email to glen e     
Here's an E-TEC that is "buried":

Here's the same engine mounted at the proper height:

a Verado at proper height:

It is important to make this observation when the engine is trimmed normally during cruise.

jimh posted 02-03-2009 09:07 AM ET (US)     Profile for jimh  Send Email to jimh     
It is harder to see the position of the A-V plate on motors with white paint than on motors with darker color schemes. On my first picture, the aft several inches of the A-V Plate are above the water. There is some spray obscuring the forward portion of the plate.

Glen--Thanks for those pictures. They show nicely the difference between too low and just right.

Any more A-V Plate pictures out there?

Peter posted 02-03-2009 09:53 AM ET (US)     Profile for Peter  Send Email to Peter     
One observation -- At rest, the water line is relatively low on Jim's motor as compared to what I typically see on my Whalers (water line is typically very close to the transom drains not several inches below). I believe that this low water line is because the original design expectation of the Whaler Drive was to support the weight of twin 400 lb V6 outboards, which would raise the static water line several inches to about where the transom drain is.

So I wonder whether this lack of weight on the transom resulting in a low static water line would have a negative impact on performance if the motor were raised up? In other words, does the motor have to be run deeper than might be the case if the expected weight were on the transom?

Tohsgib posted 02-03-2009 10:34 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Does one really know when their 200+lb passenger goes astern to take the pic? Does that extra weight that far aft throw off the results? I KNOW mine is as high as it can get because if I go 1/2 higher I can hear the exhaust which defeats the purpose of having a 4 stroke. I will one day try and get a pic.
Tom W Clark posted 02-03-2009 11:39 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Now that I am in the office looking viewing with a better monitor, I can see Jim's first photo more clearly and the AV plate that is pointed too. It is not buried.

I still think it would be worth trying a higher mounting height but I we need to remember that there is no "perfect" mounting height in general; it depends a lot on the propeller used.

Some propellers will tolerate much higher mounting heights than others.

No, a 200 pound person is not going to have a significant effect on the level of the water relative to the AV plate on a boat this size. A little skiff might be affected.

Likewise, the amount of weight on the transom and the resulting static waterline is not going to significantly affect where the motor should be mounted vertically.

A boat on plane is going to have the water come out form under the hull in a very consistent pattern. Boat speed itself will have a much greater effect on this the weight distribution within the boat.

newt posted 02-05-2009 01:16 PM ET (US)     Profile for newt  Send Email to newt     
Here's a photo that CBO took of my Revenge. Do you think the engines need to come up?

Photo: OMC gear case with A-V plate shown at speed

Tohsgib posted 02-05-2009 01:21 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
You are pretty good, try it up 2 notches and see.
Tom W Clark posted 02-05-2009 01:38 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

The Mercury 150s on my Revenge 25 Walk Through are one hole up. Your OMCs should be at least this much up if not two.

jimh posted 02-05-2009 03:47 PM ET (US)     Profile for jimh  Send Email to jimh     
Nate--That is a good picture. I will make it an in-line element. Also, nice collection of pine needles in your engine splash well. You must park the boat near pine trees.
Tohsgib posted 02-06-2009 12:16 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Jim--you should be an investigator with fine deductive reasoning skills such as yours.
newt posted 02-06-2009 02:06 PM ET (US)     Profile for newt  Send Email to newt     
Twista, in the picture above, I believe we were trimmed out for a comfortable cruise, but maybe Cascobayoutrage remembers more accurately.

Jim White pine or Red? After I win the lottery on Saturday I plan on ordering a mooring cover.

Casco Bay Outrage posted 02-06-2009 03:26 PM ET (US)     Profile for Casco Bay Outrage  Send Email to Casco Bay Outrage     
Ah, yes, that photo was taken during our Cape Ann cruise this past fall. I do recall trim was set. Speed was not slow, mid ~30's mph. According to the time stamp, It was at the end of the cruise, following our exit from the river, heading north to the Merrimack.

(Sarcastic comment at Nate's expense deleted by author) {wink}


glen e posted 02-06-2009 04:09 PM ET (US)     Profile for glen e  Send Email to glen e     
Trim the boat as you normally would at cruise, then take a look, simple as that.
JMARTIN posted 02-06-2009 09:36 PM ET (US)     Profile for JMARTIN  Send Email to JMARTIN     

How's that one?


jimh posted 02-06-2009 11:06 PM ET (US)     Profile for jimh  Send Email to jimh     
John--In your picture of your A-V Plate, it looks like the aft half of the A-V plate is right at the water line. That is about where it should be, although perhaps some will say try one more hole higher.

These motors with white paint are harder to see. Maybe we need to temporarily apply some black duct tape to the top of the A-V plate to make it easier to see.

jimh posted 02-06-2009 11:33 PM ET (US)     Profile for jimh  Send Email to jimh     
John--Congratulations on the picture. From the camera position, which I infer from the appearance of the forward portion of the spray deflector in the frame, I see you were leaning out over the transom a bit. I will have to try pushing the camera out farther next time I take a picture of the A-V plate so I can see more of the leading edge of the gear case.

Glen's pictures are also good in that regard.

JMARTIN posted 02-07-2009 02:14 PM ET (US)     Profile for JMARTIN  Send Email to JMARTIN     
I only have one hole left to go if I raised it. My picture was with my old prop. I wonder if it looks different now with my new prop? I also have to make some runs in snotty conditions and I do not like the prop to break loose, ventilate, lose traction, whatever it is called.

You have to trust your helmsman to lean out over the stern.


glen e posted 02-07-2009 02:48 PM ET (US)     Profile for glen e  Send Email to glen e     
Rmember a plate that is DRY at cruise is mounted too high. It should be skimming the surface, getting wet and splashed. Here is a good shot of the how the Merc racing team mounts:

jimh posted 02-07-2009 02:58 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a picture I took several years ago. It shows my twin Yamaha 70-HP motors running on 10-inch setback brackets off the stern of my REVENGE 20. I think the location of the A-V plate is good in this view. I might have cranked the jack plate setting up a bit later on:

kwik_wurk posted 02-07-2009 05:22 PM ET (US)     Profile for kwik_wurk  Send Email to kwik_wurk     
I think another good example would also be a doel-fin on a small tender. (While the hp is much different that x3 350.)

Having a doel-fin too deep easily slows down small hp craft, and is noticeable immediately. On larger boats with high hp, the effect is not noticed as easily because the changes in speed are fractional knots. (Beyond most home grown testing.)

The physics of extending of the bottom edge of the boat and extending the high pressure (dense laminar) water flow is luckily easy to check visually (as pictured).

jimh posted 02-17-2009 10:25 PM ET (US)     Profile for jimh  Send Email to jimh     
A picture of a motor with a Doel-Fin would be interesting. Is anyone able to oblige?
K Albus posted 02-18-2009 12:38 PM ET (US)     Profile for K Albus  Send Email to K Albus     
This is a picture of my motor with a Stingray hydrofoil:

Not a Doel Fin, but similar, and the outline of the hydrofoil can clearly be seen.

This picture was included in this thread about raising the motor on my 2002 Dauntless 180:

Upon further reflection, I may need to raise my motor another hole.

twista posted 02-18-2009 03:15 PM ET (US)     Profile for twista  Send Email to twista     
[I] was under the impression that if the boat is wearing a [Doel-Fin], or [T]urbolift as [I] have, or any of the other brands, that [the anti-ventilation plate] should be more apparent riding out of the water and more visible once on plane. [T]he hydrofoil above is barely able to be seen. [I]s that correct placement?

[I]f the A-V plate is supposed to be at or slightly above water line, then it makes sense that the addition of the plate would be at that level, also, and be very noticeable, almost OUT of the water.

R T M posted 02-19-2009 07:13 AM ET (US)     Profile for R T M    
I have an easily adjustable 4-inch setback bracket on my 13-footer, powered by a 25-HP Mercury-Tohatsu EFI four-cycle. I have tested this motor with two persons abroad, running the cavitation plate up to 1-inch clear of the water to 1-inch submerged. The difference in top speed is negligible, although I experience cavitation on hard acceleration with the high plate setting and higher RPM at wide open throttle, but not over acceleration. At the lowest setting I lose about 1-MPH. I think with the hook in the bottom of the 13 footer performance is retarded, anyway, so I run the cavitation plate in the tried-and-true position of on the surface. I realize that if I tested different props at the different engine heights, I might have gotten better results with the higher positions, but the small difference in speed is not worth the effort or expense, in a boat not designed for performance anyway.

rich (binkie)

skred posted 02-19-2009 12:45 PM ET (US)     Profile for skred  Send Email to skred     
I would think that the more desirable effect of A-V plate height adjustment would be a faster on-plane time, and a lower planing speed, rather than higher top speed. At least, that's what I'd look for.
jimh posted 02-19-2009 11:06 PM ET (US)     Profile for jimh  Send Email to jimh     
Kevin--I have been studying your photograph of the engine and anti-ventilation plate. I can't decide if I am seeing a shadow of the engine on the water surface, or if I am seeing the A-V plate and foil extension just below the water surface.

I'd say that the A-V plate and extension are not clearly visible above the water or even just at the water. I concur with your notion to try raising the engine slightly.

K Albus posted 02-20-2009 08:48 AM ET (US)     Profile for K Albus  Send Email to K Albus     
The dark area in the photo, which was taken on the port side of the motor, is definitely the outline of the hydrofoil. The sun was on the port side when the picture was taken, and there was nothing that could have cast a shadow in that area.

The picture from the starboard side (See: Motor%20Height%20and%20Prop%20Selection/UpTwoHolesStarboardSide.jpg ), taken a few seconds earlier, shows the shadow of the motor. In the starboard picture, the starboard edge of the hydrofoil is obscured by the wake coming off the depth finder transducer.

jimh posted 12-31-2009 08:58 AM ET (US)     Profile for jimh  Send Email to jimh     
I came across this nice view of the anti-ventilation plate position relative to the water flow as seen from far above a 34-foot REGULATOR with an Armstrong set back bracket mounting a pair of Yamaha 350-HP engines.

Photo: Overhead view of boat showing outboard engine A-V plate orientation.

As you can see, the A-V plates are running well clear of the water flow.

The angle of view may have something to do with how these appear. Most of us cannot hire a helicopter to take photographs of our boat to see how the A-V plate looks from this angle. An alternative might be to find a bridge or some type of overpass from which you could take a picture of a boat passing below while on plane. Unfortunately bridge passes are usually in NO-WAKE zones.

aussiejake posted 01-14-2010 09:10 PM ET (US)     Profile for aussiejake  Send Email to aussiejake     
Mercury 2006 EFI 150hp, MIRAGEplus propeller mounted on third set of holes. [The engine speed increased] 200-RPM at WOT once raised. The information I have gotten from this site has been fantastic. Keep it up.

[Dead image link deleted]

jimh posted 01-15-2010 08:26 AM ET (US)     Profile for jimh  Send Email to jimh     
That looks perfect!
glen e posted 01-15-2010 09:40 PM ET (US)     Profile for glen e  Send Email to glen e     
This stuff can drive you nuts....suffice to say if you can see the plate in full view, it's pretty much good enough. I agree with many above that said it's not vital it be perfect. It's just the ones that are completely underwater with no view possible that can come up.
R T M posted 01-17-2010 07:44 AM ET (US)     Profile for R T M    
[Repeated his narrative of his experiments with engine height, already mentioned above. Your narratives are interesting, but since they are not pictures of your anti-ventilation plate, they are not appropriate for this discussion. Here we are seeking pictures of the position of the anti-ventilation plate on the outboard when the boat is running on plane. Feel free to contribute any pictures, or to comment about the position of the anti-ventilation plate relative to the water flow as shown in any of the pictures seen or linked above.--jimh]
Jeff posted 01-17-2010 09:39 PM ET (US)     Profile for Jeff  Send Email to Jeff     
After installing a new set of 4 blade 14.25 x 17 Turbo propellers my father raised the twin Mercury XR6 150's on the 1989 Boston Whaler 22 Guardian. The boat runs up to 48mph (5300 RPM) in a hurry then begins to get squirrelly and actually porpoise above at that point unless the trim tabs are nearly in the full down position. Here are the only images I got from this year. With the full width splash gate it tough the get way back there for a photo and honestly I worry about sticking my nice DSLR out there.



This is the only view I could find of the set up before we raised the motors. Fall%20Fishing/?action=view¤t=DSCN1615.flv

Jeff posted 10-03-2011 11:33 AM ET (US)     Profile for Jeff  Send Email to Jeff     
Here is video I shot this past Saturday of our Twin Yamaha 150's at wide open throttle on a 1993 23 Boston Whaler Walkaround Whaler Drive.
boatdryver posted 10-03-2011 04:13 PM ET (US)     Profile for boatdryver  Send Email to boatdryver     
Those A-V plates look good in the video, Jeff. ASIDE: Was there any ventilation on sharp turns with those twins?
Jeff posted 10-03-2011 05:31 PM ET (US)     Profile for Jeff  Send Email to Jeff     
ASIDE: [Ventilation in turns] is not too bad. Though if you REALLY have to yank a tight 90-degree plus turn you will experience ventilation and slide off plane.(Here is a video of later that same day running in very tight conditions with a lot of turns.)
Binkster posted 10-03-2011 06:41 PM ET (US)     Profile for Binkster  Send Email to Binkster     
[Changed TOPIC to begin discussing boat racing techniques. Our topic here is to identify the position of the A-V plate from various photographs. If you have a photograph of your engine underway showing the position of the A-V plate relative to the water flow, please give us a look at it. Thanks--jimh]
jimh posted 10-05-2011 10:42 PM ET (US)     Profile for jimh  Send Email to jimh     
Jeff--The position of A-V plates looks very good in your video. If we had an overhead view available as used in the photographs above of the triple-VERADO and twin-Yamaha boats, I think your engines would look just like those--nice mostly dry A-V plates. You have the engine height dialed in.
DeeVee posted 10-09-2011 12:13 PM ET (US)     Profile for DeeVee  Send Email to DeeVee     
While going through some pictures, I found this picture I took right after I rigged my new to me 3.3 liter Etec 200 on my 1989 Outrage 22. IMG_0234.jpg

While I was looking at the pictures I found the video I made the same day. ?action=view¤t=IMG_0237.mp4

Doug Vazquez

jimh posted 10-09-2011 02:17 PM ET (US)     Profile for jimh  Send Email to jimh     
Doug--Thanks for the image and moving pictures of the engine and its A-V plate. Your images reminded me that I want to try using some black tape on the top of the A-V plate on my white engine to make it more visible in the spray. It is hard to judge the position of a white engine in all the white spray. The engines with darker paint show up better.
DeeVee posted 10-09-2011 11:31 PM ET (US)     Profile for DeeVee  Send Email to DeeVee     
The black tape would definately help. I will try to keep that in mind the next time I take the boat out. I think I will take Tom's advice and jack it up another inch before I go out again.


aussiejake posted 10-22-2011 03:29 AM ET (US)     Profile for aussiejake  Send Email to aussiejake     
I thought I would post a short video of my Mercury EFI 150-HP mounted three-holes-up. I am thinking of going to the last one. It is running a 17-pitch MIRAGEplus and can turn 5,790-RPM.
jimh posted 10-22-2011 10:37 AM ET (US)     Profile for jimh  Send Email to jimh     
[Fixed some problems with the links. Thank you to those that helped.]
jimh posted 10-22-2011 10:39 AM ET (US)     Profile for jimh  Send Email to jimh     
Aussiejake--That is a beautiful video showing the A-V plate position on your outboard engine when on plane. The top of the A-V plate is clearly out of the water and looks almost dry! I think you are at the perfect height.

How is the water pressure with this mounting? OK still?

DeeVee posted 10-22-2011 10:40 AM ET (US)     Profile for DeeVee  Send Email to DeeVee     
The black AV plate makes it much easier to see through the water spray. It looks like you are set up nicely.

Doug Vazquez

aussiejake posted 10-22-2011 04:17 PM ET (US)     Profile for aussiejake  Send Email to aussiejake     
There is no problems with water pressure at any speed and no loss of propeller grip in any water conditions.
The MiragePlus seems to be a very good propeller.

Thank you for fixing the link.

jimh posted 09-22-2012 12:18 PM ET (US)     Profile for jimh  Send Email to jimh     
Below is an image of my E-TEC 225-HP V6 25-inch shaft engine running on the Whaler Drive of my REVENGE 22 W-T with the engine mounted in the one-hole-up position.

Photo: E-TEC engine on Whaler Drive at one-hole-up mounting height
E-TEC on Whaler Drive one-hole up

The A-V plate can be seen just below the water line and covered with spray.

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