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Old 04-23-2006, 12:17 PM
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Default Anti-cavitation plate


Occasionally I get cavitations and prop blow out with my 2002, 125 Mercury. I’ll be cruising along and the motor just revs like crazy until I back off

I was thinking of getting an Anti-cavitation plate. Good idea? Will it void a warrantee?

I was looking at the SE Sport 300 @ http://sesport.com/5_29.asp

Any others to consider?

Any help would be appreciated.

Thanks

BoatGuy

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Old 04-23-2006, 12:23 PM
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Default Re: Anti-cavitation plate

check out Permatrim on this board.

http://www.thehulltruth.com/forums/f...iew.asp?fid=12
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Old 04-23-2006, 01:10 PM
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Default Re: Anti-cavitation plate

Whoa, before you buy anything, figure out what the problem is. And there is a problem! Having an engine suddenly have no water friction at the prop will cause it to redline immediately, as you already know.

I would take a look at the engine height first, then the prop and continue from there.
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Old 04-23-2006, 01:14 PM
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Default Re: Anti-cavitation plate

There is no such thing as an anti-cavitation plate, only an anti-ventilation plate. Cavitation is when you boil water on the prop and ventilation is when you suck air from the surface through the prop. Cavitation will eventually destroy your prop, ventilatiion will not. Anti-ventilation plate will help reduce your problem. Pro-Line is a very common boat and so is the Mercury motor option. I don't hear of many complaints from Pro-Line owners and it seems unusual that there would be this isolated case. Your motor may be trimmed incorrectly. Next time this happens, try trimming the motor down a little and see if it grabs the water a little better. Mine will do the same thing if I have it trimmed too high.
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Old 04-26-2006, 04:31 AM
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Default Re: Anti-cavitation plate

A few thigns I have heard:

1) The plates are supposed to lift out of the water at top end and it doesn't happen with fins on the plates for some reason, so the upward lift of the stern is always pushing the bow down, so you do lose some top end speed with these.

True?

Gostomskij: thanks for the info. I checked it out. Permatrim is supposed to be a great plate. From what others have said, “When you look at all those "wing" type foils such as that Sport SE (the other one I was looking at) or the Doelfin, Sting Ray, Bob's plate and all the others, you find that they work on the same principle as an aircraft wing. They use lifting forces to achieve some of the increased handling. But that lifting also creates drag which at some point in your RPM range (usually WOT), causes you to lose speed.

The permatrim doesn't employ any lifting foil dynamics. It just increases the size of your factory anti cav plate which allows it to direct the upper thrust of the prop wash back down where it increases thrust and adds planning/control surface. The thrust that is normally lost in prop blow out is reduced and your prop becomes more efficient. The increased length and width adds control and stabilization surface without adding drag.”

True?
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Old 04-26-2006, 07:52 AM
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Default Re: Anti-cavitation plate

Here is what Mercury has to say, in part, about the addition of "fins" to the anti-VENTILATION plate:

"Because it is not possible to know how a given boat will respond to the use of such a product without thorough testing, Mercury cannot recommend that such products be used or not used. Also, use of these products may cause or contribute to the failure of the anti-ventilation plate on the gearcase. Failures caused, or contributed to, by modification are not covered by the limited warranty."

With respect to your problem, if your motor is mounted and trimmed properly it should not normally ventilate, particularly if you are operating on relatively smooth water. If you are trimmed high and are operating in rough water then it is not abnormal for the prop to ventilate from time to time. In these conditions you need to just trim down somewhat.

A properly mounted motor will be positioned such that its anti-VENTILATION plate is even with or above the bottom of the boat. In this configuration the added "fin" will also be at or above the bottom of the boat. Once you trim above the neutral postion the anti-VENTITLATION plate and the added fin will be either skimming the surface of the water or even possibly be out of the water. If they are out of the water they do not contribute to additional drag. Lift and drag when getting on plane maybe but not once the boat is on plane.

I installed a Cobra Edge on my Mercury motor and it works well. It lets me plane at a lower speed, gets the boat on plane faster, and has minimized a ventilation problem I was having with high speed turns with the motor trimmed up. I have not noticed any decrease in top speed but then again I don't run at WOT anyway.

Rather than drilling your anti-VENTILATION plate to install a fin you can use bolts, nuts and washers to clamp it in place instead. This way, if it is not to your satisfaction you can remove it and no one will know the difference.

http://www.cabelas.com/cabelas/en/te...l&N=4887&Nty=1
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Old 04-26-2006, 03:22 PM
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Default Re: Anti-cavitation plate

another thing to consider is a 4 blade prop, if you are currently running a 3 blade.
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Old 04-26-2006, 03:56 PM
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Default Re: Anti-cavitation plate

I used to blow out with stock merc prop until I went to a Merc Rev. 4 I cannot get it to blow out to save my life now. I also picked up about 10% efficiency

See ventilation and cup here:

http://sites.mercurymarine.com/porta..._schema=PORTAL
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Old 04-26-2006, 03:58 PM
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Default Re: Anti-cavitation plate

Sounds like you need to lower the engine 1 hole IMHO.
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Old 04-26-2006, 05:24 PM
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Default Re: Anti-cavitation plate

I had some problems on my boat and concidered a permatrim. In the end I didn't need it. I tried changing the engine hieght and testing different props. My boat performs faultlessly now.

I ended up with a Mercury Revolution 4 prop. They are as good as others have stated on THT.

Good luck,
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Old 04-27-2006, 04:53 AM
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Default Re: Anti-cavitation plate

Quote:
jethro1 - 4/26/2006 8:52 AM

Rather than drilling your anti-VENTILATION plate to install a fin you can use bolts, nuts and washers to clamp it in place instead. This way, if it is not to your satisfaction you can remove it and no one will know the difference.

How would you install the plate with using bolts, nuts and washers to clamp it in place? I am trying to picture that. There must be some serious water pressure on the plate.
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Old 04-27-2006, 06:54 AM
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Default Re: Anti-cavitation plate

just get a new prop..... your problem will be solved.
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Old 04-27-2006, 08:43 AM
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Default Re: Anti-cavitation plate


[/quote]


How would you install the plate with using bolts, nuts and washers to clamp it in place? I am trying to picture that. There must be some serious water pressure on the plate.[/quote]

Send me your email via PM and I will send you a diagram that details this modification.

You are correct about the water pressure probably being significant. However, most of the pressure is upwards. Since the added fin is below the existing anti-ventilation plate the existing plate is reacting the loads of the new plate (same as if the existing plate were drilled). The existing anti-ventilation plate is tapered such that it is wider at the rear than at the front. This taper prevents the new plate from being able to slide rearward should the clamping pressure be insufficient.
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Old 04-27-2006, 09:08 AM
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Default Re: Anti-cavitation plate

I'm not sure the plate will help with your cavitation problem. My usderstanding (I put one on the 17 I had) is that they are used to help planing time, and porpoising.

I put a manual jack plate on the Sailfish 174 to be able to adjust the engine easily, I also added the stingray(one piece) foil. Between the two it greatly improved the quality of ride and handling.
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