Cavitation Plate location?

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bscott
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Cavitation Plate location?

Post by bscott » Sat May 09, 2009 6:51 pm

My E-tek 60 was dealer installed last year with the top plate level with the bottom of the boat. The actual cavitation plate is about 2.5" below the top plate. The transom bolts are in the second hole from the top which only gives me 1.5" of travel to the lowest of the 4 holes. If they installed the engine to the wrong plate and I raise the engine, I will be 1" below what I think is the actual cavitation plate.

1) Which is the real cavitation plate?
2) Is 1" below the bottom of the boat too deep?
3) Any danger in drilling a new hole in the transom and is it necessary to install a spacer between the top of the transom and the ID of the bracket?

Thanks,

bscott

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Terry
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Re: Cavitation Plate location?

Post by Terry » Mon May 11, 2009 1:47 pm

My understanding is that the anti-cavitation plate is that one that the propellar almost hits while spinning, there should be about a 1/4" of clearance or more betwen that and the propellar. My other understanding is that the ant-cavitation plate should be between one to two inches below the hull at the transom at its lowest point. This should be deep enough to prevent the propellar from sucking air from the surface during a turn but I have noiticed that it does not always work. Mine is exactly one inch below the transom, and I have about a half inch of clearance from the propellar to the anti-cavitation plate. Works well enough.

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DaveB
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Re: Cavitation Plate location?

Post by DaveB » Mon May 11, 2009 3:35 pm

My Honda BF 50 Cavatation plate has been lowered and higher from previous owner. It now is 3/4 inches from the bottom of hull at centerline. I have bought 2-4 blade and one 3 blade plus original 3 blade prop. and for my engine I do get 13.8 knots against 2 ft. waves with over 1000 lbs in extra gear on my final 4 blade.
I am telling you this because when I bought the boat 1-1/2 yrs ago I left the motor as is and new from all my other boats the cavitation plate should be 1" to 1-1/2 inch below the center keel, on our long under powered Max. it seems to work well with the cavitation plate at 3/4 inches but in heavier seas or sharp conors, I would go 1" to 1-1/4 " below on the Mac.X.
If you do a lot of 15 knot cruiseing in calm waters than you want to keep close to 1-1/4 inch, the e-Tec has a lot of tork and may cavatate your prop if you go to close to keel getting out of the hole.
Cavitation plate is the plate just above your propella.
I might add when I bought the boat with just avarage gear it toped out at 15.8 knots with 2 persons aboard and 2- 6 gal. fuel tanks with the 3 blade prop. I like the 4 blade and higher pitch to do 6 knots at 2100 rpms.
I usually sail the Gulf and would never go 14 knots with empty ballest and mast raised 95% of the time.
The 5 % would be me trying to outrun a Thunderstorm.
Dave
bscott wrote:My E-tek 60 was dealer installed last year with the top plate level with the bottom of the boat. The actual cavitation plate is about 2.5" below the top plate. The transom bolts are in the second hole from the top which only gives me 1.5" of travel to the lowest of the 4 holes. If they installed the engine to the wrong plate and I raise the engine, I will be 1" below what I think is the actual cavitation plate.

1) Which is the real cavitation plate?
2) Is 1" below the bottom of the boat too deep?
3) Any danger in drilling a new hole in the transom and is it necessary to install a spacer between the top of the transom and the ID of the bracket?

Thanks,

bscott

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bscott
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Re: Cavitation Plate location?

Post by bscott » Tue May 12, 2009 5:57 pm

We are lifting the engine 1.5" leaving the plate 1" below the bottom. I'm still 3 weeks away from launch so I won't know how much of a speed difference the change will be but I'll report the results asap. Thanks

bscott

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Highlander
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Re: Cavitation Plate location?

Post by Highlander » Tue May 12, 2009 8:39 pm

Here's my 75hp Merc install me & Beene have our's at about 1" below the transom which is about equal with the bottom of the hull @ thw dagger board !

http://i235.photobucket.com/albums/ee20 ... 010072.jpg

J

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Night Sailor
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Re: Cavitation Plate location?

Post by Night Sailor » Tue May 12, 2009 11:05 pm

According to several marine authorities, what's popularly called the cavitation plate, or anti cavitation plate is the one immediately above the prop. As stated, it's important to prevent the prop sucking air from the surface, especially during sharp turns or turns at high speed.

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Gazmn
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Re: Cavitation Plate location?

Post by Gazmn » Sun May 17, 2009 9:08 am

Note your speed and proppage [?] and if you'd like, take the boat out and go down one hole at a time and note differences.

I believe I have a similar issue with this from my original E-tec install. I've addressed this by adding an adjustable Jack plate like this one.

I didn't get this one. I bought a 10" one from Ebay from a company called Vance for about $300. Haven't tried it on the water yet; I'm in the middle of this year's major mods - this one included.
My transom holes were drilled in the uppermost and lowest holes for my motor mount and didn't have any alternative other than drilling out new holes - which I'm thoroughly against :P

The Jack plate allows 4 inches of travel, and I can change while in the water, so I'm hoping to dial in the shweet spot 8)

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bscott
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Re: Cavitation Plate location?

Post by bscott » Sun May 17, 2009 5:18 pm

Thanks guys.

Gazmn, I believe someone on this 4M has a Jack Plate installed and I thought it was Highlander. In any case my web research found that for every additional 4" the engine is mounted aft of the stern you should raise the engine mount 1" higher. The Jack plate guys report that a low mounted engine gives a better hole shot and a higher mount increases top end. Give us your report on your on the water installation--specifically if it changes your fore/aft balance. Good luck with the install 8)

bscott
Last edited by bscott on Sat May 23, 2009 7:14 pm, edited 1 time in total.

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Highlander
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Re: Cavitation Plate location?

Post by Highlander » Mon May 18, 2009 8:23 am


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bscott
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Re: Cavitation Plate location?

Post by bscott » Mon May 18, 2009 9:20 am

Thanks for the pics. How did it work out for you? Once you found the best location did you adjust it for various sea states? Are you going to install one on your :macm: ? I'm trying to decide if I need to have one once I find the "sweet spot" (thx Gazmn) as my aim is to get my E-tek to turn at least 6,000 rpm with the 9 pitch.

bscott

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Highlander
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Re: Cavitation Plate location?

Post by Highlander » Mon May 18, 2009 9:58 am

bscott

It worked great saves you from having to upgrade to a bigger eng. & once I found the sweet spot I left it their

No not at the moment I do not think I need one ! I have too many other Mods on the go right now :( , my :macm: planes out nicely with the 75HP Merc F/S with just the wedge kit on it

J

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Gazmn
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Re: Cavitation Plate location?

Post by Gazmn » Mon May 18, 2009 2:08 pm

Hey bscott,

What's your WOT range? Mine is 4500 - 5500; is it different on the 60's?

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bscott
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Re: Cavitation Plate location?

Post by bscott » Mon May 18, 2009 3:31 pm

Gazmn--E=tek 60 is 5,500-6,000 BTW my family had a summer place in Mastic Beach and Stony Brook which were great sailing venues--I left there in 1972 for a job in Denver. My dad circumvented Long Island before my arrival and I have always wanted to do the same but I absolutely dread the idea of trailering my :macx: 4.000 miles. :(

Highlander--did the set-back lower the bow and flatten the wake?

bscott
Last edited by bscott on Thu Jun 25, 2009 9:44 pm, edited 1 time in total.

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bscott
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Re: Cavitation Plate location?

Post by bscott » Thu Jun 25, 2009 9:43 pm

With the cavitation plate approx. 1" below the transom the E-tec now turns 5,600 rpm. I also sanded my Micron bottom paint in areas that were rough to the touch and touched up bare spots with new paint.

bscott

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