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Old 28 March 2016, 19:16   #1
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Aerotec transom splash issue.

Over the years before and after owning an Aerotec I've read lots of posts on splash over the transom. I think its agreed the root cause is the way the water flow from each side of the V-floor meets and bursts to the surface bouncing off the outboard leg and over the transom into the boat.

The degree of splash seems to vary from mildly annoying to a real flood.

Here's one past thread... bombard aerotec transom height

And on post #7 of this thread Chipko shared an image of a splash shield he'd seen... Old used Aerotec impressions.

And Max tried a couple of mods in this thread... Bombard Aerotec ready for the maiden voyage (b@stard son of a Y Class)

Last year by adding transom raiser blocks I eventually managed to get the splash to an acceptable degree while minimising ventilation on turns.... a best compromise. It did seem to completely stop this issue though I'd need to block the transom up to a degree that would need inner/outer outboard pads raising... and to accept some ventilation in tighter turns.

Well this year mine has stopped splashing for a very unexpected reason... an outboard change. When we first used my new Suzuki DF20 EFI over the weekend transom splash was the last thing on my mind but as soon as we'd done enough running in hours to get on the plane I suddenly realised... no splash.

(To be totally factual I did have on one of the transom raisers from last year which I thought was a 20mm but just measured to find it's a 10mm... not enough height to help with the old Mercury)

In the combined image below you can see the much larger anti-ventilation plate on the Suzuki (left) than my old Mariner 15 (right)... and that it starts at the leading edge of the leg compared to the Mercury's starting close to the trailing edge. Perhaps more important is that the upper water deflector plate is also much larger (more so than is clear from the image). In fact the upper plate is getting well on the way to the size of the wooden one Max made that fell off.

I've added a second image taken from the net that shows this better.
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Old 28 March 2016, 19:27   #2
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Thats interesting David. Whats the shaft length? I think the merc is 17" as a ss and not 15"?

I am wondering if a pair of those fins might help with the splash issue for those of us not considering an ob upgrade...
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Old 28 March 2016, 19:39   #3
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I'll measure the exact length tomorrow.

I know Chipko has the same Suzuki/Aerotec combo and I think he reports a little remaining splash but of course part of it can be down to load and trim setting so perhaps by luck all my factors coincide to give a good result.
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Old 29 March 2016, 03:20   #4
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so thinking the cav plate bigger sorts out the splash why not fit a dole fine to engines that suffer splash back which aids lift too?
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Old 29 March 2016, 03:54   #5
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Jeff I'd wondered that... well at least some sort of mini one.

However I can't say how much of the result is the increased anti ventilation plate size and how much that larger than normal water deflector plate above the anti ventilation plate.
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Old 29 March 2016, 04:59   #6
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Quote:
Originally Posted by Fenlander View Post
Jeff I'd wondered that... well at least some sort of mini one.

However I can't say how much of the result is the increased anti ventilation plate size and how much that larger than normal water deflector plate above the anti ventilation plate.
i used one years ago to get a sib on the plane with three divers on board with success but how much top end we lost i dont know but that wasn't the issue so a result for us,
the one we had was a wrap around not two separate fins if they are still available with a slight mod you dont have to drill the cav plate with just a strap across the back if that makes sense.
i dont like drilling the cav plate as it shows you have been needing more out of the engine and its possibly had an hard life plus corrosion issuess.

just a thought if anyone is into making one a piece of HDPE with a slot in it for the cav plate slid on will work, start fairly large and keep cutting it down till you get the right size the slot can be made with a soldering iron to quite a good finish and the sides that are cut smoothed with a wood smoothing plane.
cheers
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Old 29 March 2016, 06:34   #7
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Just measured.

The Aerotec transom is 15.5" and the Suzuki DF20AS is 16.75" or 17" from top of transom to anti-ventilation plate depending how you sight along it.

Wonder what the Mercury (and any other outboard Aerotec owners have) measures?
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Old 29 March 2016, 08:00   #8
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Quote:
Originally Posted by Fenlander View Post
Just measured.

The Aerotec transom is 15.5" and the Suzuki DF20AS is 16.75" or 17" from top of transom to anti-ventilation plate depending how you sight along it.

Wonder what the Mercury (and any other outboard Aerotec owners have) measures?
interestingly i have always set my engines strait on the transom top with the cav plate between one & two inches below the keel this new boat has two 1 inch spacers allowing to raise the cav plate to level with the keel if desired i suppose thats all relative to displacement though.funny in the boat hand book no mention of setting up an engine at all, the transom of the mercury 365 is 16 inches to the keel bottom.
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Old 29 March 2016, 10:41   #9
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Quote:
Originally Posted by jeffstevens763@g View Post
interestingly i have always set my engines strait on the transom top with the cav plate between one & two inches below the keel this new boat has two 1 inch spacers allowing to raise the cav plate to level with the keel if desired i suppose thats all relative to displacement though.funny in the boat hand book no mention of setting up an engine at all, the transom of the mercury 365 is 16 inches to the keel bottom.
The BAT manual I now have gives some mention to it, and says you may need to add a shim to get the correct height, as short shafts come in different lengths, then mentions cavitation if too high and splash if too low... so they know about it!
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Old 29 March 2016, 10:42   #10
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Quote:
Originally Posted by Neil Harvey View Post
I am wondering if a pair of those fins might help with the splash issue for those of us not considering an ob upgrade...
Quote:
Originally Posted by jeffstevens763@g View Post
so thinking the cav plate bigger sorts out the splash why not fit a dole fine to engines that suffer splash back which aids lift too?

Dole fins, that's the word I was looking for... great minds Jeff
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