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Old 30 May 2014, 12:19   #1
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AV Plate >< Water Flow

Been doing some trial experimentation on a 400 Mt Rib rigged with a Tohatsu tiller engine to optimize best transom height for top performance. As you know the issue to have into account when sitting an engine on transom states per owners nanual, word of mouth, rule of thumb, read it at boating forums whatever, that AV Plate must be set level or slight under keel/boat's bottom.

Water trial was performed on a rowing track with these spot on conditions : flat calm, no wind sea conditions, rib perfecly inflated, ballanced & trimmed. I already know the answer from trial, just wanted to know your opinion about : At which height number do you think water flow is passing through lower leg at plane 1-2-3 ? Which number would be ideal for your setting and why ? Just short answer as we're not discovering gun powder again...

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Old 30 May 2014, 19:39   #2
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Been doing some trial experimentation on a 400 Mt Rib rigged with a Tohatsu tiller engine to optimize best transom height for top performance. As you know the issue to have into account when sitting an engine on transom states per owners nanual, word of mouth, rule of thumb, read it at boating forums whatever, that AV Plate must be set level or slight under keel/boat's bottom.

Water trial was performed on a rowing track with these spot on conditions : flat calm, no wind sea conditions, rib perfecly inflated, ballanced & trimmed. I already know the answer from trial, just wanted to know your opinion about : At which height number do you think water flow is passing through lower leg at plane 1-2-3 ? Which number would be ideal for your setting and why ? Just short answer as we're not discovering gun powder again...

Happy Boating
Two would be my first answer but ill go with one
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Old 31 May 2014, 09:14   #3
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Dave,

Number 2 is right in the middle, valid answer. Why would you pick 1 as to understand your concept, perception about fixed objects hitting water flow at speed.

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Old 31 May 2014, 15:33   #4
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Dave,

Number 2 is right in the middle, valid answer. Why would you pick 1 as to understand your concept, perception about fixed objects hitting water flow at speed.

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sorry I ment to pick 3 instead of 1
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Old 31 May 2014, 19:23   #5
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I'd guess 2, as the water the hull displaces is returning to it's normal level, so should be a little higher than the bottom of the hull. Kind of depends on speed as well, as slower means more time for the water to rise as it comes out from under the hull before it hits the motor.

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Old 01 June 2014, 14:35   #6
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Jyasaki,

Let's say constant speed at 3/4 to full wot throttle, as to maintain a constant & state of the art perfect plane on those previosly mentioned ideal boat & water conditions.

Dave, 3 is what you assumed was my trial test result or it's your ideal personal choice you would pick for your own boat/engine combo ?

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Old 01 June 2014, 16:24   #7
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Jyasaki,

Let's say constant speed at 3/4 to full wot throttle, as to maintain a constant & state of the art perfect plane on those previosly mentioned ideal boat & water conditions.

Dave, 3 is what you assumed was my trial test result or it's your ideal personal choice you would pick for your own boat/engine combo ?

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I make that the chioce on an article I read that the when an engine is set up correctly you should be able to see the cave plate in most water states.
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Old 01 June 2014, 20:49   #8
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So... Did I miss the question? I assumed Loco was asking where the water would cross the leg in his picture; perhaps he's asking where it would cross in an ideal setup.

If the latter I choose at the AV plate. At speed, it's not needed, as hydraulic pressure from the water going past will prevent air getting sucked into the prop.

If the former, I say at the AV plate or slightly above (assuming the AV plate is even with the keel of the boat.) Doesn't say anything about correct setup, just what I think would happen in this setup.

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Old 02 June 2014, 13:15   #9
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There were 2 questions asked :

1-According to my posted pic, where do you think water flow at speed/plane is passing by 1-2-3 ? 2-Your personal 1-2-3 choice for your boat/engine combo ?

So Dave and Jyasaki chose 3, right through AV plate and with exposed AV plate when on plane, assume same on their personal choice, right ? We can't speak firmly about a "correct setup", as there are some tech parameters that must be fullfilled in order to achieve a correct set up, only done under trial and error which is not mentioned on Owners Manuals.

Find that 100% of posters goes from what owners manuals states, articles read, word of mouth, that's fully understandable untill a boating maniac, that's me, comes along to distort what's been written or said about AV plate heigt.

This is another prime example of read it on engine owners manual + some badly rigged inconsistencies. Question what odd cruising issues do you see on this picture. Boat parameters : 48 Ft long, 50 passenger off shore transport, 2-300 HP Yam engines with high thrust SS props.

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Old 02 June 2014, 16:21   #10
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We can't speak firmly about a "correct setup", as there are some tech parameters that must be fullfilled in order to achieve a correct set up, only done under trial and error which is not mentioned on Owners Manuals.
Agree 100% on this.



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Find that 100% of posters goes from what owners manuals states, articles read, word of mouth, that's fully understandable
Well, where else would they learn it?

I think the biggest shortcoming isn't that the manual says what it does, rather it is that the manual doesn't state that it is a starting point (or a generally acceptable solution for most boats), and that further refinement of the setup will likely yield better results.

In the second set of pics, the boat looks awfully stern heavy when loaded and underway.

jky
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