$txt['youtube'] = 'YouTube'; $txt['youtube_invalid'] = '#Invalid YouTube Link#'; R&D on Mokai reverse

Author Topic: R&D on Mokai reverse  (Read 2209 times)

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Offline bizler

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R&D on Mokai reverse
« on: March 29, 2014, 06:22:01 PM »
    Here is a video of my attempt to add a rudder, (or set of fins), to my Mokai reverse mechanism.  My objective is to improve the straight-line backing qualities.  While my reverse does function for short distances, it does not lend itself to continuous backing.  Here is the mechanical demonstration.  <a href="http://www.youtube.com/watch?v=To6oTABER0o" target="_blank">http://www.youtube.com/watch?v=To6oTABER0o</a>


    Here is the test on the water I did today.  The rudders seem to help, but they do not achieve the my objective 100%.  I am open to new ideas if you have them... 

<a href="http://www.youtube.com/watch?v=3AmaZQuOXtU" target="_blank">http://www.youtube.com/watch?v=3AmaZQuOXtU</a>

Offline Painlesstom

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Re: R&D on Mokai reverse
« Reply #1 on: March 29, 2014, 08:42:21 PM »
Great job, Bill. I think that performs perfectly for the extent that reverse would be needed on one of these. I would say that any improvement would come from the bucket making a better seal with the nozzle. My JetJon's steering nozzle has a square shape around the perimeter of it's exit, so it rides in the reverse bucket with a tight clearance which helps reduce any loss from leaking past. If you're exit nozzle is PVC, you could possibly get some 1/4 ABS cut into a square to fit the bucket with a hole to fit around the nozzle. PVC cement should bond the two pieces together. Hope that made sense. If not, let me know and I'll take some pics.
Tom

  >:D    

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Offline bizler

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Re: R&D on Mokai reverse
« Reply #2 on: March 29, 2014, 10:13:47 PM »
I understand what you are saying.  The gap between the output and the cup is actually quite small and the leakage is not that significant.  The notch in the slide mechanism allows the cup to move slightly which necessarily creates a small gap when it locks up.  Operation at the lowest clutch engagement speed seems to work best.  More throttle doesn't improve the performance.

I am thinking perhaps i need to somehow narrow, or concentrate, the exit stream so that it delivers a more direct flow rather than a broad one.

I would definitely like to see a photo or two of the reverse on your mini Mokai.

I would be interested to know if it has the same phenomina when backing up for a long distance.  Or in other words, can it back up in a straight line indefinetly?

Offline Painlesstom

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Re: R&D on Mokai reverse
« Reply #3 on: March 29, 2014, 10:49:49 PM »
I'm sure the issue with obtaining any thrust past idle, is one of cavitation as the jet stream hits the intake grate area. Many jet boats have a split type reverse bucket that diverts the flow in a V pattern to help prevent washout at the intake grate. "Mini-MO" has very little control in reverse,  it will go back fairly straight but it does end up wanting to turn. I think it's the same phenomena you are experiencing, as it is set up in a very much identical way.

Go to 4:35 to see it in reverse.

<a href="http://www.youtube.com/watch?v=5DLiMEH6rCk" target="_blank">http://www.youtube.com/watch?v=5DLiMEH6rCk</a>
Tom

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Offline bizler

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Re: R&D on Mokai reverse
« Reply #4 on: March 29, 2014, 11:14:55 PM »
I agree with your analysis, Tom.  That is wxactly what it feels like to me.  I have seen those on g inboard jet boats. Perhaps instead of the rudder or narrowing the flow I should try creating a "v" flow.  I'll see if I can come up with a unit that does that.  Thanks

Offline Hillbilly

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Re: R&D on Mokai reverse
« Reply #5 on: March 30, 2014, 10:58:54 AM »
Beautiful work, Bill.  I enjoy every one of your posts.  Like you and Tom, I'm thinking the split flow to avoid the intake is the ticket.