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Author Topic: Determine Center of Mass  (Read 106 times)

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Offline Californiamokai

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Determine Center of Mass
« on: January 11, 2020, 11:43:22 AM »
Over the years a lot of discussion around the difficulty of our Mokai’s not reaching plane easily, regardless of model type or year of production, and it’s consequential impact to speed.  Placement of weight along the length of the Mokai enters into that equation and, secondly all our boats are uniquely different as to what we carry and their respective placement i.e. reverse unit fixed to pump, gas tank, batteries, anchors, misc. gear, etc.  And lastly, our individual body weights.

So, how do we then determine where the center of mass is along that boat length (assuming here all lie along the center line bow to stern) with all the aforementioned variables?

What are your thoughts on this approach.  Place the Mokai on round tube (with seat removed) and incrementally move that underneath support until it balances out even (think teeter totter).  Have we then determined and ‘isolated’ the center of mass for our individual (excluding body weight) Mokai’s?   

Next, replace your seat and climb in with a friend assisting from the outside to stabilize. Incrementally, move your seat location until, once again, all balances out as you previously had done.  Is this then true center of mass for our individual Mokai’s and our individual body weights?

Your thoughts on this appreciated or am I racing down another ‘rabbit hole.’  Tight lines, John
« Last Edit: January 11, 2020, 11:46:12 AM by Californiamokai »

Offline Hillbilly

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Re: Determine Center of Mass
« Reply #1 on: January 11, 2020, 12:19:04 PM »
Something to consider:  Although the center of mass can be determined,  the functional center of mass of the Mokai is constantly changing with impeller speed.  As impeller speed increases, so does downward suction and "weight" of the stern.  It's a tail heavy boat for sure, as Tom's moving the seat forward and others placing the fuel tank forward have shown.  Over time, I've developed a sense for the balance for the throttle position where I want to plane.  For me that's about 2/3 to 3/4 throttle.  Side to side balance also affects how the boat goes through the water.   
Like you, John, I'm interested in what others have to add.  Thanks for bringing it up

Offline CC-CODER

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Re: Determine Center of Mass
« Reply #2 on: January 11, 2020, 02:19:53 PM »
Interesting question.
To add to my personal equation...3 gallons of fuel is around 18 lbs. that varies depending on length of trip. I personally gained 12 lbs from start of last year to present. Also, my gear for camping and recording videos constantly varies as much as 30 lbs. Add in my 15 lb anchor and it would be very difficult to gauge where my center of mass would be. Depending on where I fish, the grate gets partially clogged which prevents me from reaching my top speed, which would change the center of mass too? Lots of variables as you mentioned. In other words, I don't know. (Lol)
« Last Edit: January 11, 2020, 02:24:20 PM by CC-CODER »
🤦🏼‍♂️ Chuck 🤷🏻‍♂️

Offline Californiamokai

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Re: Determine Center of Mass
« Reply #3 on: January 14, 2020, 11:38:07 AM »
OK, with your initial feedback it appears to be too many variable going on at any one point of time to get a true read on this question.

So... let me address the same issue from a totally different approach.  Where then is your typical “sweet spot” while attempting to plane where you are ideally cutting through from undisturbed to now breaking water as you look out over your Mokai to either side?  Of course, if your center of mass (overall unique weights and their respective placements along the length of the your individual Mokai) is too extreme fore or aft, you will never truly reach plane.  On the other hand, when in ideal balance it easily reaches plane and that would be your that aforementioned “sweet spot.”  Your feedback on that observation, once again, appreciated. Tighter lines, John

Offline CC-CODER

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Re: Determine Center of Mass
« Reply #4 on: January 14, 2020, 12:57:27 PM »
I'm probably in the same range as Hillbilly. When going from complete stop to plane, I'd guess that it takes about 50 yards to achieve. Once on plane, I usually lower the throttle to 3/4 max. Sometimes, I can feel the boat level off and the engine quiet a little at full throttle. I might have some film of my wife going from a stop to full plane. If not, I'll get some next season. Being that she is 60 lbs lighter, it probably takes her 25 yards or less to achieve full plane. She's always way out ahead of me, on land and water. Lol
🤦🏼‍♂️ Chuck 🤷🏻‍♂️