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Nothcing The Transom At The Botton

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Old 05-04-2009, 05:58 PM
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Default Nothcing The Transom At The Botton

Has Anyone Notched The Transom At The Bottom To Get A More Stable Ride At High Speed On Older Hulls.
I Here Someone Is Doing This In Long Island Ny Any Input
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Old 05-04-2009, 06:09 PM
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Has Anyone Notched The Transom At The Bottom To Get A More Stable Ride At High Speed On Older Hulls.
I Here Someone Is Doing This In Long Island Ny Any Input
Rich Cuny
i dont think it will make the ride more stable if anything it mite make it worse if the boat wasnt desighined for it . i now of one boat builder that put a notch in the transom of a 35 foot boat then after running the boat they stoped doing it , your going to loose the last 1 foot of running surface ,,

i would think you should try extension box's to put the prop's in cleaner water and you mite gain a few mph .

just my thought's

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Old 05-04-2009, 06:10 PM
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Has Anyone Notched The Transom At The Bottom To Get A More Stable Ride At High Speed On Older Hulls.
I Here Someone Is Doing This In Long Island Ny Any Input
Rich Cuny
From a purely engineering point of view, generally speaking, the notch does very little to change stability. What it does do, is change the hydrodynamic flow of the water behind the boat, allowing for higher X-dimensions (prop shaft heights), which in turn reduces drag, and allows use of modern hi-perf props.

This can be especially useful in bravo boats.
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Old 05-04-2009, 06:49 PM
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Raybo In Lindenhurst LI Has Been Doing This On Alot Of Older 21 Superboats For Better Handling At High Speeds And Yes It Does Work
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Old 05-04-2009, 07:06 PM
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Notches do work, of course: Reggie has been using them for years and everyone knows -- seriously -- that his boats win.

There is a significant body of hydrodynamic science that backs up the concept of notches.

As you go faster, the boat needs less bottom to support the weight of the boat. Therefore, the faster you go, the part of the boat in the water gets smaller and smaller, shorter and shorter, closer and closer to the transom.

The center of lift on a planing bottom is very close to the leading edge: the pressure is highest (pushes up with the most force) within an inch or so of where the bottom hits water, and the pressure then decreases rapidly, and then gradually diminishes to almost nothing at the transom. This is true no matter how short the bottom is.

When the boat is going fast enough, the center of gravity is in front of the point where the hull enters the water. Obviously this does not work, so the bow drops. This leads to porpoising: the bow lifts, drops, lifts, ...

By adding a notch, you are moving the transom forward just for this high speed domain. You can get the forward edge of the wetted surface forward of the CG, then you've got a stable boat again.

Everything Reggie does on bottom design is very well rooted in hydrodynamic science.

So the closer you make your boat's bottom mimic a Fountain, the better off you are.
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Old 05-04-2009, 07:25 PM
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Notches do work, of course: Reggie has been using them for years and everyone knows -- seriously -- that his boats win.

There is a significant body of hydrodynamic science that backs up the concept of notches.

As you go faster, the boat needs less bottom to support the weight of the boat. Therefore, the faster you go, the part of the boat in the water gets smaller and smaller, shorter and shorter, closer and closer to the transom.

The center of lift on a planing bottom is very close to the leading edge: the pressure is highest (pushes up with the most force) within an inch or so of where the bottom hits water, and the pressure then decreases rapidly, and then gradually diminishes to almost nothing at the transom. This is true no matter how short the bottom is.

When the boat is going fast enough, the center of gravity is in front of the point where the hull enters the water. Obviously this does not work, so the bow drops. This leads to porpoising: the bow lifts, drops, lifts, ...

By adding a notch, you are moving the transom forward just for this high speed domain. You can get the forward edge of the wetted surface forward of the CG, then you've got a stable boat again.

Everything Reggie does on bottom design is very well rooted in hydrodynamic science.

So the closer you make your boat's bottom mimic a Fountain, the better off you are.




Hope Reggie paid you for that advertisement............He wasn't the first to notch a transom or add a pad!!

I will let it go at that......................

Last edited by DKerns; 05-04-2009 at 07:27 PM.
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Old 05-04-2009, 08:24 PM
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It certainly works better than notching them at the top
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Old 05-04-2009, 08:37 PM
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Hope Reggie paid you for that advertisement............He wasn't the first to notch a transom or add a pad!!

I will let it go at that......................
Bill Farmer comes to mind
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Old 05-04-2009, 09:05 PM
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Hope Reggie paid you for that advertisement............He wasn't the first to notch a transom or add a pad!!

I will let it go at that......................
Might be true, but he does it better than anyone else.
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Old 05-04-2009, 09:39 PM
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the formula I own 1995 336SR1 has a notched transom, 336 was launched in 1993, notch added in 1995. it still has deep bravos and I understand the notch added a couple mph, my boat won powerboat mag offshore boat of the year in 95
but I am told this boat really performes with shortie drives ( for reasons mentioned by appsyscons and carcrash)

someday I will try imcos shorties and higher pitch props on 1.5 drives instead of my 1.36 drives

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