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Old 08-08-2018, 05:42 AM   #1
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Draft on plane

I have always been curious... Does a boat on plane draft more or less water?
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Old 08-08-2018, 06:00 AM   #2
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Less
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Old 08-08-2018, 07:04 AM   #3
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Yep. Less on plane. But hell to pay if you bump and slow down!!!
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Old 08-08-2018, 07:08 AM   #4
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Yes, less.
My small boat can run on plane in water that I can't float in if I stop.
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Old 08-08-2018, 07:31 AM   #5
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How much less?
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Old 08-08-2018, 07:32 AM   #6
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You just have to run is shallow water and see when you hit bottom...
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Old 08-08-2018, 07:39 AM   #7
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Yes, but.

A large boat on plane can create a suction in shallow water that will pull the stern deeper than if the boat were in displacement mode. Simply, you can strike bottom with a boat on plane in a depth of water that the boat could transit safely in displacement mode. Have seen it happen with a sportfish in the back channels going to the Hatteras, NC inlet. One minute the boat is on plane, then the stern starts getting sucked down, then the smack as thousands of dollars in running gear damage occurs, engines stop, and the boat glides forward in displacement.

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Old 08-08-2018, 07:45 AM   #8
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How much less?
Depends. Inboard, outboard, keel, no keel, boat speed, waves. No way to know for sure how much without some very risky testing.
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Old 08-08-2018, 08:27 AM   #9
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Cruise ship increases speed to get under bridge.
Surly not on a plane but ”ballsey” just the same.

Cruise ship barely squeezes under bridge - CNN.com
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Old 08-08-2018, 08:28 AM   #10
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Depends. Inboard, outboard, keel, no keel, boat speed, waves. No way to know for sure how much without some very risky testing.

I would agree with that for sure.
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Old 08-08-2018, 09:50 AM   #11
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Cruise ship increases speed to get under bridge.
Surly not on a plane but ”ballsey” just the same.

Cruise ship barely squeezes under bridge - CNN.com
Damn, that IS ballsy!!!!!


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Old 08-08-2018, 10:22 AM   #12
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The bottom is not flat. Have your prop shop and seatow on speed dial.
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Old 08-08-2018, 10:35 AM   #13
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Here in South Florida we do a lot of skinny water fishing. We typically run on plane to cross shallow water. The water is so shallow that the fish backs and tails come out of the water.
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Old 08-08-2018, 10:45 AM   #14
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I've run my boat a good bit in the lower (fla) keys. There are areas that I know well, about a foot deeper than my draw. If I am running slow there, boat gets "squatty" and steering gets weird. If I try to power up on plane, boat will suck down and likely hit.

But if I am already up on step (like 16-22kts), I can feel the boat lift, speed pick up a touch and the wake gets flattened out. Feels good but I sure am on my tippy-toes!!

But this is a light planing hull. A big heavy Hatteras that is hardly planed out will most likely suck itself down into a bigger hole than usual and that will not be a good day.
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Old 08-08-2018, 11:09 AM   #15
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Oc Diver is exactly right. Bigger displacement boats will suck down in shallow water. speed slows, attitude changes and wake increases.
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Old 08-08-2018, 01:03 PM   #16
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Interesting. Like I said, just curious. We are 42' with a nearly flat bottom at the stern. A lot like a sportfish hull. The props are, by far, the lowest point on the boat and totally exposed. When we are planing with full trimtabs, she does get up on her toes, so to speak, but I do feel like her ass is in a hole. So really, it's impossible to tell. Maybe it's the same. Id sure like to test it some day with some sort of controlled test.
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Old 08-08-2018, 01:54 PM   #17
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In Vietnam I ran jet drive PBRs that were based on a 31' Uniflight hull. At draft about 24" and on plane 8". I routinely passed over shallows at speed.
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Old 08-08-2018, 02:20 PM   #18
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Parks has it right, at least when it comes to outboards built to run shallow. Jack plate up, motor trimmed part way up, tabs down, my skiff will run scary shallow on plane. Like 6 inches. Of course the consequences of a mistake there are nothing remotely close to running a big boat shallow.

Though I have spent quite a few hours waiting on the ride to come in.
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Old 08-08-2018, 03:46 PM   #19
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I honestly don't think the draft is affected that much. Look at the hole that is created when the boat is on plane. Technically the hull is at water line, but the waterline is adjusted at the transome to be lower than the surrounded water surface. The stern squats, even when on plane. Any lift gained looks like it's offset by the squatting of the stern.
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Old 08-08-2018, 04:00 PM   #20
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Quote:
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Parks has it right, at least when it comes to outboards built to run shallow. Jack plate up, motor trimmed part way up, tabs down, my skiff will run scary shallow on plane. Like 6 inches. Of course the consequences of a mistake there are nothing remotely close to running a big boat shallow.

Though I have spent quite a few hours waiting on the ride to come in.
Once I was fishing with my buddy Darrell down by Turkey Point in Biscayne Bay. Darrell dropped something overboard so he jumped in after it. His cell phone was in his pocket. A while later we got caught on a flat by the falling tide. I started rationing food and water. Went into full survival mode.The wind picked up and it got cold. Darrell and I tried to get out of the wind but no place to hide on this boat. To make it worse we were both soaked from trying to push the boat off the very soft mud bottom. Six hours later we floated enough to push it to deep enough water. That was six miserable hours.
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