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How will my boat still float without flappers?


Michigan boarder

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This may be a silly question, but how does this work? Boats with STE's have no flapper, and there are basically two holes in the back of the boat then, under the waterline. When the engine is not running what keeps the water from just pushing up thru the exhaust tubes, and sinking the boat? Is it that the weight of the water inside the tubes does not drop the boat further down enough to keep more water pouring in? Like, it stops filling when it is even with the outside water level, unless something else weights the boat down further?

I installed STE's and have not launched the boat yet. I've done my share of staring at it asking this question though.

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The water in the exhaust wont go above the waterline outside of the boat, its science. My understanding is that you don't need flappers on STE because the tips face down, so there is no "ram" effect on the exhaust when you slow down or waves come at the bank of your boat.

  • Like 1
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Water seeks its own level. If your pipes ran straight into the engine at the level of the outlets then you would have problems, but that is why boat manifolds exit at the top and then curve down to the water.

With downturns and no flaps the only risk is that the engine tries to suck water in via vacuum in the case of a serious misfire.

Edited by oldjeep
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Silent ride mufflers and STE's. ..no issue here! Then I do have the headers that rise a little

higher then stock manifolds. Like the OP, pressure within the system keeps the water at bay.

Remember that the water wanting to go in to the pipes will need to push the water out at the raw water

Intake which is below the water line. ..lots of pressure.

Edited by Dare2goBare
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Remember that the water wanting to go in to the pipes will need to push the water out at the raw water

Intake which is below the water line. ..lots of pressure.

Huh? Water wanting to go into the pipes only has to overcome the level of the pipe and then go into an open exhaust valve. The secondary path out the raw water intake wouldn't be an issue since that whole system is full of water.

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Huh? Water wanting to go into the pipes only has to overcome the level of the pipe and then go into an open exhaust valve. The secondary path out the raw water intake wouldn't be an issue since that whole system is full of water.

Yes true enough. ...but wouldn't you think the pressure in the system would keep water out just the same,

or am I missing something here to?

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Yes true enough. ...but wouldn't you think the pressure in the system would keep water out just the same,

or am I missing something here to?

When the boat is off - not really. The only thing keeping the water out is the uphill run into the manifolds, you get water up there and the water will drop into the cylinders that have open exhaust valves and the air will bubble out.

Edited by oldjeep
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When the boat is off - not really. The only thing keeping the water out is the uphill run into the manifolds, you get water up there and the water will drop into the cylinders that have open exhaust valves and the air will bubble out.

Ya, I see your point, so there is a concern, hummmmm obviously the manufacturers have taken all

this into account in there redesign. I've never heard of an issue.

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This may be a silly question, but how does this work? Boats with STE's have no flapper, and there are basically two holes in the back of the boat then, under the waterline. When the engine is not running what keeps the water from just pushing up thru the exhaust tubes, and sinking the boat? Is it that the weight of the water inside the tubes does not drop the boat further down enough to keep more water pouring in? Like, it stops filling when it is even with the outside water level, unless something else weights the boat down further?

I installed STE's and have not launched the boat yet. I've done my share of staring at it asking this question though.

Two words: exhaust risers...you have nothing to worry about.

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@MB: It is a buoyancy question, the boat displaces the amount of water needed to seek buoyancy equilibrium or the force pushing down is equal to the force pushing back up. The floatation foam and volume occupied by it is what keeps the vessel afloat or the force that resists the boat sinking.

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My STEs have a rubber flapper (90 degree rubber piece, hinged at center), that's what stops flooding the block thru risers when backing..

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OK. Just checking. I get it - it seeks the same level, and when it reaches that level it stops flowing in. The buoyancy of the boat keeps the boat at the same height regardless of the extra water weight that has flowed in.

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