Bubble injection behind the step on seaplanes

[Adam Aulick]

I have been reading up on seaplanes (Seaplane Operations, by Cesare Baj
and Dale DeRemer) and one frequently repeated fact is that it is very
hard to get a seaplane up on the step on glassy water, because the lack
of bubbles under the float/hull causes the heel of the float/hull to
adhere to the water surface.

This seems like an easily solved problem -- inject bubbles behind the
step. Clearly if it were that easy it would be common practice. What
am I missing?

Here is my hull profile at the step:

To Heel <-- Step --> To Bow
_____________________
O| /
x|______________________/


When moving at speed through the water, it seems that at point O there
should be a circulating eddy or turbulence, and at point x there should
be significant suction, yes? So if we attach at point x a hose, whose
one endpoint is at x and the other is above waterline, without any
further mechanics the low pressure at x should be sucking air through
the hose and introducing a trail of bubbles, slipping past the
turbulence at O and running along the undersurface of the heel. If we
put in a bunch of such hoses, or one long hose running along the back of
the step with a bunch of holes spaced along it, we should get a lot of
bubbles. Yes?

What am I missing?

~Adam

[Doug]

It's not a bad idea. You would have to build one and see if it works.
For all things seaplane go to www.seaplanes.org. They know a lot on
there.

[JP]

Yep! The concept works. The basic idea is at least 100 years old.

Some racing speed boats use this.

JP


"Adam Aulick" > kirjoitti
...
>I have been reading up on seaplanes (Seaplane Operations, by Cesare Baj and
>Dale DeRemer) and one frequently repeated fact is that it is very hard to
>get a seaplane up on the step on glassy water, because the lack of bubbles
>under the float/hull causes the heel of the float/hull to adhere to the
>water surface.
>
> This seems like an easily solved problem -- inject bubbles behind the
> step. Clearly if it were that easy it would be common practice. What am
> I missing?
>
> Here is my hull profile at the step:
>
> To Heel <-- Step --> To Bow
> _____________________
> O| /
> x|______________________/
>
>
> When moving at speed through the water, it seems that at point O there
> should be a circulating eddy or turbulence, and at point x there should be
> significant suction, yes? So if we attach at point x a hose, whose one
> endpoint is at x and the other is above waterline, without any further
> mechanics the low pressure at x should be sucking air through the hose and
> introducing a trail of bubbles, slipping past the turbulence at O and
> running along the undersurface of the heel. If we put in a bunch of such
> hoses, or one long hose running along the back of the step with a bunch of
> holes spaced along it, we should get a lot of bubbles. Yes?
>
> What am I missing?
>
> ~Adam

[john smith]

In article >,
Adam Aulick > wrote:

> I have been reading up on seaplanes (Seaplane Operations, by Cesare Baj
> and Dale DeRemer) and one frequently repeated fact is that it is very
> hard to get a seaplane up on the step on glassy water, because the lack
> of bubbles under the float/hull causes the heel of the float/hull to
> adhere to the water surface.
>
> This seems like an easily solved problem -- inject bubbles behind the
> step. Clearly if it were that easy it would be common practice. What
> am I missing?
>
> Here is my hull profile at the step:
>
> To Heel <-- Step --> To Bow
> _____________________
> O| /
> x|______________________/
>
>
> When moving at speed through the water, it seems that at point O there
> should be a circulating eddy or turbulence, and at point x there should
> be significant suction, yes? So if we attach at point x a hose, whose
> one endpoint is at x and the other is above waterline, without any
> further mechanics the low pressure at x should be sucking air through
> the hose and introducing a trail of bubbles, slipping past the
> turbulence at O and running along the undersurface of the heel. If we
> put in a bunch of such hoses, or one long hose running along the back of
> the step with a bunch of holes spaced along it, we should get a lot of
> bubbles. Yes?

Look at the hull of any Lake Amphipian.

[pbc76049]

">> What am I missing?
>>
>> ~Adam
>
>

Simplicity......

You need to look at pictures of any large seaplanes to see how they get the
step
"energized". The Shin Meiwa, for example, uses fences along the fuse side
to force a high volume of air into the step area. A fairly simple thing to
do
and you don't need to make hull penetrations to make it happen......

Have a great day

Scott

[[email protected]]

JP wrote:
> Yep! The concept works. The basic idea is at least 100 years old.
>

Indeed.

The lapstrake construction of the Viking longboats carried bubbles
down from the bow under the hull.

People sailing modern replicas report a sort of 'surge' and an
associated loss of rudder authority that corresponds to reaching
a certain critical speed.

--

FF

[JP]

There is a picture about the subject ("Super Ventilated Positive Lift" in
this case)

http://www.fountainpowerboats.com/teamfountain/racing.htm

JP



"JP" > kirjoitti
...
> Yep! The concept works. The basic idea is at least 100 years old.
>
> Some racing speed boats use this.
>
> JP