I'm going out for the evening and hope to get an answer by the time I
return. Can a fellow sailor explain what semi planing is on a SAILBOAT
and how one knows when it's happening? Thanks.

I'm going out for the evening and hope to get an answer by the time I
return. Can a fellow sailor explain what semi planing is on a SAILBOAT

and how one knows when it's happening? Thanks.

I won't post the source until Loco makes a fool of himself again...and
if you have this, please shut the hell up! Loco KNOWS BOATS!

"Some light to moderate displacement racer/cruisers are capable of
semi-planing if conditions are right. Heavy air combined with wave
action can conspire to defeat waterline limits. The displacement hull
will clear enough mass to achieve higher speeds, though this is not
planing in the classic sense as too much wetted surface (see figure 19)
remains."


Robert B
35s5...a boat that semi-planed on our second sea trial!
NY

rgnmstr wrote:
I'm going out for the evening and hope to get an answer by the time I
return. Can a fellow sailor explain what semi planing is on a SAILBOAT
and how one knows when it's happening? Thanks.


Sure. Think for a second about what planing is... when the boat's weight
is supported by the force of the water going under her hull, rather than
by sitting down in the water, making a hole big enough to displace her
weight.

Displacement sailing, limited to "hull speed" by wave-making resistance,
is easy to see. As the boat speeds up, bow and stern wave build and get
further apart until the stern waave is right at the aftmost part of the
waterline. The hole in the water, caused by the boat's displacement, is
closing up behind the boat as it goes along.

Now make it go just a little bit faster. Still making big waves, that
hole is still closing up behind... but the crest of the stern wave is
now a little bit aft of the aftmost point on the LWL. If the power is
available to push just a little faster, you will notice that the crest
of the stern wave may be two or three feet aft. At this point, the hole
in the water is not really closing up behind and the boat is partially
supported by hydrodynamic force.

If there is yet more power available, the stern wave will get further
back and start to diminish until the boat is fully planing and there is
only a very small stern wave or perhaps none. The Johnson 18 when
planing fast leaves a wide smooth track of bubbles.

Somewhere along the way, you can say you are "semi-planing" but few
sailors of planing boats bother to talk about it. Sailors of heavy boats
that will not lift never notice the stern wave because their boats are
getting really squirrelly about that time.

Fresh Breezes- Doug King

Somewhere along the way, you can say you are "semi-planing" but few
sailors of planing boats bother to talk about it. Sailors of heavy
boats
that will not lift never notice the stern wave because their boats are
getting really squirrelly about that time.


No, Doug. There's no such in-between point, semi planing or otherwise.
I've heard the term, and just posted a book excerpt, but Loco says it
doesn't exist so that's that.

RB
35s5...a boat that never semi planed....it just went FAST, almost
planed topping 11 knots and then we went home!
NY

I thought it was Donal that said it didn't exist?
Or was it Jeff?
S.

"Capt. Rob" wrote in message
ups.com...
: but Loco says it
: doesn't exist so that's that.
:
: RB
: 35s5...a boat that never semi planed....it just
went FAST, almost
: planed topping 11 knots and then we went home!
: NY
:

thought it was Donal that said it didn't exist?
Or was it Jeff?


IS one typo all you have? It was Loco who claimed the term does not
exist and he never heard it.

RB

Actually, it was about 6 "typos." (if that's what
you want to call it)
S.

"Capt. Rob" wrote in message
ups.com...
:
:
: IS one typo all you have? It was Loco who
claimed the term does not
: exist and he never heard it.
:
: RB
:

Actually, it was about 6 "typos." (if that's what
you want to call it)


Donal has not been in this discussion, Steve.


RB

Somewhere along the way, you can say you are "semi-planing" but few

sailors of planing boats bother to talk about it. Sailors of heavy
boats
that will not lift never notice the stern wave because their boats are
getting really squirrelly about that time.

Doug, I guess I have been semi-planing. Once last summer while under
spinnaker right before we put the pole in the water and my chute
trimmer's back got soaked. He was standing at the shrouds. We were a
little squirrelly.

rgnmstr wrote:
Doug, I guess I have been semi-planing. Once last summer while under
spinnaker right before we put the pole in the water and my chute
trimmer's back got soaked. He was standing at the shrouds.

heh heh did you manage to sneak a look at the knotmeter?

Usually when the boat is going really fast, everyone is too busy to look.

... We were a
little squirrelly.


The issue for boats that don't generate much lift with their hull is
that the power in the rig drives the wedge-shape bow deep into the bow
wave, where pressure oscillates from one side to the other, sometimes
quite sharply. At the same time, the rudder begins ventilating and
lifting, generally losing effectiveness. The keel & rudder foils are
getting out of their envelope of effective lift-drag flow, lots of
turbulence & drag, tends to build up then shed quickly. The result is
that the boat starts acting more & more like a kicked puppy, scampering
in all directions except the way you want it to.

Fresh Breezes- Doug King