Tom, to answer your first question...my two boats are a
1. a narrow, tunnel-hull, high bowed, 16 ft. flats boat known as an El
Pescador http://www.elpescadorboats.com/
& 2. a 16 ft. Carolina Skiff STD, flat bottomed, skiff style
www.carolinaskiff.com
These two boats are as different as night and day in hull configurations.

With regard to "theory on bow lift"....I'm no engineer...(a big
understatement)... but all tabs that I am familiar with... Lenco (
electric) Bennet (hydraulic) and SmartTabs (pneumatic) ....all work on the
same principle and produce similar, (though differing in degree and amount
of control), results. It is my simple impression that TABS ( any tabs)
effectively make the boat "longer" by extending the stern hull surface
outwards.

Most planing style boats have the "bow rise" built-in. Just start any
planing-hulled boat forward and the bow will rise and stay up, far too long,
until the boat gradually comes back down to "plane". I've owned over twenty
boats so far, and never had any of them that would instantly go to "plane"
without the ....Up first, level later... process. The use of trim tabs
counters this excessive bow rise and brings the boat into plane quicker. Any
planing-style hulled boat, moving on plane, is using less fuel than it would
while plowing through the waves.

It may well be that if you had a non-planing ( displacement style) hull,
that the UP/LEVEL movement was minimized. My displacement hulled sailboats
did NOT have any UP/LEVEL style startup problem, but I believe that the
questioner was speaking about a planing hull.

On the other end, when the boat is slowing down...it settles at the heaviest
stern-end much too quickly, bringing it back into an in-efficient bow-up
position. Tabs ( any tabs ) help to stop the stern from sinking quite as
fast, allowing for a longer planing time at a lower speed. I'd believe that
this attribute is caused by the "longer hull" extension effect of any tab
system.

I'm certain I can find chapter & verse on Tab's efficiency and usage in
Bennett's and other websites. The engineering studies have been done long
ago, and many thousand, perhaps millions, of boats have used tabs for well
over 30 years. If you'd like more data, I can Google it for you.

I was a skeptic about the effectiveness of tabs, too. Now that I am a user
though, I wouldn't boat without them.
regards,
--
RichG manager, Carolina Skiff Owners Group on MSN
http://groups.msn.com/CarolinaSkiffOwners
..

"Short Wave Sportfishing" wrote in message
...
Rich's post got me to looking - just for my own edification.

This is from the Nauticus web site about Smart Tabs:

****

"SPEED REGULATION
SMART TABS start in a downward angel to maximize lift at slow
speeds. As the boat accelerates, the water pushes up on the trim
plates providing lift to the stern which minimizes bow rise, and
allows the boat to plane quickly.

Once the water pressure exceeds the actuator load rating (maximum
lift) the trim plates move up to a horizontal position eliminating any
drag."

****

Besides the fact that angels are not relevant to this discussion
except for praying for good weather, doesn't this seem counter to
accepted theory on bow lift?

Bow lift is what you need to get up on plane as I understand it. It
would seem to me that lifting the stern is exactly what you don't want
to do - you want to keep the stern as neutral as possible acting as a
pivot point - or am I wrong?

On the opposite end of this planing deal, I'm not sure how this allows
you to stay on plane longer. Even if you set the actuators to a heavy
setting, that kind of defeats the purpose - yes/no?

Later,

Tom - who is not looking to start an argument, just being curious.