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What's the main benefit of a center tab on a cat?

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Old 12-06-2005, 07:24 PM
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Default What's the main benefit of a center tab on a cat?

Besides improved planing and a better ride in rough water, what else does a center tab do on a cat?

Here's a hypothetical question? After trimming the bow up is there any chance of gaining speed by lifting the stern with the tab, thus lifting entire boat for less drag??

Last edited by Harper220; 12-06-2005 at 07:26 PM. Reason: change thread title
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Old 12-06-2005, 07:25 PM
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Default Re: What's the main benefit of a center tab on a cat add speed?

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Originally Posted by Harper220
Besides improved planing and a better ride in rough water, what else does a center tab do on a cat?

Here's a hypothetical question? After trimming the bow up is there any chance of gaining speed by lifting the stern with the tab, thus lifting entire boat for less drag??
the tunnel tab can gain you some serious speed, but can put you on your head to if your not careful... (this is why offshore race cats have tunnel tabs, not for planing reasons..)
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Old 12-06-2005, 07:32 PM
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Default Re: What's the main benefit of a center tab on a cat add speed?

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the tunnel tab can gain you some serious speed, but can put you on your head to if your not careful... (this is why offshore race cats have tunnel tabs, not for planing reasons..)
At about what speeds will the gains start to happen and how much more speed?

How much more on a 28 Daytona 496 ho's? low 90's
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Old 12-06-2005, 07:52 PM
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Default Re: What's the main benefit of a center tab on a cat add speed?

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Originally Posted by Harper220
At about what speeds will the gains start to happen and how much more speed?

How much more on a 28 Daytona 496 ho's? low 90's
i don't know how you would duplicate the results with that center pod thing that eliminator sticks on the bottom of their boat, for optimal results, the tab needs to "seal" the tunnel, so when its down, all the air runs under the tab and not around it... i guess put it on and see and be careful, remember it stays up in the corners...
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Old 12-06-2005, 09:49 PM
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Default Re: What's the main benefit of a center tab on a cat?

Harper220,

The Kplane that Eliminator installs adds 1 - 2 mph in the 115 -120 mph range on a 28TD. It helps when planing with big props such as 36" B1s. Their other use is a step to get in boat.
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Old 12-06-2005, 10:07 PM
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Default Re: What's the main benefit of a center tab on a cat?

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Harper220,

The Kplane that Eliminator installs adds 1 - 2 mph in the 115 -120 mph range on a 28TD. It helps when planing with big props such as 36" B1s. Their other use is a step to get in boat.
That won't do me much good then.

I'd like to find another 6-8 mph without going too crazy. I've considered Imco shorties or boxes, but can't seem to get much feedback on oso. I spoke with Mike at Eliminator and he suggested Imco 2" shorties with a 1" spacer to bring the x dim up 1". Not sure why he recommended doing it that way, but he said I'd be able to go up 2 prop pitches and gain 6-8 mph. Does this sound realistic?
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Old 12-06-2005, 10:09 PM
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Default Re: What's the main benefit of a center tab on a cat?

reduces air flow
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Old 12-06-2005, 10:14 PM
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Default Re: What's the main benefit of a center tab on a cat?

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reduces air flow
Which in turn does what on a cat? More lift?
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Old 12-06-2005, 10:20 PM
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Default Re: What's the main benefit of a center tab on a cat?

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Which in turn does what on a cat? More lift?
a tunnel tab (or more correctly a compression flap) makes the air go under the flap and raise the boat... some people call a k plane or a large trim tab mounted in the center of the tunnel a tunnel tab, it basically acts its force on the water, no real lift from air compression since the air go around the tab...

look at the bottom of UIM cats or bigger cats, their compression flap will match the tunnel exactly..
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Old 12-06-2005, 10:25 PM
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Default Re: What's the main benefit of a center tab on a cat?

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Which in turn does what on a cat? More lift?
Yes more lift. On my 30' motion in Calm water I can trim the motors and lower the tab and feel the whole boat lift quite a bit. Top speed gain in Flat water is maybe 1-3 mph. The biggest gains are keeping the bow level in the rough
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