Are all these tunnel tabs I'm seeing custom made by the builders? I was hoping to find one to test with before I spent the time to make a custom one...

Some of them are just trimtabs with an oversized aluminum plate bolted to it.

https://www.marineindustrieswest.com...nnelSeries.htm

Not sure why they would call these tunnel tabs and say for V bottoms. Tunnel tabs are the width of the tunnel in cats and VERY dangerous. Even if you’re skilled enough to use one, if you lose a trim gauge it’s bad news. Forget a tunnel tab is down in a turn and you’ll end up on your lid.

Totally agree on the use of these tabs. Almost turtled a twin engined 21 skater coming off speed and I forgot to bring the tab up....started to pitch severely to the starboard until I realized what was going on. Tunnel tabs is like a love/hate relationship. They work great to correct a catamarans hull design flaws or used to try to eliminate the most common cat hop. Designed one for a 30 prostock cobra that with twins 2.5s would run 92 and with trips it ran 96 then violently started to hop. Installed a tab articulated around the center engine, pull the tab down, no hop and the cobra ran 109 as a race boat. But not paying attention can get you hurt.

It’s interesting to look at the different versions on the OB race cats.

when they were in cocoa some were fixed others could be adjusted.