mikesufka

Gentleman -

I just purchased a 30 Spectre with twin 300 Promax's. It comes with the factory tunnel tab.

This may sound like a stupid question, but how,when, and why do I use this? Is it dangerous if not used properly? I've done a search already but didn't really get the answers I'm looking for.

Thanks,

Mike

Tantrum

Yes it is very dangerous if not used properly. IMO there is no reason to run one on a 30 w/ 300's. I would at the very least put it in the full upright position and pull the fuse if not remove it. Spend some time to learn the boat and then get someone with lots of experience to run the boat with you and show you how to use it.
I run a 30 AMT and run with several other cats (one is a 30 Spectre) and none of that group runs a tunnel tab.
PM me your number and I will be happy to talk to you about it if you wish.

Tantrum

Congratulations

Not a stupid question at all.
A full tunnel design (30 Spectre) works by compressing air within the tunnel to create lift, this gives you less friction with the water, which makes you fast. The faster you go the greater compression and the more lift you will get.
The way in which your hull is compressing is that its shape bow to stern is like a big wedge. Big/tall opening in the bow, small narrow opening at the transom.
The idea of a tunnel tab is that you can change the size of the opening at the transom, thus increasing compression by lowering the tab.
There are to basic reasons you would want this control.
1) All full tunnel hulls have a certain point at which they will "lope". Loping is similar in sensation as a V bottom proposing. What is happening is that the hull is compressing air to create lift but can not support its own wait and falls back down into the water. This is completely normal for a tunnel hull and the only way to remedy it is to increase compression.
If you have a tunnel tab, you can lower it to increase compression by making the exit smaller.
2) If you are trying to squeeze every last MPH out of the boat. Youve held the throttles down for 5 miles and you cant get anymore out of her. You can drop the tab, increase compression and get the boat even higher out of the water...looser....faster..

It becomes dangerous when the tab is in the down position. If you stand at the bow of your boat while it is on the trailer and look down the tunnel w/ the tab down...what do you see? The Tab! That is the same thing a wave is going to see at 40, 60, 80 100 mph. Now the important part is AIR compresses....WATER does not.
Compress air? good, nice smooth ride, fast
Compress water? you cant do that so the boat trips which pulls the bow down. This is were it can go very wrong..fast. Stuff, hook, buck passengers out...alot of ugly stuff "could" happen. There are alot of people driving cats and never had a problem. There are also some very experienced drivers that forgot to lift their tab and had accidents which did turn out so good.

Again, I would strongly recommend running you boat for a good amount of time to get a good feel for it without the tab. Then work you way into it IF you still think its necessary.

Good luck and I hope this helps.

mikesufka

Tantrum -

Thank you for your reply. That helped, ALOT! Does it help at all with getting the boat on plane? Especially with a load?

Mike

Tantrum

No...if it does its by accident.
Cats are not like V bottoms in that the bow doesnt get very high. My AMT planes nearly flat, the Spectre does get slightly higher but still relatively level.

VEGAS36CAT

congrats on the 30' Awesome boats and a blast to drive. I own a 98 30' with Pro Max's, in the process of selling it as we went up to a 36' earlier in the season.
Anyway we run the tab down with the motors basically trimmed neutral at porpoise speeds (60-80) if cruising in that speed range or on sticky flat water. The tunnel tab makes a massive difference in the porpoise if used correctly, and you will feel very quickly whats right or wrong. With the tab in the full up position, the boat will throttle right through the porpoise window in just a matter of seconds, take a nice set at 80-85 and its on from there, trim up the motors and off ya go
A few other 30's running around here at Lake Havasu, the consensus from those guys is about the same...to avoid the "dolphin dance" keep the motors trimmed neutral and the tab down until somewhere around 80, then up with the tab, up with the motors, forward with the sticks and bye bye to the DCB, etc next to ya

VEGAS36CAT

I would leave the tab up for getting on plane, put it down when the boat starts to porpoise, on ours that is right about 4,000 RPM and 55-60 MPH.
With the tab down just after the boat rolls onto plane it feels like it wants to stuff the bow, didn't care for that feeling

Sydwayz

iTrader: (1)

Tantrum, that is AWESOME information. Thank you.

berns29scarab

Tantrum you are the man. He's the guy that wanted to trade me the viper plus some cash for my boat...Mike as a rookie cat owner, put that tab ALL THE WAY UP AND PULL THE FUSE...TRUST MEi've got almost 200 hrs on mine and have NO DESIRE TO INSTALL A TAB AND IF I DID IT WOULDNT BE A FULL ONE...have seen and heard to many instances where inexperience has won...GOOD LUCK AND BE SAFE

VEGAS36CAT

didn't think about a different sized tunnel tab...for reference the tab on ours is approx 10" wide and 14" long