Mounting trim tabs - along bottom or horizontal?
 

I'm re-rigging my 24 Pantera to go racing with a 496 HO, Bravo One X drive and Dana HP900 tabs.

Is mounting the tabs horizontally the better alternative or should I go with the traditional way and mounting the along the bottom?

Horizontally sounds like the correct way of doing it but I'm not sure...

I think you'll find that if you use the "search" function here, you'll find this one has been beat up pretty well in the past. In fact if I recall correctly, several folks with your hull have posted in on it too.

I took Tres's class and there I found out why they should always be mounted along the bottom.

Would you care to explain the theory? :)

Not having taken Tres Martin's class (yet), I'd be willing to bet it goes something like this. From a less drag = more speed standpoint, horizontal works great. From a pure mechaincal engineering standpoint, horizontal mounting leads to an uneven loading (twisting actually) of the tabs - which will shorten the life of the tabs. More even loading unfortunately = more drag and less speed though.

How'd I do?

i think you passed with flying colors:evilb:

That depends on how far out the V you mount the tabs and how fast and high the hull rides.

If it rides high the horizontal tabs can have horizontal water -> no twisting. In the same scenario the bottom aligned tabs would be twisting - like in this pic:
http://www.blocket.se/stockholm/PANT...=11&w=3&last=1

http://212.112.179.24/images/35/3503296448.jpg

So I don't think you did very well. :drink:

My 28' vee bottom (no step) I mounted them horizontally.

Horizontal tabs create lift and stability creating the least drag. The tab is using water already full of energy from the hull pulling it along (drag). They also need less movement to have an effect. This way they stay out of green water (water below the surface water that no energy, not moving)

Parallel mounted tabs are in contact with the water for a longer duration in their travel (more drag). When they are negative from neutral (bow down) they gout out as they go down creating a wedge (more drag) They also pierce through the energy layer of water into green water (more drag).

Think about this. If you put a vee bottom boat on an H stand aft and blocking or flat stand at the bow and pulled down on the gunnel it will slide in the H of the stand (tabs parallel).

Now take out the H stand and use boat stands at the hard chines and pull down on the gunnel, it is stable. (tabs horizontal).

That being said short tabs do not perform as well as long ones when horizontal because the surface area is greater on the long tabs. {more surface area usually means more drag but in this application the water already has energy minimizing the drag on the larger surface.}

Yea, I like this one a lot better. Thanks!

Thanks!