I have a set of k-planes collecting dust in the shop. I am planning to install them on my 21' Scout. I cant decide whether to install them parallel to the V or place them horizontal like some of the newer race boats. What's your thoughts? I'll start popping some corn.....

I think it was Eddie Young that explained to me that the water coming off the back of the boat leaves in a v shape so the tabs would be more effective mounted parallel rather than horizontal. Randy

A lot of arguments for both ways, I'll give you my 2 bob.
I have a set of dana hp1100's mounted on the angle on my 21' ski race boat.
On the angle is very aggressive and quite touchy to adjust but they have a much bigger effect on hull attitude.
Parallel is a lot softer acting and seems to be more forgiving when making adjustments, however you'll find this way won't give you as much overall trim adjustment.
I love mine on the angle and I wouldn't have them any other way, but it depends a bit on your skill level in making adjustments and hull shape. I know of some hulls that you would stuff real easy set up on the angle.

Here's my thoughts.......

I had a 24' boat with 280's mounted parallel, and now have a 30' boat with 380's mounted horizontal. Granted, different size boats, but both 7' beam. I prefered the tabs mounted parallel. Once I was on "3" on my indicators, the tabs started making a big difference. With them mounted horizontal, It seems like I have to put them down to 5 or 6 before noticing a profound difference.

the reason the tabs are muted when mounted horizontal is as the tab starts to move down into the water flow only a small sliver of the surface of the tab is initially available. When mounted in a traditional manor the full width of the tab is introduced to water flow. See quickie graphic

I have never ran a boat mounted horizontal but my next build will be set op this way.

Wouldn't mounting them horizontal have much less of an effect of "making it run like a bigger boat"

It would appear like that. Why not just buy smaller tabs if you don't want as much tab surface rather than do the horizontal?

We like our tabs at the same angle as the V of the boat. We have run a few different boats with the level tabs and did not like them at all.

Why are you gonna set the next boat up horizontal Dave?

Don't confuse racing and pleasure driving. When racing its about as little drag as possible to get the job done. Your tabs are your last option you ever want to use and at that they are used very sparingly. We tend to use negative trim first then ballast tank. The tabs are for fine tuning and quartering seas IMO