What determines which way to mount trim tabs ( straight or angled )
 

My hull is 27 ft 25deg V with strakes all the way to the back and single big block/bravo,
it had K-Planes once but somewhere along the way they were removed .
It rides awesome and cuts waves like butter but wants to chine walk when I am
approaching 70mph. I plan on getting 24-28" tabs and wondering what are advantages
to both ways of mounting tabs.
Thanks!

Running attitude at around 55mph with very little trim:
http://damncarrera.com/SS8Msig.JPG

This has been discussed on there several times over the years. Do a search and you will find some good info.

It all depends how many beers you've had. :coolcowboy:

lol And what kind of oil you use.....:food-smiley-007:

Cool, I will do the search and see what I find..
I just hate using the search feature on here because it wont let you do a search for a phrase such as "trim tab" no matter how you put it , it still searches for individual words giving you far more results than you want.

My 2 cents is that the majority of boats I have seen with them "straight" had notched transoms, and pad bottoms. Although, I have seen notched transom boats with them "angled" too. I personally have not seen any deep vee straight transom boats with them mounted straight. Good luck with your search.

Mount them straight.....

Mounting them angled does nothing to stop your chine walking and the tabs act more like brakes than leveling devices.

T2x

That looks like a lot of bow lift for light trim at 55 MPH. Were you porposing at this trim level?

I had that issue once. I put 380 K-Planes on angled. They were huge for the boat, but nailed the chine walk -- gone. Tapped them down until they just kissed, but no more! Any more than that and the bow steered the boat. After I got it right, I put sleeves on the trim cylinder rods so I could not under tab. Felt like the boat got 3 feet longer.

Agreed!

Nope, with a powertech 4 blade 26p it doesnt bounce at any speed.
Its not a light boat either.. :)

wouldnt that prevent you from putting them all the way up instead of all the way down?

I have tried them both ways on my race boat. Same boat,same power. For what ever reason my Krytonite likes them angled better. It cost me a ton to move them and then put them back. Maybe each boat has its own reasons for why its better on one than another. I can also tell you when I run my tabs at level on my SVL Extreem race boat trimmed out on the edge it makes my boat chine worse. If I raise the tabs out it takes the chine walk out. In my opinion tabs can be your worst or best friend. Use them right for your boat and you will see great progress. Wrong AND YOU MIGHT GET HURT AT SPEED. One of the best set up factorys in the world puts them level (Fountain) Im sure after all the testing they do it works best for them.
MD

I am pretty sure you are having handling issues because it looks like you have lost water contact with your inter strakes....nothing to hold the boat steady which causes porpoise in a twin or torque "lean" with a single that leads to chine walking. We fixed the handling of our Scarab by lengening the inter strakes to just stay in contact with the water to give the boat stability. The faster you go, the longer the strakes need to be. If there are no stakes in contact with the water, you have nothing but a flat bottom to run on. It is not a big deal to get the strake length right. Look at you picture closely....
Ben

trim tabs help in 90 % of boat set up over bare stock
what they do is extend the wetted surface of your hull
theres a lot of science to where exactly we place them
i run mine
angled 3 inches in from the chine
3/8 inches above absolute transom bottom acts a bit like a third step
the comments all the way back to the beginning are spot on
i use them as a third step and to keep my hull level
attitude of the hull to the water with my rig is important
fun boat to drive
my set up is average mom and pop performance boats up to the 70mph margin

Angled works for me.

http://i763.photobucket.com/albums/x...s086Medium.jpg

My strakes all run all the way to the back..

You're right. Bad memory (this was 20 years ago). I did it to keep the tabs engaged to prevent the chine walk.

I tell everyone in my experience, straight is best as the water just rolls under the trailing edge when angled they act like 2 rudders pushing water in opposite directions. However, you don't get as much bite in the water if you think you need it. Just something I found.

Flat. Mine are flat. They create more lift and less drag this way. On an angle they actually spread out making the V wider and deeper, like dragging a sea anchor. This fixes chine walk and other handling problems because it slows you down. To correct these issues and not loose speed mount them flat. They can then use the water all ready moving forward (from the energy from the hull) to stabilize and lift with little loss of energy. Angled tabs also get into green water that is static (IE not moving forward) and this takes more energy drag them through the water, again slowing you down not fixing the problem.

Okay, I was thinking flat as well and by the posts
I am leaning that way now.
Now how do know where is best?
Is it like angled tabs, just slightly above bottom on outside edge but then continue staight across?

Angled works fine for me. I'm sure it's not going to make a ton of difference unless your racing. For the occasional rough water adventure and cruising around I can't imagine you going wrong either way.

Race boat is this way.
http://img690.imageshack.us/img690/5686/90761116.jpg

The same way on the Monza.
http://img9.imageshack.us/img9/7173/80111996.jpg

I put mine on a angle. They work good for what I use it for. I have them 3/4" above the bottom edge.

Please note: Your boat will also chine walk at max trim if you have ANY SLOP OR MOVEMENT of the outdrive (in any direction). You should have full hydraulic steering and make sure every pivot point is tight with no play.

Well I have a question since everyone is talking about trim tabs. I wanted to put some trim tabs on my 28' cat and the shop said it isn't a good idea on the smaller cats, that you don't get much out of them and can cause me more problems then it is worth. He said something about tripping the boat up and said if I didn't really know what I was doing they could get me into alot of trouble and fast with that size cat. What do you guys think?? I wanted them more for looks then anything because I think boats look really cool with them.

Anyone have pictures of tabs mounted flat?

Dude, WHAT? GET REAL!!!!!!:eek::eek::angry-smiley-038:

Just check out the transom of about any Fountain built in the last 4 years or so.

What's your problem?? Why do people like you always have to talk s**t and try to start something?? You couldn't just try to help and answer the question.

with the boat being short what they mean is. if your running them even and your bouncing around in 3 footers they could dig in and force the bow to stuff causing possible death to you or hurting you and the boat. the small cats that I have been in run great without and just using the trim, boats were a trip ob 30 spectra and a twin skater 24. we ran the 30 in 4 to 5s off block island in a pokerrun at 90:eek::eek: it was hairy at times and only lasted ten minutes then back to the bay where it was only 2 footers and wakes. you should be fine without them even the 24 ran good in the bay running in 2 to 3s and jumping wakes from big yachts. so save your money. art

I dont know if this will help, but here are some pics of transoms from my last two boats.

Cool, thank you so much for the info. The shop told me to put the money to better use like full hydraulic steering. I was just wondering what that meant because i see other smaller boat with trim tabs. My boat runs and handles great, but I'm not running in the 90s yet, still need some work:)

yup,have it ..

The 27 Carrera is prone to chine walking from the 25deg vee
and the fact it is actually made from a longer boat.
( 30 Carrera with a 3ft plug in the mold )

I guess some clarification is needed.

Trim tabs mounted at an angle simply extend the running surface when set level or slightly above the bottom. Chine walking is a very subtle problem when it starts, and gets progressively worse with each rebounding cycle. Therefore you want to stop it with a slight subtle "nudge". To do this you insert a small outer corner of two opposing trim tabs into the water flowing off the bottom which creates a stabilizing (centering) affect on the hull without increasing drag beyond the bare minimum. You can't do this with angled tabs since they are an "all or nothing" proposition. You either put the entire tab surface in the water...or take it out. The Bennett style tabs shown in most of the pictures above are used more to help in planing and holding the bow down than to reduce chine walking, and they are a medium duty unit rather than a high performance tab. In addition when you mount tabs at an angle you are creating a "hook" at the transom which will create more bow steer and scrub speed. The only reason I can see where this might improve a hull is if the builder or rigger put too much rocker into the hull, or the C/G is too far aft, and you need artificial means to correct what is basically a flaw in construction, rigging, or design.

The hull that started this thread has an extremely deep vee and certainly could benefit from properly fitted and mounted tabs IMHO.

I hope this helps.

T2x

Lavey did it both ways and flat works better on my hull.

Uncle Dave

Thank you all for your input, I will try mounting them straight and see how I like,
since i dont have any tabs right now i think I will like it.. :)
[email protected]

Also remember that where you mount the tabs on the transom - whether it be angled or straight across - makes a difference too.

Most folks mount tabs all the way out towards the chines. I talked to a number of folks and looked at lots of pictures of Progression 22's before electing to mount mine a bit further in - over the lifting strakes. Why? Take a look at the picture below and note where the tabs are a just under 80 MPH. If I mounted them at the chines, no matter how low I dropped them, not much would happen at speed.

http://i37.photobucket.com/albums/e6...tSpeed2009.jpg

Flat mounted tabs on my Donzi. Rarely need to use them except in quartering seas.

With my Kryptonite, the angled tabs gave me more length and I ran them even with the bottom and a touch down in following seas.

As T2X said, different set ups depending on how they are being used.

generally for top end, flat. but general use (i.e., all around use) level with the hull.

Flat tabs really won't do much to help you with a list from weight, etc. while cruising. So if you want to use them for the all purpose tab use, angled is best. if you really want to fly top out, generally flat is best.