Trim Tabs

[GC1]

My new boat has trim tabs and I get it next week, having never tried these before can anyone give advice on do's and do not's please. I have heard that some boats can go a bit wild if you press the switches the wrong way, I have also heard that up is down and down is up /forums/images/graemlins/confused.gif

Thanks

 

[t7mby]

Hi, I had exactly the same questions and found a simulator on Bennett's web site quite helpful.

http://www.bennetttrimtabs.co.uk/

All the best with the new boat, and try not to sink the sim boats !!

 

[compie1]

You can always switch the wires so up is up and down is down!!! /forums/images/graemlins/smile.gif

 

[andis]

Ussually, the wires are crossed, so that the left switch moves the right tab, etc. The switch is meant to simulate the angle of the boat, so that depressing the top of the left switch, one lowers the bow on the port (left) side. This is done through the lowering of the opposite tab (right), but that is not how you should think; just look at the switches as your boat, and then everything becomes clear.

 

[KevB]

Start off with both tabs in the up position, you shouldn't need them to get you on the plane (some under powered boats need their tabs down to help get the bow down). When you are on the plane, if the boat is listing slightly to either port or starboard you adjust the tab down on the side which is listing until you are level.

You can also use the tabs when going slow to help reduce your wash. By having the tabs down this lifts your stern up a bit lessening your wake.

Remember to adjust your tabs back to the up position whne you have finished.

You should use your leg trim to adjust the angle of your boat when going along not the tabs.

Kevin.

 

[GC1]

Thanks for some great replies /forums/images/graemlins/wink.gif. As a safety concious person, can anything bad happen if you cock up or is it just a matter of re adjusting?

 

[andis]

Nothing bad can happen; you just re-adjust.
If you are so worried, fit a pair of trim tab indicators.
Also, a couple of interesting accessories are
a) an inexpensive device that returns tabs at the fully up position once you turn the engines off
a) an expensive device with a gyroscope that you program to keep the boat level using the trim tabs irrespectve of conditions
Both are available by Bennett.

 

[[2068]]

Depending on the tabs and the boat, you could end up bending them if you put them fully down at high speeds (e.g. 25knots plus). A session with a vice and a lump hammer normally solves the problem...

dv.

 

[wakeup]

Auto Leveler

Wot you not going to buy the auto leveling system that keeps the boat level wot ever the conditions/ trim settings. With this you could make toast even on the plane!!!!!

 

[Planty]

Don't disagree with any of the above replies except that they don't mention probably the most 2 important use of Trim tabs,

1. that of changing the presentation of the bow into differing sea conditions to increase comfort and decrease possibility of damage to boat due to slamming, broaching etc.

In essence when punching into a heavy head sea get them trim tabs right down, this will drop the bow and thus present a far sharper bow angle into the sea thus "cutting" into it and not slamming against a shallower dead rise further along the hull. You will be suprised at how this really "softens" the ride. Makes some really scary seas bearable. One has to adjust the amount of tab to get a "comfy" ride yet not dig the bow in too deep.

However in following seas you want the trim tabs right up so that the bow rides high and you literally "surf" along, having the bows down could encourage a "broach", ie the hull spins on its axis, not nice!

Again in a beam sea your trim tabs can be helpful to flatten the boat across its beam but you may have noticed the boat will naturally dip sideways towards the prevailing wind, apparently very complex aerodynamics cause this, (beyond me) ??

2. To optimise performance, in a flat sea at cruising revs, just try playing with the tabs, set a position then wait a bit and watch the speed, one can see differences of + or - 3 knots either way on our boat. Over the years we have found an optimum position which is about 2 lights down on port and 1 light down on starboard.

Hope this helps but in my view the most important understanding of the use of trim tabs is to deal with varying sea conditions and to optimise performance in flat seas. All the best with the new boat.

Paul

 

[KevB]

[ QUOTE ]
1. that of changing the presentation of the bow into differing sea conditions to increase comfort and decrease possibility of damage to boat due to slamming, broaching etc.


[/ QUOTE ]

You may be right on a boat with shafts but on a boat with legs you trim the leg to change the 'presentation' of the bow not the tabs. Tabs will lift the stern forcing the bow down so it does have a similar effect but triming the leg is a more efficient and the correct way of doing it on an outdrive boat.

[ QUOTE ]
To optimise performance, in a flat sea at cruising revs,

[/ QUOTE ]

Again, not sure this is strictly true on a boat with outdrives, increasing the angle of the tabs jsut introduces more drag. The effect of putting the boat on a better planning angle may increase the speed but again it's best and mor efficient to have the tabs in the up position and change the angle of attack using the leg trim, keeping the use of the tabs to a minimum just to keep the boat on an even keel.

 

[Nick_H]

On most boats having the trim tabs down as you accelerate will get you on the plane quicker, but this may be more relevant on larger boats. Also I find I can apply a fair amount of trim to bring the bow down without any effect on speed or fuel consumption. This improves visibility, and feels a bit more natural.

 

[duncan]

it can be even more relevant on a smaller boat as hull speed is so much slower and more in that area before the engine is really kicking out power - especially non supercharged diesel duoprops with little prop slip etc - and the R hump more pronunced.

 

[hlb]

By whichever method. The real importance, is to keep the bows down in head seas, but more importantly, up in following seas. Else maybe cartwheel the boat!!!

 

[KevB]

[ QUOTE ]
it can be even more relevant on a smaller boat as hull speed is so much slower and more in that area before the engine is really kicking out power - especially non supercharged diesel duoprops with little prop slip etc - and the R hump more pronunced.

[/ QUOTE ]



As I said earlier "you shouldn't need them to get you on the plane (some under powered boats need their tabs down to help get the bow down). "

 

[duncan]

Kev - why are you constantly looking for an argument?

You even contradict yourself in one simple sentence - [ QUOTE ]
you shouldn't need them

[/ QUOTE ]
[ QUOTE ]
some under powered boats need their tabs down to help get the bow down

[/ QUOTE ]

where does my post differ from what you are saying? (god forbid that anyone does!)

you don't NEED to trim the drive all the way in from start but most OB/OD boaters will as it takes excess strain of the engine and drive unit. If you have a smaller craft with a diesel and shafts you do the same thing with your tabs - more and more craft are being built with this configuration as well.

However I was responding to the question of relative boat size and the resistance hump anyway................

 

[KevB]

Get your facts right, I said HE shouldn't need them and explained that under powered boats may need to have the tabs down to help get on the plane. Where did I contradict myself?
What's a matter with you didn't you get it last night? /forums/images/graemlins/grin.gif

 

[duncan]

when you replyied to my generalisation you opened the application of your statement.

you even said as much yourself -

"as I said earlier..." implying that this applied to my generalisation re smaller boats as much as Pete.

I am happy to accept that my words are only opinions - you are the one who believes that if you 'state it' it becomes fact.

 

[Its_Only_Money]

[ QUOTE ]
You should use your leg trim to adjust the angle of your boat when going along not the tabs.

[/ QUOTE ]

I do the reverse, use the tabs to correct the running angle if required (roll and pitch), then trim the leg for max efficiency. Why imitate a shaftdrive by using the prop thrust to support or depress the stern???? Sure you get some drag from tabs but then you get a sizable efficiency loss by running the leg at an angle away from the horizontal.

No argument with using an outboard or leg for trim on a boat without tabs tho....

 

[KevB]

[ QUOTE ]
you are the one who believes that if you 'state it' it becomes fact.


[/ QUOTE ]

Where do you get this idea from?

I'm at a loss as to what you are on about

Why not grow up and stop throwing your toys out your pram?

(edit)

Just sussed why you feel a little greeved. Couldn't be something to do with engines could it?? /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif