Tim Tab keels

[sailingdaniel]

Hello hello , im Daniel ,new here..

I wonder if someone know abaout a book ore a webpage whit info abaoute trimtab keels? Ive looked around and found some info here, but not mutch.

I wonder, how big effect it can have if done right , reching ore beating ?

How long the tab has to be in persent to the chord to work well?

Is there a big difference effect whit high/low aspectratio keel?

Is there lot of extra drag ore wibrations if the tab is made in a way that only smooth on the low pressure side when its at an angel?

What type of keel section works best whit a trimtab?

Will a slender boat that dont sidetracks mutch whit heel benifit more , ore need a smaller angel on the tab..

If a bigger sidefors is on the keel and less on the hull is there a chanse that it gives to mutch heel on the boat?

Many questions i know , ill be happy if ill get just some good info.. Ill leve Brunai for Kuching towmorrow so it will be a few adays befor ill be here again.

Happy sailing, hope u nderstand my swinglish . thanks Daniel

[michael pierzga]

Ive sailed racing yachts with keel trim tabs. They work, but are complex to build, maintain, and are difficult to trim correctly to gain performance. ...very much trial and error with accurate instruments or sailing against a sistership was required before we understood how to best use the tab. I rarely see trim tabs these days.

[keysdisease]

I agree with Michael, and to add when you finally get a setting "dialed in" the conditions change and your now out of synch.

If they contributed to performance enough they would be more common and you would for sure see them in the big stakes races like America's cup.

The idea and examples have been around for a long time, like at least a hundren years.

Steve

[michael pierzga]

With the race boat ,the trim tab was only valuable when the helmsman choose to steer in " high Gear" to climb to windward for short bursts....the rest of the time the tab was locked fore and aft. I view them as needless complexities...best to concentrate on a pure foil, underwater profile designs, fore and aft hull stiffness and tight sheeting angles for the jibs.

[Paul B]

Originally Posted by keysdisease

If they contributed to performance enough they would be more common and you would for sure see them in the big stakes races like America's cup.

They were. Since Interpid in 1970 every 12m that sailed for the America's Cup had a trim tab on the keel. Ditto every IACC boat since they took over from the 12s. The only America's Cup events in that time frame that did not feature keel trim tabs was 1988 Catamaran/Big Boat and last year's DOG Multihulls.

They were not used under other rules like the IOR or MORC due to penalites for multiple moveable appendages.

[Paul B]

Originally Posted by michael pierzga

With the race boat ,the trim tab was only valuable when the helmsman choose to steer in " high Gear" to climb to windward for short bursts....the rest of the time the tab was locked fore and aft.

What race boat are you referring to? All the IACC boats and 12s used their trim tabs upwind, not only for a "High Gear". Since only a couple of IOR boats ever tried them (only to soon remove them due to the penalty trade off) I wonder what racing boats were produced with trim tab keels that you could trial against non-tabbed keel sisterships?

[Tim B]

There can be no doubt that increasing the Cl for a given leeway, or (if you can do it) reducing the drag for a given Cl is beneficial. The problems are mechanical, and are generally related to control-surface stiffness and fouling.

There are a number of ways to achieve the ultimate "flexing foil", but none of them are easy when done in water.

Once the mechanical problems are solved, then the primary difficulty is in measuring the leeway, and applying a suitable amount of flap. I suspect this is where many examples have failed.

Tim B.

[sailingdaniel]

Thank you everyone for your reply.
Maybee its a bit kompicated. But the basic ide sounds good i think. Sail and rig has almost endless ways of being trimmed: IQ 100 , The rudder can only do one thing , turn: IQ 10 maybee. The keel if not tilting just sitts there waiting for the boat to go sideways befor it does one of its two jobs. I would say IQ 0.1 for the keel. .
I dont know mutch of racers, but thought some of them use the keel mostly for ballast while deviding the lift between forward or aft rudder.
As for compexesy, i agree its probobly way more compext the a normal keel. But if to compair it to other system on a boat , like props and drivelines, roller furling , etc etc its lookes simpel to me.
Its the ide of having to go sideways thats really gets to me.. So ill keep on locking in to it as best i can..
Take care. Daniel