Trim Tab on a Daggerboard?

[cmetzbower]

I have a Dolphin 15 Senior I’m fixing up and need a daggerboard for it. I could buy one off the internet but that’s no fun.

I was wondering how effective a trim tab on the trailing edge of the daggerboard would be. And if I did that, what shape the foil should be.

Does anyone have any experience with this or recommendations?

Thank you in advance!

 

[skaraborgcraft]

There were some boat designed in the 60,s with tabs on the keels trailing edge. Not something you see today, probably a reason for that.

 

[Tops]

https://sailboatdata.com/sailboat/dolphin-15-senior/

I would go NACA0009 on the dagger board and forget any sort of trim tab, and perhaps work on the shape and foil of the rudder. My old Sunfish boats' 'foils' were not foiled, just tapered.

https://www.sunfishclass.org/assets/06670/Documents/Rules__amp__regs/ISCA_measurement_diagrams.pdf

 

[gonzo]

There were keels with tabs on the leading and trailing edges. It would be possible on a daggerboard, but there is a considerable complication. The system was a way around handicapp rules. If you are trying to beat a rule, they are effective. Otherwise, maybe at some points of sail, and worse at others.

 

[wet feet]

They were effectively obsoleted by the introduction of the Movable Appendage Factor to the rating rule of the time.The penalty imposed outweighed any advantage they may have conferred.For a small boat,it would be quite challenging to make the trim tab and to design an effective system for controlling the geometry and the slot gap.A very long time ago I believe a Hornet raced quite successfully with one,the fact that one of the crew worked for an aircraft builder might be relevant.

 

[philSweet]

You do what the tab does by moving forward or aft a bit in the boat. The asymmetry doesn't gain you anything. You want the rudder to have about half the angle of attack of the board. So if you have 6 degrees of leeway, you should have about three degrees of lee helm. If you find the board stalling, build a better rudder (deeper) and then run less lee helm.

 

[wet feet]

That is a rather novel theory,could you please expand on it for us?

 

[CarlosK2]

Intrepid
mahogany and oak

1967, win
1970, win
1974

Trim-tab on Keel was a America Cup thing ...

... When rudders were very small and not used to produce Lateral Force

A good-sized rudder that works with the centerboard to produce Lateral Force is better and more efficient

The work can be distributed, for example, 60-40. 60% of the lateral force centerboard and 40% the rudder.

(There are racing sailboats with huge rudders that distribute the load 50-50)

 

[CarlosK2]

Forty years ago the easiest way to cheat a race measurement was to tilt the mast aft (thus putting more load on the rudder) and install a rudder with more draft.