Mast/centreboard position/size

[Peter Rhodes]

How do I work out where to put the mast and centreboard in the merlin-rocket I am designing and how big to make the board

[Skippy]

The Rules

Skippy,I clicked on The Rules and expected to find the rules of the Merlin Rocket instead I find a golden nugget! Where did you find this?

[tspeer]

Ah, the Merlin. I used to race the Smoker's Satisfaction "Special Brew" at Cookham Reach.

Although written for catamarans, this might be relevant: http://hem.bredband.net/b262106/Boat/dagger.html.

Some basic things to keep in mind:
- the lift on the board is dictated by the sail rig, not the board area. But if you don't have enough area, you can stall the board when it tries to match the rig at low speeds (like coming out of a tack).
- drag due to speed depends on the area of the board. Smaller is less wetted surface and less drag, especially at high speed.
- drag due to lift depends on the depth of the board, not the area or the aspect ratio. Deeper is significantly less drag, especially at low speeds.
- there's not all that much to be gained by a complex planform. A rectangular or straight-taper planform makes it easier to accurately profile the board and an elliptical shape isn't the optimum planform to begin with.

As for the proper lead, you'll have to look at what other boats use and be prepared to experiment a bit to get the balance right. Depending on how you arrange things, it may be easier to move the mast step or the board to balance the boat.

[Skippy]

I really don't remember. Scouring the net one way or another.