Stub keel/ center bd vs centerboard question

[Bruce46]

Which is more efficient in 18 to 30 foot trailerable sailboats, a centerboard or a centerboard mounted in a stub keel? The stub keel does give shallow water maneuverability, however, the water flow off the stub keel can present hydrodynamic challenges.

[Petros]

The centerboad boat will have less drag than one with a centerboard and stub keel. The stub keel is done to lower the center board in the hull (it will be protected when inside the stub keel), this gives more room in the cabin since the trunk will not be above the cabin floor. The stub keel will also add more weight lower on the hull.

Presumably you can have less total ballast with the weight lower, making it lighter. I would presume the stub keel would be more comfortable at anchor, as as pointed out, give better control with the center board up.

So there are trade offs either way.

[philSweet]

Bruce ,
There is no simple answer to your question; it depends on the boat, and how and where you sail it. At 18 foot, most require no ballast. They rely on crew weight to provide RM. As the vessel gets heavier compared to crew weight, Ballast becomes more desirable to manage heeling angle. Once you get past a steel plate CB, it costs more to put it in a movable board than in a fixed stub keel.
My personal preference for skinny water sailboats is a shallow V bottom with twin asymmetric bilge boards built into cockpit seat transoms. When fully retracted, they protrude to the same depth as the keelson, filling the slot. Lots of extra costs to make two board boxes, but they also do a fine job of aligning the boat on the trailer if the bunks are just outside the boards.
So tell us what your requirements are. Displacement and draft limitation being the two most important in my way of thinking.