Hi Larry: Hard to answer your question without looking at a complete set of plans. However, there are a couple of tests you can do which will give you the answer. Basically, see how the boat balances without the mizzen when beating and reaching. If the helm is neutral or has a slight weather helm, you will be OK. If the helm is leeward without the mizzen, this is a big hit on performance and it will be worse when you just increase the existing sailplan.

I assume that once the breeze comes on, you do not need the mizzen, and that it creates excess weather helm. One thing to consider in making the rig taller is to lengthen the main book a hair, to add area and move the center of effort back at the same time.

Generally speaking, most boats have a net benefit from removing their mizzens–less drag, less weight, and better overall performance.

One thing to keep in mind is rig weight. You would not want to end up with a heavier rig! And wood is a pretty efficient material when used correctly. Steve Dashew