I would have to agree that the Mac''s are not very well suited to making often very rough passage to the Bahama''s. I would suggest that you look for a more robustly constructed older boat.
With regards to water ballast, the issue with this type of water ballast is the same as with all forms of low-density ballast. If you compare water to lead, water is approximately one tenth the density of lead. That means you need ten times more volume of water to equal the weight of lead. This means that you will end up with some combination of either:
- The water being higher in the boat resulting in a higher center of gravity and less stability than the lead,
- More water ballast to overcome the higher center of gravity meaning a heavier boat (Remember weight, in and of itself, does nothing positive for a boat and does have a lot of negatives.),
- Appendages that are shaped to hold water rather than to be efficient as sailing foils,
- More dependence of form stability which means a less comfortable motion and a poorer ultimate stability,
- Less interior storage or no sump for bilge water to sit,
The bottom line
a well-designed water ballasted boat will always be an inferior sailor when compared to a properly designed fin keelboat. As in all things in sailing there are trade-offs. In my book, even if water ballast reduces towing weight (which is questionable since the retractable bulb keel boats do not have to weigh that much more than a dry water ballast boat), I really think its too much of a compromise in performance and safety for my taste. There are people who are perfectly comfortable with water ballast, but having been aboard a variety of boats from 20 to 41 feet that have been knocked down to close to 90 degrees I see water ballast as too much of a risk for my taste.
There are other more pragmatic issues. Water ballast tanks when used in salt water tend to build up marine life in the tanks. These produce some really awful odors. If you search the archives there was a discussion about this problem perhaps 3 or 4 years ago. It was such a serious problem that one fellow cut his tank apart and poured in concrete.