Welcome to the forum Scott! I'm sure you will be looking forward to your next R&R.
You indicate that you are new to the hobby, or at least that's how I read it. If so, getting into one of the more 'advanced' detectors will seem daunting at first, but it can actually be the way to go for those who are sure this hobby will be for them. Many do decide to go with a lower end machine when starting. By this I don't mean a machine lower in quality, but rather, one with not as many useful features and options as the more expensive detectors.
To add to the good info already provided, the ACE250 is reasonably priced, and it is a very good machine to start with if you are unsure you will remain in the hobby, though chances are that once bitten, you won't be able give it up. Another machine you would enjoy using is the DFX. The E-Trac and the Spectra V3 would be excellent machines to own as well. However, they are expensive, and the learning curve may be much more steeper for someone completely new to the hobby. I wouldn't hesitate to recommend them though.
The coils on the above machines are waterproof, but not the electronic box. You would end up having a dead machine if that part were to be immersed in water. They are, however, great for detecting at the beaches, on wet or dry sand, and on land. If you are looking to detect in shallow water though, as Ricko and the others pointed out, having a machine dedicated to the task at hand is the way to go.
One machine that is designed for underwater detecting is the Minelab Excalibur. It can be used for detecting on land as well, but it can be awkward and heavy for that use, and will not provide the flexibility the detectors mentioned earlier will offer.
The forum members are quite experienced with the above machines, so ask questions. They will be more than willing to be of assistance and share their experience and knowledge.
Have fun, and once again, welcome!