A simple and cheap grill on boat. Reuse existing standard grill or, like in ths case, not operating electrical grill - just remove electrical part. This is very cheap comparing to similar comercial products. And it is DIY easy.
Step 1: Attach Wooden Console to Grill
It is enough to find old wooden beam, long about 0.5m and to fix it with two screws to grill box bottom from outside. Crossection should be proper - strong and corresponding to boat element where you are going to mount system.
Console can be additionaly secured with additional universal fixation element or in some other way with rope...
Step 2: Install Wave Protector
In the case of waves you should protect your food from falling in water. You can use aluminium foil or aluminium plate like in this case. Simply cut it and use its bottom to fix it to grid. Place food inside this border and don't worry. There is also additional securing rope to keep grid safe.
Step 3: Light Fire and Grill It!
Bring some dry wood and you can start your boat BBQ. It is safe, out of boat, above water. Just keep your sails far from fire! And fuel tank also!