Since this is the Floodmod sub-forum, and I've played a good amount of the mod. I'll leave some suggestions
1. Propulsion items (thrusters)
Speaks for it's self doesn't it?
Items that you can attach to parts of your boat in order to make your boat a moving target, travel towards other players for closer and more fun combat, to stop these from being overpowered, set them with their own durabilities and possibly make the power of the thrusters drop with the condition.
2. Dropable hazards
Items you can drop off of your boat to serve as hazards in the flooded battle feilds, the Gmod Racer has items such as the mines to serve as this so why not put these here to, buy a special block that will emit a floating mine on a button click and causes massive damage if a player collides with one but of course limit the uses, for example the cheapest only dropping one and more expenive ones dropping a large number, maybe up to 3-5 mines per game.
3. Ramming damage
With the idea of propulsion on your boats, turn you sea vheilcle into a moving weapon as well by giving damage on collisions.
The damage given on items from these collisions would be based on both the material of your ramming object, and the speed of which your were going at, metal items will give more ram damage and higher speeds will also boost damage. a minor ammount of damage is given to the ramming object as well
4. NPC teammates on boats
Pay a very large sum to get a NPC character help you sink your enemies for those who are too lonley to have human teammates, given about half of a human player's hp they will only target enemy boat objects instead of players, the more expensive ones will hold better equipment ranging from the standard pistol, to the imfamous RPG and the NPC player model will be completley random from a list of permitted NPCs such as combine soldiers and rebel characters.
These need in, the times a player suffers falling off their boat becuase they loose their footing and if propulsion is included, this will be a bigger problem so seats could be a good option as long as they can be damaged while sitting and chairs can be destroyed.
The silence of each match is only broken with occasional gunfire by other players and that is not going to be great, music can have a major effect on the atmosphere of gameplay so it would be great to hear some sort of combat music or pirates of the carribean theme tune playing while we kill eachother.
7.bigger play areas.
if a lot of what is mentioned gets put in, then we will require a much larger playing feild than what is currently given to us in the beta map, more freedom on where you build your warship of death and possibly flood hazards that are naturaly there such as the roof of a house that failed to flood or large rocks rising from the water.
8. water not being lethal (by it's self)
Bugs me in all flood related games is that the water is a lethal item alone, Take a sip of the water and you'll die a slow painful death.
A better idea would be to put in underwater hazards in the game like sharks that crave your blood, and players who die can also respawn as one of these water hazards to send players to their doom when they go for a swim near the wreck of their boat.
9. Upgrading Boat parts
Like reinforcing the structure on your Gmod racer chassis, take individual parts of your boat and upgrade them for a fee to increase their boyancy, health or ramming power, these could be applied ot thusters to make thme more powerful and to npcs to improve hp and weapons,
10. If you kill a player, you can take the remains of their boat.
For players who kill another, all the parts of the boat they have left are given to you, they are put into a sort of tempary backpack where you can then spawn them after the round ends and attach them to your ship or sell these items for extra cash or use them as parts to repair existing parts of your boat.
So yeah, feel free to discuss these 10 things with me here and heres hoping that the admins can apply some of these to new versions later on in time.