This game seems to make some unrealistic assumptions; the balance problems can be a consequence of going against the grain.
Naval war takes place between navies, not between ships: linking the player to a ship is meaningless. When a new player joins, creating a new ship out of thin air is economically absurd; upgrading ships with player experience is equally meaningless and physically unreasonable.
It can be better to have well defined sides (e.g. in WW2, Japan vs USA or Germany vs UK) and have players enlist with the role of an officer, successively assigned to larger ships; entry level ships should be very small ones, like lightly armed yachts that can be assumed to be readily available and limited by lack of personnel.
Ships should be available according to a fixed schedule for each side; the best commanders should get the best ships, probably through elections.
This way, a suicide attack from a throwaway account makes the perpetrator an underachiever: he not only died, but he permanently wasted a limited resource of his navy whereas a better player would have defended his ship.
As already observed in other replies, suicide attacks should be, like in real life, less effective than shooting; only the desperate commander of a sinking ship would try to ram an enemy and die heroically, and only in unusual close combat situations.

I think griefers do not care about being being underachievers/little to gain, more so, if they can frustrate others by wasting limited resources they will probably be just as happy running into docks/lighthouses rather than other ships.

I feel that griefers will use the easiest way to annoy others. Giving ramming attacks a high damage with no restriction on usage will attract them to use it. lowering ramming damage will force them to use guns to shoot weaker boats. Implementing some sort of protection against unprovoked attacks will usually make them resort to verbal abuse as a last resort.

I go with the small ships can't really harm big ships by ramming. This takes care of griefer accounts to annoy higher players. The opposite (large bullying small) might not really be an issue. A big ship probably has enough firepower to destroy small ships rather than ram them. If the big ship can't kill a small ship via guns, I doubt it could be fast enough to ram the little ship.

Of course you'd still have high level griefers fooling newbies into making a fleet and crushing them from behind but hopefully this can be reported easily and losing the high level account might deter the griefer a bit.

For added strategy, have special attachments, upgrades to smaller ships to enable them to ram big ships and deal high damage for strategic purposes (a small ship sacrifices itself to let the other small ship finish the big ship) the attachment serves as a warning to the big ship that this small ship MAY cause trouble and let the higher level player prepare accordingly.

The effectiveness of ramming could depend on:

1: The speed of the rammer relative to the rammee.
2: The mass of the rammer
3: The point of contact on both ships and the armour at that location
4: The existence of a purpose built ram on the rammer

A small ship will have trouble causing large amounts of damage to a large ship because of 2 - it's hard for a little dinghy to get enough momentum up to seriously damage a battleship.

A large ship will have trouble causing large amounts of damage to a small ship because of 1. The heavier the ship, the harder it will be to get speed up, and a small ship will likely be able to evade it easily.

Typically, ships ram with the front - therefore, this part of the ship will be the most resilient to ramming damage. Some ships might have a purpose built ram, which, in addition to having big scary spiky bits below the waterline in order to cause maximum damage, will probably be heavily braced to prevent damage in the impact. The side is not so tough, and is also the biggest target - but has the disadvantage of being covered in cannons, so ramming someone in the side is a risky proposition. The ideal would be a ram in the rear, although it's a narrow target to hit.

Ramming probably won't be that effective unless it's fairly deliberate - you'd actually need to get up a fair bit of momentum in a straight line in order to do real damage, and you'll need that momentum to be piled straight into the target - glancing blows won't do a great deal. That said, a successful ram could be totally devastating. It's a risky and difficult tactic to pull of, but could have great rewards.

There are also other things you might want to consider, such as ramming ships getting entangled, boarding actions etc.

Hang on, if your sailing ships are even half realistic, then they just don't damage each other very much by ramming. They just aren't fast enough in relation to their ability to absorb damage. And broadsides at close range should be devastating. I think you are over-designing yourself into an unrealistic hole, here. Just go with the flow. "No captain can do very wrong, who lays his ship alongside that of an enemy."