Here's my Strategy for the tail. First, make sure Shield Oath is on.

Pop Fight or Flight while the slam is occurring. When the tail appears, do Fast Blade -> Circle of Scorn -> Savage Blade -> Spirits Within -> Rage of Halone.

Now, here's where things split.

If the adds appear on your side of the boat: Grab yours and hope your fellow tank isn't too stupid to grab a mob that's 2 feet away. Give both the tail and the add a couple of flashes. Tail hate established.

If the adds appear on the other side of the boat: Hit the tail with an uncomboed Rage of Halone and run to the adds. Your GCD will be over by the time you're in range to do anything. Keep an eye on tail aggro and provoke immediately if you lose it. Drag the add(s) across the entire boat to keep tail aggro if you have to(You'll want to do this if you have a SMN anyway. Dots Baned to the tail don't reflect back to the caster). There's time to kill the adds, but less time to deal with a dead healer.

For adds in specific:

First, this should only be difficult if adds appear on the far side of the boat. You have some ground to cover and your allies are already attacking.

If you aren't worried about tail hate: Shield Lob add 1, Provoke + Shield Lob add 2, flash a few times. Hate established, usually. Do not worry about positioning until you have hate. If a DPS gets hit by tail spines, it's not your problem :P

If you are worried about tail hate: Shield Lob 1, Shield Lob 2, flash, and pray. You can also try Fast Blading the tail on the way out, hitting add 1 with Savage Blade, and then add 2 with Rage of Halone, but that's a lot of movement.

Alternately, enact a strategy where both you and the MT both take one add each. It's easier to keep hate on one enemy than two, after all.

The Tail and the second add:

If you lose aggro on the tail during the second add, either you're doing something very wrong or the WHM is overhealing like crazy. As for the add itself, don't worry about who has aggro on it. It'll spend enough time stunned that nobody's going to get killed.

Other things worth considering:

-If your WHM is using Medica at the very beginning, one of a few things are happening. One, you don't have hate on the add(s) and they're hitting your party. This is your fault. Two, DPS is standing too close to the healers and getting waterspouted. This is usually the DPS' fault. Three, your WHM is an idiot and overhealing for no reason. This is your WHM's fault. Four, someone is getting hit by the tail or head because they're between a tank and the boss.

Long story short: Your WHM should not have to use Medica during the first adds. If it's necessary, someone screwed up. Or maybe the entire party did. Either way, reevaluate the way you're doing things.