How do I prevent hallowed jhen from breaking the boat?

I have attempted to slay the mighty Hallowed Jhen Mohran a couple times now and the expedition has always ended in failure due to our boat taking too much damage. Every time we've had about 10 minutes left in the quest in the second stage of the fight. I'm looking for tips on how to prevent this from happening and I have a few questions about the boat mechanic.

• Which of Jhen's attacks damage the boat?
• Do the boat damaging attacks all do the same amount of damage to the boat?
• How much "health" does the boat have?
• In addition to the above questions, what are some things to keep in mind during this fight?

Some further background: I only have the 3ds version so going online is unfortunately not an option. I either hunt solo or with 1 other friend. Typically I take the ballista binder, but I am still learning the attack patterns so I must admit I miss quite a few of the opportunities. I use gunlance and lance and my friend uses switch axe. At this point we've build up our arsenal enough to have a g-rank weapon of each element and rarity 9 armors.