What is Haitei? Under the Sea Tsumo Win Explained for Beginners

What is Haitei Moyue?

Haitei Moyue (海底摸月), often shortened to “haitei,” is a 1-han yaku in mahjong that completes when you win by tsumo on the haitei tile (last tile from the wall). The name means “scooping the moon from the bottom of the sea” - a beautiful name for this yaku.

It’s a luck-based yaku that’s difficult to aim for deliberately, but if you’re in tenpai, it’s a bonus 1-han added when you draw the last tile. It only works with tsumo, not ron.

Detailed Explanation of Haitei Moyue

Conditions for Completion

To complete haitei moyue, you must meet these conditions:

What is the Haitei Tile?

Position of haitei tile:

Wall composition (136 tiles):
- Drawable tiles: 122
- Dead wall (wanpai): 14 (including dora indicators, replacement tiles)

Haitei tile = 122nd drawable tile (last before dead wall)

Usage Examples

Real Game Situations

Example 1: Win Declaration

"Tsumo! Haitei moyue!"
"Got it with haitei!"

Example 2: Confirming Yaku

"It's haitei so +1 han"
"Haitei tsumo for 2 han"

Example 3: Expectations at Tenpai

"If I tsumo haitei, +1 han"
"Keeping tenpai hoping for haitei"

Haitei Moyue Shapes

Basic Form

One turn before haitei:
Hand: 123m 456p 789s 22E 5s (tenpai)
Haitei tile: Draw 5s
→ Haitei moyue established

Yaku: Tanyao + Tsumo + Haitei moyue = 3 han

Combined with Riichi

After riichi:
Hand: 234m 567p 345s 999s 8p (tenpai)
Haitei tile: Draw 8p
→ Haitei moyue established

Yaku: Riichi + Tsumo + Haitei moyue = 3 han (+uradora)

Related Terms

• Haitei: The last tile from the wall
• Houtei Raoyui: Ron win on last discard
• Menzen Tsumo: Commonly combined yaku
• Rinshan Kaihou: Win after kan draw
• Wanpai: The 14 dead wall tiles

Common Mistakes and Points to Note

Points Beginners Often Mistake

1. Confusion with Ron

   • Ron doesn’t count
   • Tsumo only

2. Position of Haitei

   • Last after dead wall
   • 122nd drawable tile

3. Combining with Other Yaku

   • Can combine with menzen tsumo
   • Can combine with riichi

4. Kan Restriction

   • Can’t kan on haitei tile
   • Can’t riichi either

Tactics for Haitei Moyue

Decisions at Tenpai

Tenpai near haitei:

Haitei-Conscious Play

Tracking remaining tiles:

1. Always check the wall
   - Count remaining tiles
   - Calculate turns to haitei

2. Decisions near haitei
   - If tenpai, maintain
   - If iishanten, hurry

3. Balance with defense
   - Fold before haitei?
   - Push until the end?

Haitei Moyue in Practice

Path to Haitei Moyue

Typical flow:

Mid game: Reach tenpai
↓
Late game: Haitei approaches
↓
One before haitei: Last chance
↓
Haitei: Tsumo → Haitei moyue established

Effect on Scoring

Value of +1 han:

Compatible Yaku Combinations

Commonly Combined Yaku

Combination Example

Riichi + Tsumo + Haitei + Dora 1:

Hand: 234m 456p 567s 345s 55p
After riichi, tsumo 5p on haitei tile
→ 4 han (5,200 or 7,700 pts) + uradora

Haitei Moyue Probability and Value

Occurrence Rate

Statistics:

• Haitei moyue completion: ~2-3%
• High completion rate if in tenpai
• Relatively common among luck yaku

Comparison with Other Luck Yaku

Occurrence rate ranking:

1. Menzen Tsumo (~40%)
2. Haitei Moyue (~2-3%)
3. Houtei Raoyui (~2-3%)
4. Rinshan Kaihou (~0.3%)
5. Chankan (~0.01%)

Haitei Moyue Strategy Points

Importance of Maintaining Tenpai

Policy near haitei:

1. Offensive tactics

   • If tenpai, maintain
   • Aim for +1 han
   • Take risks

2. Defensive tactics

   • If not tenpai, fold early
   • Avoid payment penalty
   • Safety first

Effect on Opponents

Psychology at haitei:

• Make them think you’re in tenpai
• Pressure opponents
• Invite folding

Special Rules at Haitei

Restrictions on Haitei Tile

What you can’t do:

1. Kan

   • No minkan
   • No ankan
   • No added kan

2. Riichi

   • Can’t riichi on haitei
   • No next draw

Display in Online Mahjong

Conclusion

Haitei Moyue (Under the Sea) is a 1-han yaku that completes when you win by tsumo on the last tile from the wall (haitei tile). It’s a luck-based yaku difficult to aim for deliberately, but if you’re in tenpai, it’s a bonus 1-han when you draw the last tile. Beginners should learn the basic “haitei tsumo = +1 han,” and if you’re in tenpai near haitei, maintain it and aim for the tsumo. It combines well with riichi and tsumo, and has the potential to create dramatic last-second reversals - an attractive yaku.