They are currently 10 members in the Straw Hat Crew, Monkey D. Luffy (captain), Roranoa Zoro (vice captain), Nami (Navigator), Go D. Ussop (sniper), Vinsmoke Sanji (cook), Tony Tony Chopper (doctor), Nico Robin (Archaeologist), Franky (shipwright), Brook (musician), Jinbei (helms man).

Captain

Monkey D. Luffy

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Vice Captain

Roronoa Zoro

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Helms Man

First son of the sea Jinbei

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Chef

Vinsmoke Sanji

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Archaeologist

Nico Robin

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Sniper

Go D. Ussop

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Shipwright

Franky

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Musician

Brook

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Navigator

Nami

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Doctor

Tony Tony Chopper

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Straw Hat Theory

Basically the theory says that the name of each strawhat corresponds to 2 letters of the alphabet and 3 members are missing.