i think another teory
maybe if franky who ar build going merry after come back to water seven
franky think it fail build going merry a ship who protect the one you loves
he really loves it
but he dont enough money to makes franky family n he sell to get money for that n more important he need money to build dream ship
he work as dismantle n pirate hunter to get money for buy stuff for dream ship
he dont want iceburg give him money coz iceburd build ship for world goverment
then when going merry come back at water 7
when franky know straw hat krew really loves gm n gm loves them too
gm protect them
he surprise when his know going merry really being a ship who protect the one you loves before that he think his fail built it
not tell usop he a shipwright n he build gm
maybe going merry not only protect them but want to go water seven coz
she know who ar build him n lives at water seven
after straw hat crew defeat cp 9 n beat all officer goverment world in puffing tom . robin come back being a real straw hat crew
when acua laguna coming n gm still alive n appear
luffy n his crew n franky really happy
ussop say sorry to luffy n being luffy crew
n franky tell them he build gm
they surprise n want franky fixed gm n want him change GM become super strong n super faster ship .
franky makes GM not only stronger n faster more important can protect who ar you loves
n franky to be new crew straw hat
luffy think it cool if cyborg guy being their friend n he get now the best shipwright in the world
i alway think skill shipwright franky more better then iceburg
when oda tell us he want out one luffy crew n makes new crew old friend from alabastar
who out his usopp
n after settle all trouber
usop being luffy crew again
who ar old friend from alabastar is Niko robin
think it niko robin start being luffy crew at alabasta
this arc water seven only makes a good reason for niko robin n us
Niko Robin become luffy crew forever
it same wat happen to nami
before arc arlongpark
she not become real luffy crew
then after luffy beat arlong
since that nami makes decisition to be luffy crew forever
then luffy get new crew a shipwright
i think all trouble from straw hat crew n give luffy trouble
look likes big test to makes them being luffy crew forever