This could have been an imitation of earlier vessels which were made of leather sewn onto wood.
prep. to be onto sb：发现某人违法；察觉某人做坏事
I had told people what he had been doing, so now the police were onto him.
prep. to be onto something：即将有重大发现
Archaeologists knew they were onto something big.
The cargo was loaded onto another ship.
We got onto the bus and sat down.
I'll see you onto the train.
The drug first came onto the market in the 1960s.
His novel has made it onto the short list.
prep. （与step、walk、 run、drive等动词连用，表示位置的移动）向，朝，到
I stepped out onto the balcony.
The players ran out onto the pitch.
We drove onto a ring road.
She stood at the window, gazing out onto the sea.
The rooms face onto a central courtyard.
I lowered her gently onto the bed.
Smear cream onto your baby's skin.
Let's get on to more important matters.
Richard turned over onto his back and began to snore.
Her father lifted her onto his broad shoulders.