on board 既可以用作介词，也可以用作副词。

1. 用作副词时，表示“在船上”。如：

My wife and I were the first to arrive and hopped on board

我和妻子是最早赶到登船的。

We went on board and saw these people packed shoulder to shoulder on the decks.

我们上了船，看见这些人在甲板上肩挨着肩挤在一起。

The cargo on board have been damaged by sea water.

船上的货物因水湿而残损。

The captain refused to leave his sinking ship while there were others on board.

在船上还有其他人的时候，船长不肯离开正在下沉的船。

Have the passengers gone on board? 旅客都已上船了吗?

As soon as I’m on board, I always feel sick. 我一上船就想呕。

The Pioneer probes have on board ultraviolet instruments which are measuringlight that we can‘t measure on the earth.

“先驱者号”太空探测器上装有紫外线仪器，能够对在地球上探测不到的光进行测量。

2. on board 用作介词时，其后可直接跟表示车、船、飞机的名词。如：

They arrived at Gatwick airport on board a plane chartered by the Italiangovernment

他们乘坐意大利政府的包机到达盖特威克机场。

He went on board the train just now. 他刚上火车。

Mr Smith is on board one of those ships. 史密斯先生在其中的一条船上。

There were ten people on board the plane. 当时飞机上有十个人。

The six astronauts on board will spend ten days in space.

飞船上的6名宇航员将在太空度过10天。

On board were enough provisions for two weeks.

船上有足够两周吃的食物。

I hope that they will take on board some of what you have said.

我希望他们能采纳你们所提出的部分想法。

最后一种用法比较特别，希望大家重点掌握。