By 09.30 we had cast off and were heading down-river.是什么意思？

By 09.30 we had cast off and were heading down-river.

9点30分时我们就解缆向下游出发了。

by

prep. 在…旁边，表示方式，由于，经过；adv. 经过，表示保留或保存时用，短暂拜访；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

we

pron. 我们，咱们，笔者，本人，朕，人们；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

cast

vt. 铸造，投掷，投射，脱落，脱皮；n. 铸型，演员表，轻微的斜视，投，掷骰；vi. 掷，投，计算，加；

例句
He cast her an admiring glance...
他向她投以钦慕的目光。

off

prep. 从…落下，离开，从…去掉，下班；adv. 离开，距，离，被取消，下班；adj. 不新鲜的，不能接受，不礼

例句
He eased his foot off the accelerator.
他松开了油门。

and

conj. 和，与，而且，于是，然后，因此；

例句
I spend a lot on expensive jewelry and clothing...
我花很多钱购买昂贵的首饰和衣服。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

heading

n. 标题，题名，信头，[航]航向，斩首；v. 用头顶(head的现在分词)；

例句
Holiday mad Brits are packing their buckets and spades and heading for the sun.
酷爱假日的英国人正收拾小桶和锹铲前往阳光充足的地方。