The helmsman could tack the boat singlehanded.是什么意思？

The helmsman could tack the boat singlehanded.

舵手独自一人就能变换航向。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

helmsman

n. 舵手；

例句
The helmsman could tack the boat singlehanded.
舵手独自一人就能变换航向。

could

aux. “can”的过去式，能够，打算，用于假设语气的条件句，用于虚拟语气的结论句；

例句
The regulations were relaxed and the prisoners could get out and about a bit.
规定有所放宽，犯人可以出去短暂放风。

tack

n. [航]食物，劣质材料，赝品，方针，方法，航向；vt. 用平头钉钉，附加，增补；vi. 帆船抢风行驶，用粗线脚缝；

例句
This report takes a different tack from the 20 that have come before.
这份报告和此前的 20 份报告采取的思路不同。

boat

n. 小船，小艇，轮船；vi. 乘船，划船；vt. 用船运输，用船装运；

例句
The boat is now leaning at a 30 degree angle.
船正以30度角倾斜。