The water was not very deep and the boys stood one of the posts upright and attempted to work the end down into the bottom by swaying the top back and forth.
"It's no go," panted Walter after half an hour of hard labor which only sank the post a few inches in the hard sand. "It would take us ten years to put them all far enough down to hold."
"I expect we will have to give up the dock for the present," Charley agreed, ruefully. "Too bad. Of course one is not absolutely necessary but it would save us a good deal of trouble and also wet feet."
"It is lucky that your assistant is a person of great intelligence," Walter observed, slyly. "Your methods are primitive, clumsy, hand-labor methods. This is an age of machinery and brains. Now, if I were boss of this, job, I would call in the aid of machinery to replace the hand methods which have been tried and found wanting."
"I resign as superintendent in your favor," Charley grinned. "There is more honor than pay attached to the position, anyway. It will be a good opening for you. You will be able to say in future years that you held at least one position where you were not paid more than you were worth."
"Your words are prompted by intellectual jealousy," declared his chum, calmly. "However, it is the misfortune of the truly great not to be appreciated until they are dead. If you will bring the launch in here, I'll explain my plan so simply that a child, or even you, can understand it."
Charley, deciding that he was getting the worst of the good-natured banter, obediently waded out and brought the launch in.
"I don't know whether you are well enough acquainted with engines to realize it," mocked Walter, who had only made the discovery himself that morning, "but the cylinder of this engine, as you will see when I point it out, is inclosed in a hollow iron jacket. This thing down here is a pump, and you will notice that there is one pipe running from it down through the bottom of the boat and also another pipe leading into the jacket. Observe also that there is a short piece of pipe in the jacket to which is fastened a piece of hose that runs out over the side of the boat. Do you take in all that?"
"I do," said Charley, briefly.
"All right, though I am quite surprised. Now, when the engine is running that pump sucks up water through the pipe that goes through the bottom of the boat. The water is forced through the other pipe into the jacket and passes overboard again through the short pipe and hose. The constant circulation of cold water keeps the engine from heating up and exploding."