Since the price of the ETF fluctuates, you may want to set a certain price which is the absolute highest price you want to pay for shares. This would be a "limit" price, and your order might be something like "Buy 500 shares SEA at limit $12.22" meaning you will only buy shares at or below the price of $12.22. The trade-off with limit orders is that you are assured of the price, but you are not assured of getting your order completed.

If the shipping companies can charge higher prices for their services, it give them a better chance to show an operating profit and a better chance that the price of their stocks will trade up. Since the ETF owns stock in shipping companies, the ETF should rise when the shipping stocks rise.

SEA has been paying a quarterly dividend, every three months, which may be re-invested to buy more shares of the ETF. Reinvesting the dividends isn't precisely a dollar-cost-average method since the declared dividend fluctuates from quarter to quarter, but it still affords long term investors the benefit of cost-averaging over time.