I am not a sailor. But the principles Flavel expounded still apply to something which I do regularly: travel. So here is a summary of John Flavel's advice to sailors, adapted to travellers. (Source: The Works of Flavel, Vol. 5, "The Seamen's Companion, Sermon 1: The Seaman's Farewell", Banner of Truth Trust)
Scripture: Acts 21:5,6 "And we kneeled down on the shore, and prayed; and when we had taken our leave of one another, we took ship, and they returned home again."
Doctrine: When travelling, we must pray.
(1) What special mercy should we pray for when travelling?
First: Above all, for the forgiveness of our sins, "a mercy which must make a part of every prayer." "If sin be pardoned, you are safe, you need fear no storms within, whatever you find without: But woe to him that finds at once a raging sea, and a roaring conscience; trouble without and terror within; ship and hope sinking together." The troubles of travel are nothing compared to the troubles of sin, and only when the latter is dealt with at the cross are the former put in their proper place and faced with the courage that comes from being forgiven.
Second: "That the presence of God may go with you, I mean not his general presence, which fills the world, but his gracious special presence." This is the presence of the Holy Spirit in the hearts of the believers, which reminds us that 1. God is sovereign over all dangers, and shall "work all things to the good of those who love Him"; 2. God commissions his angelic servants "to sing above and watch below... as a life guard to that man with whom the Lord is"; 3. God hears our "cries in a day of distress."
Third: For the avoidance of temptation. "Every place, every employment, every company hath its snare and temptations attending it: And you know you have corrupt natures, as much disposed to close with temptations as tinder is to catch fire: So that unless the preventing, restraining, and mortifying grace of God be with you, they will but touch and take. If there were no devil to tempt you externally, yet such a corrupt heart meeting with a suitable temptation and occasion, is enough to overcome you."
Fourth: "for divine protection in all the dangers and hazards to which you shall be exposed. You know not how soon your life and estate shall be in jeopardy." The number of random factors in travelling -other drivers, ourselves as drivers, weather conditions, vehicle function, etc- makes it amazing that driving is as safe as it is. Given how often we take our eyes off the road, our hands off the wheel, or even just put ourselves completely into the care of others, it's amazing that we don't spend hours on our knees pleading for safe passage before setting out, and even go so far as to forget to pray at all.
Fifth: "for counsel and direction in all your affairs and undertakings, and lean not to your own understandings.... The Lord can blast your enterprise, though managed with never so much wisdom and contrivance. You are not only to look to God as the author of success, but as the director and guide of the action. It is by his conduct and blessing that all things come to pass."
Sixth: "for success upon your lawful employments and designs, and own it to be from the Lord." We are wonderfully blessed as Christians, in that not only God forgives our sins but allows us to ask for yet more.(2) What influence does prayer have upon mercy in travel?
First: It is the means God has given us by which we are to obtain mercy. "This is the stated method in which our mercies are conveyed to us; and therein the wisdom and goodness of God are eminently discovered. His wisdom in making us to see the Author of every mercy in the way of receiving it, and securing his own glory in the dispensing of every mercy: His goodness to us in sweetening every mercy this way to us, and raising its value in our estimation." This is not to say that God needs our prayers, for "though payer be altogether needless to his information, yet it is very necessary to testify our submission."
Second: It is the means by which God makes mercy pleasant and sweet. "No mercies [are] so sweet as those that are received upon the knee." Without prayer, we forget that God is the source of all mercies, and they quickly become common.
Third: It makes our enjoyment of God's mercy holy. "Prayer hath a sanctifying influence upon all our enjoyments." When we remember and delight in the great truth that God is the source of all mercy, our delight becomes pleasing to God, and sets us apart from the world, which looks to itself as the source of joy and in doing so loses both joy and holiness.