When sailing to a foreign land, is it necessary to show your passport to the harbormaster?

Yes – you have to go in and check in with the Harbormaster. Usually, there are custom officials in the major ports and it can be quite an elaborate procedure, involving payment many times.

In terms of procedure, you would radio ahead when you were coming near the port and the Harbormaster would direct you to an available slip or mooring. You would dock the boat and then go to the Harbormaster or Customs House to check in.

plus you are likely to be approached even before you reach the harbour.
(Dont quote me on this but I think you are also required to fly the flag of your nationality as well as the flag of the country from where your yacht came from, Greek/turkish. But I suspect this may be etiquette more than law.)
You will also need a visa, but this can be purchased at your port of entry

Yes… it’s usually the same routine as when you land by plane. Your ship can be boarded and searched for contraband by customs officers. There will be fees to pay, depending on the country and depending on your passport (where it’s from) you may need a visitors visa also.

Before radios and cell phones, there was flag etiquette. Besides keeping you out of a foreign jail, being heavily fined and just making the port authorities’ jobs easier, using flag etiquette sends a message to them that you are a seasoned sailor and you probably know what the fuck you are doing. Trust me, this really helps. Know your flags: Declaring when entering a Port of Call is serious business. Doing it right gets respect.

Whenever you enter foreign waters you must hoist the Quarantine flag, or “Q” flag. This is not just some quaint seafaring tradition, this is law, the breaking of which can result in you being held for ransom in some filthy little jail far from home. The “Q” flag is a plain yellow, rectangular flag. Hoisting this flag signals that the “vessel” is healthy and that you are requesting clearance into the country. This flag is flown from the starboard spreader. On a boat with more than one mast, the flag is flown from the starboard spreader of the forward mast. The “Q” flag would displace any other flags that you had hoisted on the starboard spreader (yacht club burgee, Seven Seas Cruising Association pendant, state flag, etc.). These flags can now be flown from the port spreader. The “Q” flag is brought down only after you have formally cleared into a country.

You must fly your national ensign in it’s proper place. An ensign is your national flag. It identifies the country from which your boat is registered. A boat that is registered in the US and is located in US waters can fly either the US ensign (this is “Old Glory” – 50 stars and 13 stripes) or the US yacht ensign. The US yacht ensign shows 13 stars with a fouled anchor in the union. But once you begin cruising in international or foreign waters, US registered boats must fly the US ensign (50 stars).

Generally, your ensign is flown from a stern staff. However if this is not possible, there are other locations from which it can be flown. Check with Chapman Piloting, one of the best reference books for sailors, for more information. The stern staff is considered a place of honor. Do not fly state flags, pirate flags, gag flags etc. from the stern staff.

You need to choose the proper size national flag for the size of your boat. It should be one inch for each foot of overall length of the boat. For example, a 40-foot boat would choose a flag whose length is 40 inches. Round up if necessary to find a flag of the right size.

It’s customary to fly the flag of a foreign nation just below your starboard spreader when you are in foreign waters. These flags are called courtesy flags. Although the word “courtesy” is used, in many countries it would be considered disrespectful to not fly the courtesy flag and it is possible to receive a fine for not flying it. These flags are available from marine stores such as West Marine or Boat US. You can also sew your own courtesy flags. But be sure to have accurate copies of the flag and be sure to match colors correctly. It’s important to fly the courtesy flag right side up.

As an example of the importance of flying flags properly and in their proper place, in some countries, such as Cuba, flying their flag upside down is considered to be a declaration of war. Easy to avoid, right? Hmph. If you look at the Cuban flag, it can be quite difficult to tell which way is up. It has blue and white stripes with a white star set on a red triangle. It looks precisely the same up or down, right? Hint: The star has five points. The flag must be flown with the point of the star facing up. I have personal experience in this regard. It is serious business to the Cuban Coasties. They look for this mistake and will give you shit to no end for being so ignorant of their country and it’s ways that you do not even know how to fly their flag. And they pray you will smart off while they tell you this. You have no idea how endless the shit stream is if you do. And, if you are an American, you already have three strikes against you: Your countrymen have left you a legacy of arrogance in the past for which you may have to answer, your country has prosecuted an extremely damaging economic embargo against Cuba for the past 53 years, and lastly, your country doesn’t want you in Cuba in the first place and you have no US diplomatic presence to protect you if shit goes south. Due to the latter, Cuban customs usually won’t stamp your passport if you’re an American. This is a courtesy to make your stay less worrysome and keep you from having a lot of explaining to do when you get back home. But all courtesies fall by the wayside if you come sailing impudently into their country without acknowledging that it is at their good graces that you do so.

Bon voyage, stay out of trouble, learn your flags, and play nice.

Short answer: Yes.