A new flotilla aimed at reaching Gaza left Barcelona on Sunday. Around 20 vessels are participating in the flotilla, which is dubbed the Global Sumud flotilla. However, strong winds gusting at some 30 knots forced the vessels back to port by Monday, according to reports. The flotilla has had a tough start. The organizers should have known that they would encounter bad weather along the route. The fact that some of the vessels may face challenges in strong winds illustrates that all of the vessels might not reach waters near Israel.

Israel, nevertheless, will face a challenge if some of the ships reach the eastern Mediterranean. According to reports, the 20 initial vessels that make up the flotilla are supposed to be joined by more along the way.

CNN reported that up to 70 types of watercraft may join. The CNN report was also optimistic in timing the arrival of the flotilla to September 14 or 15. These dates do not seem reasonable. Nevertheless, the flotilla is being organized so that it heads to Gaza during the timing of the UN General Assembly, slated to take place in September in New York City.

Israel has intercepted two activist flotilla vessels already, during the Israel-Hamas War. Those interceptions went smoothly. Israel has learned lessons since the Mavi Marmara raid in 2010. During that raid on a large cruise ship, the IDF faced off against almost 600 activists. Many of the activists were hardline backers of the Turkish group IHH. Other smaller ships joined the flotilla.

The challenge on the Mavi Marmara was that initially soldiers rappelled down onto the deck without their usual rifles but rather with paintball guns. Later in a scuffle, 10 of the flotilla activists were killed. This led to extreme anger in Turkey. While the activists were overcome on the ship, the deaths were unplanned, and Israel considered it a failure.

Since then, Israel has dealt with several flotillas, including an attempt by activists to fly en masse into Israel in 2011 aboard commercial flights. So far, Israel has done a good job of stopping the flotillas. In some cases, vessels were prevented from sailing in their home countries. In other cases, boats have had mechanical problems that prevented the activists from reaching their destination.

The challenge with 20 ships, or even up to 70, will be in stopping them all at the same time and towing them back to Israeli ports. Some of the activists might be deterred by threats of prison sentences. In the past, vessels stopped in international waters have seen their crew detained and deported. This makes sense, since grabbing the crew in international waters would not enable a conviction in a court because it does not break Israeli law. It’s not illegal to sail a boat in international waters, even with the stated intention of getting to Gaza. It’s unclear if Israeli courts would sentence people detained far out at sea to lengthy prison terms.

So far, the weather has been Israel’s best ally in dealing with the flotilla. Because the activists want attention and exposure, it appears that, along the way, they will be filing regular reports on their position. This means that there won’t be much of a need to pursue the flotilla because its position will be known.

The flotilla is supposed to be joined by Tunisian and Italian ships

It will reportedly be joined by ships sailing from Tunisia and Italy. That likely means the first leg of the flotilla will be from Barcelona, crossing around 850 km. (530 miles) of sea to the coast of Tunisia. From there, the flotilla will need to sail another 2,170 km. (1,350 miles) to the coast of Gaza.

With almost 3,200 km. (2,000 miles) of sailing required, it’s unclear how long it will take the vessels to get close to Israel. If they make around five knots an hour for most of the journey, then it would potentially take 15 to 20 days, depending on the vessels’ speed at night and whether they have to stop along the way. This is why estimates report that they could reach the coast by September 15. However, to do that, they will first need to reach Spain and link up with the other boats.

Trying to manage the affairs of some 50-70 vessels at sea is also no easy matter.

At this time of year, the Mediterranean is expected to be relatively hot and calm. For instance, Malta is expected to have sunny days for the next week, and winds are expected to be relatively calm around the island, except on September 3, when gusts may reach 17 knots.

In general, the flotilla should have good conditions from Spain to Tunisia over the next week.

However, the activists’ decision to return to port illustrates their challenges. The flotilla sailboats should be able to handle well in winds of 30 knots. The fact that the organizers already feel concerned reflects the logistical and mechanical issues they already face.

They wouldn’t be the first. The Persian navy in 480 BCE lost a third of its 1,200 ships in a gale off the coast of Magnesia (today, Manisa in Turkey) during the invasion of Greece. Adm. Horatio Nelson also faced challenges due to gales and storms during his attempt to pursue Napoleon across the Mediterranean in 1798.