The affect of wind on a vessel without a sail

[Neta Friedman]

Hello,

I'm an archaeology student and currently working on possible ways in which prehistoric humans could have reached islands in the Mediterranean.

I have a question I hope you can help me with,
and please excuse me if I'm posting in the wrong forum, I wasn't sure in which one to write.

My question is, how much would the wind influence a vessel that doesn't have a sail? and what would influence it more, the wind or the sea currents?
Of course, the wind affects the currents, but what would be the influence on the vessel in addition?
It probably depends on the strength of the wind and current and so on, but if you could just give me your general impression.

Also, let's say we're talking about a simple small boat, and/or a raft.

Thanks!

[Steadman Uhlich]

Wind and Waves and Current can take a raft (even one without a sail) a long way. Waves generally go with the wind. Current does not always. When working together (such as Gulf Stream) they can move a floating object about 4-5 knots at times. In some areas (for example off the east coast of Australia) strong currents can be very strong too.
___________

What about examples of drifting distances?

The first example that comes to mind is that of a sailor whose sailboat sank. He abandoned his boat (as it quickly sank) and got into his life raft.

He survived in that small liferaft for 76 days as he drifted (with wind and waves) across the North Atlantic, eventually reaching an island in the Caribbean. He drifted a LONG way, but I don't recall how far. You can probably find out by reading about him.

You can read about him online or buy his book.

Here is a 40 page preview you can read. Published originally in 1986, based on his 1981 attempt to sail across the atlantic singlehanded.

If you just want to read about the sinking of his boat, and how he had to quickly abandon it, skip to page 20-22 of the linked preview.

His small boat (he built himself) was struck by a whale (he speculates) and sank in just one minute, or filled with water to the point he could not stay on it. . He barely had time to launch his life raft (luckily he had one). He then drifted and survived for 76 days in his life raft.

https://books.google.com/books/about...kp_read_button

_____

There is a good article about his adventure in Wikipedia. Here is a short excerpt:

"On the eve of April 20, 1982, he spotted lights on the island of Marie Galante, south east of Guadeloupe. The next day, on Callahan's 76th day afloat in the raft, fishermen picked him up just offshore, drawn to him by birds hovering over the raft, which were attracted by the ecosystem that had developed around it.[5] During the ordeal, he faced sharks, raft punctures, equipment deterioration, physical deterioration, and mental stress. Having lost a third of his weight and being covered with scores of saltwater sores, he was taken to a local hospital for an afternoon, but left that evening and spent the following weeks recovering on the island and while hitchhiking on boats up through the West Indies."

https://en.m.wikipedia.org/wiki/Adri...ys_Lost_At_Sea
_________

His example of 76 days is a long time.

But it is not the record for people surviving while adrift on an ocean. Here are a few more notable (well documented) examples:

Dougal Robertson, Scottish author and sailor who with his family survived being adrift at sea after their schooner was holed by killer whales in 1972. They survived for 38 days in the Pacific, before being picked up by a passing ship.

Maurice and Maralyn Bailey, survived 117 days adrift in the Pacific Ocean.

Rose Noelle, trimaran on which four people survived 119 days adrift in the South Pacific. This was a capsized large trimaran (sailboat).

Poon Lim, who survived for 133 days adrift in the Atlantic. This was during WW2 era.
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More recently have been claims that some have drifted for several months (e.g. Thousands of miles across parts of the Pacific).

________

Good luck on your project about the effect of wind.

Hope that helps.

[Neta Friedman]

Hi,
Thanks for the quick reply.
It was very interesting and I'll have a look at what you sent me.
How strong are the currents in the Mediterranean, and specifically the area between Africa Crete and Greece?
Is there a website or some other place I can look into seasonal data regarding the winds waves and currents?

[Steadman Uhlich]

Originally Posted by Neta Friedman

Hi,
Thanks for the quick reply.
It was very interesting and I'll have a look at what you sent me.
How strong are the currents in the Mediterranean, and specifically the area between Africa Crete and Greece?
Is there a website or some other place I can look into seasonal data regarding the winds waves and currents?

You could find a free “Pilot Chart” for the Med.
It will show (by month) the prevailing winds and currents and typical seas based on historical data that was reported by mariners over decades. It shows, by use of some graphical icons the direction of the winds (by percentage of direction) and an average of their strength. I think you could understand how to read these after a few minutes study, and it is free. They are published by month. Should be available from governments in the Med area or your own country.

I don’t have a link handy. But other CF Members may have a link to the Pilot Charts for the Med.

You can also buy a book that shows this data, using more recent data. You could get one for about $85 (as I recall) published in 2018, written by Jimmy Cornell and son, called Ocean Atlas (as I recall). The graphics are easy to understand, and their book uses more recent (satellite and buoy observed) data.

[Steadman Uhlich]

IF you want to see something that shows the current projections of currents, winds, and waves, you could download or use browser to access a free app that is intuitive and easy to use. It is called “Windy” or Windytv.

It has tabs that will show you the predicted wind, waves, current, for the next 5 days. You can zoom into the area you area writing about. It is based on complex computer models and data.

It is free and nice to use and intuitive. Nice visuals.
https://www.windy.com/overlays?35.65...4,8,i:pressure

[Snore]

Instead of an Internet forum (not footnote grade) - Google “drift model” to see discussions of engineering models that calculate drift based on currents.

Then google “pilot chart Med” to see historic wind patterns for different times of the year.

Finally there are models on qtVlm.com and fastseas.com that provide info based on current weather.

[Adelie]

https://msi.nga.mil/MSISiteContent/S...106/106dec.pdf

Dec ember pilot chart for North Atlantic chichi includes the Med.

I bet you could replace “dec” in the URL to get any other month.

[JPA Cate]

Hello, Neta,

I, too have an interest in ancient history. My suggestion to you is that if the people in question had fabrics or skins, there would be no archeological record of such use of sail, but it was probably far more ancient than will ever be able to be proved.

What you learn about winds and currents will give a hypothesis.

My experience is that people we visited in the South Pacific routinely used palm branches to move downwind in canoes that they paddled. It is a question of inventiveness and saving one's energy. They could paddle downwind, but it was not a race, it was the end of a day in the gardens, returning to their home island, and it was restful. I have also seen a girl on a log, using a branch to paddle with. Human beings just love to move around..........and a discarded branch leaves no historical record.

Ann

[Snowpetrel]

^^Yes Ann, exactly my first thought. In Vanuatu I have seen this, with palm fronds being used as an impromptu and effective downwind sail.

I can easily imagine any simple stone age vessel would have done something similar, I have great respect for the seafaring capabilities of our ancestors. Almost every culture back as far as we know that lived near a large body of water has quickly evolved effective watercraft from the availible materials.

OpenCPN and the climatology plugin has a good set of weather and tide data. But 30,000 years ago the climate would have been very different, and that will have a big effect on your modelling.

[Snowpetrel]

If you can get hold of the IAMSAR search and rescue guide, it has details of drift rates for different types of vessels and conditions. A lot would depend on the type of vessel. A heavy raft would be predominantly effected by the current, a lighter canoe, or skin boat would be very effected by the wind. The ancient seafarers would have had extremely good knowledge of the local weather patterns and seasons, and how to best use them.

[Don C L]

Welcome aboard Neta,
Locally the native Americans used canoes called tomols, human powered and pretty fast and they were used to travel the 20 or 30 miles or so regularly. But a boat just adrift in the wind would need a strong wind, blowing in exactly the right direction, to be of much use. A canoe or raft, broadside to the wind I suppose could get up to a knot or two in 15 knots of wind, along with the aid of periodic surfing of the waves. But I am sure folks immediately figured out that's a pretty dumb way to travel. I'd look at the dhows and Nile river boats of ancient Egypt for a good possible proto boat design. Considering what native Americans, Polynesians and early sea-farers worldwide for that matter, could and did accomplish, I suspect we grossly underestimate what prehistoric people could do. I'd contact Brian Fagan to help you out too:
Brian Fagan

https://en.wikipedia.org/wiki/Dhow
https://en.wikipedia.org/wiki/Tomol

[norulz]

Originally Posted by Neta Friedman

Hi,
Thanks for the quick reply.
It was very interesting and I'll have a look at what you sent me.
How strong are the currents in the Mediterranean, and specifically the area between Africa Crete and Greece?
Is there a website or some other place I can look into seasonal data regarding the winds waves and currents?

Hi Neta,

I would recommend to be careful of seasonal data for your purposes. Seasonal data uses averaging algorithms which can distort the effects of wind and current on a vessel in reality.

I recently did a study to address the question "How did the ancient Greeks sail back to Greece from the Levant as all pilot charts show prevailing NW winds in all seasons and the square sailed ships had absolutely no upwind capability". It took 10 years of historic (recent) wind data and 40,000 weather routing simulations to show that there are many opportunities to sail downwind from East to West (SE to NW) in certain months. This does not show up on averaged data.

Similar to wind, one should be careful of seasonal current data published in Med sailing guides and pilots. Recent advances in observing currents (by satellite) and in current modeling show that there are large fluctuations on daily and even hourly basis. Interestingly there are several recognized cyclic factors involved in these fluctuations.

Current data for your areas of interest can be found freely in the openWRF grib files covering the Mediterranean. They include hourly current data and high resolution wind data that also shows land and sea breezes that the global models miss. NOAA keeps historic grib files that include wind but not currents. CMEMS provides access to historic current data for several years.

Happy to help more if I can. David

[drakes]

Kon Tiki.
https://en.m.wikipedia.org/wiki/Kon-Tiki_expedition

Kon Tiki. Think these guys had a sail. But similar research different area of the world if I remember right.

[skipmac]

One thing to consider is exactly what kind of boat. If a log raft or heavy dugout then the current will overcome the influence of any but but very strong winds and waves.

A light boat with lots of windage IE one that sits high out of the water and presents a lot of surface to the wind like a skin on frame boat, will be more subject to the influence of the wind than a low, heavy boat or raft.

If the winds blow in a different direction than the currents, the light boat may take a course that is one or the other or a combination of the wind and current depending on relative strengths and the boat.

[Classicsailboat]

The hull shape is very important, a flat hulled boat like a dinghy will be more affected than a deep v hull.