Category Archives: travel

Sailors, boaters, and motor sailing at the hull speed.

I’ve gone sailing a few times this summer, and once again was struck by the great difference between sailing and boating, as well as by the mystery of the hull speed.

Sailors are distinct from boaters in that they power their boats by sails in the wind. Sailing turns out to be a fairly pleasant way to spend an afternoon. At least as I did it, it was social, pleasant, and not much work, but the speeds were depressingly slow. I went on two boats (neither were my own), each roughly 20 feet long, with winds running about 10-15 knots (about 13 mph). We travelled at about 3 knots, about 3.5 mph. That’s walking speed. At that speed it would take about 7 hours to cross Lake St. Clair (25 miles wide). To go across and back would take a full day.

Based on the length of the boats, they should have been able to go a lot faster, at about 5.8 knots (6 mph). This target speed is called the hull speed; it’s the speed where the wave caused by the bow provides a resonance at the back of the boat giving it a slight surfing action, see drawing.

This speed can be calculated from the relationship between wave speed and wavelength, so that Vhull = √gλ/2π where g is the gravitational constant and λ is the water line length of the boat. For Vhull in knots, it’s calculated as the square-root of the length in feet, multiplied by 1.34. For a 20 foot boat, then,

Hull speed, 20′ = 1.34 √20 = 1.34 x 4.5 = 6.03 knots.

While power boats routinely go much faster than this, as do racing skulls and Americas cup sailboats, most normal sailboats are designed for this speed. One advantage is that it leads to a relatively comfortable ride. There is just enough ballast and sail so that the boat runs out of wind at this speed while tipping no more than 15°. Sailors claim there is a big increase in drag at this speed, but a look at the drag profile of some ocean kayaks (12 to 18 feet, see below) shows only a very slight increase around this magical speed. More important is weight; the lowest drag in the figure below is found for the shortest kyack that is also the lightest. I suspect that the sailboats I was on could have gone at 6 knots or faster, even with our current wind, if we’d unrolled the spinnaker, and used a ‘screecher’ (a very large jib), and hung over the edge to keep the boat upright. But the owner chose to travel in relative comfort, and the result is that we had a pleasant afternoon going nowhere.

Data from Vaclav Stejskal of “oneoceankyacks.com”

And this brings me to my problem with power boating. Th boats are about the same length as the sailboats I was in, and the weight is similar too. You travel a lot faster, 20 to 25 knots, and you get somewhere, but the boats smell, and provide a jarring ride, and I felt they burn gas too fast for my comfort. The boats exceed hull speed and hydroplane, somewhat. That is, they ride up one wave, fly a bit, and crash down the other side, sending annoying wakes to the sailboaters. We crossed lake St. Clair and rode a way down the Detroit river. This was nice, but it left me thinking there was room for power -assisted sailing at an intermediate speed, power sailing.

Both sailboats I was on had outboard motors, 3 hp, as it happened, and both moved nicely at 1 hp into and out of the harbor, even without the sail up. Some simple calculations suggest that, with I could power a 15 to 20 foot sailboat or canoe at a decent speed – hull speed – by use of a small sail and an electric motor drawing less than 1 hp, ~400 W, powered by one or two car batteries.

Consider the drag for the largest, heaviest kayak in the chart a move, the Cape Ann Double, going at 6.5 knots. At 6 knots, the resistance is seen to be 15 lbs. To calculate the power demand, convert this speed to 10 fps and multiply by the force:

Power for 6 knot cruising = 10 fps x 15 lbs = 150 ft lbs/s = 202 W or 0.27 hp.

Outboard motors are not 100% efficient, so let’s assume that you need to draw more like 250 W at the motor, and you will need to add power by a sail. How big a battery is needed for the 250 W? I’ll aim for powering a 4 hour trip, and find the battery size by multiplying the 250 W by 4 hours: that’s 1250 Hrs, or 1.25 kWh. A regular, lithium car battery is all that’s needed. In terms of the sail, I’m inclined to get really invovative, and use a Flettner sail, as discussed here.

It seems to me that adding this would be a really fun way to sail. I’d expect to be able to go somewhere, without the smell, or the cost, or being jarred to badly. Now, all I need is a good outboard motor, and a willing companion to try this with.

Robert Buxbaum, Sept. 9, 2024

Ferries make more sense than fast new trains.

Per pound mile of material, the transport cost by ship is 1/4 as much as by train, and about 1/8 as much as by truck. Ships are slower, it is true, but they can go where trucks and trains can not. They cross rivers and lakes at ease and can haul weighty freight with ease. I think America could use many more ferries, particularly drive-on, fast ferries. I don’t think we need new fast rail lines, because air travel will always be faster and cheaper. The Biden administration thinks otherwise, and spends accordingly.

Amtrak gets $30 Billion for train infrastructure this year, basically nothing for ferries.

The Biden administration’s infrastructure bill, $1.2 Trillion dollars total, provides $30 Billion this year for new train lines, but includes less than 1% as much for ferries, $220 million, plus $1B for air travel. I think it’s a scandal. The new, fast train lines are shown on the map, above. Among them is a speed upgrade to the “Empire Builder” train running between Chicago and Seattle by way of Milwaukee. I don’t think this will pay off — the few people who take this train, takes it for the scenery, I think, and for the experience, not to get somewhere fast.

There is money for a new line between Cleveland and Detroit, and for completion of the long-delayed, and cost-over-run prone line between LA and San Francisco. Assuming these are built, I expect even lower ridership since the scenery isn’t that great. Even assuming no delays (and there are always delays), 110 mph is vastly slower than flying, and typically more expensive and inconvenient. Driving is yet slower, but when you drive, you arrive with your car. With a train or plane, you need car rental, typically.

New Acela train, 150 mph max. 1/4 as fast as flying at the same price.

Drive-on ferries provide a unique advantage in that you get there with your car, often much faster than you would with by driving or by train. Consider Muskegon to Milwaukee (across the lake), or Muskegon to Chicago to Milwaukee, (along the lake). Cleveland to Canada, or Detroit to Cleveland. No land would have to be purchased and no new track would have to be laid and maintained. You’d arrive, rested and fed (they typically sell food on a ferry), with your car.

There’s a wonderful song, “City of New Orleans”, sung here by Arlo Guthrie describing a ride on the historic train of that name on a trip from Chicago to New Orleans, 934 miles in about one day. Including stops but not including delays, the average speed is 48 mph, and there are always delays. On board are, according to the song, “15 restless riders, 3 conductors, and 25 sacks of mail.” The ticket price currently is $200, one way, or about as much as a plane ticket. The line loses money. I’ve argued, here, for more mail use to hep make this profitable, but the trip isn’t that attractive as a way to get somewhere, it’s more of a land-cruise. The line is scheduled for an upgrade this year, but even if upgraded to 100 mph (14 hours to New Orleans including stops?) it’s still going to be far slower than air travel, and likely more expensive, and you still have to park your car before you get on, and then rent another when you get off. And will riders like it more? I doubt it, and doubt the speed upgrade will be to 100 mph.

Lake Express, 30 mph across Lake Michigan

Ferry travel tends to cost less than train or plane travel because water traffic is high volume per trip with few conductors per passenger. At present, there are only two ferryboats traveling across Lake Michigan, between Michigan and Wisconsin, Milwaulkee to Muskegon. They are privately owned, and presumably make money. The faster is the Lake Express, 30 mph. It crosses the lake in 2.5 hours. Passenger tickets cost $52 one way, or $118 for passenger and car. That’s less than the price of an Amtrak ticket or a flight. I think a third boat would make sense and that more lines would be welcome too. Perhaps Grand Haven to Racine or Chicago.

Route of the Lake Express. I’d like to see more like this; St. Joseph to Milwaukee say, and along Lake Erie.

Currently, there are no ferries across Lake Erie. Nor are there any along Lake Erie, or even across Lake St. Clair, or along the Detroit River, Detroit to Toledo or Toledo to Cleveland. These lines would need dock facilities, but they would have ridership, I think. New York’s Staten Island ferry has good ridership, 35,000 riders on a typical day, plus cars and trucks. In charge are roughly 120 engineers, captains and mates, one employee for every 300 passengers or so. By comparison, Amtrak runs 300 trains that carry a total of 87,000 passengers on an average day, mostly on the east coast. These 300 trains are run by 17,100 employees as of fiscal year 2021, one employee for every 4 passengers. Even at the slow speeds of our trains the cost is far higher per passenger and per passenger mile.

The Staten Island ferry is slow, 18.5 mph, but folks don’t seem to mind. The trip takes 20 minutes, about half as long as most people’s trips on Amtrak. There are also private ferry lines in NY, many of these on longer trips. People would take ferries for day-long trips along our rivers, I think. Fast ferries would be nice, 40 mph or more, but I think even slow ferries would have ridership and would make money. A sea cruise is better than a land cruise, especially if you can have a cabin. On the coal-steam powered, Badger, you can rent a state-room to spend the night in comfort. Truckers seem to like that they cover ground during their mandatory rest hours. The advantage is maximized, I think, for ferry trips that take 12 hours or so, 250 to 350 miles. That’s Pittsburgh to Cincinnatti or Chicago to Memphis.

New York’s Staten Island ferry leaves every 15 minutes during rush hour. Three different sizes of boat are used. The largest carry over 5000 passengers and 100 cars and trucks at a crossing.

A low risk way to promote ferry traffic between the US and Canada would be to negotiate bilateral exemption to The Jones Act and its Canadian equivalent. Currently, we allow only US ships with US crews for US travel within the US.* Cabotage it’s called, and it applies to planes as well, with exemptions. Canada has similar laws and exemptions. A sensible agreement would allow in-country and cross-country travel on both Canadian and US ships, with Canadian and/or US crew. In one stoke, ridership would double, and many lines would be profitable.

Politicians of a certain stripe support trains because they look futuristic and allow money to go to friends. Europeans brag of their fast trains, but they all lose money, and Europe had to ban many short hop flights to help their trains compete. Without this, Europeans would fly. There is room to help a friend with a new ferry, but not as much as when you buy land and lay track. We could try to lead in fancy ferries going 40 mph or faster, providing good docks, and some insurance. Investors would take little risk since a ferry route can be moved**. Don’t try that with a train.

In Detroit we have a close up of train mismanagement involving the “People Mover.” It has no ridership to speak of. Our politicians then added “The Q line” to connect to it. People avoid both lines. I think people would use a ferry along the Detroit river, though, St. Claire to Wyandotte, Detroit, Toledo — and to Cleveland or Buffalo. Our lakes and rivers are near-empty superhighways. Let’s use them.

Robert Buxbaum, January 2, 2024. *The US air cabotage act (49 U.S.C. 41703) prohibits the transportation of persons, property, or mail for compensation or hire between points of the U.S. in a foreign civil aircraft. We’ve managed exemptions, though, e.g. for US air traffic with Airbus and Embraer planes. We can do the same with ferries.

** I notice that it was New York’s ferries, and their captains, that rescued the people on Sullenberger’s plane when it went down in the Hudson River — added Jan. 6.