Stationary Sailboat Configuration


(Kim Cowdroy) #1

One idea that has come to mind for keeping vessels stationary on the open seas, would be to connect sailing boats together so that they are all facing into the wind at an angle, such that the forces compensate.

In effect they are all tacking into the wind. Such a configuration is given below, with the wind, waves and surface stream all going in the same direction, from the upper part of screen to the lower part. Not unusual, and certainly occurs around the equator in the Pacific and Atlantic Oceans, with trade winds and South Equatorial Current going from East to West.


(Kim Cowdroy) #2

All four vessels will be tending to move into the wind as in normal tacking, but sails are set so there is not enough force to actually go forward into the wind. The two inner vessels have their bows pushing up against each other, so have no lateral movement at the bow. The sterns of these two vessels will tend to be pushed together by the wind and stream.

The two outer vessels have rope at the stern working in the opposite lateral direction, tending to pull the inner vessels apart at the stern. Thus the outer vessels are prevented from moving outwards themselves. To further be sure the inner vessels sterns do not move too far apart, a rope could be connected between these inner sterns.

It could be possible to have an automated system to make adjustments to the rudders, and possibly the sails to keep the vessels in equilibrium and set by GPS position. The system (software and hardware) would then be added to any new vessel that joins the configuration.

Gangplanks would be set between the vessels, at the closest point of bow or stern.

Cruisers without sails may be able to be attached bow to stern of a sailboat, given the stream will drift the cruiser’s stern away. And perhaps add a floating pool to the stern of one sailboat.


(Kim Cowdroy) #3

Admittedly, it would require more than a couple of tyres and some rope as shown above. And vessels are not exactly designed for bumping together or pulling apart. However, equipment should be able to be beefed up to prevent damage, and if seas get too rough it would be easy to separate the vessels and have them tacking independently.

The use of wingsails is what prompted me to think about this method. If the vessels had wingsails, with an automated system, such as is used with unmanned, remote vessels, that use GPS positioning to navigate, then the software would seem to be fairly straightforward to set up.

Lots of practical problems no doubt. But would it actually work? Will the keel perform its function of resisting sideways movement, even though there is no actual forward movement? Can the connections be set so no damage will occur and there is sufficient movement allowed for wave motion?


(Larry G) #4

No, keels don’t do anything without relative motion. If you’re anchored and current move past you, that is relative motion. If the current moves perpendicular to your keel, you will “make leeway”. In this case you would have to turn your heading some degrees into the current to make headway against the current.

The wing sail can work with wind coming from any direction. But the combination of wind and current will cause movement. If they’re going in the same direction, You’ll have to tack to get back where you were.


(Bob LLewellyn) #5

If you want to stay in one place, the less resistance to the water, the easier it will be. A flat bottom boat (barge) gives a smoother ride when staying still. V hauls are better moving under power.


(Kim Cowdroy) #6

Yes. You are right. I do not think there can be enough relative motion, so the whole configuration is likely to drift with the wind and stream.


(Kim Cowdroy) #7

However, a configuration that I think has potential would be to have a line of sailboats all set to move to windward.

In the set up below, the vessels do move from South to North, so there is actual motion, allowing the vessels to also provide force from West to East as with sailing boats making headway. However, the actual movement from West to East is kept at zero, so at least the configuration is now stationary in this direction. And the vessels are now not bumping together normally.


(Kim Cowdroy) #8

Say we are happy for the vessels to move North, a certain distance, then all the vessels tack at the same time, to go back to the original point (shown below), after which they then tack North again.

Tacking may only be required once every few hours, and at least the vessels do come back to an original spot which may be sufficient stationary-keeping in the middle of the ocean.


(Larry G) #9

I think you want to go out and find someone to take you sailing and explain a few things with first hand demonstration. You’re missing the concept pretty broadly, my friend. There’s a reason sailors have not been doing this for 3000 plus years.

You’ve accounted for (kind of) station keeping N/S but your diagram provides no eastward vector whatsoever, while applying two westward vectors (additive) in the form of perfectly aligned current and wind. You might move north or south, but you’re most definitely moving west at a combination of wind speed and a percent of ocean current. Wind and current rarely align perfectly, your boat is not the same aspect (resistance) from all directions, and your mooring solution must be effective across a broad range of vector combinations.

Don’t worry about sails and hull shapes. Just draw your vectors in as arrows and see what I mean. All the vectors must add up to zero to stay in one place. Keep in mind a vector is a direction with a magnitude and water is roughly 800 times denser than air. 1 knot of water current is 800 times the force of one knot winds, applied against the exact same shape, orientation, and size of object.


(Kim Cowdroy) #10

Thank you for your reply.

I certainly agree that I am having trouble with the concept. And I am no sailor.

However, I fail to understand how there is no potential Eastward vector.

You say the East/West vectors of wind and surface stream are only westward and the “diagram provides no eastward vector whatsoever”, but my understanding is that if the keel is pointed in a slightly eastward direction, and the sails are at the right angle, then the boat will indeed follow the direction of the keel. This is how a sailing boat moves to windward ie Easterly AGAINST the Westerly wind direction as described in http://physicsforarchitects.com/sailing-against-the-wind .

The surface stream I have described, certainly will be pushing the keel and boat from East to West. The question then becomes, is this enough to counteract the keel direction to the East to force the vessels Westerly.

It may well be, but I do not see cumulative Westerly forces only. And note I do not want to go East, I just want the vessels to stay still in regards to the East/West direction.
Please also note I am picking the worst possible scenario here to push the concept. If the current came from the East, and wind from the West they should be able to counteract each other.

Also wind from the South, and surface stream from the East may result in minimum movement, possibly without ever having to tack, as below. Similarly with wind from the North.


(Larry G) #11

How far into the wind a particular boat can sail is a complex combination of design features, each of which has trade offs when doing other maneuvers.

No sailboat sails directly against both wind and current at the same time, as in your first drawings. Sail in into the wind loses efficiency and effectiveness every degree closer to zero you try to go. Even with the wing sail you’re losing a great deal of thrust once you get to zero degrees into the current and 91 degrees off the wind.

The more directly into the wind you want to go (and in your case, attempting to keep station by sail power alone) the more sea miles of tacking you’re going to have to do. So you would end up doing a great deal of N/S axis travel to minimize the E/W axis travel.

Another factor is stealing the wind from other boats. When you are directly upwind from another sailboat, you can cause their sail to go slack. It even causes accidents sometimes if it happens during a critical maneuver. This phenomena is also present in windmills. The rule of thumb for windmilldistances is 8 times the diameter of the turbine blades between them. Sailboats can steal the wind several lengths from the downwind boat and naval (and pirate) vessels made use of this in battle back in the day. So that makes engineering your bow tether a great deal more expensive and difficult.

Again, look at it in terms of vectors.

Westward current
Northerly wind
Keel force at an angle to the current (depends on angle, NE or SE bow direction)

Give it some nominal numbers (hard to do without a specific example configuration providing data, but this is speculative)

Add the vectors’ directions and magnitudes. Use two keel force vectors, one for tacking south, one for north, and consider that each of those is different depending upon the relative strengths of current vs wind. In you latest scenario with wind blowing north, that vector will have more efficiency (and therefore greater magnitude) than tacking SE.

So are you trying to solve for station keeping, or are you trying to solve for group mooring, or for more deck surface?


(Kim Cowdroy) #12

Both.

I am specifically considering a position on the equator about 240 nautical miles west of Nauru in the Pacific. Put it at 0 degrees N, 163 degrees E. Here there is the northern part of the South Equatorial Current flowing at 0.03 to 0.06 metres/sec (0.07 to 0.14 mph) from East to West. It is a very slight stream compared with Gulf Stream say, which averages 4 mph, but it is consistent. Trade Winds also flow East to West but at 5 to 6 metres/sec (11 to 13 mph and up to 30 mph). Again consistent wind, though may vary I think in the Monsoon season. The main reason for on the equator is it is almost cyclone free.

I am looking to get costs right down by not having seasteads or even mooring lines/dynamic positioning motors, but using existing vessels to still come up with a permanent community by providing facilities.

In this case, I am trying to use the sail power that comes with the sail boats to provide some form of reasonable station keeping, so the community is permanent in nature. I also need to have at least pedestrian access between the vessels. Also I would look to have flexible electricity/Internet cables and water pipes under the gang planks.

In the diagrams above I was demonstrating a gang plank system between the bows. To keep costs down I am now considering using the vessel masts to suspend a central plank between the vessels, and then a gang plank from each vessel to the central plank, so movement of the side gang planks is made on the central plank. Tacking complicates this and means these side planks on the hull need to swivel around but could be done with wheels perpendicular to the plank or with a mini turntable supplied.

With the vessels needing to be fairly close together, there is a very real issue of the sails taking air from one another or even just disrupting the air flow, as you have rightly pointed out. Perhaps a very long box-shaped, strong but light central gang plank so the vessels are much further apart.

Another option might be setting the vessels bow to stern, and in a diagonal SW to NE line and later tacking one by one to NW to SW. The gang plank options from bow to stern become interesting, and now there would be public access along each vessel which I was trying to avoid.

The central body or company would provide and install distance sensors for each vessel to obtain distance between vessels, and software for each vessel to use these sensors and tacking instructions from a central computer to override the autopilot and make adjustments to the rudder to keep each vessel in relative position to the next vessel alongside it and which is closer to a lead vessel.

So I am after a low cost means of creating a permanent community in International Waters, but not surprisingly there are some issues. Note there are Equatorial Counter Currents going from West to East against the Trade Winds to provide another option, but this takes you into cyclone/typhoon territory.


(Larry G) #13

Purpose-built (bespoke) identical sailboats, or any group of sailboats?


(Kim Cowdroy) #14

The idea would be to allow most ocean-going sailboats to be able to join the configuration, so whatever systems are required, they need to be generalised for easy installation. There will however be some minimum requirements for a vessel to be able to join the configuration.


(Kim Cowdroy) #15

Conga Line

As a result of the discussion, I am considering the configuration below. I am assuming now that the vessels will be far enough apart and at such an angle to not interfere with the wind effects on one another.

Once the vessels have gone far enough, then it would be necessary to disconnect the gangplanks, pipe and cable facilities and all the vessels then tack to the South. Gangplanks etc. need to connect/reconnect automatically.


(Kim Cowdroy) #16

The first thing is to consider if the line of vessels can remain stationary in respect of the East/West direction.

If the sailboats move ten times in a northerly direction compared to how far they are being pushed by the current, then given the worst case speed of the current at 0.14mph, very conservatively the speed of the vessels needs to be slightly over ten times this or 1.5mph say.

To overcome the movement of the stream, the vessels then need to be pointed to windward in the ratio of one to ten or six degrees.

Then can the vessels maintain a speed of 1.5mph at this angle with a wind that is as low as 11mph.
To me this all looks feasible. In any case, I consider this is the worst case given the figures available, so something easier than this then becomes the minimum requirement for a sailboat to join the line.


(Kim Cowdroy) #17

There would be a lead vessel on the end of the line, that would maintain a course, like a head goose in a geese formation. Each vessel then needs to have an ultrasonic sensor (like a fish finder), to determine and maintain distance to the vessel alongside. I expect this would be at the stern pointing at the bow of the next vessel.

Software needs to be written to take this sensor information and provide adjustments to the autopilot system and hence continual adjustments to the rudder to maintain direction. The software will need to be able to handle a variety of interfaces. The software also needs to be able to take a command from the lead vessel when it is time to tack.

Also vessels will need to be able to easily speed up or slow down to keep proper distance from the vessel alongside. It may be possible to do this using the sails, but I think best to leave the sails alone once they are filled with the wind, and instead have two what I will call brake fins attached to the stern. The software then instructs these to move to affect the speed of the vessel and maintain distance between them.


(Kim Cowdroy) #18

Gangplank

The use of a gangplank to connect moving vessels looks problematic. The wave condition at the given site on the equator I believe is one of the most favourable on the open seas. However relatively small sailing vessels will be bobbing up and down as they move along, so causing lots of problems for a gangplank between the vessels even if the distance case be kept within tight tolerances.

A simple gangplank would need to be connected to the stern of a vessel on a partial turntable of sorts. The moveable end is on the foredeck of the boat behind. There would be considerable movement and there would need to be rubber straps keeping it in place. There would be wires from the top of the mast of the vessel whose stern has the gangplank attached, to the sides of the gangplank. The gangplank might be articulated on the foredeck to reduce movement on getting onto the gangplank. Either way it sounds pretty scary.

Another method that might just be practical would be to have a central gangplank section that is elevated with four wires one to each corner and connected to the top of the mast of the vessel with gangplank at the stern, so the gangplank is horizontal. Fixed steps from the stern to one end of the gangplank keep it in place. The base of these steps is on a partial turntable. The base of the steps will need to be able to swivel from one side to the other on tacking but otherwise are centred with springs to stay in place, At the other end of the gangplank are concertina seastairs on a partial turntable on the gangplank and connected to a partial turntable secured on the other foredeck. These seastairs then need to move to be able to take all the movement.

A mechanism for automatically connecting and disconnecting from the foredeck is required, and also a mechanism on the gangplank to be able to retract the seastairs is needed.
There needs to be connectors for the water pipes and electricity/Internet/communication cables passing from one boat to another, and an automated mechanism to connect and disconnect.

Concertina Stairs:


(Kim Cowdroy) #19

Adding up all the items that are required for a vessel to join the Conga line, we are looking roughly at a total of US$3000 – US$5000 including installation (but ignoring delivery cost for the moment). In reality there would likely be an installation price of say $200 to $800, and a weekly rental of say $30 - $50.

Note this would not include the actual cost of electricity, Internet, satellite TV, fresh water etc. as these would have to be billed separately. The ability to connect to these though, the automated station-keeping and the pedestrian access to other facilities like a general store, laundry service etc. is what is being paid for.

And you need your own sailboat, unless the company separately leases these out.


(Larry G) #20

I think a couple afternoons of sailing will cause you to abandon this concept. The characteristics of sailboats vary too much to do synchronized water ballet or anything else on the exact same track. Racing sailboats don’t take the exact same track through the water even when trying to shave those last few seconds off a course.