Stationary Sailboat Configuration

(Bob LLewellyn) #21

The other problem with this concept is that it isn’t needed as a floating marina provides docks for loading and unloading, stay aboard or go to town. With all the conveniences of a marina, why would we want to reinvent the wheal so to speak?
I like your creativity, and I acknowledge that there may be a need for the system that you are thinking of, even though I don’t see it myself. You are aware that anchoring in the deep ocean is not an attractive option, so we do need another way to hold large platforms in place.

For the Marinea project, this is phase 3 (deep ocean) and we are still working on phase one however, my initial ponderings about the subject required large diesel motors and props in a low current area. We wouldn’t have to run the motors all day just to periodically to re-position. It could even be automated but it is still expensive. A way to reduce the fuel cost would be to grow it ourselves. All oil was algae and grasses at some time in the past. We can make our own, but again, we won’t have to worry about deep sea until we get the shallows under our belt so I’ll just follow along.

(John) #22

I’m shocked and stunned that this conversation could have gone on this long…


If somebody has an idea, it doesn’t cost much to explore it from many angles.

In theory, a floating “island” (aka “seastead”) could be built to have the form of both a “keel” and a “sail”. Then it actually might be able to maintain “relative position” without tethering or motoring into place.

It might not be practical (now), but who knows how a discussion might plant a random brainstorming seed in someone’s brain.

So I followed this dialog from a distance, skimming over it from time to time.

My own experience with sailing was to capsize the boat … so I don’t have much to offer on this subject, other than singing the praises of wearing lifevests at sea. :stuck_out_tongue_closed_eyes:


Yes, the concept of a SAILSTEAD has been discussed before. I did introduced few designs. Here is one of them from the archives :slight_smile:

(Kim Cowdroy) #25

Agreed. I must admit I am just throwing out some ideas in relation to trying to use sails for station keeping. And yes maybe with some exploring something useful may come up. And in the process I and others may learn something!

There are less than ten alternatives to the station-keeping issue in International Waters, excluding deep-sea mooring and dynamic positioning, which both have significant issues for a cost-effective seasteading community. None of the these alternatives is an obvious answer so I think sailboat use is worth exhausting even if I get beat up in the process.

(Kim Cowdroy) #26

For other reasons, I was considering the wrong place really for use of wind propulsion, so pushing the ideas I admit.

Best to have the wind in one direction and the current in the other, in order for sails to be considered as the main means of remaining stationary.

One place that could satisfy this in International Waters would be at about 4 degrees North and 170 degrees West. Here the prevailing Trade Winds are from the East or slightly North East. The current is the North Equatorial Countercurrent which goes from West to East. Speed of the current is given as less than 0.5 mtrs/sec or about 1 mph. Prevailing winds are presumably around 10 mph and reasonably steady.

Main centre for Kiribati would be to the South West, which would be the nearest place for supply and access. All very remote, but better than further East in the Pacific.
Similar setup in the Atlantic could also be an option.

Issue of possible monsoonal winds from the West for part of the year may need to be addressed.


I don’t know anything about sailing, so please excuse my ignorance. But why not use the mechanism for sailboats that sail into the wind? In the middle of the ocean, wind don’t always come from the same direction and while strong wind and wave usually go in the same direction, sailboats can still sail into the wind at an angle and in theory keep its position by continuously sailing against the wind (and wave). Granted, the ‘captain’ of such a structure will be very busy ‘sailing’.

So in theory, if a structure has enough sail or large enough sails all at the same angle, it should be able to keep its position using only wind, wouldn’t it?

Is there something wrong with my assumption? If it is wrong, can someone explain what I got wrong?

Just wondering if there’s a method to keep a concrete structure floating in deep ocean without having to use the thruster too much.

(Larry G) #28

Can a heavy floating concrete platform keep station with nothing but wind power?

The answer, as with most very broad questions, is “it depends”.

How big of a concrete structure? What shape? Above water and below? How mch draft? How smooth is the hull, is there biofouling?

How much sail area? What direction is the wind blowing? How fast? How much wind and what direction? How constant are both wind and current?

The more succinct answer, for most any significant size/draft of heavy concrete platform, is “probably not”.

Water is just MUCH more dense and therefore has a lot more inertia than air, and will act proportionately that much more strongly on a floating object.

(Larry G) #29

As for using thrusters, how much is too much?

These things need quantifiers attached. Relative terminology leads to sloppy thinking and meaningless questions. Get rigorous about defining requirements and you have a better chance of finding real answers.

(.) #30

Sailing something with wind power depends on the sails
and on the hull too. Whatever is immersed in the water would also determine
the sailing with wind power.
Optimization is difficult
sail fast and well, and able to live aboard.

(stephen russell) #31

Awesome Seastead concept, cheap to build & produce.
& can be add on Module to other Seastead types for Mobile exploration ventures alone.
Use sails for power & mobility.
Need aux thrusters for when No Wind days come & strong enough to take storms or a rogue wave.
Semi dome enclosure to house occupants during stormy days at sea IE State 6 seas.
Venues for: Caribbean, HI, Baja CA Mex, Mex, Med Sea, Indian ocean Java.
Thrusters can retract when not in use.


@Shiina_Ai … Ocean “currents” are often described as a global conveyer belt of ocean water, moving in a very predictable pattern at a very predictable rate. For any given geo-position, the ocean current is usually fairly constant.

In contrast, Surface Waves (a specific type of wave energy … not simply waves that happen to be on the surface) vary with (because they are caused by) the wind.

So … yes, in theory, a floating island (seastead) could use wind to maintain its relative position.

To “sail”, the floating structure would need both a huge “keel” and “sails” built into the entire structure … since the interaction of the keel and the sails is what makes “sailing” possible.

But the “sails” would need to be moveable … and the energy required to reposition a seastead’s “sails” might exceed the value of using “sails” (vs using, for example, engines and propellers) to reposition (i.e., maintain relative position) of the seastead.

I suspect this process would be impossible without a dedicated computer program managing the configuration of the “sails” … and the repositioning process might require days or weeks to complete, using a fairly large amount (square kilometers) of ocean surface to accomodate the back-and-forth movement of the seastead as it “tacks” back into position.

Not impossible, in theory …
… but currently difficult, in practice.


There is a big misconception being perpetuated here. That of Ferrocement equating to ‘heavy’… A STEEL hull can and usually does have more mass than a Ferrocement composite hull of the same outward design.

The issue is proper design, for the structure.

(.) #34

specific gravity of iron = 7.8 g/cm3
specific gravity of concrete = 2.4 g/cm3
7.8 is greater than 2.4, therefore iron is heavier concrete.

(Kim Cowdroy) #35

Considering further the case of stream and waves coming from near the opposite direction to the wind. The sailboats would be pointed into the stream with the wind behind. I would expect any ocean-going vessel would be able to do 4 to 5 knots with a 10 mph wind behind it.

The stream considered is only doing 1 mph, so sailboats can readily sail directly against the current in order to remain stationary.

The movement of the stream means the vessel is doing 1 mph relative to the stream. Is this sufficient speed to make the keel and rudder effective for ensuring the direction of the boat? I would think so, but if not then the boats may have to drift and then catch up afterwards at a higher speed.

(Kim Cowdroy) #36

I have made a rough drawing of the gangplank setup between two sailboats in this configuration, using the masts to hold up the central plank. There are guide wheels on the roof of the central gangplank, so it will slide along the ropes that go to the top of the masts. This means the central plank will remain close to horizontal. There are ropes to the mast from the central plank to help ensure it does not move too far away from the hulls.

The side gangplanks are attached with rope with some give, to a platform that needs to be installed to the mast. The side plank is then able to swivel and allow the other end of the plank to move up and down, but cannot move in and out. All of that movement is done on the central plank. Steps or ladder provide access to the platform. The gangplanks and platforms would have railings of course.

(Kim Cowdroy) #37

Instead of having software and direction finder/brake system/automated sail adjustment as previously discussed, it might be possible to keep the vessels aligned with ropes as shown between them. The autopilot on each could be set so the rudder is slightly pushing the vessels apart with the forward rope keeping them together.

The speed of the vessels needs to be kept close, but given the low speeds, the ropes from bow to stern may adjust enough for slight differences.

A spring mechanism from the hull to each of these ropes needs to be provided to ensure there is no snapping of the ropes on the hull connections.

(Kim Cowdroy) #38

So we may be able to set up a relatively low-cost seasteading community using existing sailboats only. We could have a row of sailboats or maybe even a number of rows if sufficiently apart.

The masts then act like towers of a suspension bridge. A sailboat on the end would need a counterweight on the other side. Or one end may be connected to a barge say, with the last mast connected from the top to the barge.

Electricity, Internet, water may be connected from the barge in cables and flexible pipes where the lower connection is shown from the central plank to the mast.

So people can show up with their sailboat and just like people with a caravan going to a caravan park on land, they get utility services provided, and pedestrian access to the centre and all the facilities.

Also a separate marina is not required. This would involve mooring costs of some description as well as the cost of the pontoons.


Well, the only way to be (relatively) stationary in the water while sailing is by HEAVING TO.

So, your drawings are off since in fact your sailboats, as shown, are on a starboard tack broad reach, judging by the position of the jib and main. Therefore, they will make headway.

This is the actual position of the sails (main & jib) and rudder, relative to the boat and wind direction that will hove the vessel to.

If all 4 sailboats are in tow OR rafted up then they can all hove to, given relative equal displacements.

But, to connect them athwartship (in a direction at right angles to the fore-and-aft line of the vessel) as shown AND achieve that angle to the wind, in tandem, AND by using just a plank rigged to the masts,… I doubt the practicality of such move.


Not necessary so. There are some big electric furlers and winches out there and there is no reason (or technical barrier, for that matter) that HUUUUUGE ones cannot be built.

Sailing is done by flipping a switch now. :slight_smile: