Sea Anchor | Hacker News Reader

Sea Anchor

en.wikipedia.org

67 pointsbo0tzz23 comments

Sea anchors are generally not recommended these days - they are difficult to effectively deploy, maintain, and recover - far preferable is a jordan series drogue: https://www.jordanseriesdrogue.com/

It depends. Lin and Larry Pardey do recommend them in heavy winds and seas, but they use a fairlead from the stern or midship to pull the sea anchor to an angle off to the side so that the boat lies at 50-ish degrees to the wind.

It's basically an aid to help with heaving-to. They are big fans of heaving-to in dangerous seas, and have collected a lot of anecdotes from other sailors who also recommend it as a heavy weather tactic.

It's certainly a good solution if you've got a full or mostly full keel. Light cruising boats may not fare as well, though some correspondents indicate that it works for them as well. My daysailer heaves-to with it's swing keel, but I only use it to go below to make lunch or whatever.

But you are very correct. Deploying a sea anchor can be very dangerous if you're not exceedingly careful, and retrieving them is a gigantic PITA.

Isn't that a specific kind of sea anchor?

Sea anchors are deployed from the bow of the boat and meant to hold it more or less facing into the waves.

Drouges are deployed from the stern and meant to slow the boat down as it travels with the waves.

but still pointing it's bow towards the waves. Both are designed to prevent rogue broadsides flipping your vessel. Drouges are preferred now because it's easier to deploy and recover from the cockpit. I have a Catalina 36. I also have a drouge on board.

Sea anchors can be used to steer a sailboat in some situations in the event that the rudder is lost, as one guy demonstrated when he lost his rudder 1609km (1000mi) from Hawaii:

https://www.youtube.com/watch?v=1AZXXKj0p0s

You can also use them to pull you. I used to work deep sea in the merchant marine, we had them in lifeboats/liferafts. Part of the training had us sitting in a liferaft, in a pool, throwing a sea anchor, and then hauling on the line to pull us through the water. Useful if you are trying to rescue people.

Many sailors also use them for speed-limiting if they are in bad seas, specifically a Jordan Series Drogue, which is a really long line of drogues such give you a lot of drag despite the howling wind.

Yesterday I was looking into rogue waves and found this video[1] where they have a sailing yacht with and electric engine and they say they use the engine in regenerative mode to generate drag in rough, kind of like a sea anchor would do.

[1] https://www.youtube.com/watch?v=7wM_CNN3x-I

Checked out the video but didn't want to fish through 20 minutes for the specific part about regen. engine mode. To be fair don't all props create drag (less so if it's folding) - maybe the prop is "in gear" or similar and would enable more drag that way? Just curious how this works - also a response with the timing in the video when they mention this could maybe be helpful

I wonder if a lot of the confusion in this discussion is for the same reason I was confused - most descriptions of a sea anchor are missing the details of why it works, and calling one style a "parachute" makes it even worse IMO.

Hopefully some folks with actual marine experience can correct me if I'm wrong here, but based on the most descriptive source I could find[1], this is what's going on:

For a traditional sea anchor (including the ones that look like parachutes), the force of the waves is pushing the anchor away from the vessel. The anchor is either submerged or very low profile, so wind/air resistance effects on it are nonexistent or negligible. i.e. the anchor should be moving in exactly the same direction as the waves.

Meanwhile, the vessel sticks up well above the waterline, so there is resistance from the air itself against it being pulled in the direction of the sea anchor. This should make it always trail behind the sea anchor, being pulled in the same direction as the waves are pushing, and this keeps its long axis perpendicular to the waves so it can't roll over.

In other words, if I understand correctly, this type of sea "anchor" is more like an underwater sail. This is why they're connected to the front of the vessel.

For drogues, it seems like the idea is to allow the waves to push the vessel continuously (like a surfer riding a wave), with the drogue trailing from the stern and tuned to slow the vessel the exact right amount to stay in a safe position relative to the wave it's riding?

[1] https://www.schoonerman.com/heaver-weather-sailing/what-is-a...

> For a traditional sea anchor (including the ones that look like parachutes), the force of the waves is pushing the anchor away from the vessel.

It's actually the opposite of this.

A sea anchor acts like a parachute in that it slows the vessel by increasing drag (although obviously with water as the medium). As with a parachute, where the parachutist will always be below (excepting acrobatics) the canopy as both are falling in the same direction through the air, a sea anchor behaves the same way in the water.

So both the vessel and sea anchor are being pushed by waves, like the parachutist and canopy are being pulled by gravity, but the submerged sea anchor (down in calmer waters below the largest influence of the waves) has greater drag than the vessel in the water and slows the vessel.

In heavy seas, a vessel without a sail will have the current and sea state as the most significant influence rather than the wind (although this can vary). When deployed from the bow/front of the vessel, a sea anchor works to both slow the vessel's overall speed over ground (which can be useful to avoid excessive drift into hazards or losing progress) and it also acts to keep the bow into the weather. This is important as vessels generally are prone to damage/capsize if taking heavy seas/big waves abeam/onto their sides.

Ah, thank you. That makes a lot more sense.

I use a small sea anchor (drift sock) when my sailboat is at anchor. The current on the sock keeps her from sailing the wing keel onto the anchor rode.

When I was a kid my dad used a sack with a hole in it all time as a drogue while out fishing.

Oh what must have been felt aboard the James Caird when ice finally wrenched away their sea anchor, alone and afloat in the peril of the Drake Passage

> and were even used by sea-landing naval Zeppelins in World War I.

This parachute shape looks ineffective.. wouldnt a shape be ideal, that takes up stream direction of the water and redirects it partially into the exact oppossite direction, so the ideal shape would look somewhat like a jellyfish, converting the potential energy of the water streaming into directional energy countering the stream direction.

Or just a underwater kite going in circles? https://en.wikipedia.org/wiki/Kite

> takes up stream direction of the water and redirects it partially into the exact oppossite direction

Well, the “outlet” is now also an inlet then, since you can’t position the outlet outside of the incoming stream. So you’ve got a U, where water slams into itself in the center. Add a second U rotated, so viewed from the current it’s a + with water meeting in the middle. Repeat this infinitely and you end up with a parachute shape with an extra blockage in the center. That extra blockage doesn’t add much extra resistance, so you remove it. Now we have our parachute shape.

Not if the outlet is smaller?

If the outlet is smaller, the current pushes it closed, unless it's rigid, in which case all the current getting pushed to the outside isn't being redirected in the opposite direction as you said. Instead, that current is just being directed aside, which does cause drag. Taking that design out to the logical conclusion, you end up with a drogue, as also mentioned on that page.

Note that a rigid design also has other constraints (storage) that may make it less desirable even if it is more efficient.

A jellyfish is a parachute that can pulse a little

Imagine a dragon like sail for water streams, it runs below the surface in the stream, and allows you to milk the potential energy of the water toward a direction change for your boat..

https://en.wikipedia.org/wiki/Sailing_into_the_wind

But with the gulf stream and automated underwater dragging dragons

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