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The Forward Slope of the Borei's Sail (Patreon)

Published:
2020-04-20 15:21:59
Imported:
2026-06
Tags:

Content

One unique feature of the Borei SSBN is the shape of it's sail.  I discuss why its this shape in the Sub Brief.  Why do you think they did this?

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Comments

Knothead

I think they did this because they accidentally put the conning tower on upside down and didn't realize it until it was too late.

Raven Coldheart

Hydrodynamic advantage, probably manipulating/delaying vortex shedding and thus making the sub quieter at higher speeds. Edit: Could also be a measure against active sonar to reduce the reflection from the front, though I don't know too much about how effective that would be.

Robert Sanges

I'm going for the simple idea... so the waves are less likely to break over the sail during surface transit. I was sometimes a bridge phone talker during maneuvering watch on a 688. I would have appreciated that feature.

Harish Rajan

That occurs for a raked design too ? I thought blended sails like the seawolf, made sure that the boundary layer would not break up causing vortex shedding. Which in turn made it noisy. I guess its like sweep back wings in aircrafts to delay the critical mach number.

Harish Rajan

But isn't the sail in borei a bit far back from the front of the boat compared to a 688 ?

Spartaner 251

maybe they put some of the wake search sensors in there ?

Robert Sanges

Harish Rajan, I'm not thinking I'm correct -just fun. The bridge is certainly farther back from the front of the sail. I doubt they can even see the bow.

Raven Coldheart

The X-29 and Su-47 have significantly reduced wingtip vortices (forward swept wings) and in many ways water and air work the same.

Raven Coldheart

They are normally located on the side or top of the sail with small protrusions.

Joseph Orr

All good ideas above. I suspect it was a number of things as well as accepted tradeoffs. Whatever it was, it didn't work out perhaps, as it was removed for the subsequent model 955A to my understanding.

Phil Wood

Given the fact that they love operating around ice could it be ice breaking properties when surfaced?

Harish Rajan

Yes, but forward swept wings are used for other reasons that just critical mach number, it increases air flow to the tip of the wing and shockwaves develop at the root of the wing which does not render the control surface useless. Also forward swept wings are dangerous, static divergence is much more pronounced and can rip apart the wing. But i think ill wait to hear the sub brief on why the sail is forward sloped. I can ask one of my friend who is a naval engineer too, if i get a reasonable answer i will post it here.

Raven Coldheart

Harish Rajan, would be awesome to read, I'm "just" a civil engineer, so my dynamic fluid know how is restricted to my 2 years of aerospace engineering studies.

Harish Rajan

I checked a book on submarine hydrodynamics, there isn't much on sail design however i did see some regarding sail-hull-tail interactions including a ansys simulation of what appeared to be a 688. If you look at the picture of borei 1 and borei 2 in hi Sutton's website u can see that in borei 2 they changed the tail section when the sail was changed. I guess something to do with interactions ? Anyway me and my friend couldn't come up with a reasonable answer, so we messaged his professor, waiting for his reply. Also how did you do courses on aerospace while doing civil engineering ? Does your university allow that ?

Toni Krause

Since this sail is changed on 955A, I think it is related to the change at the rudder.

Raven Coldheart

I changed fields after I couldn't wrap my head around differential equations/instationary regulation properly and I already had a done a student job in civil engineering at that point. And yes, my university even allows you to study multiple fields at the same time, one of the perks of living in Germany I guess.

Seahour

Easy, "it look better comrade!" :D

DrPatreon

I agree with Phil... Has to do with ice ops. Possible point of broach advantage.

Hub

Hello, on this website (in french), there is a picture showing comparison between the project Izd955 and Izd955A Knyaz Vladimir where the sail have been change to reduce this slope.

Hub

The link