# Why doesn't the US Navy use hydrofoils?
**URL:** https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684
**Category:** Factual Questions
**Created:** [October 15, 2015, 2:02am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684 "2015-10-15T02:02:16Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@chacoguy](https://boards.straightdope.com/u/chacoguy)
#### Post date: [October 15, 2015, 2:02am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/1 "2015-10-15T02:02:16Z")
They were always touted as _THE FUTURE_ like jet packs and lazer rifles. But there are obvious advantages; they’re in the America’s Cup, for instance.
So, why not?
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [October 15, 2015, 2:12am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/2 "2015-10-15T02:12:41Z")
They used to: [Pegasus-class hydrofoil - Wikipedia](https://en.wikipedia.org/wiki/Pegasus-class_hydrofoil)
If I’m not mistaken, hydrofoils are limited in size, so they were never considered for anything larger than patrol boats, limited to coastal operations.
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### Author:  [@GaryM](https://boards.straightdope.com/u/GaryM)
#### Post date: [October 15, 2015, 2:25am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/3 "2015-10-15T02:25:51Z")
Saw these docked at Key West many years ago. Very cool looking boats.
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### Author:  [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)
#### Post date: [October 15, 2015, 2:27am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/4 "2015-10-15T02:27:12Z")
> [@](#):
>
> All other PHMs in the class have been scrapped, except for Gemini, which was converted into a yacht.
:dubious:
Was it bought by a chap named Largo, by any chance?
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### Author:  [@mousetrap](https://boards.straightdope.com/u/mousetrap)
#### Post date: [October 15, 2015, 1:56pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/5 "2015-10-15T13:56:25Z")
The Canadian Navy tried a hydrofoil, built by an airplane company. My dad originally worked on it in De Havilland Aircraft. See [HMCS Bras d'Or (FHE 400) - Wikipedia](https://en.wikipedia.org/wiki/HMCS_Bras_d'Or_%28FHE_400%29) The boat itself was an engineering success, but my dad said the problem was they wanted it as a quick response anti-submarine warship, but there was no way to equip it with Sonar that wasn’t deafened by the airfoil fins, even when just sailing as a regular boat.
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### Author:  [@racer72](https://boards.straightdope.com/u/racer72)
#### Post date: [October 15, 2015, 3:00pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/6 "2015-10-15T15:00:29Z")
As a side note, my first job with the big airplane company in Seattle was building PHM’s for the Navy. From what I remember, cost overruns during construction and the high expense to operate these things is what ultimately killed them. Right now, 35 years later, I am sitting about 20 feet from where these were built in the Renton plant.
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### Author:  [@spifflog](https://boards.straightdope.com/u/spifflog)
#### Post date: [October 15, 2015, 3:58pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/7 "2015-10-15T15:58:38Z")
Because the cost isn’t worth the very, very minor benefit.
The PHMs clocked in at about 48 knots, or about 20 knots fasters than a DDG, or FFG. The only advantage of the PHM over these ships was speed (and cost I suppose). And with technology making weapons systems so much more accurate, be that guns or missiles, speed isn’t really an advantage at all.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [October 15, 2015, 4:07pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/8 "2015-10-15T16:07:54Z")
> [@Lumpy](#):
>
> They used to: [Pegasus-class hydrofoil - Wikipedia](https://en.wikipedia.org/wiki/Pegasus-class_hydrofoil)
MPSIMS: When I was a kid I had a [model](http://www3.sympatico.ca/wmburns/Btitle_file/hydro.jpg) of [USS _Tucumcari_](https://en.wikipedia.org/wiki/USS_Tucumcari_(PGH-2)).
.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [October 15, 2015, 5:32pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/9 "2015-10-15T17:32:55Z")
My understanding is that [wave-piercing hull](https://en.wikipedia.org/wiki/Wave-piercing_hull) design can achieve nearly the same speeds. The US Navy has used several wave-piercing catamarans, most recently the [HSV-2 Swift](https://en.wikipedia.org/wiki/HSV-2_Swift), for trials.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [October 15, 2015, 5:39pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/10 "2015-10-15T17:39:56Z")
P.s. The [LCS-2 USS Independence](https://en.wikipedia.org/wiki/USS_Independence_(LCS-2)) appears to be a wave-piercing design as well. Its top speed is listed as 44 knots. Compare to 48 knots top speed for the Pegasus class hydrofoil mentioned above.
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### Author:  [@gnoitall](https://boards.straightdope.com/u/gnoitall)
#### Post date: [October 15, 2015, 5:46pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/11 "2015-10-15T17:46:19Z")
And if attack/closing speed is that important, the Navy already has a [class of vessels](https://en.wikipedia.org/wiki/Naval_aviation) that completely outperforms anything that has to touch water.
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### Author:  [@smithsb](https://boards.straightdope.com/u/smithsb)
#### Post date: [October 15, 2015, 10:25pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/12 "2015-10-15T22:25:31Z")
> [@scr4](#):
>
> My understanding is that [wave-piercing hull](https://en.wikipedia.org/wiki/Wave-piercing_hull) design can achieve nearly the same speeds. The US Navy has used several wave-piercing catamarans, most recently the [HSV-2 Swift](https://en.wikipedia.org/wiki/HSV-2_Swift), for trials.
These are craft that have useable capabilities. The hydrofoil has a speed slight speed advantage but limited usefulness. The HSVs could carry 600 tons of vehicles, cargo, and troops at up to 35 kts for 1200+ nautical miles. Also launch and retrieve helicopters and aerostats (aerostats are blimps with a $0.25 name - contractors charge more for them).😃 My son works on aerostats [“don’t call them blimps”] for the US Army.
> **[Tethered Aerostat Radar System](https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System)**
>
> Download coordinates as:
> The Tethered Aerostat Radar System (TARS) is an American low-level airborne ground surveillance system that uses aerostats (moored balloons) as radar platforms. Similar systems include the EL/M-2083 and JLENS.
> The aerostats used in the TARS system are large fabric envelopes filled with helium that can rise to an altitude of 15,000 feet (4,600 m) while tethered by a single cable. The largest lifts a 1000 kg payload to an operating altitude providing low-level, downward-...
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### Author:  [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)
#### Post date: [October 16, 2015, 6:04am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/13 "2015-10-16T06:04:24Z")
It seems the Soviets were even more interested in hydrofoils than the US. They also [built this monster,](https://www.youtube.com/watch?v=V8Nu94khHoo) though not a hydrofoil but a ground-effect aircraft. I seem to remember watching the rest of this documentary about it and although the Soviet Navy seemed impressed by it when a film of it was finally shown to Brezhnev he watched for a while, seemingly bored, until finally saying “Nyet”…
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### Author:  [@Isilder](https://boards.straightdope.com/u/Isilder)
#### Post date: [October 16, 2015, 12:27pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/14 "2015-10-16T12:27:06Z")
Wouldn’t the enemy just be able to use pieces of wood , logs off a tree thrown into the water, as a barrier to the hydrofoil ?
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [October 16, 2015, 1:33pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/15 "2015-10-16T13:33:40Z")
> [@Isilder](#):
>
> Wouldn’t the enemy just be able to use pieces of wood , logs off a tree thrown into the water, as a barrier to the hydrofoil ?
Just how big a barrier are you thinking of? Generally, physical barriers to ships are only practical in very narrow places- harbor entrances and so forth.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [October 16, 2015, 2:33pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/16 "2015-10-16T14:33:13Z")
I think **Isilder** ’s theory is that simply by salting the area with enough floating debris that a hydrofoil would not dare to run at speed for fear of hitting something and damaging a foil. Think of the logs as just a very low-tech minefield.
To the degree the risk of damage is real, it would not take much density of debris to deny the area to foil-borne operations. Which would be enough to convert any enemy hydrofoil into just a normal low-speed patrol boat, albeit one with wimpy weapons.
I can’t say whether the risk of damage is real. I’d certainly expect that issue to have been well-explored in design and testing. For all I/we know, that may be a large part of why they aren’t in tactical use today; too damage-prone.
My $0.02 and worth all you’ve paid for it.
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### Author:  [@Pleonast](https://boards.straightdope.com/u/Pleonast)
#### Post date: [October 16, 2015, 2:58pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/17 "2015-10-16T14:58:27Z")
> [@smithsb](#):
>
> Also launch and retrieve helicopters and aerostats (aerostats are blimps with a $0.25 name - contractors charge more for them).😃 My son works on aerostats [“don’t call them blimps”] for the US Army.
>
> [Tethered Aerostat Radar System - Wikipedia](https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System)
Aerostats are always tethered. Blimps are only tethered when parked.
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### Author:  [@busterpickle](https://boards.straightdope.com/u/busterpickle)
#### Post date: [October 16, 2015, 3:07pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/18 "2015-10-16T15:07:09Z")
Most Navies are going to want a ship that can go anywhere, even into and around the arctic and antarctic circles. Plus, you have frozen water even off the coasts sometimes. At least you get those massive chunks of ice floating around. So, at that point, the hydrofoil is a disadvantage.
I can also think of being in rough seas (like riding through a hurricane) where a hydrofoil or catamaran might be at a disadvantage. Intentional and unintentional grounding. Maintenance on those hydraulics. Hrmm… many things really.
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### Author:  [@Habeed](https://boards.straightdope.com/u/Habeed)
#### Post date: [October 16, 2015, 3:19pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/19 "2015-10-16T15:19:46Z")
Would a hydrofoil save you from torpedoes? I mean, probably not, it just seems like if you were higher up in the water, a torpedo detonating under your keel would do less damage.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [October 16, 2015, 6:10pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/20 "2015-10-16T18:10:20Z")
Depending on how smart your torpedo fuze is or isn’t, it may not detonate at all. The magnetic anomaly or sonic signature might be different enough to not be recognized as a triggering event.
Oddly enough, this strikes me as one of those situations where possibly a “smarter” computerized fuze would be fooled by the weird signature and a dumb WWII magnetic influence fuze would function correctly.
I definitely don’t know for sure, but it strikes me as at least plausible unless an anti-hydrofoil mode was explicitly programmed into the modern fuze.
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