# Why doesn't the US Navy use hydrofoils? **URL:** \ **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:** 10\ **Page:** 2
**Author:** ![spifflog](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@spifflog](https://boards.straightdope.com/u/spifflog)\ **Post date:** [October 16, 2015, 7:13pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/21 "2015-10-16T19:13:12Z")
> [@Habeed](#): > > 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. The biggest threat to a surface ship is a missile. Hydrofoil isn’t going to help you there at all. ---
**Author:** ![dba\_Fred](https://avatars.discourse-cdn.com/v4/letter/d/c37758/32.png) [@dba\_Fred](https://boards.straightdope.com/u/dba_Fred)\ **Post date:** [October 17, 2015, 8:58am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/22 "2015-10-17T08:58:27Z")
The Navy really should deploy hydrofoils. That way, as the SEAL Team zips away after a successful mission, the bad guys would exclaim _Curses, **foiled** again_! ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [October 17, 2015, 9:47am UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/23 "2015-10-17T09:47:24Z")
I guess the real question is why doesn’t the Coast Guard use hydrofoils? Seems like they would be ideal for the interdiction of high speed smugglers boats. A bit of googling doesn’t seem to bring up any countries coast guard as using hydrofoils? ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [October 17, 2015, 2:25pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/24 "2015-10-17T14:25:14Z")
> [@Lumpy](#): > > 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. I once talked to the chief engineer on a Pegasus hydrofoil. To put it politely, they are not operationally viable. The high power engines needed are simply too difficult to control effectively in actual maneuvers. Think about operating a hydrofoil next to a conventional ship for at-sea resupply. Obviously the hydrofoil isn’t up on the foils, but the foils are still sticking out like knives. That one cost the captains of both ships their careers. The only reason the chief avoided trouble is he had his objection logged before the maneuver started (seas were too rough and the ships collided. The hydrofoils almost sank the much larger cargo ship). These were jet engines. They have a very narrow range of acceptable operating temperatures. A range that was way too easy to get out of. When you have a small ship covered in large Harpoon missiles, a backfire is very bad… They look really cool in the publicity pictures. Some ports considered them so dangerous they weren’t allowed in. ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [October 17, 2015, 10:56pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/25 "2015-10-17T22:56:46Z")
> [@spifflog](#): > > 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. Demurral. Small and fast is always harder to hit. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 17, 2015, 11:09pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/26 "2015-10-17T23:09:49Z")
> [@the\_diego](#): > > Demurral. Small and fast is always harder to hit. Yes, but even the hydrofoil ships are slow as a snail compared to a missile. ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [October 23, 2015, 3:19pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/27 "2015-10-23T15:19:54Z")
The bigger, slower snail will get hit. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 23, 2015, 3:21pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/28 "2015-10-23T15:21:52Z")
> [@the\_diego](#): > > The bigger, slower snail will hit. This doesn’t remotely follow. If one ship is evading at 30 knots, and another at 50 knots, and the missile is incoming at 1200-1800 knots, from the missile’s perspective, if it’s control hardware is good enough to hit the slower ship, it can hit the larger ship. From the missile’s perspective, the angular rates of change are comparable. ---
**Author:** ![spifflog](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@spifflog](https://boards.straightdope.com/u/spifflog)\ **Post date:** [October 23, 2015, 3:53pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/29 "2015-10-23T15:53:50Z")
> [@the\_diego](#): > > The bigger, slower snail will get hit. This isn’t that hard. For a missile incoming at Mach 2.5 (about 1,900 miles per hour) a ship traveling at 48 knots vice 24 knots doesn’t make any difference at all. Do you get that? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 23, 2015, 4:27pm UTC](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684/30 "2015-10-23T16:27:20Z")
Like we used to say during the war: “How can you strafe women & children?” “Easy: just don’t lead 'em as much.” From the POV of a tactical aircraft or missile a ship, any ship, is almost but not quite stationary. Ditto land vehicles. Only trivial adjustments are needed to offset their pitiful attempts at running away. [Previous page](https://boards.straightdope.com/t/why-doesnt-the-us-navy-use-hydrofoils/734684.md?page=1)