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From: budden@manta.nosc.mil (Rex A. Buddenberg)
Newsgroups: sci.military
Subject: Re: Hydrofoil carrier (was: Nuclear Powered Planes: Feasibility?)
Message-ID: <11596@cbnews.ATT.COM>
Date: 21 Nov 89 04:20:30 GMT
References: <11493@cbnews.ATT.COM>
Sender: military@cbnews.ATT.COM
Organization: Naval Ocean Systems Center, San Diego
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From: budden@manta.nosc.mil (Rex A. Buddenberg)
Henry,


I haven't heard of anyone proposing a hydrofoil as hull form, but
there has been a continuing discussion of non-conventional hull
forms for large ships, especially carriers, in the Naval Institute
Proceedings for several years.  

The most ballyhooed hull form was SWATH and the naval engineers 
finally weighed in with some substantive answers and some homework
to back it up.  Both SWATH and hydrofoil use hull forms that rely
on means other than displacement shift to handle displacement changes.
     To explain.  In a conventional hull, as weight is added and
subtracted, the hull immersion changes -- automatically.  And
conventional hull forms are such that fairly substantial displacement
changes result in fairly minor draft and handling characteristic
changes.  And with the exception of submarines, there is no dynamic
compensation mechanisms required on any major class of warship today.
     Non-conventional hulls such as hydrofoils, SWATH,...and submarines,
must use dynamic compensation systems -- as in parts that can break.
SWATH (and submarine forms) require dynamic displacement compensation --
that is, as weight changes, the hull form can't rely on displacement
shifts to compensate.  When the weight changes are sudden -- as in
aircraft launch/land, this presents a major problem which has ruled
out SWATH use for aircraft-capable ships anytime in the near future.
     Hydrofoils have similar problems.  Foilborne operation is 
a high-dynamic operation anyway, so if you could scale to the appropriate
size, the problems presented by aircraft could probably be managed.
But that theoretical speculation is overwhelmed by the difficulties
in getting that big.  The Pegasus class foils have an underwater
(foilborne) form somewhat larger than the hull -- call it wingspan
if you must.  And a significantly larger maintenance bill comes
along with that wingspan.  Somehow scaling what works for a 200 ton
vessel up to an 80,000 ton one seems to me to present some major
problems in strength of materials and stress control.
     Worse, I'm not sure what payoff there would be.  CVs can
crank out 30+ knots when working aircraft.  Hydrofoils advertise
55+ knots.  What good is a 25 knot increase when dealing with
aircraft that operate at 300+ knots?

Rex