Re: [PSUBS-MAILIST] Underwater pod on surface vessel.

["Greg Cotton" <gregc02@attglobal.net>]

> 
> > Surface vessels are limited in speed by a surface effect, perhaps
> unfamiliar to psubbers as it
> > does not apply underwater


> 
> An effect I once heard a British friend refer to as "running with a bone in
> her teeth" (describing the bow wave).   In the first half of the 20th
> century, military submarines had naviform bows, and suffered from this
> phenomenon when running on the surface.  That changed with the arrival of
> streamlined "teardrop shaped" hulls (ALBACORE, SKIPJACK, and successors).

It mostly changed because suface speed became unimportant; the true submarine could stay 
down as long as it liked and could make higher speeds submerged than surfaced. The Albacore 
hull shape may have modified the hull speed formula but I think it still applies.
 
When I went from diesel boats to nukes, one of the wierdest changes was standing topside when 
leaving port and not hearing any engine sounds (if you've never heard four Fairbanks Morse ten 
cylinder opposed piston diesels running flat out, you've missed one of the great experiences) and 
just listening to the waterfall from the bow. On that hull shape water doesn't divide like in a normal 
bow wake, it just flows up the curve of the hull until gravity makes it flow off sideways into the 
trough behind the bow.

http://www50.dt.navy.mil/gallery/submersibles/ssbn735.jpg

and

http://www50.dt.navy.mil/gallery/submersibles/ssn725.jpg

All that turbulence has got to cause huge amounts of drag, so I suspect there is still a hull speed, 
maybe just with a modified formula.
We were certainly faster submerged than surfaced, it just didn't matter anymore; we were only 
sufaced comming in and out of port. As soon as the water was deep enough we just submerged 
and spent the entire patrol (60 days) submerged.

On the diesel boats we really got diminishing returns with added power. One engine gave us 
something like eight knots, lesser increases with two and three, and adding the fourth engine just 
increased speed one knot, from eighteen to nineteen knots (if memory serves).

Hull speed would work out like this with the earlier formula:

Hull 311 ft. X 1.34 = 417 
   
Sq root of 417 = 20.4 knots

This is pretty close to what we actually got.

And yes, my heart is still with the diesels and with my qualification boat.

http://www.usstorsk.org

Yes, in some cases, you can go home again.

Greg








> 
>  surface waves plowed up by the bow cause a bow-up pitch once the boat
> > exceeds "hull speed" which is generally quoted as 1.34 x waterline length
> in feet = hull speed in
> > kts.
> 
> For the general information of all, howsabout providing an example of this
> formula in use based on an arbitrary hull length of your choice, to
> demonstrate how works?
> 
> Pat
>