FAST2011 Conference Papers Available

Very true on your first part. I disagree vehemently with the second one though; what I witnessed very close up and personal in most cases was the almost-arrogant 'destruction' of the concept by very many 'designers' whose reach far exceeded their grasp. A sort of 'critical mass' occurred sometime in the late 80s whereby so many different groups in so many different countries and yards or design groups were pursuing SES designs that it left most everyone with two false premises or impressions:

1. If everyone else if doing it, then of course we had better design and build one too.

2. If everyone else is designing one, it can't be hard for us to design one too.

 

I cannot speak to the 'hybrid' Textron designs; I will simply note that no successful examples have been built and trialed at anything resembling full scale.

In the passenger SES realm, in the beginning there were the Cirr120Ps. Not exemplary examples, but successful enough to get the type in service. They suffered from a poor stern seal geometry and some structural issues but a number are still in service. They also served to whet the Nowegian Navy's interest in the type (along with some Cardinal MSH and SES-200 navy-to-navy exchanges) leading to the 9 SES MCM vessels and the 6 Skjold-class fast-attack-craft.

Otherwise...the only other well-performing SES were the composite passengery ferries built by SEMO in Korea (40m) and one of the two aluminum 38m SES built in Australia by Oceanfast..which had some structural issues later on.

Yes..sadly it is a short list and, not surprisingly, there is a clear line of 'design pedigree' that can be drawn from John Chaplin's BH-110 and SES-200 through the Cirr120P, the SEMO 40m, and the RNoN MCMV and MTB vessels. That solid T-craft designs came out of the end of that program from the Textron and Umoe teams is not accidental at all; same bunch of folks that were involved in most every step of the way from BH-110 to Skjold. But we're getting long in the tooth, some of us...

 

Thanks, Bill.
The scaled-up Skjold design (from Umoe Mandel/JJMA) had trouble meeting
the endurance requirement at low speed. Hence the interest in split-cushion
systems. As you saw, I can confirm the significant potential for resistance
reduction. Whether it is viable after many other factors come into play (e.g.
seal drag) is another matter entirely.

 

This is true; we (the Umoe team) made a 'command decision' during T-craft not to further complicate an already incredibly complicated vessel design with the split or segmented cushion details; we also recognized the inherent technical risks in implementing same at full scale. Having studied the segmented cushion concepts at length during earlier design exercises (LCS and HSSL) we were well aware of the potential benefits that were being predicted analytically...and had Larry's help in trying to make sense of all that too.

 

There's no doubt it's complicated!
If I had more time and energy I'd draft up some patent applications for my ideas, but the chance of anything actually being implemented is remote so it's
just not worth the effort. (I'm getting long in the tooth too.)

 

Btw..The Umoe design did meet the endurance requirement for unrefueled range...it was simply that the speed for that maximum range was above (well above) that laid out in the requirement set. That happens sometimes with SES; they end up being penalized, in a sense, by requirements that reflect more traditional naval thinking and existing fleet CONOPS. The SES version of the Swedish corvette lost out over the monohull option for exactly that same reason; a requirement to operate continuously for some missions at what amounted to the 'peak' of the drag hump.

But if not penalized for that, SES are just as often (or nearly always, in fact) 'sunk' by the overwhelming weight of combined naval requirements. Dey no like carrying a lot of heavy stuff around.

 

It's not surprising that some changes were made subsequent to the paper
by Doctors, Tregde et al from FAST 2005.
"The traditional SES design, with one cushion, had difficulty in meeting the
additional requirements at the much lower, long-range, endurance speed.
This was mostly due to its large resistance at the hump speed."

That's a very silly speed to operate at for any length of time, or to assess a ship's overall performance.

 

Last question, and I'll stop bothering you...

(I'm guessing) that the same criticism could be made for large SES, as in the T-craft. Are there any successful SES of 1500t or 2000t?
Scaling up the Skjold's 260t to 1500t or more seems replete with risks.

 

The largest SES known to ahve been built was a former-Soviet 'missile corvette' of which little is known. The Norwegian MCMV fleet is the upper limit for size of SES that have actually been launched and in service. Roughly 350 mt displacement when new..not sure what kind of growth they might have experienced in their 20 years of service.

The single biggest (and in my opinion, only truly significant) risk for building an SES over about 600 metric tons displacement 'now' is the bow and stern seal design/build/service life. But that is indeed a big risk area..a huge unknown. The technical/project risk for realizing an intermediate or cushion-segmenting seal is even higher.

Ironically, perhaps, the risks for achieving performance in terms of speed and range actually continue to decline as the SES gets bigger and bigger...to a point at least. It's the really 'small' SES attempts that have typically been the greates failures.

But heck, lets step back just a moment...what was the SES concept first selected in the 1960s and then developed for, after all? The best solution on which to base the design of an 80-knot 2000-ton frigate.

Now, leave me alone.

 

That statement is correct..as far as it goes. One has to realize, however, the the speed range for that 'long range, endurance' requirement was an arbitrarily imposed one; NOT the output of the design process.

Same thing happened with the Raytheon LCS..or was than an LCS paper you were referencing?

 

It was about the LCS and the scaled-up Skjold (80.14m, 1993t).
"Optimization of a Split-Cushion Surface-Effect Ship" by Doctors, Tregde, Jiang and McKesson, FAST 2005.

 

I guessed it was..since I was on that design team/effort too, and that title looked 'vaguely familiar. The LCS had more difficulty with the arbitrary-but-required low speed number imposed than even did T-craft. We blew the "range at high speed" requirements clean away, though.

 

It seems quite impressive at high speed (when turbines are running at their best,
and when waterjets are operating at their most efficient).

My drag predictions for your LCS are close to, but a little higher than
Doctors'. I don't like his transom stern model, the skin-friction line he uses,
the high form factors he favours, nor the low-speed attenuation method he
employs. Apart from that, we use very similar methods

I have a great fondness for Lawry's papers, most of all because they are
nearly always accompanied by careful towing tank experiments (with repetitions).
Not all are of direct use to real ships (and N/A needs) but they are invaluable to us hydronerds.

 

*snort!*

 

All that rot might have something to do with it..that and the funny-looking drag curve with the 'dip and plateau' after the big hump.