boat design - art or science?

I trust you don't mind me taking a shot at it.

The concerns I have of your design, I have of my own design (on paper and as foam model three feet long).

The stability comes from craft length in a straight line, and from width in a turn.........in a very simple argument model, right? And also a three-legged wheelbarrow is a rather unstable configuration.

I see your design doing pretty good in a straight line; it's the first turn, which turns me pale with fear. Mind you I have the same reservation with my design, which is pure amphibious hovercraft, using inflated tri-hull sponsons. My side sponsons are twice the length of yours, and the center front sponson is half as long (more or less). I have a double bag stern skirt planned (built one on my 10' hovercraft to get the feel for) and over sized giant fingers for the in-between bow seal and compartmentalization underneath connection between all inflatable air cushion sponson bag skirts.

I see the design you linked to dccd, performing much like a mono-hull until in a turn the drag or torque generated by the inside side sponson kicks the stern around in a unpredictable way. I hope I’m wrong, because it would only help my own design to be so.

Cheers, George/kach22i

 

I would have to ask the same questions as Leo did..i.e. I can't quite envision how you are integrating seals and air supply in that concept.

I don't quite agree that aero drag is as big a factor..at least not in the range of 60 knots. Having a Cd of 0.25 vice 0.5 might mean halving the aero drag component, of course, but that component is still a very small part of the total drag. That's not to say that I think reducing aero drag is not a good goal..and a 'sleek' design is always going to be viewed more kindly than one that looks like a BH 110. That was the point of my earlier post, after all.

Our paths must have crossed at some point or other..since I worked on all the same vessels that you mentioned. When I'm feeling verbose, I'll tell the story of my miserable 'encounter' with a Burg 'SES' design - longest short boat delivery trip I've ever made.

 

But this sounds like the skirtless SES cat you seemed to favor?

http://www.seacoaster.com/High-Speed-SeaCoaster.htm

Things did not go as planned I assume?

 

I seemed to favor that thing??..au contrare mon frer! (pardon the Spanish) ...where would you ever get that idea? The concept is notable however..notable in the number that have been built but didn't work. I've never seen a 'concept' that had legs like that one..it's as if nobody wants to admit it's crap and are hell-bent on building one after another to 'get it right' someday.

 

..said passenger ferry being up for sale in Boats and Harbors rag for..just about forever. Fire sale price..

 

Sorry, maybe you just said some people were working on eliminating skirts altogether for maintenance reasons.

 

Not 'some people'..just Don. The skirtless SES has been his 'Holy Grail' for as long as I've known him (20 years). Don's a great fella..just permanently fixated on the idea that somehow the SES would be better if it had no flexible seals. I have to disagree with that..and always have. The 'proof' has been visible to all..there are plenty of true SES vessels that worked well.

 

Hybrid yacht

I feel I owe this thread some more on-subject comment:

Art Vs Science? My own interest in this thread was due to the mention that the SES hull is a technically better hull form, but was too ugly to sell as designed by engineers. I hope to show that my attempt to use the superior performance of a SES can be made aesthetically acceptable or at least not ugly with a little proportion and streamlining.

No dispute that a talected artist can sell a beautiful yacht design that is difficult to construct, but I have never seen one styled that could not be creatively engineered to work below the waterline. By the same token we have seen many expert engineered concepts with no mega yacht buyers (SES, SWATH, most Catamarans). I think this is the the frustration of many engineers in that they went to University and suffered to be highly trained in their "Art" but the "flighty artist" always gets the credit for the high profile yacht. They feel overlooked in the glamorus world of yacht design, Its the only reason for this debate

So IMHO, art or science is dependent on type of vessel. Mega yachts are sold by triggering some passionate response in the client due to a pleasing or sometimes bold form (well engineered always being assumed by the megayacht buyer), commercial boats are sold on cost, efficiency and utility, military on performance and reliability. Only in the motoryacht arena is the focus on art, when their are no more appreciative rich clients, the art of it will be gone. That has happened in land based architecture, I am sure their are talented artistic architects frustrated with no individualist capitalist clients looking to make a statement as in the 30's to 50's. Read Tom Wolf's "From Bauhaus to Our House" for more about that. I fear the day when mega yachts are designed by committe of number cruchers as all "mega" building are done today.

BMcF is very right about the other seal less SES's, the US Navy is still pumping money into many repeated public failures which only wound us in the marine design world. More private, I'll conceived "advanced" marine projects are presently in the works and I cringe for the repercussions coming our way.

Leo, I hope I managed to attach a new seal graphic in answer to your recent post, if not, stay tuned to my web site.




A view of the perimeter seal, with sponsons and centerline hull removed, there is a center line internal web seal and a transverse seal about 1/3rd back from the bow, see orange lines.

 

Thanks, dccd.

I think that the "equivalent lift" is going to be a greater problem that air resistance. Have you calculated the drag components yourself to estimate the power and the engine size you will need to get your beautiful set of teeth over 50knots?

 

teething

Yes lift is known, keeping the weight down is the typical challenge . The seal design shown is a incomplete sketch, it will have closed fingers along the sides, open fingers forward. The new LCAC deep skirt is interesting in that they closed all the side fingers ,the side finger bottom planeing flaps fold onto the one aft of each other, sort of forming semi-ridged sidewall. Also removed the center longitudinal cushion divider and the drag went down considerably. only the mid transverse seal is left, a more simple fore and aft cushion cell design now. I guess the stiffer side seal/fingers make up for the loss of the centerline divider. All in all very interesting.

I will leave my cushion in a triple divided design one cell forward of the transverse, the center hull dividing the aft cushion into P&S cells.

 

I'm probably using the wrong terminology. By "equivalent lift" I mean the power required to sustain the cushion. This can be converted into a resistance component as shown in the graph in my previous post. To me it seemed that there would be greater losses because of the longer than usual perimeter. However, if your skirts are unconventional it might not be a major problem.

Cheers,
Leo.

 

I'm assuming that the fore-aft division is envisaged to be aprt ofthe felxible skirt system. Why do you have that added level of complexity?

Your design is certainly a 'looker', something always lacking in most SES concepts. About the 'best looking' we've ever come up with is shown below; it was part of a proposed demonstrator for a new propulsion system and the client wanted a vessel that would reach speeds that got a lot of attention for their new hardware. It was not an SES development effort..quite the opposite in fact - it was 100% grounded in prior art so that the actual vessel did not indavertently become part of the propulsion system development effort.

..based on a very conventional SES platform configuration. It still has a lot of the "BH110 slash commercial pasenger ferry" look to it.

 

Sesmy

The complexity of my bi-furcated cushion is there for an additional measure of pitch stability.You represent, by way of good questions, the professional nature of this forum, it is like re-living the early design cycle questions we solved before moving forward. I'll answer as brief as possible since if I were to diagram it out, it would only invite more detail request and none of us have that much time.

The 110' SES was a great demonstrator (circa 1980), but built before its time, those old DD16v engines were half the power of the same weight of 4 stokes today. I also did a looker design based on the same 110' proven design for Trinity Yachts, back in 1989! (attached) It is showing a longer length due to the swim platform and a little sharper bow piece. As with my recent design, I think there are going to be sales for SES's as soon as we make something marketable for that clientele. I hope it also shows that the "proven art" can be made handsome too, I have seen a few Euro ferries adopt swept-form techniques like in this design since it was publicized 18 years ago (wow).

 

Diana Yacht Designs had a sleek SES on the boards..Cheoy Lee's was not bad looking but was, unfortunately, of Burg heritage..and you probably know all about John Conner and his Gentry project. So I know that the combination of designers and artists can get it done..but I'm only and strictly a designer..a techology guy.. I design whats below the gunwales (SEMO's 40m and the RNoN Skjold and MCMVs to my team's credit) but heck if I can make one look good.

I'd like to chat further with you about your approach to pitch stability..vice the single cushion with 'staggered LCG, LCB and LCF lift centers' approach that we evolved and is evident on Skjold, for example.

Who the eff are you anyway?..too many 'common' projects to not have run each other over at some point. Shoot me a PM.

For Leo: Lawry and Chris McKesson and I got to shoot the breeze yesterday..where were you? Just as well..yr eyes would have been rolling out of yr head as once again a bunch of ivory-tower computer guys explained in depth why linear simulations can't work for predicting vessel motions. What they have not explained yet is the apparent anomoly of why mine have worked so well for 25 years. Compare junk with data and ya got nuthin..I don't care if its linear frequency-domain stuff or not. But I digress yet again in to a rant that 25 years of repeating has worn slap out...

 

Yes, I agree and see SES sales taking off long before fully amphibious hovercraft. The major reason being the SES looks and behaves much more like a boat. After isn't a SES a derivative of a fast catamaran?

Really nice design(s) dssd, did you get my e-mail?

SES pdf I just found in my computer, what timing.

What's the poop on the Harley SES? See pages 39 thru 43.