s.w.a.t.h

[jimbot]

I was wondering if anyone was still designing these. I have been doing research on various "green" initiatives, mainly auto, and have found some interesting items. First was this neat idea for a car. http://www.worldcarfans.com/news.cfm...-electric-mini

By going to the PML website, I discovered this. http://www.pmlflightlink.com/motors/EW_details.html
While a powerful electric motor is interesting, you would need some battery to power it, so I found this. http://www.altairnano.com/markets_amps.html#innovative

They claim a 10 minute recharge time (but you have to use 480 volts to do so), years worth of deep discharge, and a light weight/power ratio.

I would think that this would allow you to design bulbs for the swath that were more hydrodynamic. By using electric motors, and placing the batteries in the bulbs, you could put the generator motor where it's accessible, rather than having the engines in the bulbs.

So I thought I'd ask the pros. Can you design one of these things that doesn't look like a floating city block?

[marshmat]

Regarding Altarinano's batteries. As I understand it they are similar to conventional Li-ion batteries but with a lithium titanate spinel oxide anode and some tweaks to the electrolyte chemistry. This plus a finer surface structure than is possible with normal graphite anodes gives the high power density. Their energy/weight ratio is comparable to NiMH and nowhere close to normal Li-ion, but they appear capable of handling much larger surges in charge and discharge current than either NiMH or graphite based Li-ion types. Promising for an electric car, but a boat drive doesn't have the huge surges in current that a car does, so the main advantage of the Altairnano battery would be wasted in a boat.
PML's wheelmotors are very promising for automotive applications and the same technology is equally valid in the marine case. They need to be much more widely available before they'll really catch on.

[JonathanCole]

Matt wrote:
Promising for an electric car, but a boat drive doesn't have the huge surges in current that a car does, so the main advantage of the Altairnano battery would be wasted in a boat.

That may not necessarily be true. To quote the web site:
http://www.altairnano.com/markets_amps.html#innovative

"High cycle life—10,000 to 15,000 charges vs. 750 for existing batteries"

Depending on the cost of such batteries, this could be a major breakthrough. If you need to recharge your batteries once a day, that suggests a life of 27 to 41 years -well matched for the life of the photovoltaics in my solar live-aboard catamaran that I am currently working on manufacture of. Even if they cost 50% more per cycle as existing technology, it might be a great deal in the medium to long term.

Also, the ability to recharge in one minute (that rivals the charging speed of a supercapacitor) means that it can make use of transients normally dissipated as heat in devices with lower power characteristics. Regenerative devices can also easily be used in electric boat motors. When the boat is called on to stop, all of that momentum can be converted to fast charging through the prop.

These batteries may in fact be useful in Marine craft.

[Rick Willoughby]

I built a small boat based on submerged buoyancy. The shape of the sebmerged section had the proportions of an optimum submarine. From memory it was 8:1 length to diameter ratio. Wetted surface was much lower than a surface hull designed for the same speed.

It did not perform quite as well as I expected from the testing I did with models.

When I eventually learned how to drive Michlet I did a review of the design. I found that I needed to have the hull about 3 diameters below the surface to reduce wave drag to a negligible level. My full-size hull was only 1D while my model was around 2D under the surface.

You will see from the atttached photo that it is already a cumbersome design so an extra 2D of draft was not tolerable. As a devopment, I added foils to the outriggers to reduce drag and these were quite easy to fly so it becomes an assisted hydrofoil. I could get foil borne at 10kph with 15% of the displacement carried by the outriggers and foild 300mm wide by 100mm long. I gave up on exploring the idea but it had some interesting characteristics. Like riding on a huge spring cushion.

The main point of the post is I gained some confidence that Michlet would give good performance prediction for these vessels if the hulls are near surface. If they are deep then it still works but you can forget wave drag and go for the optimum L/D ratio for the design Reynolds number.

Another aspect that emerged was the need to keep the buoyancy low. With my CoG about 2 feet above the waterline and the line of thrust 2ft below the waterline I could get the thing to almost backflip if I accelerated with conviction. Once in this attitude I would need to slow to a crwal before the front outrigger seetled back down.

For those who cannot contemplate the pure fun of human power you might find this one of interest:
http://www.stevproj.com/Carz/StvHyFly.jpg
The blend of foils and underwater flotation offer some interesting opportunities to explore. It is possible to get lift off with moderate power. The result is good ride quality with very little wake.


Rick W.

[yipster]

interesting lay-out and thanks for sharing experience Rick. made a start on a similar expiriment few years back, made some delicate models and was told the 2 feet deep pods werent deep enough. outboard long shaft as the tubing and centerpod never realised but still find it a very interesting concept

[BMcF]

Island Pilot had a very interesting semi-SWATH eco-yacht model on display at the last Miami boat show. Semi-SWATH means, in a nutshell, a small waterplae (waisted) hull but without the struts. It had a DC-electric hybrid propulsion system (diesel gensets + solar arrays). Having been involved in the design, construction and stabilization of many (most even) SWATH vessels, including even the old USN 'Kaimalino', I recognised that the hull on the model was SWATH-based..something that the designer appreciated since everyone else at the show apparently did not recognize that.

I have found actively-stabilized SWATH's to be the most incredibly sea-kindly vessels ever built (some hydrofoils aside..arguably) . But I have also seen that they can be the most prone of any to be 'over driven' in to sea conditions where they are over-matched (some hydrofoils aside..arguably)..and bad things happen then.

I think the semi-SWATH configuration is inherently 'safer' in many respects, simply because when conditions get rough, the waves will be acting against the hull in a more traditional way and will definitely let you know about it before you have reached a critical operating limit.

I have heard that Abeking and Rasmussen (who have built a number of pilot and survery SWATH vessels) is working on an expedition yacht SWATH design. That would be something to see...to date, only the owner of Swath Ocean Systems in California (no longer in business) ever built SWATH yachts to my knowledge.

[charmc]

Yipster,

Thought you might be interested in a SWATH vessel operating for about 10 years now:
http://oceanexplorer.noaa.gov/techno...ternflyer.html

As a low speed research platform, Western Flyer does not deal with some of the design questions raised here, but she's provided a lot of data on strengths and weaknesses of SWATH.

[PI Design]

This link shows a submerged body (SSGT submarine) that has been optimised for near surface operations.
Talking of batteries, this uses zebra batteries. I wasn't involved in the propulsion side of things and know little about batteries, so don't know whether they would be appropriate for a SWATH, but thought I'd mention them anyway.

http://www.bmtdsl.co.uk/BMT/bmt_medi...over4pages.pdf