Designing hulls for efficient slow motoring

[BillyDoc]

Hi Jon,

Thanks for the reply and the info! VERY interesting sites. And I am most pleased to see that my guess about lower power requirements with electric was good.

Actually, I think that designing for an offshore cruiser is easier than what you are attempting. Most of the time I will be using fairly direct solar power conversion for propulsion (sails!) and will only need the electric motors for docking. Still, sometimes it is very convenient to travel down a ditch. I spent a month slowly traveling down the intercostal from Anapolis MD to Florida once, and it was quite a pleasant trip. A safe anchorage every night and eight hours of actual sleep does have its appeal. On the other hand, I have never run aground when at least a hundred miles offshore . . . and I got a lot of practice with getting off the mud in the intercostal waterway. (Um, do you go to the right or the left of the green thingy...?)

Wow, eight KW of peak photovoltaic is a lot! How much area does that require? And are lead-acid batteries still only about 50% efficient?

[Raggi_Thor]

Very interesting :-)
At 15 meters (45 feet) and 6-7 mph (5-6 knots?) you have a very low speed/length ratio. I think your best shape will be simple with smooth lines and low vetted surface, no bulb etc to optimize for a specific speed.

[JonathanCole]

One square foot of PV is about 10 watts peak power. On a sunny day multiply peak power times 5 hours to get total energy (in watt/hours) converted. This is an approximation. It varies by time of year (more in the summer, less in winter) and latitude, much more in Hawaii than Norway. But Norway does have those long days in the summer!

Flooded lead acid batteries operated in the proper charge/discharge regime are 90% efficient. If you keep them above 50% of charge and below 90% of charge they are around 90% efficient. Above 90% of charge and below 50% they can be as little as 40% efficient. Of course this means that to get that efficiency you have to have twice as much battery as their nominal amp/hour rating to get the rated energy storage in an efficient device. A rule of thumb is 600lbs of weight of batteries for 2000+ watt/hours. Some people don't want to use flooded lead acid batteries on a boat because they vent out the caps. You can get special caps that can be plumbed with tubing to vent any gases to the outside and prevent spills. Closed batteries can be had but generally have a much shorter life.

The beauty of my all solar drive is that during the day, when I plan to do my cruising, I can run directly off the sun and avoid batteries all together. Even in cloudy weather I can travel, I just have to match energy in with energy out. Batteries give you emergency backup for protracted cloudy weather. Even in cloudy weather (unless its very dark clouds) PV can deliver 10-20% of its rated output. With some small wind turbines on board that can often make up for cloudy weather.

Jon

[BillyDoc]

Those rules of thumb are very handy to do my guestimating with.

[mackid068]

Try a heavy, full displacement for slower speeds.

[JonathanCole]

Originally Posted by mackid068

Try a heavy, full displacement for slower speeds.

Well I can understand just going with a full displacement tub (do you mean monohull?), many solar boats have done just that. But why would you want heavy? Doesn't that just translate to more work to push through the water? Also if your cargo is not too heavy wouldn't you want just enough wetted area to float?

[mackid068]

Heavy, generally, seems to be an unavoidable feature of full displacement monohulls. Well, maybe you could try one of those torpedo style boats like those used for pedaling across oceans, unless you actually WANT a practical boat. Solar power, in this current time, is not particularly viable except for those with huge amounts of funding and lots of time on their hands/money to purchase other's labor or if you just want an impractical boat. Solar power is best for recharging batteries and powering ventilation more than for powering a vessel (heating, maybe but not powering). Eco friendly is only available as a sailboat with a small four stroke but EFFICIENT is available as a diesel powered trawler (efficiency doesn't necessarily equal eco-friendly, as diesel produces copious amounts of choking, global-warming causing fumes, though in less amounts in total than gas due to the increased efficiency of diesel, or so I've read)

[mackid068]

I'm anti-solar, but I would say, for your purposes, that the best idea is a full displacement boat powered by a moderately sized diesel, with a hull of steel and an aft pilothouse (a'la a Nordhaven trawler). Trawlers seem to generally be efficient, large and slow.

[JonathanCole]

I'm anti-diesel, myself. I hate the smell burned or unburned. Plus polycyclic aromatic hydrocarbons coating each particle of soot belched by a diesel engine is as carcinogenic as it gets. So I'll just continue to pursue alternatives.

To say that a solar powered boat cannot be practical is the same as saying an electric boat can't be practical. Yet there are many electric boats in use, even some huge ones. Have you looked at any of the web sites of solar powered boats that are listed on this thread? Those folks who are using solar powered boats as we speak would be surprised to hear that they are an impractical pipe dream. Besides aren't you the guy who says its all about going nowhere slowly at great expense?

[Packeteer]

I think its wise to consider other sources of energy other than photovoltaics

wind, wave, biodiesel, methanol, fuel cell

[yokebutt]

Jonathan,
Have a look at the boat Jim Antrim designed for the Duffy-dude.

Yokebutt.

[SAQuestor]

Originally Posted by JonathanCole

Is there any information out there about hyper-efficient hull forms? I want to build a slow motoring boat that is extremely fuel efficient.[snip]

Jonathan - May I suggest that you contact Jim Antrim about his 30' electric boat hull. Take a look at the 30'-er at http://www.antrimdesign.com/electricboats/

Two reasons 1) Electric boats need efficient hulls as there is not great gobs of raw power available. 2) This hull form looks (to my eye) like at expanded Whitehall pulling boat of the late 1800's - arguably one of the most efficient low power hull forms every devised by the mind of man.

Best,

Leo

[CDBarry]

The NPL series is a very efficient series for this speed regime, and is well documented.

Note also recent double chine series. Also, Noblesse has a very good process for optimizing hull forms in this regime, and it ought to work especially well, since it uses sthe slender hull assumption. See SNAME Transactions, for the last few years, for both of these.

[mackid068]

I suggested wave energy a while ago, what about a diesel powered...or electric OR solar boat with turbines on the underside to generate power from pushing slowly through the water. Yes, and I suppose you're right. Solar, though not necessarily fast or economically-efficient, holds significant promise and, eventually, ought to be tried as a consumer product.

[JonathanCole]

Originally Posted by Packeteer

I think its wise to consider other sources of energy other than photovoltaics

wind, wave, biodiesel, methanol, fuel cell

I agree, and my plan includes several small 500 watt wind generators, a backup ICE generator when more power can't wait and a plug-in battery charger for use wherever an electrical outlet can be found, such as marinas and fuel docks.

I think some people seem to have an aversion to the idea of solar boats, but if you don't have to go somewhere in a hurry, you can wait until your batteries are charged. Typical 30-50 foot catamaran PV powered electric boats are demonstrating a range of 30-60 miles a day on sunny days. Not too bad for a leisurely cruise. On the inland waterways on the European continent where you can tie up for little or no money in most places, this range would allow for a nice slow paced journey, say from Holland to the south of France which would be very economical and pleasant. You might disprove the maxim that a boat is a hole in the water that you throw money into!

A previous thread suggested that solar was only for people with excess money, but it seems to me that the cost of sails, hardware and rigging on a 16 meter boat could be more expensive than PV panels, batteries, backup generator and control electronics. Properly utilized, deep cycle batteries can last for 15 years. Since motoring boats on a per mile basis are very fuel intensive, the amount that can be saved in fuel over a fifteen year period, can exceed the cost of the batteries by a large amount. Also electric drives can be over 90% efficient with essentially one moving part (aside from direction changing gearing). Way less maintenance required. No messy bilgewater or open water pollution. It may not meet everyone's requirements for thrills or speed, but it sure has a lot to recommend it.

Besides I can always carry a small hot runabout on board. Maybe a Mini-Cooper too!