View Full Version : Which is the most economical kind of small vessel?


Guest
07-24-2003, 06:51 PM
Which kind of vessel do you people think is the most economical:

1: Classical large cargo-ship type. Slow-moving, displacement type.

2: Hydrofoil

3: Hovercraft

4: Regular speed-boat

5: Ground-effect aircraft

6: Submarine

7: Other?

With "economical" I mean for the vessel to be able to transport 500kg of cargo across the atlantic. Speed is not important.

They have different advantages:

Hovercraft/ground effect aircraft: No viscous drag from water, and no wave making drag.

Hydrofoil/Speedboat: Less waves and water drag.

Submarine: Little wave-making drag.


I think my bet is on the submarine.

Guest
07-24-2003, 07:01 PM
Maybe I should have written that I mean energy-conservative when I say "economical".

gonzo
07-24-2003, 07:56 PM
500 Kg of cargo is minimal compared to the load of fuel, water, fuel and other necessities for the crew. A submarine would have to be nuclear powered to stay below for such a long time. Are you putting any other restrictions to your query? I think that a displacement sailboat is the most economical; particularly for a small load.

tspeer
07-27-2003, 10:02 PM
There's actually been a lot of research on this topic, most of it starting with the work of Von Karman and Gabrielli (Gabrielli, G. and von Karman, T. (1950). What price speed? Mech. Eng. 72, 775-781). They found there seems to be a limit to transport performance of all kinds of locomotion. This is variously expressed as speed * Lift/Drag = constant or speed*fuel consumption*payload = constant.

Here are some examples applied to
submarines: http://www.acq.osd.mil/dsb/suboffuture.pdf
SES ships: http://www.se-technology.com/wig/html/main.php?open=commercial&code=0

Since you specified no time limit, the winner will be the long, narrow displacement hull. It's hard to beat this for moving bulk cargo, because the drag goes to zero at zero speed and the L/D goes to infinity. If fuel costs are greater than payroll costs, you can make it even cheaper by using sail power. Yep, you're right back to the age of the clipper ship.

I put my money on #7.

SailDesign
07-28-2003, 06:57 AM
The problem with "time not an otion" is that it becomes a theoretical exercise. If you had to move X tons of material every day, then the equation is very differnet to that if you have to move X pounds every day.
As gonzo says, crew resources are an important factor, and the cost of making fresh water vs. carrying sufficient for the trip may have an effect on the "economy".
You should look at "cost per ton-mile" as a relative factor. Add in ALL costs, crew wages, crew life-support (food, etc.), cost of vessel, lifespan of vessel, machinery purchase price and maintenance costs, and so on. Then divide this figure by the number of tons you could hve carried times the number of miles you would have travelled (remember to allow for maintenance days/weeks) and you will have an overall cost per ton-mile for that vessel.
It can be scary....

Steve

gonzo
07-28-2003, 10:45 AM
In the theorethical realm, it would be possible to float the cargo across the ocean. The currents would eventually carry it across where the cargo could be retrieved. Of course the current pattern is limiting, but in a world without thieves this system would work.

Guest
07-29-2003, 03:56 AM
I really appreciate all these replies! Much more than I had expected.

I wasn't thinking economy as in "money", just as in fuel-economy, energy-efficient. How many joules have to be expended to transport 500kg from some specified location in europe to some specified location on the american east-coast?

If using a submarine, it would be allowed to go to the surface at any time, to replenish air-supply.

I've done some simulation with the michlet program to determine which is best, submarine or surface vessel. It seems that skin drag is greater on the submarine because of its greater surface area / volume.

Maybe we should put a time-limit on the journey, so that a message-in-a-bottle design is disqualified :-)... Say a maximum time of 6 months.

I'm pretty sure an unmanned craft will be more fuel-efficient (if it doesn't break down halfway over :-)).

According to
http://www.trektracker.com/WS_HomePg1.htm
it's 2500 miles across the atlantic (somewhere).

According to the michlet-program a 3 metric tonne craft travelling at 1.6m/s needs a thrust of 0.18kN.

2500 miles = 4000km.

4000e3m*180N = 0.72GigaJoules (=approx 200litres of diesel (approx 50 gallons), at 10% engine efficiency)

Anyone think it can be done with substantially less energy?

Portager
07-29-2003, 10:07 AM
I think your calculations fail to consider the effect of waves. The displacement vessel will be more efficient than the submarine in dead calm conditions, however when you add in sea states and winds the balance reverses.

Diesel electric submarine can and have crossed the Atlantic submerged using diesel power and their snorkel.

I think you could have a smaller craft than 3 tons to carry 1000 kg of cargo, although it will depend a lot on the cargo density, which you haven’t specified yet. Low density cargo like mail and electronic equipment in boxes with crush space and light weight packing material will be a bigger problem than high density cargo, especially for the submarine, which must have sufficient mass to sink the cargo.

If you’re interested in the optimum unmanned vehicle, then I think a semi-submersible would be the optimum. Rockwell built one for the US Navy for a remote controlled mine hunter. It worked quite well when it was in the water, but launch and recovery was a pain. It was a torpedo shape with a mast that penetrated the surface for the diesel engine air intake/antenna and a keel for ballast. A significant advantage of this design is it can be made nearly immune to storm conditions.

If you are going to send an unmanned vehicle across the Ocean, you are going to need really good communications and reliable navigation. I’d consider Iridium and HF radio since they are the only truly global system. Running lights and a beacon that says, “Vessel running blind” would be a good idea also.

Regards;
Mike Schooley

tspeer
08-01-2003, 10:07 PM
Actually, this problem is solved for real every day. Just look at the kinds of boats people use for cruising. They have pretty much the same criteria - has to be economical and seaworthy, time is not the most pressing constraint, but they still want to cover long distances carrying a reasonable load.

The vast majority settle on the sailing yacht.

Given how difficult it is to operate underwater, I think the advantage of the sub is it can cruise beneath the waves - provided it doesn't have to draw air from the surface. So a sub would make sense if your operating area is the Southern Ocean.

dionysis
08-02-2003, 12:28 AM
I don't know whether this is beside the point, but will you include the energy expended in producing the vehicle? A sub, yacht or any moderately complicated vessel can take a lot of energy to build, both in manufacture and materials.

tspeer
08-02-2003, 04:58 PM
If you want to include the energy of building the vessel, then you have to start dealing with the question, "Over how many trips will the building energy be amortized?"

Wood construction is pretty energy efficient to produce, and I suspect modern composite materials are, too. Bottom of the list has got to be aluminum.

Energy = cost. The whole point of economics is how to optimize over many conflicting and competing criteria.

So the most energy efficient solution for carrying a modest payload over large distances still comes back to the classic wooden sailing yacht. And the vast majority of the energy required to build and operate it comes from renewable sources!

dionysis
08-03-2003, 12:42 AM
Yes, they are grand!

Guest
08-04-2003, 11:19 AM
Portager: Very interesting!

As you might have guessed, I'm really interested in making a small autonomous vessel. The remote controlled mine-hunter that you described is almost exactly the kind of vessel that I'd like to build!

Having a keel seems like a reasonable design decision.

What is HF-radio?

I was thinking Sattelite HAM-radio. As I understand it's got really great coverage, and doesn't require large transmission power.

How about this idea:
Include a very small diesel engine. Include lead-batteries and an electric motor. The craft runs for apx 20hours submerged, then surfaces and starts diesel engine to recharge for about 3hours. The the cycle is repeated. Let the snorkel be a long pipe sticking out of the front of the craft. Make the center of gravity of the craft be exactly at the center of buyancy. Then it's possible to make the craft stand up in the water simply by displacing a weight to the rear of the vessel. This way the snorkel doesn't have to protrude upwards from the craft and it can be more hydrodynamical. And it might be easier to design than to design for the snorkel to be raisable.

Portager
08-05-2003, 01:01 AM
Interesting idea, but unless you need to dive deep, I think it would be easier to use a fixed vertical mast with a water trap. If the engine can breathe and run all the time you can use a smaller engine and eliminate the batteries.

How would you maintain neutral buoyancy as you consume fuel? The conventional approach is to provide ballast tanks which are empty when the tanks are full and you flood as you consume fuel, of course you need additional mass to make the overall system neutrally buoyant. I would use a bladder tank for the fuel and as fuel is consumed from the bladder allow sea water to fill the void in the tank. By adding a little air to compensate for the difference in density of fuel and sea water you maintain neutral buoyancy with minimal additional mass.

Regards;
Mike Schooley

dionysis
08-05-2003, 02:28 AM
if you have an "all the time up air pipe" then you have the problem of the sub having to follow the contour of waves and swell. This will consume quite a bit of energy, in terms of friction and induced drag of plane rudders, in going up and down.

Portager
08-05-2003, 11:11 AM
I think that depends on the length of the mast, the sea state and the running depth. Besides it is hard to argue with success.

http://www.ise.bc.ca/dolphin.html and http://www.ise.bc.ca/dorado-old.html

Regards;
Mike Schooley

Guest
11-13-2003, 09:44 AM
This is an interesting thread for me. I was introduced to this subject by a photograph in a British newspaper of a semi-submersible that a man in Bristol had built. The vessel was made of steel, as I recall, and was actually in the water in a Bristol dock. A relative in the area tells me that the boat was later put on a trailer and used as an advetisement for a pub! I have tried to find out more about it but have not been able to. Anyone know anything about it? Did it work?

My interest is in making a survivable craft that can routinely cross the atlantic in any weather. Surface craft of almost any size are at risk. (the excerpt from the skipper's log on the Cutty Sark in London has a phrase that goes someting like this: "In all my 30 years of sailing I never saw a wave like that". The wave nearly sank the vessel. Also, the QE2's skipper tells of the day they were hit by a 90 foot wave). I was thinking of a boat that would let the waves break over the top and keep the vertical G's down.

My concept would be an almost cylindrical hull about 6 to 7 feet in diameter, made of steel with a stabilizing weight (keel?) suspended a few feet below. The craft would be self-righting, of course, but should not roll much even in beam seas. A snorkel (with a good active radar!) would stick up to let the small diesel breathe. If I could get (say) 10 miles per gallon of fuel, then a 2500 mile run across the Atlantic would use 250 gallons which, at present diesel prices, would only cost around $500. But going slowly with a nice big prop might yield 20mpg. I have no real idea how low the fuel consumption could get. About the same as a whale, I suppose! There would be a kind of conning tower with a deck for nice weather; but when things got rough, that would fold down to minimize drag and damage.

Would it work? I have the money to build one if it makes sense. Please comment on any pros or cons.

gonzo
11-13-2003, 10:39 AM
It makes sense. How do you feel about being submerged for a long time? I think that the psycological effect will prevent many people from accepting the concept.

Guest
11-13-2003, 02:23 PM
Gonzo,
I would not expect to be submerged for long periods, just enough for the wave to pass over. And only then in heavy seas. A transparent skylight would ease clautrophobia.

I guess my view is that it is better to be submered occasionally than permanently! It is folklore that a large fisherman was tethered over the stern when a large wave came by, flooding the cockpit and sinking the vessel in seconds. I was sceptical but, if you calculate the volume of water taken aboard in the cockpit alone (say, 15 foot beam x 12 foot length x 3 feet deep) it would weigh around 33,000 pounds which would certaily be a problem. It seems to me that most large "cruisers" are fair-weather craft and simply could not survive a severe storm. Can you imaging doing a 360 rollover in a floating Winnebago! My aim is first to survive; everything else is optional.

Willallison
11-13-2003, 06:30 PM
For most, the joy of boating is not simply getting from A to B. It is the pleasure taken from simply being afloat - and all that it entails. If all you are after is a means of transport across the Atlantic, why not take a plane - it'll be faster, more comfortable, safer and MUCH MUCH cheaper!

by the way...Make the center of gravity of the craft be exactly at the center of buyancy ... a vessel will naturally trim to a position where the CG and CB are at the same point - that's one of the reasons for the ballast tanks that Mike referred to.

Guest
11-13-2003, 08:42 PM
Will,
I already have a boat that I enjoy in fair weather and of course it is fun. The joy here, however, would be the sheer adventure of crossing from the US to Europe single handed - in reasonable safety. Besides, in good weather, I could sit topsides and enjoy the scenery like any other boat. The boat would only be about 70 percent submerged; more a wave piercer than a submarine.

I didn't understand your advice to make the CG and CB coincident. Surely the vessel would be neutrally stable and just as happy upside down as right side up. I was planning a very stable platform with the CG well below the CB - like a sailboat.

Willallison
11-13-2003, 09:01 PM
Sorry - you're right - I didn't explain that very well.
Let's work with longitudinal CB / CG - the same applies laterally as well though.
If the LCG is forward of the LCB then the vessel will trim down by the bow until the LCG and LCB are in vertical alignment. (As the bow is submerged, so the immersed volume forward is increased, which moves the LCB forward). The same applies if the LCG is aft of the LCB - the vessel will trim down by the stern until the two are aligned vertically.
In order to self-right, as you suggest the CG needs to be below the CB when the vessel is right-way-up

Doug Carlson
11-13-2003, 09:57 PM
Guest,

That the vessel had high initial stability, low cg, low metacenter, significant lateral plane for motion dampening, a secure place for you to hang out in when the going got rough, impervious bouyancy chambers, and was self righting through 180 degrees would seem to be important to your concerns.

Whether your position in it was a few feet above or below the surface wouldn't seem to matter much. Either way your riding to the top of the wave you are worried about and if its breaking your going over on your head with all the associated excitement.

To avoid wave dynamics, you would have to submerge to what I would imagine would be an impractical depth for the low energy consumption, relatively low tech, craft you seem to be envisioning.

You might be better off to design for absolutely marginal bouyancy to minimize the vertical effects of wave motion.

Absolutely marginal bouyancy would seem to have some inherent risks of its own however.

Be advised I am not qualified to make any of these statements, they are only my thoughts as an interested layman.

Doug Carlson

Willallison
11-13-2003, 10:27 PM
I'm with you Doug. If I recall correctly wave energy extends to a depth equivalent to its height - so a 20 ft wave creates turbulence 20ft below the surface. In order to ensure that you didn't cop this you'd need a snorkel over 40ft long - and a 20 ft wave isn't exactly huge.

I would have thought that the cheapest way to do this would be to convert a motorised self-contained lifeboat - they're certainly seaworthy enough, and you'd have the added benefit of knowing that the design is well tested...

Guest
11-14-2003, 10:34 AM
Will and Doug,
Thanks for some very good points. Doug's point that my main aim is to survive, and that I could make a safe vessel without it being a semi-submersible, is a good one. Will also suggeststed a lifeboat. However, I think my efficiency requirement would not be met with the lifeboat, but read on. Wills explanation of the longitudinal CG and CB is excellent. I had not thought of that; the less buoyancy the vessel has, the more critical that factor would become, especially if fuel loads shifted. Good stuff indeed

Now here is an insight that just arrived: All boats are partial submersibles because they all displace water. It is just the degree that is different. So, if we classify them according to their "percent submersible" factor (the percent of their volume submerged) a heavy monohull sailboat would be pretty high on that submersible scale (perhaps 50%?) whereas a sailing cat or a powerboat would be low (20%?). The higher mass of the monohull sailing boat is better for passagemaking because it slows the frequency of response to the waves. This prevents the pounding that the relatively lightweight powerboats suffer which makes for a much more comfortable ride in rough seas.

So, maybe what I am really looking for is a variation of a sailing boat hull (50% submersible) but with a narrow beam (since it has no sails it doesn't need a wide beam) and a heavy ballasted keel (torpedo type to minimize drag?). The bow would be sailboat pointy to pierce waves and the topsides would be clean to allow the big waves to pass over without too much drag. Oh yes, and strong hatches for when the bad stuff arrives. Wow! That sounds quite practical, and it could even look gorgeous. How about the length? About 30 or 40 feet seems about right to me with, perhaps, a 6 foot beam.
I am getting excited!

Portager
11-14-2003, 10:58 AM
I think you have just reinvented the motorized passagemaker.

You are correct that the heavier displacement will provide a more comfortable ride and as long as you are willing to travel slowly, it is also very efficient.

The longer you make your length to beam ratio the more efficient it will be to power. The down side is the long length to beam tends to increase hull stress, so the ideal is probably in the 4:1 to 6:1 range.

Another problem is weight management. If you put the fuel down low it makes pretty good ballast, but as you consume fuel the empty tanks tend to destabilize the craft. This means that you need to have a great deal of ballast to stabilize it in the lightly loaded condition and then you need extra buoyancy to make her float fully loaded.

I have toyed with the idea of bladder tanks, like the racing boats use, except I would fill the bladder with sea water as I consume fuel. This allows you to maintain constant displacement and reduce your design range.

Good lock and keep us informed of your progress. If you are interested we could point you towards some similar designs to consider as a point of departure.

Regards;
Mike Schooley

gonzo
11-14-2003, 11:15 AM
I used to think heavy displacement "passagemakers" were better. After owning a 34" James Wharram catamaran with flexible beam mounts my opinion changed. It didn't pound and was more seakindly than any monohull I've ever been on. I sailed that boat in North Atlantic gales with 25' plus seas.

yipster
11-14-2003, 04:03 PM
Which is the most economical kind of small vessel?
gettin to the hole(s) in the water idea(s). thats great. its worse than havin a hole in the hand though :D

Guest
11-15-2003, 01:08 AM
When I was young and boating on lakes, I thought Catamarans and Trimarans were the only boats but then I started boating in the Ocean and spending nights onboard and I developed a sleep dependency.

My work requires me to spend a lot of time on high speed boats, generally with guns firing or missiles launching, so when I go on vacation I’m looking for the smooth, quite and safe ride of a full displacement or semi-displacement boat.

Regards;
Mike Schooley

Guest
11-15-2003, 01:50 PM
Mike and Gonzo,
I replied but lost the message in the registration process!
Mike, My "passagemaker" is a lot smaller than the big tawlers that usually go by that name. Yes please, send me anything you can on vessels of a similar concept. I like your idea of using seawater to replace the spent fuel; it would be pretty easy to do with inflatable bags.
Gonzo, I know of the James Wharran cats. But even he tells of scary situations with them and recommends turning and running away from squalls. With my luck I would flip over.

I have re-read Dave Gerr's book on boat design and, on balance, think the monohull is more survivable. I would like to use a prismatic, seamless, rolled-steel hull (U-shaped section) with welded bulkheads and deck as the main structure, and use add-on molded or shaped bow and stern fairings for streamlining. The non-compond curve would be low cost and immensely strong. The bow and stern fairings would have a tubular frame support and filled with foam flotation. The interior bulheads would have waterproof doors. The weight and moment of intertia would be adjusted to give Dave's recommended roll and heaving frequency for a nice ride in heavy seas.

One basic question: If displacement hull speed is always proprtional to the square root of the length, why does a boat with a narrow beam go faster than one with a wide beam? Surely the wave-making drag is more on the wide boat? Or is it just that the wider boat needs more horsepower to reach its hull speed?

yipster
11-15-2003, 07:28 PM
One basic question: If displacement hull speed is always proprtional to the square root of the length, why does a boat with a narrow beam go faster than one with a wide beam?
the narrow beam(s) cutting wave resistance down is the reason why cats are more efficiently going faster, that even apply's to displacement monohulls. and the bigger a small vessel is; the more economical (froude's square root of the length law). have a look at the hullspeed calculator (http://www.users.globalnet.co.uk/~fsinc/yachts/spreads/fred.htm)

yipster

Portager
11-15-2003, 11:35 PM
I think that Boojum 25 which can be seen at http://www.xsw.com/Boojum/index.html & http://www.kastenmarine.com/boojum25.htm with a range in excess of 2,600 NM and a full load displacement of 18,500 lbs she is a capable passagemaker although admittedly compact.

My personal favorites are the Greatheart 36 http://www.kastenmarine.com/greatheart36.htm and the Wave Runner 36 http://www.kastenmarine.com/wave_runner.htm .

I don’t think the fuel tank with sea water in a bladder is as easy as it sounds and a failure could be disastrous if it occurred far out to sea. OTOH it provides tantalizing potential.

In the size that you are considering, I think aluminum would be a better choice. Steel runs into minimum gage limitations which makes it too heavy for smaller boats. Aluminum is lighter, has a higher strength to weight ratio and the ease of working and lower painting requirements offset the material cost difference.

For full displacement hulls, displacement speed is proportional to the square root of waterline length, however the power required to achieve displacement speed is affected by beam. Therefore, a narrow beam is more efficient.

Regards;
Mike Schooley

tspeer
11-16-2003, 04:55 AM
Originally posted by Guest
...One basic question: If displacement hull speed is always proprtional to the square root of the length, why does a boat with a narrow beam go faster than one with a wide beam? Surely the wave-making drag is more on the wide boat? Or is it just that the wider boat needs more horsepower to reach its hull speed?

You're right that the narrow boat produces less wave drag than the wide boat. Even for a narrow hull there is an increase in drag in the vicinity of hull speed. However, the magnitude of the drag increase is far less.

This figure from Leo Lazauskas' paper on solar-powered boats (http://www.cyberiad.net/library/multihulls/solar1/solar.htm) shows the total resistance vs speed for several configurations.

http://www.cyberiad.net/library/multihulls/solar1/s2a.gif

The "Tri 0.6" configuration has three short hulls with the weight well distributed among the hulls. The other three configurations have long, narrow hulls. At 5 knots, the short hulls are experiencing a definite hull-speed problem as the wave drag increases dramatically. In order to get past 5 kt, the "Tri 0.6" configuration would have to have the power for 8 kt or above.

The other configurations show an increase in drag betwen 6 and 7 kt, but it's not very pronounced. The speed at which the drag rise occurs depends on the length for all the boats. But the magnitude of the drag rise is not the same.

Below 4 kt, all the boats can cruise efficiently. The slender hulls can also cruise at 5 kt with a reasonable increase in power. Let's say the total thrust available is 150 N or less. The slender hulls will respond well to adding power, and starting from 4 kt can almost double that speed. But the short fat hulls will hit the wall at 4 kt and all the power available will serve to squeeze out less than one more kt.

So whether or not a boat appears to have a hull speed limit depends on how severe the drag increase is and how much power is available. A typical powerboat also has a very definite hull speed, but has enough thrust to get through drag hump and plane on out to higher speeds. But a classical sailboat doesn't have that power and stays stuck at hull speed. A sailing multihull with the same rig would be able to sail past hull speed because the modest drag increase for its slender hulls doesn't provide the same barrier. The same principles apply to all three but the consequences are different for each type.

gonzo
11-16-2003, 12:36 PM
That's a very clear explanation.

Tad
11-16-2003, 06:47 PM
Tom;

You state that a narrow hull produces less wave drag than a wide boat? I am not sure about this, is this true if displacement and length remain the same? It seems to me that so-called "low wash/wake" forms are wide, flat, and shallow. Is a lower displacement/length ratio not part of the equation?

I would certainly suspect drag differences due to entry angle, but they would be slight compared to the D/L ratio difference between half a cat and a monohull.

I just did a comparison between a Krogan 58, at 100,000 pounds displacement and 52' DWL and Dashew's FPB at 81' DWL and 100,000 pounds. Theoretically fuel consumption for the longer hull will be half that of the Krogan when both hulls are traveling at a S/L of 1.25. This is around 9 knots for the Krogan and 11.5 for the Dashew.

All the best, Tad

Guest
11-17-2003, 04:08 AM
You asked:

One basic question: If displacement hull speed is always proprtional to the square root of the length, why does a boat with a narrow beam go faster than one with a wide beam? Surely the wave-making drag is more on the wide boat? Or is it just that the wider boat needs more horsepower to reach its hull speed?

Your question is much like asking:

If the strength of a beam is proportional to its width why does a 2x6 seem stronger than a 2x4.

In both cases there are other factors affecting the process.

Guest
11-17-2003, 07:15 AM
Wave drag is crudely proportional to beam squared, because you have to push sideways more water, faster, to get it out of the way of the hull.

Twice as wide, twice as much water, twice as fast, four times the resistance (again, very roughly).

gonzo
11-17-2003, 09:18 AM
It is also proportional to submerged area. The shape of the hull also affects it. For example a full bow creates a larger wave than a fine one. However, the speed at which the speed increases is roughly the same; it is the amount that changes.

JCFARER
10-03-2004, 05:13 PM
Which kind of vessel do you people think is the most economical:

1: Classical large cargo-ship type. Slow-moving, displacement type.

2: Hydrofoil

3: Hovercraft

4: Regular speed-boat

5: Ground-effect aircraft

6: Submarine

7: Other?

With "economical" I mean for the vessel to be able to transport 500kg of cargo across the atlantic. Speed is not important.

They have different advantages:

Hovercraft/ground effect aircraft: No viscous drag from water, and no wave making drag.

Hydrofoil/Speedboat: Less waves and water drag.

Submarine: Little wave-making drag.


I think my bet is on the submarine.


Hmmm... my bet would be on #7, other. A blimp? Just thought I'd throw wrench into the tool box. :idea: Ahem, although I would probably think that pacific proa would do nicely. :)

Jay

FAST FRED
10-04-2004, 06:20 AM
Once asked for the most "efficent" sail boat design the AYRS answer was a submersablew towed by a box kite.

With the remarkable advances in chute technology perhaps a steerable chute would do even better.

Yes they will work to windward ,
and running lights 75 ft off the water might even be noticed by the one man "crew" of the "Esso Maru".

FAST FRED

georgewuu
11-24-2004, 02:33 AM
Is there a term used in hydrodynamics for displacement drag

View Full Version : Which is the most economical kind of small vessel?