Retractable Hydrofoil Powerboat

http://www.gizmag.com/hydros-hy-x-retractable-hydrofoils/34281/

Here is their half scale prototype. Their goal is to make a 41 yacht. I think the retraction design eliminates many of the shortcoming of fixed foils, namely the deep draft and protrusions that complicate docking. Whether the additional cost can be justified is another story. Saving fuel sounds great, but may not be a big factor in powerboat purchases. I think the smooth ride would be a better selling point.

 

I think there's market for an urban commuter boat. Many large cities (Seattle, New York and San Francisco come to mind) are located around large bays or waterways that form natural choke points to land routes. Home prices are much less on the opposite side of the bay, but commutes can be 1 - 2 hr to get to one's office in the city. Public transportation is usually pretty good once near the city center. It should be possible to commute by boat from a suburban location to near downtown in about the same time it takes to drive in rush-hour traffic.

The mission requirements for a boat like this would probably be along the lines of:
- Complete 30 - 35 nm journey in less than an hour
- Able to commute by water 95% of the time. Driving by land would be necessary in extreme weather.
- Fuel costs comparable to a 1.5 hr commute by car.
- 4 - 6 passengers, with a cabin size comparable to a compact car's.
- No special facilities required.
- Acceptable ride quality.
- Safe handling qualities.
- Cost comparable to mid-range sedan (say, <$35,000)

The first requirement implies a top speed on the order of 40 kt. The second would imply a sea state with a significant wave height of 1.0 to 1.5 m, especially for areas like San Francisco Bay that routinely generate steep chop.

The combination of sea state, fuel economy and ride quality pretty much dictate some sort of hydrofoil. A planing boat is not likely to have acceptable ride quality in the specified sea state at the necessary speed, or to meet the fuel economy requirement.

No special facilities means the boat has to fit into a conventional slip (beam < 16 ft) and be launched from a ramp instead of by crane. Retractable hydrofoils might not be essential, but would be very useful in meeting this requirement.

The Hydros prototype might be developed into a craft that could be a viable trans-bay commuter.

 

Interesting concept. Docking on the city side might be a challenge. There was once a hydrofoil commuter service in New York.

http://www.histarmar.com.ar/InfGral/Hidroalas/ALBATROSS I.htm

Although it was a business failure, from a boat design standpoint, 24 passengers, 40 mph with 181 hp is pretty impressive.

 

My father worked on developing the Up-Right Hydrofoil kit, designed to be retrofitted to ~16' runabouts. It reached ~35 MPH on a ~30 HP outboard. An overview of the entire story is at:

http://www.foils.org/upright.htm

 

The hydraulic drives would be an energy-sapping compromise.

 

Safe handling qualities? Just wonder what happens if debris tangles in the foils or the foils hit solid debris while deployed at speed?

PC

 

Small debris would probably get sliced. Large debris would probably damage the foils and bring the boat down from "flying" in a hurry. Of course, running over large debris would damage the running gear or hull on any boat. I suppose the possibility for injury is greater with a hydrofoil since you will be dropping off the foils.

 

This be pure sex apeal
http://www.sunreef-yachts.com/es/no...rofoil-System-for-Luxury-Open-Catamarans.html

 

I think that if the foils were designed to break away, the possibility for injury might well be less than that of a planing boat when hitting large debris at the same speed. The deceleration of the boat would depend on how much energy the foils can take, not how much energy the hull can absorb. Since the hull is above the water, it would tend to fly over the debris and land on top of it or on the other side.

The impact on a foiling boat would be farther below the c.g. than for a planing boat, so the pitch disturbance may be greater, causing the boat to enter the water with a more bow-down attitude, as well as a vertical velocity from coming off the foils. This may affect the design of the shear and bow shape.

How about the other requirements? Can anyone suggest a better and/or more detailed set?

 

Would there be additional spin and tumble possibilities upon impact due to multi point foil contact permutations? Seems like a typical planing boat would only have a single significant point of contact at the stern area lower unit, perhaps giving a more predictable landing and having occupant ejection less likely.... Would high windage effects be a consideration with the hull riding higher at speed?
Your requirements set seems good, any significant extra maintenance/repair considerations?

PC

 

Maintenance and repair would need to be comparable to existing runabouts.

I think a big challenge would be to make it safe at 40 kt in the hands of inexperienced operators.

Debris impact has been a major problem in coastal areas for hydrofoils. That's why the Boeing hydrofoils had to stop operating on Puget Sound. With a planing boat, debris hits the hull at a glancing angle, while the same debris hits a hydrofoil head on. The frontal extend of a hydrofoil is also greater than for a planing hull, making it more likely to encounter debris. So it's not a trivial issue, and could prove to be the make-or-break factor in operation.

Highly swept foils might help to mitigate the debris problem. The impact angle would be reduced, and sea weed may slide down the foil and off the tip.

 

I think in debris strewn waters, the hydrofoil concept certainly becomes less tenable. I haven't seen many highly swept hydrofoil designs. With regard to your commuter boat idea, are you thinking the boats would be owned by private commuters like a car, or would it be more like a water taxi or small bus, where an operating company owns and operates the vessel? The advantage of the latter is that you wouldn't need to dock for the day on the city side, which seems like a problem to me.

 

Large passenger hydrofoil ferries were quite common in cities around the world 40 or so years ago, I have seen them in Auckland and Sydney and I think they were both built in Russia, I believe they were very high maintainance.

 

There are a number of passenger ferries operating now, although they aren't hydrofoils in the areas where I've lived. I was thinking more along the lines of a personal boat.

Docking on the city side would be a problem, as urban marinas typically have long waiting lists. However, with the foils retracted, it might be lifted by forklift onto a rack like a conventional runabout. That would help where such facilities exist.

I think a lot of cities also have areas of disused docklands. Urban waterfront development is fraught with NIMBY and environmental obstacles, but a commuter dry storage facility would minimize the aquatic impact and bring in revenue where none is being generated now. It could provide the economic incentive to clean up rotting piers and be a positive contribution to the ecology.

 

In San Francisco at least, dockage would be the killer since you would need to pay for two slips, unless you are lucky enough to live on the water and have your own dock at the house, and it that case I doubt money is much of an issue. Its a lot easier to pick up a casual carpool or ride a motorcycle to get across the bridges quickly.

My Dad has actually thought about this quite a bit since he is a yacht surveyor and lives aboard. Since he is going from marina to marina and could dock most places he has surveys without paying anything it would be a simplest case for boat commuting. Seems like the choice always ends up being between higher costs than driving or much slower commute times, plus maintenance and dockage for the commuter boat.

Seems like it could work better somewhere you could run a small open boat, but San Francisco is too rough for that unless you are willing to get to work soaking wet.

Also, would be pretty hard to get public support for a few wealthy folks to have cheap dockage so they could commute on highly polluting (compared to cars) motor boats.