Typical Rescue Scenarios for
Generic Specifications for a Light
A Note on Rescue Hovercraft by Robert Wilson
Hovercraft make rescue possible in minutes, rather than hours,
by keeping you above the danger – not in it. The ability
to hover above land, thin ice, and water, even during flood
conditions, is a lifesaving asset to both victims and rescuers.
Due to their unique capability to safely access areas that
no other rescue vehicle can reach, hovercraft are used in
a diversity of rescue scenarios. These include, but are not
- Rescue operations on rivers, lakes and oceans in ice,
swiftwater and mud
- Search and rescue missions in floods, shallows, wetlands,
bogs, marshes and sand
- Animal rescue and wildlife retrieval
- Dive team recovery missions
- Aircraft crashes
The following will provide an overview of the general requirements
and performance specifications for rescue hovercraft.
Typical Rescue Scenarios
for Rescue Hovercraft.
1. Hovercraft Mud & Ice Rescue on Rivers and Lakes
Rescue of person(s) falling through or trapped on ice
- Usually short distance from shore.
- Low temperatures, possibly limited visibility, could
be day or night operation, usually low wind speeds.
- Deploy hovercraft rapidly from road trailer and launch
from river or lake bank.
- Proceed to victim(s) at low to medium speed depending
upon distance, 25 mph (40 km/hr).
- Maneuver up to or around victim(s) to achieve best retrieval
position given the situation. Could be loaded from either
side or front of hovercraft. It is essential that hovercraft
does not overshoot and overrun victim(s) at speed.
- To retrieve victims clinging to ice ledge, deploy in-water
rescuer wearing Mustang Ice Suit so hovercraft will not
dislodge victims' hold.
- Load into hovercraft or onto stretcher if required. May
be necessary to drag up to 250 lb (113 kg) person over the
side and onto a stretcher. Three persons may need to be
carried at one time. Could be grossly overloaded with multiple
- Return hovercraft to ambulance pick up point at medium
speed fully loaded and unload victim(s) on dry land if possible.
- Hovercraft may be required to rescue animals from mud
2. Hovercraft Swiftwater Rescue
Rescue of persons trapped in fast flowing water
- Usually short distance from shore.
- Temperate conditions, wind up to beaufort 4 (15 mph,
24 km/hr), strong current with small wavelets (1 ft max)
- Rapidly deploy and launch hovercraft from riverbank or
suitable area nearest to victim(s).
- May need to carry hovercraft over steep or wooded bank.
- Proceed to rescue at low to medium speed.
- Maneuver up to victim(s) to achieve best retrieval position
in given conditions. Important that craft is able to hover
stationary close to victim to facilitate loading even in
fast current conditions.
- Board one or two persons from tree, rock or log refuge.
May be necessary to pluck victim(s) from fast flowing waterway.
- Return hovercraft to dry land or ambulance pick up point
at medium speed fully loaded and unload on dry land where
- Hovercraft may be required to rescue animals from fast
3. Hovercraft Flood Rescue
Search and rescue over flooded areas
- Ability to search for 2 hours at up to medium speed 25
mph (40 km/hr), over wide shallow and narrow twisting waterways.
- Temperate conditions, low to moderate winds 15 mph (24
km/hr), low currents. May be necessary to proceed at night
at low speeds for limited periods.
- Ability to locate and rescue 2 or more victims from isolated
land, trees, roof, etc.
- Hovercraft must be able to maneuver in relatively confined
waterways even inside flooded buildings, and retrace passage
if necessary. Ability to manhandle hovercraft over fallen
trees and around large obstacles is needed.
- May be required to carry limited amount of emergency
rations and supplies to remote areas 400 lbs. max. (181
- Hovercraft may be required to rescue animals from floodwaters.
Many more applications could be postulated, such as deployment
of inflatable raft(s) at aircraft crash sites and ventilation
of smoke filled buildings. However, the above three categories
provide the general requirements and thus generate a logical
performance specification for small rescue hovercraft.
Specifications for a Light Rescue Hovercraft
Hovercraft should be capable of rescue operations over thin
ice, open water, swiftwater, floodwater, salt water, mud and
- Payload Capacity
- Average payload 500 lb (227 kg)
- Maximum Overload 1,000 lb (455 kg)
- With average payload cruise 25 mph (40 km/hr) over
- Average payload and maximum power 6 – 9 in.
(152 – 228 mm)
- Average payload, calm water 50 – 60 miles (80
– 96 km).
- Stationary Hover
- At average payload, hovercraft must maintain static
horizontal hover over ice, water or mud in 25 mph (40
km/hr) tail wind.
- With average payload, hovercraft must be capable of
backing up against 6 mph (9.6 km/hr) current while on
hover and in 10 mph (16 km/hr) tail wind conditions.
- Floating Stability
- In calm conditions, hovercraft must float indefinitely
even if totally submerged. With 800 lb (364 kg) load
on extreme edge of cockpit floor, no water should enter
cockpit during any 5-minute period.
- In calm conditions, 250 lb (113 kg) dead weight person
must be easily recoverable from water by a crew of two
150 lb (68 kg) persons. Hovercraft sidewalls must permit
easy and rapid body recovery. Cockpit should be free
of obstructions. Over-the-bow-retrieval in swiftwater
conditions must be possible. Hovercraft must be capable
of transporting a person on a backboard or onto a stretcher
or laying one or two persons lengthwise inside cockpit
area. Option of carrying a crew of two plus one stretcher
victim or crew of two plus two victims in prone position
or driver with up to 3 passengers for ferry operations
or driver plus secured cargo. Hovercraft may also have
to rescue animals.
- Lifting and Moving
- Hovercraft must have 3 or more structural points (stressed
to 3G) suitable for crane or helicopter lifting and
for mooring, winching or tie down.
- Weight Empty
- 500 – 600 lb (227 – 272 kg)
- Hard structure must not exceed 8 ft 6 in (2,590 mm)
- Hovercraft must be capable of passing under 5 ft (1524
mm) solid obstruction (such as a bridge) when hovering
- Hovercraft must operate between -30° F and 110°
F (-34 and 43° C) and up to 10,000-foot (3048 m)
elevation without major modification.
- A large capacity screw in/out cockpit drain plug
min 4 in (101 m) diameter should be provided for ease
of cleaning and emergency dumping of excess cockpit
Electric as well as manual start. Gasoline, diesel or other
Fan and engine must be protected from ingress of foreign objects.
Must be easily and quickly replaceable in the field. Average
use life 100 hours. If segment type, must not blow out if
one safety breakaway tie is broken.
- Safely Switch
Must be equipped with lanyard or similar type of emergency
- Engine Icing
Must have some provision for preventing carburetor icing.
Battery charging 13V minimum of 120 watt at full power
Under hull pads or skids must permit a safe emergency landing
from 15 mph (24 km/hr) in any direction on blacktop, ice or
mud without digging in or rolling.
Trailer weight under 250 lb (114 kg). Capable of one-person
operation and suitable for retrieving or loading hovercraft
when engine is not operating.
When shut down, hovercraft must be capable of being manhandled.
Four average persons (160 lb, 73 kg), wearing rescue gear,
should be capable of walking hovercraft 100 ft (30 m).
Hovercraft must be constructed from all new materials and
components, which will last more than 25 years under normal
rescue and training use. Maintenance of structure, power plant
and components must be of a level similar to any vehicle(s)
having the same characteristics.
A range of hovercraft rescue options must be available,
- 100-watt siren and public address system. Useful for
operation in low visibility conditions.
- A minimum capacity spotlight of 200,000 Candela.
- Either a light bar or a strobe light.
- Navigation lights, instrument panel and headlights.
- Fire extinguisher.
- Partial or full winter cab.
- Backboard or stretcher mount.
- Reflecting rescue decals.
- Equipment storage compartment(s).
- Bosun's hook
- Throw bag(s).
- Bilge pump (electric).
- On board and ship to shore communications.
- Portable fuel tank(s).
- Salt water marinization package.
A Note on Rescue Hovercraft by Robert Wilson
A NOTE ON RESCUE HOVERCRAFT
Neoteric Hovercraft Inc
Ma 7th, 2012
The purpose or use of a rescue hovercraft varies from a single person rescue, for example someone falling thru thin ice, to a mass rescue such as an aircraft crash on normally inaccessible mudflats. The distance to the rescue could be a few meters to hundreds of kilometres from safety.
No one hovercraft configuration could be expected to suit all types of rescue so it is proposed to limit this discussion to hovercraft suitable for rescuing at most a few persons relatively close to conventional transport and help.
Rescue terrain – the terrain over which rescue craft must pass could include mud, salt flat, ice, water (fresh, salt, shallow, deep, fast flowing or strewn with rocks). The landscape could be open with few obstacles or congested with large rocks, trees or undergrowth. There could be a straight line of sight between rescuer and victim or a narrow winding and largely hidden path to the rescue site. Ideally a single rescue hovercraft should be capable of efficient operation over any terrain where any hovercraft is capable of progressing.
Operational requirements for some typical types of terrain
- Open mudflat or saltpan, shallow water, with or without wind.
- Good directional control needed, especially in side winds.
- Sufficiently high thrust to weight ratio for good hump performance in moderate winds.
- Ability to proceed directly and stop at point of rescue irrespective of conditions.
- Search and rescue down a narrow and winding waterway congested with undergrowth, odd fallen tree limbs and low bridges.
- A high level of control is paramount, including the ability to ‘back-out’ of tight or impassable passages. Pilot errors of judgement should not result in the craft being ‘stuck’.
- Where odd fallen limbs and undergrowth makes a passage ‘too difficult’ it’s a big advantage if the craft is light enough to be manhandled around or over an obstacle or up/down an embankment.
- Ice rescue with or without rough ice areas.
- Whilst some ice fields are completely impassable to any sort of vehicle with low clearance it’s often possible to pick a path between around larger ice chunks or along water leads. The craft must be small enough and manoeuvrable enough to accomplish this.
- Temperatures can fall below minus 40 degrees with significant wind chill factors so engines must readily start and operate at these temperatures and crew will need appropriate protection.
- White-water including operations near dams and waterfalls.
- Rescues of capsized rafters are often required in fast moving water or near dam heads (both upstream and downstream). It does not take much imagination to foresee the results of poor craft control or mechanical failure under such conditions. An ability to move relatively close to the outlet or inlet of a dam and hold position is important if nerve racking.
- Climbing up a ‘white water’ stream requires a high thrust to weight ratio and safely descending such a stream requires a high level of craft control. Operating close to or below hump speed, where the Hovercraft’s air cushion is carried in the direction of the moving water, in these situations reverse and differential thrust is essential if any semblance of control is to be maintained.
Rescue craft are often operated by small town fire services and voluntary rescue groups with very limited budgets so a low purchase price and economical operating costs are essential. This factor usually precludes larger hovercraft and high capital cost vehicles like helicopters.
Operational safety is a concern, especially so because of the volunteer operator with limited training. Craft safety measures such as adequate fan guarding and conservative component loadings are important – fans should not be over sped and engines and transmissions should not be stressed beyond manufacturer’s recommendations.
The ideal rescue hovercraft
From the foregoing remarks it can be seen that not all designs of hovercraft are suitable for all rescue scenarios but the following general points should be considered.
- Craft weight – unlike wheeled and tracked vehicles, hovercraft must lift themselves essentially clear from the surface i.e. they could be regarded as flying machines, thus they must be light. Too often we have seen heavy craft that wont ‘perform’ and the makers response is to add more power – which usually means a heavier engine and transmission thus negating most of the performance gains expected from the extra power. Henry Ford is reputed to have said “weight kills performance” which is as true for hovercraft as it is for racing automobiles.
- Engine selection – Whilst there are many economical and reliable engines on the market few are suitable for small rescue hovercraft. The following table gives some indication of the performance of various types of power plant.
Type Typical HP range Typical installed weight Weight/HP Typical Cost
2-cycle gas 50-120 hp 70-130 lb (32-59 kg) 1.3 $5 to 9,000
4-cycle gas 50-200 hp 120-200 lb (54-91 kg) 1.6 $5 to 7,000
Rotary 50-150 hp 130-170 lb (59-77 kg) 1.5 $7,000
Diesel 50-160 hp 300-400 lb (136-181 kg) 3.0 $10,000
Gas turbine 300+ hp 180-220 lb (82-100 kg) 0.5 $100,000+
Obviously some engine types will be unsuitable because of high cost or high weight per horsepower but other considerations such as emissions or corrosion problems in salt water may be overriding. Currently the 2-cycle or light 4-cycle engines are the main contenders. Rotary engines look promising but lack large scale production availability. The 4-cycle engine is now in favour because of emission concerns but new direct injection 2-cycle designs may offer a lower weight alternative whilst meeting emission standards. Operation at extreme low temperatures tends to favour the 2-cycle, especially air-cooled designs.
- Control – In the majority of rescue scenarios a high level of craft control is required for useful and safe operation. Often operating conditions are far from ideal with moderate to high winds being most troublesome.
The older designs of hovercraft with simple thrust devices, especially if the lift and thrust are integrated, can be most difficult control in strong wind conditions. Rescue craft must be designed to handle, as well as possible, these conditions by employing thrust vectoring means, such as reverse thrust, puff ports or whatever else can be devised to maintain adequate control. An ability to statically hover and creep forward, under full control, overcomes the danger of pushing slabs of broken ice into the victim.
Picking up individuals from water or ice demands precision craft control – there’s no point in running down or drowning a victim in spray whilst attempting to manoeuvre close enough to pick them up.
- Propulsion – Unfortunately in fully amphibious hovercraft no highly efficient means of propulsion has yet been devised. Air propellers and ducted fans typically only produce 3-6 lb of thrust per horsepower.
If very large diameter thrust rotors could be used ratios in excess of 10 lb per horsepower could be achieved but this is impractical – even moderately sized propulsors can make craft passage under obstacles such as low bridges and tree branches impossible. Also the windage effects on large rotors and thrust ducts can be a severe embarrassment in other than calm conditions. The best that can be achieved currently is to keep the thrust devices as small as possible, consistent with maintaining adequate performance without excessive power input or over-speeding rotors.
Reflecting on other fields of fan and propeller technology, such as jet engine development, it can be judged that light hovercraft propulsion has to travel a long developmental path before anything like ‘most efficient design’ can be claimed.