CA1094397A - Warm air canopy system for providing ice free zone - Google Patents
Warm air canopy system for providing ice free zoneInfo
- Publication number
- CA1094397A CA1094397A CA294,098A CA294098A CA1094397A CA 1094397 A CA1094397 A CA 1094397A CA 294098 A CA294098 A CA 294098A CA 1094397 A CA1094397 A CA 1094397A
- Authority
- CA
- Canada
- Prior art keywords
- floating
- ice
- barge
- vessel
- around
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000007667 floating Methods 0.000 claims abstract description 39
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- 229940000425 combination drug Drugs 0.000 claims 1
- 238000005553 drilling Methods 0.000 description 18
- 238000000034 method Methods 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000012423 maintenance Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- GRYSXUXXBDSYRT-WOUKDFQISA-N (2r,3r,4r,5r)-2-(hydroxymethyl)-4-methoxy-5-[6-(methylamino)purin-9-yl]oxolan-3-ol Chemical compound C1=NC=2C(NC)=NC=NC=2N1[C@@H]1O[C@H](CO)[C@@H](O)[C@H]1OC GRYSXUXXBDSYRT-WOUKDFQISA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 238000001994 activation Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
- B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
- B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
- B63B35/08—Ice-breakers or other vessels or floating structures for operation in ice-infested waters; Ice-breakers, or other vessels or floating structures having equipment specially adapted therefor
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/008—Drilling ice or a formation covered by ice
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/12—Underwater drilling
- E21B7/128—Underwater drilling from floating support with independent underwater anchored guide base
Landscapes
- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- Ocean & Marine Engineering (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Structural Engineering (AREA)
- Civil Engineering (AREA)
- Architecture (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Novel apparatus is provided for maintaining a substan-tially ice-free zone around a vessel out to 100 feet or more.
The apparatus includes (a) a plurality of floating modules disposed around, and each connected at one end to, the vessel;
(b) a continuous, downwardly depending skirt extending complete-ly around the outer periphery of the plurality of floating mod-ules; and (c) an air/water heat exchanger in a selected plurality of such floating modules. The combination of the floating can-opies around the vessel, and the hot air contained within the ice-free zone by the skirts, provides an ice-free zone around the vessel.
Novel apparatus is provided for maintaining a substan-tially ice-free zone around a vessel out to 100 feet or more.
The apparatus includes (a) a plurality of floating modules disposed around, and each connected at one end to, the vessel;
(b) a continuous, downwardly depending skirt extending complete-ly around the outer periphery of the plurality of floating mod-ules; and (c) an air/water heat exchanger in a selected plurality of such floating modules. The combination of the floating can-opies around the vessel, and the hot air contained within the ice-free zone by the skirts, provides an ice-free zone around the vessel.
Description
3~
This invention relates to improvements in the drilling of oil and gas wells in polar regions. More particularly, it relates to improved techniques for effectuating such drilling in the wintertime in the Arctic Ocean and more especially in the Beaufort Sea, although it is feasible for application in other areas where similar conditions exist.
Still more particularly, it relates to a method and apparatus for provid-ing an ice-free zone around a drillship to enable such wintertime drilling.
At the present time drilling in offshore Arctic regions is carried out in the summertime either by the use of drillship anchored at a drill site where the risk of impingement by ice floes is minimal, or through the use of artificial islands. Summertime drilling is feasible for depths from 60 to 200 feet or more. Artificial islands currently being used in the shallow water regions of the Beaufort Sea become excessively expensive in water depths of 40 feet or greater. It appears uneconomical at the present t:Lme to build artificial islands for exploratory drilling wells in water depths exceeding 40 feet. It may be economical to drill production wells from artificial platforms in water depths exceeding 40 feet. Moreover, :Lt is presentLy not feasible to drill exploratory wells from floating ice islands in the regions where ice movement is too great (i.e., more than few feet).
One of the chief obstacles to overcome in drilling in Arctic regions is the Arctic pack ice. The ice grows to a thickness of approxi-mately 6 feet and is laced with pressure ridges and ice islands which can reach thicknesses of over 100 feet. The pack ice moves at speeds from 0 to 20 or more miles per day with an average movement of approximately
This invention relates to improvements in the drilling of oil and gas wells in polar regions. More particularly, it relates to improved techniques for effectuating such drilling in the wintertime in the Arctic Ocean and more especially in the Beaufort Sea, although it is feasible for application in other areas where similar conditions exist.
Still more particularly, it relates to a method and apparatus for provid-ing an ice-free zone around a drillship to enable such wintertime drilling.
At the present time drilling in offshore Arctic regions is carried out in the summertime either by the use of drillship anchored at a drill site where the risk of impingement by ice floes is minimal, or through the use of artificial islands. Summertime drilling is feasible for depths from 60 to 200 feet or more. Artificial islands currently being used in the shallow water regions of the Beaufort Sea become excessively expensive in water depths of 40 feet or greater. It appears uneconomical at the present t:Lme to build artificial islands for exploratory drilling wells in water depths exceeding 40 feet. It may be economical to drill production wells from artificial platforms in water depths exceeding 40 feet. Moreover, :Lt is presentLy not feasible to drill exploratory wells from floating ice islands in the regions where ice movement is too great (i.e., more than few feet).
One of the chief obstacles to overcome in drilling in Arctic regions is the Arctic pack ice. The ice grows to a thickness of approxi-mately 6 feet and is laced with pressure ridges and ice islands which can reach thicknesses of over 100 feet. The pack ice moves at speeds from 0 to 20 or more miles per day with an average movement of approximately
2 miles per day.
If drilling were to take place in waters where there was con-siderable ice movement, a very solid structure would be required in order to withstand the forces exerted upon it by the ice pack and yet to be :
3g~7 able to remain on position in order to drill a well. For exploratory drilling operations, a solid bottom founded structure should be provided which could resist the movement of the ice pack and yet would be mobile enough to be transported from one exploratory drilling site to another.
Drilling with structures on the sea bottom has numerous prob-lems. Firstly, there is the problem of designing hulls whic~ could with-stand tne ice forces from deep ice keels against these structures. In the second place, subsea systems would have problems of buoyancy, life-support systems, power supply, and access for crews and maintenance.
It woula, therefore, be desirable to develop another technique that would a~low exploratory drilling during winter months. Such system should also be able to extend operational capability into the shorefast ice. This technique has the potential for drilling wells more economi-cally than any other method in the shorefast ice regions. Using the technique, the rate of exploration in the Beaufort Sea would be increased by a factor of from two to four times. This technology of using drill-ships in shorefast ice could be applied to other regions of the Canadian Arctic. The techniques used for drilling in shorefast ice are a logical step toward developing year-round drilling systems in pack ice regions.
The development of such technology is important since the risks to the environment of a drilling system in the shorefast ice are rela-tively low. One advantage of operating in shorefast ice is that the ice moves very little throughout the winter. Any oil spilled underneath the ice would be confined to a very small area where it could be removed from the environment.
The initial problem which the present invention proposes to overcome is the maintenance of a substantially ice-free area around the drillship, and in particular, an ice-free area around a drillship opera-ting in shorefast ice zones during winter.
.
~: - 2 -~, , ~
.
, , .:, , ~
31~9~39~
An object of a principal aspect of the present invention is to provide an apparatus for maintaining a substantially ice-free area around a drillship out to at least 100 feet from the vessel, including the combination of a set of floating barges around the perimeter of the ship.
An object of yet another aspect of the present invention is to provide an apparatus which is simple to construct and may be easily deployed.
This inventioA in its broadest aspects provides an appar-atus for providing a substantially ice-free ~one around a vessel out to 100 feet or more, comprising, in combination with the ves-sel:
~a) a plurality of floating modules disposed around, and each connected at one end to, said vessel;
~b) a continuous, downwardly depending skirt extending completely around the outer per-iphery of said plural:Lty of floating mod-ules;
20 and (c) an air/water heat exchanger in each of a selected plurality of said floating mod-ules.
; By one variant of the apparatus of an aspect of this invention, the plurality of floating modules comprises a series of alternating floating barges interconnected by roof modules.
By another variant, each floating module comprises a floating barge provided with an air/water heat exchanger.
By another variant of this apparatus, each floating module comprises a fLoating barge including a floating barge section and a cantilevered canopy section.
- ~
If drilling were to take place in waters where there was con-siderable ice movement, a very solid structure would be required in order to withstand the forces exerted upon it by the ice pack and yet to be :
3g~7 able to remain on position in order to drill a well. For exploratory drilling operations, a solid bottom founded structure should be provided which could resist the movement of the ice pack and yet would be mobile enough to be transported from one exploratory drilling site to another.
Drilling with structures on the sea bottom has numerous prob-lems. Firstly, there is the problem of designing hulls whic~ could with-stand tne ice forces from deep ice keels against these structures. In the second place, subsea systems would have problems of buoyancy, life-support systems, power supply, and access for crews and maintenance.
It woula, therefore, be desirable to develop another technique that would a~low exploratory drilling during winter months. Such system should also be able to extend operational capability into the shorefast ice. This technique has the potential for drilling wells more economi-cally than any other method in the shorefast ice regions. Using the technique, the rate of exploration in the Beaufort Sea would be increased by a factor of from two to four times. This technology of using drill-ships in shorefast ice could be applied to other regions of the Canadian Arctic. The techniques used for drilling in shorefast ice are a logical step toward developing year-round drilling systems in pack ice regions.
The development of such technology is important since the risks to the environment of a drilling system in the shorefast ice are rela-tively low. One advantage of operating in shorefast ice is that the ice moves very little throughout the winter. Any oil spilled underneath the ice would be confined to a very small area where it could be removed from the environment.
The initial problem which the present invention proposes to overcome is the maintenance of a substantially ice-free area around the drillship, and in particular, an ice-free area around a drillship opera-ting in shorefast ice zones during winter.
.
~: - 2 -~, , ~
.
, , .:, , ~
31~9~39~
An object of a principal aspect of the present invention is to provide an apparatus for maintaining a substantially ice-free area around a drillship out to at least 100 feet from the vessel, including the combination of a set of floating barges around the perimeter of the ship.
An object of yet another aspect of the present invention is to provide an apparatus which is simple to construct and may be easily deployed.
This inventioA in its broadest aspects provides an appar-atus for providing a substantially ice-free ~one around a vessel out to 100 feet or more, comprising, in combination with the ves-sel:
~a) a plurality of floating modules disposed around, and each connected at one end to, said vessel;
~b) a continuous, downwardly depending skirt extending completely around the outer per-iphery of said plural:Lty of floating mod-ules;
20 and (c) an air/water heat exchanger in each of a selected plurality of said floating mod-ules.
; By one variant of the apparatus of an aspect of this invention, the plurality of floating modules comprises a series of alternating floating barges interconnected by roof modules.
By another variant, each floating module comprises a floating barge provided with an air/water heat exchanger.
By another variant of this apparatus, each floating module comprises a fLoating barge including a floating barge section and a cantilevered canopy section.
- ~
3~7 By a further variant, each floating module comprises a floating barge provided with an air/water heat exchanger and also with a cantilevered canopy section.
In the accompanying drawings, Figure 1 is a perspective of an embodiment of an ~apparatus of one aspect of the present invention;
Figure 2 is a partial top view of an embodiment of an apparatus of an aspect of thè present invention;
- Figure 3 is a section through line III-III of Figure 2; and ~ 4 -39 1~
Figure 4 is a side view of the transportation system for deploying the barges used in the apparatus of an aspect of the present invention.
Referring to Figure 1, a drillship 10 is shown, the drillship being generally of the type used in offshore drilling operations and particularly in Arctic zones. When operating in this environment, there is a severe hazard associated with the effect of ice encroaching on the drillship itself and consequently, the invention disclosed and claimed in copending Canadian application Serial No. 294,056 filed December 29, 1977, provided an ice-free zone close to the drillship. Another manner of main-taining such substantially ice-free zone around the drillship involves the deployment of such canopy system of an aspect of this invention about the perimeter of the drillship, as shown in Figure 1.
As seen in Figure 1, the canopy system 20 includes floating modules 30 and roof modules 40, as well as membrane 50 which covers the non-linear areas in close proximity with the drillship 10 and within the periphery of the canopy system not covered by floating modules 30 and roof modules 40. Floating modules 30 and roof modules 40 are provided with flexible downwardly depending skirts 35 and 45s respectively, which : 20 extend downwardly from the outer edge of floating module 30 and roof module 40 to slightly below the water surface 60.
As seen in Figures 2 and 3, floating modules 30 comprise a : floating barge section 32 and a cantilever section 33. Skirt 35 depends from the outboard end of cantilever section 33 to slightly below the water surface 60, thereby forming an air compartment 36 below the canti-lever section 33.
Barge section 32 is provided with a forced air heating system 70 which makes use of heat, partially the waste thermal energy from the drillship 10. Warm waste water pipe 37 from the drillship 10 is connected to the warm water input of an indirect contact heat exchanger 39, and the ~ 5 ~
- ,
In the accompanying drawings, Figure 1 is a perspective of an embodiment of an ~apparatus of one aspect of the present invention;
Figure 2 is a partial top view of an embodiment of an apparatus of an aspect of thè present invention;
- Figure 3 is a section through line III-III of Figure 2; and ~ 4 -39 1~
Figure 4 is a side view of the transportation system for deploying the barges used in the apparatus of an aspect of the present invention.
Referring to Figure 1, a drillship 10 is shown, the drillship being generally of the type used in offshore drilling operations and particularly in Arctic zones. When operating in this environment, there is a severe hazard associated with the effect of ice encroaching on the drillship itself and consequently, the invention disclosed and claimed in copending Canadian application Serial No. 294,056 filed December 29, 1977, provided an ice-free zone close to the drillship. Another manner of main-taining such substantially ice-free zone around the drillship involves the deployment of such canopy system of an aspect of this invention about the perimeter of the drillship, as shown in Figure 1.
As seen in Figure 1, the canopy system 20 includes floating modules 30 and roof modules 40, as well as membrane 50 which covers the non-linear areas in close proximity with the drillship 10 and within the periphery of the canopy system not covered by floating modules 30 and roof modules 40. Floating modules 30 and roof modules 40 are provided with flexible downwardly depending skirts 35 and 45s respectively, which : 20 extend downwardly from the outer edge of floating module 30 and roof module 40 to slightly below the water surface 60.
As seen in Figures 2 and 3, floating modules 30 comprise a : floating barge section 32 and a cantilever section 33. Skirt 35 depends from the outboard end of cantilever section 33 to slightly below the water surface 60, thereby forming an air compartment 36 below the canti-lever section 33.
Barge section 32 is provided with a forced air heating system 70 which makes use of heat, partially the waste thermal energy from the drillship 10. Warm waste water pipe 37 from the drillship 10 is connected to the warm water input of an indirect contact heat exchanger 39, and the ~ 5 ~
- ,
4~7 thus cooled water returns to the drillship lO via return line 38. The heating system 70 is provided with the use of suitable fans and ducts (not shown) in order to distribute hot air in a manner and quantity suffi-cient to prevent formation of ice under tlle canopy system.
Disposed between each floating module 30 and connected therein is a roof module 40. The warm air from the forced air heating system 70 is circulated through the floating barge section 32, then through canti-lever section 33 and thence into the roof module 40 and back again to the heating system 70.
A stream of warm air is injected into the skirt 35 to keep the skirt free of ice. This method and structure is disclosed and claimed in copending Canadian application Serial No. 305,628 filed June 16, 1978.
While Figure 1 shows the barge system already deployed, it is nevertheless necessary to transport the barge system easily from one location to another, as the drillship 10 is shifted from one drilling ; site to another. Figure 4 shows an embodiment of the present invention for transporting and relocating the barge modules. Special carrier barge 80 is used to support the barge modules in a stacked formation.
Once at the site, the modules are moved from the carrier barge 80 by means of a ship's crane. An appropriate spreader system is used to dis-tribu~e and support the modules. Pre-assembled roof modules are simi-larly put in place. Deployment of the pre-assembled barge and roof modules once they arrive on site is carried out expeditiously. Activa-tion of the heating system involves only connection of two flexible hoses and a power supply to each of the barge modules.
Disconnection of the barge system can be carried out, for example, within a few hours. It requires hose and power, mooring line, and membrane cover (over the cap between barge and ship) disconnection.
If the ship changes location, the barges can either be towed in a train or restacked on the carrier barge and transported.
, : ~ :
: ;:
~9~3917 To summarize, the present invention provides a method and apparatus of maintaining a substantially ice-free zone around a drillship, consisting of the set of floating barges deployed around the perimeter of the ship, spaced one barge width apart with an intermodular roof con-necting the barges. The entire perimeter of the system is enclosed with a flexible skirt which permits ice movement underneath while sealing the heat within into the system. A forced air heating system is integrated into the barge modules to distribute air at least partially heated by the drillship waste heat, in a manner and quantity sufficient to prevent ice formation under the barge hulls and roofs.
Once deployed, the barge system operates virtually automatical-ly. The barge system is thermostatically controlled for optimal heat distribution. Snow clearing and temperature and ice movement monitoring are the only operating functions apart from regular inspections and maintenance required for barge system operation.
. ;, ' ~ :
Disposed between each floating module 30 and connected therein is a roof module 40. The warm air from the forced air heating system 70 is circulated through the floating barge section 32, then through canti-lever section 33 and thence into the roof module 40 and back again to the heating system 70.
A stream of warm air is injected into the skirt 35 to keep the skirt free of ice. This method and structure is disclosed and claimed in copending Canadian application Serial No. 305,628 filed June 16, 1978.
While Figure 1 shows the barge system already deployed, it is nevertheless necessary to transport the barge system easily from one location to another, as the drillship 10 is shifted from one drilling ; site to another. Figure 4 shows an embodiment of the present invention for transporting and relocating the barge modules. Special carrier barge 80 is used to support the barge modules in a stacked formation.
Once at the site, the modules are moved from the carrier barge 80 by means of a ship's crane. An appropriate spreader system is used to dis-tribu~e and support the modules. Pre-assembled roof modules are simi-larly put in place. Deployment of the pre-assembled barge and roof modules once they arrive on site is carried out expeditiously. Activa-tion of the heating system involves only connection of two flexible hoses and a power supply to each of the barge modules.
Disconnection of the barge system can be carried out, for example, within a few hours. It requires hose and power, mooring line, and membrane cover (over the cap between barge and ship) disconnection.
If the ship changes location, the barges can either be towed in a train or restacked on the carrier barge and transported.
, : ~ :
: ;:
~9~3917 To summarize, the present invention provides a method and apparatus of maintaining a substantially ice-free zone around a drillship, consisting of the set of floating barges deployed around the perimeter of the ship, spaced one barge width apart with an intermodular roof con-necting the barges. The entire perimeter of the system is enclosed with a flexible skirt which permits ice movement underneath while sealing the heat within into the system. A forced air heating system is integrated into the barge modules to distribute air at least partially heated by the drillship waste heat, in a manner and quantity sufficient to prevent ice formation under the barge hulls and roofs.
Once deployed, the barge system operates virtually automatical-ly. The barge system is thermostatically controlled for optimal heat distribution. Snow clearing and temperature and ice movement monitoring are the only operating functions apart from regular inspections and maintenance required for barge system operation.
. ;, ' ~ :
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for providing a substantially ice-free zone around a vessel out to 100 feet or more, comprising, in com-bination with the vessel:
(a) a plurlaity of floating modules disposed around, and each connected at one end to, said vessel;
(b) a continuous, downwardly depending skirt extending completely around the outer per-iphery of said plurality of floating mod-ules;
and (c) an air/water heat exchanger in each of a selected plurality of said floating mod-ules.
(a) a plurlaity of floating modules disposed around, and each connected at one end to, said vessel;
(b) a continuous, downwardly depending skirt extending completely around the outer per-iphery of said plurality of floating mod-ules;
and (c) an air/water heat exchanger in each of a selected plurality of said floating mod-ules.
2. The apparatus of claim 1 wherein said plurality of floating modules comprises a series of alternating floating barges inter-connected by roof modules.
3. The apparatus of claims 1 or 2 wherein each floating mod-ule comprises a floating barge provided with an air/water heat exchanger.
4. The apparatus of claims 1 or 2 wherein each floating mod-ule comprises a floating barge including a floating barge section and a cantilevered canopy section.
5. The apparatus of claims 1 or 2 wherein each floating mod-ule comprises a floating barge provided with an air/water heat exchanger and also with a cantilevered canopy section.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA294,098A CA1094397A (en) | 1977-12-29 | 1977-12-29 | Warm air canopy system for providing ice free zone |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA294,098A CA1094397A (en) | 1977-12-29 | 1977-12-29 | Warm air canopy system for providing ice free zone |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094397A true CA1094397A (en) | 1981-01-27 |
Family
ID=4110410
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,098A Expired CA1094397A (en) | 1977-12-29 | 1977-12-29 | Warm air canopy system for providing ice free zone |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1094397A (en) |
-
1977
- 1977-12-29 CA CA294,098A patent/CA1094397A/en not_active Expired
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