A Mechanical Escalator Harvester forLive Oysters and Shell

D. S. HAVEN, J. P. WHITCOMB, and Q. C. DAVIS

D. S. Haven and J. P. Whitcomb are with theVirginia Institute of Marine Science, GloucesterPoint, VA 23062. Q. C. Davis, 1364 West QueenStreet, Hampton, VA 23669. This paper is Con­tribution No. 877 from the Virginia Institute ofMarine Science and the School of Marine Sci­ence, College of William and Mary, GloucesterPoint, VA 23062. This work was completedunder a matching fund grant from the VirginiaMarine Resources Commission using P.L. 88­309 funds; NOAA, NMFS Grant No. 3-193-R.

Introduction

A mechanical oyster harvester wasdesigned, constructed and tested inChesapeake Bay, Va., from 1972 to1976.1 It couples the escalator systemof a conventional Maryland soft clamdredge with a newly designed head.Revolving spring-loaded teeth attachedto two drums in the head pull or rakeoysters from the bottom and horizontalwater jets and the action of the revolv­ing teeth impel the oysters onto a con­veyor belt which carries the oysters tothe boat. This design eliminates severalproblems associated with previouslydesigned harvesters.

Most mechanical devices for harvest­ing molluscs are based on the designFletcher Hanks developed in Marylandin 1954 to harvest the soft clam, Myaarenaria. It jetted water at high pres­sure into the bottom just ahead of aboxlike device which slices throughthe bottom. A blade extending about 16inches below and slightly behind thejets guides the soft clams loosened by

I Virginia Institute of Marine Science. 1973.VIMS scientists develop oyster harvester. Mar.Res. Inf. Bull. 5(11): 1-2.

ABSTRACT-A mechanical oyster har­vester has been developed by coupling anewly designed head with a chain-link con­veyor. The head consists of a rectangularsteel frame set on steel runners and tworotating drums armed with spring-loadedteeth. The teeth of the outermost drum rakeoysters from the substrate. The teeth of thesecond drum and water jets impell the oys­ters to the escalator where they are broughtto the surface. Harvest rates of500 bushelsof oysters an hour and 774 bushels of shellan hour have been achieved.

December J979

the jets onto a moving chain-link con­veyor belt (Manning, 1957).

This design was later modified toharvest oysters in Canada (Medcof andMacPhaif, 1955). Wheels were added,and the depth at which the blade cut thebottom was decreased. This oyster har­vester was again modified to harvesthard clams, Mercenaria mercenaria,and other species (MacPhail, 1961;Godcharles, 1971; and Jolley, 1972).

Two harvesters have been developedon the west coast to harvest theJapanese oyster, Crassostrea gigas.One, the Bailey harvester, is very large,and it is based on the principle by whichwater currents set up by large impellersare used to create a flowing mixture ofsand, water, and oysters under a headwhich rests on and makes a seal with thebottom. The moving oysters are depos­ited on a conveyor (Bailey, 19502

). Thedevice is reportedly about 25 percentefficient (Quayle, 1969).

The second was developed by theOlympia Oyster Company in Washing­ton. This harvester (patent pending)uses three units. The first consists of a15- x 30-foot barge containing the pilothouse, propulsion unit, an air compres­sor, and a powerful water pump. Thesecond component is open and supportsa harvester head and scoop similar tothat developed by Hanks, which istowed over the bottom. As this headslides over the bottom, powerful hori­zontal jets of water sweep the oystersoff the bottom into a collecting box.From this latter unit they are trans­ported to the surface through a pipe bythe air lift principle. The water-shellmixture is expelled into a barge with a

2R. H. Bailey. 1950. U.S. Patent No. 2,508,087.

screened bottom (Malloch and Kolbe,1976).

The cutting blade is a necessarycomponent to all but the Bailey har­vester. The cutting blade operates satis­factorily on soft bottoms, but when bot­toms contain significant quantities ofembedded or buried shells, the scoopoften encounters so much resistancethat the efficiency of the gear is greatlyreduced. Such hard substrates arecommon in many oyster growing re­gions.

Design and Construction

The harvester utilizes a conventionalchain-link conveyor 39 feet long, sus­pended from a 40-foot Chesapeake Bayworkboat with an II-foot beam (Fig.1). The harvester head consists of arectangular boxlike structure whichslides over the bottom on steel runners(Fig. 1,2). Within this rectangular boxare two chain-driven rotating drumspowered by a variable speed hydraulicmotor located on the top of the box.Each drum has six rows of spring-teeth(Fig. 3). In operation, the harvester'sforward drum teeth are set to dig 3 in­ches into the bottom. The back drumteeth are set, permanently, to rotateflush with the base of the steel runnersand about 1/2 inch forward from a shortinclined plane which ends at the es­calator belt; the inclined plane is setflush with the steel runners.

To operate the harvester the vessel ismoved forward at about 1,4 knot (25feet/minute) and the teeth are set to ro­tate clockwise, facing the right side, atone revolution per second (60 rpm); atthese speeds the harvester head slidesforward on the runners and the teeth ofthe forward rotating drum separates theoysters from the substrate. The backdrum teeth sweep oysters and shell

17

112" STEEL PLATE

Figure 1. --Research vessel Mar-Bel showing escalator and mechanical head. Waterpipes to jets are shown on the outside of the rectangular frame.

Figure 2. -Side view of escalator during construction showing method of attach­ment of hydraulic drive motor and details of frame construction.

1/4" STEEL PLATE

STUL PLAT[I 1/8" STEEL SHAfT

THROUGH SIDEARMSTO ROTOR

loosened by the forward drum up theinclined plane and onto the upwardmoving escalator belt. Jets of water (50psi) are directed toward the escalator tohelp move the oysters or shell up theinclined plane and to wash debris fromthe shell.

Most of the details of constructionand the critical measurements may beobtained from the figures and Appen­dix, but certain aspects need emphasis.

The central core of each drum is ahollow 3-inch outside diameter (aD)pipe. Each end of this pipe is welded toa circular 5-inch diameter plate reamedat its center to receive a bushing; thisbasic unit turns freely on a l3fs-inchstainless steel shaft (Fig. 4). Bolted toeach 5-inch end plate is a circular W­inch plate; around its circumference aresix equally spaced 2-inch tapered plugsbolted to the disc. These plugs and theirduplicates on the opposite disc hold six28-inch long 1%-inch aD hollowpipes. On each pipe are strung (throughtheir central spring coil) the rows offlexible tines. The basal end ofeach tineis held firmly in a grooved strip weldedto the 3-inch pipe. This system of con­struction allows removal ofeach row ofdrum teeth to replace broken teeth.

The cog-wheel drives for the drumsare bolted to the outer face of each W­inch disc.

The depth to which the forward tinespenetrate the bottom may be adjusted.Each end of the spindle shaft of therotating drum nearest the escalator pas­ses through two elliptical steel platesfitted with bushings; this shaft also hasbushings in the outer rectangular frame.This construction assures that thespring-loaded teeth always remain in afixed position relative to the bottom andto the inclined plane. In contrast, theforward rotating drum has its bushingsonly in the two elliptical plates. Con­sequently, the forward drum may beadjusted and bolted in the most effec­tive position for a particular type ofsubstrate (Fig. 3, 5).

The high pressure water jets impacton the inclined plane inside the headjust behind the after drum unit.

Field Tests

The harvester underwent extensive

field trials in Virginia during 1976 and1977 on a wide variety of subaqueoussubstrates. In all instances, it removed

the shell and/or oysters in its path to adepth of 3-4 inches.

In a typical trial in the Rappahannock

18 Marine Fisheries Review

1----------36':...'---------;

Figure 3.-Front view of head showing details of drums and the steel rake teeth.

River where seed oysters had beenplanted and oyster density was high,oysters were harvested at rates rangingup to 138 bushels per hour. The bottomwas originally soft mud, but applicationof 5,000 bushels of shell per acre ~ad

firmed the bottom prior to planting theseed oysters.

In the York River on a firm sand-claybottom where oyster density was verylow, it harvested oysters at the rate of27 bushels per hour. In the same estuaryon a very hard shell bottom where oys­ters were scarce, shell material wasraised at rates ranging from 180 to 774bushels per hour.

In all trials, the oysters raised by theharvester were virtually undamaged.Moreover, the shell material and oys­ters had been washed free of sand ormud by the action of the jets. In alltrials, it was observed that the harvesterobtained less than about 5 percentblackened shell material (with the tinesset at 3 inches), indicating that the har­vester was skimming off only the sur­face layer and not harvesting the loweranaerobic substrate.

The preceding observations werecorroborated by a diver. The harvesterwas first operated on an oyster bottomwhere the substrate was a hard matrix ofsand, clay, shell, and a few oysters.During this test, shells and oysters wereraised at the rates of 774 and 30 bushelsper hour, respectively. Inspection ofthe bottom by a diver showed the teethhad dug a shallow trench 3 to 4 inchesdeep and 28 inches wide (the width ofthe rotating drums). The bottom of thetrench was firm. It was concluded thatthe disturbance of bottom substrate wasminimal and that it did not exceed thatof drag-type oyster dredges.

In 1978 a slightly modified copy ofthe VIMS harvester was constructed bythe North Carolina Division of MarineFisheries and used during 1978 to har­vest seed oysters (Burnett, 1979). Theharvester worked well and harvested up

ato 500 bushels an hour.

ADJUSTABLESIOEARMS(31" .. II 1/2")

BUSHING

I24"

Bushing

2" Tapered spacersballed to disc

HYDRAULIC MOTOR

_____ 28"------

I 3/4" O.D. hallowpipe holdingtines

""

3" BUSHI NG INADJUSTABLESIDEARMS TO FIT I I/e"SHAFT

10" SOLID END PLATEDISC BORED TO TAKESIX ROWS OF TINES

F=

/r----R. 1=5" End plate with bushing welded :..: --~ F=

to end of 3" hallow pipe F=

10" Circular end plale balled 1'-10 5" plate - Holds tines. --

'-

=\I lis" Siainiess steel

shafl -------=-------------~d::===1I==t-=~~_ ____ _ cenler line

-- - ------1=---

- r---

r-­III

2S" Slee I bar welded :to 3" pipe 10 hold L_end of tines '---(grooved 5/S") ~

~------- ------------ ------- ~ -- --~

3Walter Godwin, Regional Coordinator, NorthCarolina Division of Marine Fisheries, Wil­mington, NC 28405, pers. commun. August1979.

/plate1/4" Elliplical

Drive sprocket welded to10" steel plate

Figure 4.-Frontal view of the forward drum showing details of its construction.

December 1979 19

Marine Fisheries Review

Appendix

Supplementary Information onCritical Measurements

Box frame: 14-inch sheet steel.Bushing: brass .Chain drive from hydraulic motor: size

50.Drive sprockets: ¥a-inch thick.Elliptical steel plate: 31 inches x 11%

inches x 14 inch.End plate: 5-inch diameter' %-inch

thick. 'End plate: lO-inch diameter' ¥a-inch

thick; six o/a-inch holes for boltsaround outer diameter; six ¥a-inchholes for bolts around axis.

Hydraulic motor: variable speed (con­stant torque).

Inclined plane: forward of escalator 18inches x 12 inches.

Longitudinal ~ar welded to 3-inch pipe\ to. hold t~nes): 28 inches long,Va-m~h WIde, and "Va-inch high;machmed to form a channel o/a-inchdeep, %-inch wide.

Pipes to hold tines: 28 inches long1~-inch O.D. '

Rotational speed of drums: 60 rpm.Set screw to adjust tension: ¥a-inch

diameter.Skid width: 5~ inches.Spindle shafts:

Forward shaft: 28 inches x 1!AI-inchdiameter (solid).

After shaft: 32 inches x 1!AI-inchdiameter (solid).

Tapered spacers (2-inch): machinedsteel.

Water pressure: 50 pounds/squareinch.

Jolley, J. W., Jr. 1972. Exploratory fishing forthe s~nray venus clam, Macrocallista nim­bosa, In northwest Florida. Fla. Dep. Nat. Re­sour. Tech. Ser. 67,42 p.

MacPhaIl, J. S. 1961. A hydraulic escalatorshellfish harvester. Fish. Res. Board CanBull. 128, 24 p. .,

Malloch, R. D., and E. R. Kolbe. 1976. TheevaluatIOn of an oyster harvester. Oregon StateUniv. Sea Grant Coli. Prog., Rep. ORESU­R-76-020, p. 1-20.

Medcof, J. c., and J. S. MacPhail. 1955. Surveyof bar clam resources of the Maritime Prov­inces. Fish. Res. Board Can., Bull. 102,6 p.

Quay.I~, D. B. 1969. Pacific oyster culture inBnllsh Columbia. Fish. Res. Board CanBull. 169, 192 p. .,

!O" END PLATE TOWHICH IS BOLTEOA 3" HOLLOW PIPE

3" HOLLOW PIPE

HOLES TO AOJUSTWORKING DEPTH

operat~d the harvester. Ifoyster densitywas hIgh, an additional person wouldbe needed to assist in culling.

The harvester constructed by thestate of North Carolina utilizes a bargewhich it positions under the end of theescalator to receive the harvest. If thecatch consists largely of oysters thissystem saves much labor.

~hile this harvester was primarilydeSIgned to harvest oysters, it haspr~ven efficient in raising shell. Shell is~ Important adjunct to growing oystersSInce up to 5,000 bushels per acre areoften planted as a substrate to collectspat. Cost of shell is about 25 cents perbushel when it is purchased from shuck­in~ houses. The use of this gear to ob­tam shell, we believe, could result in asubstantial reduction in cost.

Literature CitedBurnett, W. E. 1979. Replanting project aims to

reverse the decline of North Carolina oysterharvest. Natl. Fisherman 59(10):46-47.

Godcharles, M. F. 1971. A study of the effects ofa commercial hydraulic clam dredge on benthiccommunities in estuarine areas. Fla. Dep. Nat.Resour. Tech. Ser. 64, 51 p.

.Figure 5.-Details of the elliptical adjustable plate, idler gear, and chain drive.

20

Discussion and Conclusions

The described harvester performedsatisfactorily in a series of trials withcatch rates of oysters ranging up to 178bushels per hour and shell at 774bushels per hour. A slightly modifieddesign used over a year by the NorthCatolina Division of Marine Fisheriesalso performed satisfactorily. Catchrates of about 500 bushels an hour havebeen reported for this latter unit.

Observations by a diver indicate thatwhen properly operated, only the top 3to 4 inches of bottom are harvested and?istu.r~ance of the surrounding bo~tomIS mInImal.

The harvester developed by VIMShas several advantages over other har­vesters. It has no vertical jets whichcould dig deep trenches in the bottom or~ projecting blade which could impedetts forward motion on hard shelly bot­toms:

During the field trials in Virginia,two persons operated the vessel and theharvester. One person culled the oys­ters from the belt, another steered and