RV Investigator Long Core System

Mark Lewis. Senior Mechanical Technician

Overview

My experience with these systems is limited so I have been talking to

as many people around Australia and New Zealand as I can as well

as overseas including helpful staff from IPEV, IFREMER and NIOZ

and web searches on a few other institutions. My principle reason for

being here is to get as much information as I possibly can about how

to get the best out of our system.

Marine National Facility

Abstract

The RV investigator has purchased a long core system from SEAS Australia. The vessel deploys the system from a Triplex overhead boom, core head handler and twin cranes to support the barrel. The core barrel used is drill pipe capable of having a 100mm outer diameter liner inserted. We have both polycarbonate and PVC liners. The system is capable of having 24 metres of barrel and being used in either gravity or piston mode. The main coring cable is 24mm dyneema, 8,400m long with a maximum working load of 20 tonnes.

Theoretically our system is capable of retrieving 24 m cores from 7,000 m water depth. To date the system has only been used on a few research voyages and after tuning has retrieved up to 10.2m of core in gravity mode (12m of barrel) and 13.62m of core in piston mode (15m of barrel). Our piston is in two parts and capable of using a range of shear pin sizes.

Background

The system we have was purchased through a technical advisory group that

sought information from a wide range of experts and potential users

Triplex were selected to supply the hydraulic systems to launch and retrieve the

corer

SEAS Australia were selected to supply the coring system

RAPP HYDEMA supplied the main coring winch and cable

Core Handling System

The triplex system consists of:

Overhead boom with upper and lower auxiliary winches

Two corer davits

One LARS

Photo of Overhead Boom

7 t upper

auxiliary

winch

0.5 t lower

auxiliary

winchCoring

Sheave

Overhead Coring Boom

The over head boom has both a lower and upper auxiliary winch as well as the

main sheave for the 24mm cable

The boom has a lifting safe working load of 30 tonnes and a side towing capacity

of 1 tonne

The upper auxiliary winch is used to handle the piston cable (35m of 26mm cable)

and has a working load limit of 7 tonnes so is capable of lifting the entire core rig in

piston mode

The lower auxiliary winch is used for lifting piston core components such as the

trigger weight, trigger mechanism and pilot core

It has a working load limit of 500 kg

Triplex corer davit

Corer Davit

The davit has a Working Load Limit (WLL) of 2.4 tonnes

The first davit is positioned to handle the first 12-15 m of core barrel

The second davit handles the rest of the core barrels up to 24 m

Each davit can be controlled individually or can be electrically linked and driven

from one controller

LARS with head weight

(6 weights)

Core Head Handler (LARS)

The LARS has a WLL of 5 tonnes

Two sections of the bulwarks need to be removed to deploy the system

The unit is hydraulically driven clear of the vessel

Once clear the unit can either be driven around to vertical or put into a free

mode where the weight of the core barrel causes the head to rotate

The latter mode only works if the weight of the head and the core barrels

are matched

Coring Winch

The winch is transverse mounted in the scientific winch room on the first

platform deck. The cable runs up to 02 deck via a cable trunk, and out to the

base of the coring boom

The cable can also be run aft from the cable trunk for over the stern

operations

The coring winch was supplied by Rapp Hydema and has a WLL of 30

tonnes

It is a fully electric winch capable of automatic heave compensation

The cable is 24mm Kapaneema SK 75 Dyneema with a WLL of 20 tonnes

The cable is 8,400m long

The minimum break load is 52.05 tonnes

Drive Motors

Spooling

Gear

Head Weight

The stem of the head weight is 130 kg and each weight is 260kg

The stem is capable of holding 10 weights

When rigging in gravity mode a valve is bolted between the weight stem

and the barrel flange

When rigging in piston mode the piston stops are bolted between the stem

and flange after the piston cable has been fed through

Total weight can be over 3.2 tonnes

Barrels

The barrel is constructed from 3 m sections (65kg) of drill pipe with an

internal diameter sufficient to allow 100mm liners

Core cutters

We have the standard simple cutter that utilises fingers to retain the core

The old fingers were 0.3mm and the new ones are 0.5mm 304 spring

stainless

The second style of cutter is a cam shell retainer with a long cutter

head

The cam shell style utilises the pull out force to close the clams

and retain the core

• Core barrel adapter

• Core cutter pivot bolt

• Grub screw covering

the core cutter mount

• Retainer activation

fingers

• Core cutter

Photos of the core cutter in the open position,

then when closed

Lower section of

Upper Piston

Shear pin hole

Lower Piston

Retainer Ring

Piston Seal Ring-1

Glide Ring

Piston Seal Ring-2

Brass

Shear strength 234 Mpa*

Diameter (mm) 2 3 4

Strength, double shear 1,470.27 3,308.10 5,881.06

Strength, double shear (kgf) 149.93 337.33 599.70

Spring Steel

Shear strength 1380 Mpa*

Diameter (mm) 2 3 4

Strength, double shear 8,670.80 19,509.29 34,683.18

Strength, double shear (kgf) 884.18 1,989.40 3,536.71

Core

length

Number of

3m

Number of

weights

Piston

Corer

Weight

required Total Trigger Number of

TOTAL

System

core barrelson Piston

Corer

Total

Weight

(F1) to

Balanceweight

Weights

Required Weight

n1 n2 F2 F2 * d2 / d1 F1 t1

(m) (kg) (kg) (kg) (kg) (30kg each) (kg)

W

12 4 0 420.0 21.0 40.0 0 460.0

1 680.0 34.0 70.0 1 750.0

2 940.0 47.0 70.0 1 1,010.0

3 1,200.0 60.0 100.0 2 1,300.0

4 1,460.0 73.0 100.0 2 1,560.0

5 1,720.0 86.0 130.0 3 1,850.0

6 1,980.0 99.0 130.0 3 2,110.0

7 2,240.0 112.0 160.0 4 2,400.0

8 2,500.0 125.0 160.0 4 2,660.0

• The system in piston mode

showing the trigger mechanism

clamping onto the piston cable and

the head weight

• The pilot core hangs off the trigger

arm

• The amount of freefall is

determined by the loop of piston

cable between the clamp and the

core head

Trigger mechanism

Trigger or Pilot core

Piston core release arm

Barrel gripper supplied with the Triplex system

New barrel gripperIt is lighter and slides up and down the pipe a lot easier

The Core being deployed in

gravity mode with 6m of barrel

Core is rotated, lifted out of the LARS

then deployed down to 100m above the

sea floor

After stabilising at 100m up we lowered

the core into the seafloor at 60 m per

minute

On later voyages we slowed this to

30m per minute as we had suffered pipe

breakage after some faster deployments

Free fall and recoil

We have decided to use 3m of free fall

Cable recoil was initially discounted as we are using a low stretch

polyamide rope Kapaneema dyneema SK-75 (MBL 52.05 t)

After contacting the manufacturer I obtained some basic data on expected

stretch with load and calculated the formulae:

%S=0.0006(core wt t)^2+0.0817(Core wt t)-0.1841

Elongation at failure was stated as 5%

On the deployment to 3,100m of water we allowed 3m of freefall and 3m

of recoil (calculated at 0.03% but we used 1% stretch) so the piston cable

loop was 6m long

Gravity mode

• Our best result so far is 10.2m of core out of 12m of barrel with a 2.21

tonne head weight lowering @ 30m per minute into the seafloor

Piston mode

This system uses a 2 part piston with facilities for 2, 3 or 4mm shear pins

At this stage we are still testing different sizes and materials for the shear

pins

Best result was using a 2mm brass and a 3mm spring steel pin

(2,139kg) with 15m of barrel and 2.21 tonnes of weight

13.62m of core was returned with piston still at the water sediment

interface from 3,100m of water and 15m of barrel

Conclusions

The system is relatively new to my team and we have had some good

results, interspersed with some interesting ones

Some results have been disappointing i.e. when the fingers in the cutter had

reversed and the sample been lost

We have since increased the strength of the fingers and had good results in

a mixed clay/sandy substrate

On another occasion the cam jaws were still open and no sample had been

retained

Upon inspection of the jaws were found to have tried to close but

damage in the centre indicated that a rock had held them open causing

the closing levers to bend and distort the pivot screws

Feedback please

Penetration speed into the sea floor

The amount of recoil in polyamide ropes

The strength of shear pin to use in 100mm diameter core pipe and if this

should vary for different sediments

Barrel gripper design

Types of steel used in the retaining fingers of the core catcher

Internal diameter of the core cutter compared to the internal diameter of

the core liner

Future research vessel projectFor further information:Mark LewisCSIRO, O&A Hobart.Email: mark.lewis@csiro.au

Thank you for your attention

Questions?