Skrew Anchor

1- Introduction

2- Which size to choose -Price list

3 - Operation and choice of the models

4 - Holding force compared to the torque

5 - Installation of a permanent mooring

INTRODUCTION

SEA TECH & FUN, in complement of its line of anchors Spade and SWORD, proposes to you his line of helicoid anchors SKREW. These anchors can be posed manually at low tide, or installed by a diver.

The helicoid anchors are frequently used in sailing, to carry out permanent moorings, to anchor floating docks, fish farms, etc…

At equal weight the helicoid anchors have a higher holding than any other type of anchor.This type of anchoring can also be used for many terrestrial applications, when it is necessary to anchor something temporarily or definitively in a soft ground (mud- sand)

SKREW Anchors are perfectly adapted to :

• A permanent anchoring for a boat, a floating dock, a signalising buoy . • An anchoring of fish farms etc. •A permanent or temporary fixing on movable grounds (this type of anchor can not be used on rock bottoms)

Advantages :

• For a low cost, the holding of the helicoid anchors is highest. • Out of hot dip galvanized steel by steeping in a zinc bath in fusion, their lifespan is very important. • Contrary to the temporary anchors, they do not dredge on the funds, and do not require a great scope water height /length of the line of mooring. They are thus respectful ecology of sea-beds SKREW Anchor is made out of high strength steel. The rod is forged in only one metal bar with an fixing eye. Fixing is carried out using a bar passed in this eye.

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WHICH SIZE TO CHOOSE?

For boats of higher size, it is possible to use several anchors SKREW : • for example in bahamean mooring (anchors in front and anchors back in the zones to shift of current, estuary of river) • In star mooring: three anchors (or more) joined together by a mother chain.

REF					LENGTH		WEIGHT kgs		SHANK LENGTH		SHANK DIAMETER (mm)		NUMBER OF DISC		RAY OF DISC 1(cm)		SURFACE DISC 1(cm²)		RAY OF DISC 2(cm)		SURFACE DISC 2(cm²)		HEIGHT OF DISC(cm)		ANCHOR TOTAL SURFACE		PRICES WITHOUT V.A.T. euros		TARIFS WITH V.A.T. euros
Modèle 20 (200 cm2)					< 7.50 m		< 1 tonne		40 cm		30		1		8		201						7		201		95.00		113.62
Modèle 30 (310 cm2)					< 7.50 m		< 2 tonnes		40 cm		30		1		10		314						7		314		115.00		137.54
Modèle 40 (400 cm2)					7 à 10 m		< 4.5 tonnes		75 cm		40		2		8		201		8		201		7+30		402		175.00		209.30
Modèle 50 (500 cm2)					7 à 10 m		< 8 tonnes		75 cm		40		2		8		201		10		314		7+45		515		195.00		233.22
Modèle 60 (600 cm2)					10 à 16 m		< 12 tonnes		140 cm		60		2		10		314		10		314		7+30		628		240.00		287.04
Modèle 80 (800 cm2)					10 à 16 m		< 16 tonnes		140 cm		60		2		10		314		12.5		491		7+30		805		255.00		304.98
Modèle 100 (1000 cm2)					16 à 20 m		< 20 tonnes		140 cm		60		2		12.5		491		12.5		491		7+45		981		270.00		322.92
Modèle 130 (1300 cm2)					20 à 25 m		< 25 tonnes		140 cm		60		3		10		314		12.5+12.5		981		7+45+45		1295		310.00		370.76

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OPERATION AND CHOICE OF THE MODELS

Holding calculations are adapted as well to compression as with the tension, according to the grounds characteristic.

The realization of moorings is done according to two criteria : • Choose the configuration of SKREW anchor according to the characteristics of ground and loads considered • Choose the dimension of the rod according to the load and the torque envisaged.

Calculation of the holding :

The calculation of holding capacity uses a generally accepted equation :

With = © (Nc) + (B) (Nq) With = final pressure of holding of the ground C = cohesion of ground B = pressure of overload Nc & Nq = factors of holding capacity of the local conditions of shearing of the ground

For anchors SKREW MULTI-spirals, the load capacity of the whole of the spirals is the sum of the capacity each spiral. The individual behavior of a spiral is the projected product of its surface (Ah) and of the holding pressure (A)). A reduction in the capacity of load should be applied for the sensitive grounds. Tolerances should be applied when the zone of influence of a spiral includes layers of different resistance. This analysis depends on a mode "of major anchoring". This condition is satisfied when the depth ratio/diameter is a minimum of 5.

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HOLDING FORCE COMPARED TO THE TORQUE

The measurement of the torque during the installation is a good indication of the holding capacity of the anchor. The relationship between the holding capacity and the couple of installation is in general 10. This value varies from 7 to 12. The use of a measuring apparatus of the couple is recommended.

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INSTALLATION OF A PERMANENT MOORING "SKREW"

General

The installation of a permanent mooring SKREW must respect the local legislation concerning the installation of the permanent mooring.

• It should not obstruct the access to the other existing mooring • It should not be an embarrassment or a danger with the circulation of the other ships or with sins • It should not cause degradation of sea-beds or marine life.

Specifications

The following specifications must be regarded as a minimum: • The installation must be carried out by a specialized company, having the equipment necessary for the installation of anchors SKREW and the measuring apparatus of the couple. • It is responsibility for the fitter to select the model of anchor SKREW and other components of mooring according to the characteristics of sea-beds, dimensions and displacement of the boat and conditions of the place of mooring. • The fitter must make a precise measurement of position GPS of mooring. • The diameters of the chains and the ropes must be selected according to the following characteristics :

Even with an anchor able to support several times the force generated by a cyclone, it is of primary importance to consider the whole of the components of the mooring line. The chain, the swivel, schackle, the hawser and even fastenings on the bridge level of the boat.

If the place available allows it, the principal line in heavy chain will have to make 1,5 times the height of high waters, the second chain of lower diameter and length equal to once the height of water, will be fixed at the first by a strong swivel.

This second chain will be then fixed at a buoy of which buoyancy will be higher than the weight of the small chain.

Foot-note : The chain will have to be able to pass in the center of the buoy or to be connected to a crossing axis, in order not to create a weak point.

A hawser will be then fixed at the end of the small chain, dimensioned buoy, sufficient length to be able to be fixed at the blocks of mooring of the boat - approximately 2,5 times the height of the freeboard of the boat. If necessary, to envisage a anti-chafing device on the level of the listel of the boat.

Foot-note : these suggestions do not take account of the possible matter losses after several seasons in a corrosive medium. To also avoid as much as possible to connect between them different metals to avoid the electrogalvanic problems. The stainless steel was brought back to present problems when immersed permanently in salted water, to prefer the hot dip galvanized steel.

In the event of positioning of anchor SKREW in an ecologically significant medium, it is recommended to place a buoy of sufficient buoyancy on the large primary chain, so that the chain cannot shaft on the funds. The buoy will have to be maintained with less than 2.50 m surface of water with low tide.

mooring on multiple anchors When the characteristics of the ship justify it, or when the holding of the funds is poor, it must be planned to pose several anchors in order to obtain the necessary holding :