Anchoring Solutions

Windlass & Capstan Selection

The windlass is used to raise the chain and anchor (weigh the anchor) and to control the lowering (drop the anchor). Whilst riding at anchor a yacht needs to be securely held by the ground tackle. A chain stopper is required to transfer the holding forces directly to the yacht. The windlass, a raising and lowering device, should not be used to secure a yacht when at anchor. Never anchor off the windlass.

For any given vessel and any given anchorage situation there is a safe anchor type and size and a safe chain strength and size.

It is unlikely that a motor yacht will ever experience anchoring conditions even close to the “worst case scenario”. But if this ever does occur it is vital that the safety equipment does not fail. Therefore reasoned and conservative requirements have to be applied. There is no better way than to be guided by an independent classification body. They exist for this very purpose.

When ordering a windlass the type and size of chain must be correctly specified. It may be necessary to supply an minimum two meter chain sample to ensure the correct chainwheel is provided.

The mooring line requirements for a yacht can be determined from classification rules; the requirements being stated in terms of breaking strength. The strength of the chosen material will then determine the rope diameter.

Diameter of mooring line: At least three wraps of mooring rope around the capstan are required to ensure adequate grip. The capstan must be tall enough to allow for this, and the wraps would appear as four rope layers above the point of rope entry. The most effective way of increasing grip between the capstan and the rope for high load applications is to apply more wraps around the capstan. No more than five wraps are ever required.

Certification: Maxwell windlasses are fully compliant with current rules of major classification societies. Witness test certificate and full design approval certificate are available upon request.

The vessel’s equipment number (EN) will dictate size and length of the chain, weight of the anchor, length and breaking strength of mooring lines.

Weight of the anchor and chain: The windlass has to be capable of retrieving the full length of chain and anchor on board the vessel and have some extra power to break the anchor free from the sea bed. It is important to note, especially with a non-fan cooled DC powered windlass (with no continuous pull rating) that the anchor sometimes has to be lowered and raised several times before a satisfactory anchorage is found, which may result in excessive heat build-up.

Chain type and size: Make sure that the windlass can handle the type and size of chain aboard the vessel. The chainwheel must have at least five chain link pockets to ensure safe and reliable operation of the windlass. Windlass size, chain locker volume and acceptable weight in the bow are all factors in selecting suitable chain of approved material and strength. Refer to ‘Which Winch 15 Easy Steps’ under Windlass Selection section of this website.

Drive Selection

Some windlasses are available with AC, DC and hydraulic drives, others with just AC and hydraulic drives.

DC Drives: Very practical on smaller boats as DC power can be stored, allowing the windlass to be battery powered without the need to run a generator. DC motors that are not fan cooled cannot run continuously without overheating.

AC Drives: Simple and efficient, driven by asynchronous 3 phase induction motors. The motors, where required, are equipped with an electromagnetic brake to prevent back winding of the winch.

Direct On Line (DOL) is the simplest method for starting an AC windlass. DOL simply connects a power source directly to the motor. Relays and a manual switch operate the contactor that carries the high current to the motor. The current draw at start up will be considerably greater than the running current at full power. Such a demand on the power supply can cause power loss to other equipment and may cause lights to dim momentarily. If these starting disadvantages are not critical to a particular installation or they can be mitigated by other techniques, then DOL starting offers a simple and cost effective solution.

Variable Frequency Drives (VFD) are a more sophisticated starting solution for AC motors. A VFD is able to start a windlass at full torque with no surge current. Different speed settings, variable speed and user defined ramp up and down operation are part of the VFD capability. Most basic units have a number of programmable functions but windlass control and protection is almost unlimited with some units.

Maxwell can offer a complete solution for a VFD motor starter, installed in a stainless steel enclosure. It is possible to use a more efficient and compact three phase motor run from a VFD, that is being supplied from a single phase source, should a three phase supply not be available. Some limitations apply.

Hydraulic drives: Light weight, reliable and compact. Windlass speed can be easily controlled by adjusting fluid flow. Some hydraulic windlasses have different load limits when lowering and retrieving the anchor. This protects the chain pipe and deck from damage if a knot of chain attempts to enter the chain pipe. It is possible to achieve the same pull capacity and speed with several different combinations of fluid flow and pressure.