Product comparison

Windsurf Mast Extensions

Jorren Eggenkamp at

Driven by consumer feedback, Unifiber have developed the most complete range of windsurf mast extensions available. Here, we review their different functions and components, so that regardless of budget you can fully enjoy your ride

US-Pin or U-Pin System?

The first thing to establish is that the baseplate (sometimes called the "deckplate") and the extension are compatible. There are two different systems that you may encounter.


This is the most commonly adopted standard.

U-Pin compatible mast extensions are equipped with a single push-button or trigger mechanism that enables connection and release in the most ergonomic way.


Also referred to as US Push-pin or US-Cup. This system has traditionally been popular in America. Two push-pin buttons are simultaneously depressed to enable disconnection of the mast extension from the baseplate.

This is a very robust system, but it is less ergonomic to operate and has more play between the baseplate and mast extension when connected.

RDM or SDM Compatibility

You also need to know which of the two available mast diameters your extension needs to fit. There are two "families" of mast: RDM - Reduced Diameter Mast, and SDM - Standard Diameter Mast.

 RDM - Reduced Diameter Mast

Number of Pulleys

Also, consider how many pulleys the extension is equipped with.

There are two types of pulley configurations available for mast extensions: 2-pulley - that offer a maximum 6:1 advantage, and 3-pulley - that offer a maximum 8:1 advantage.

The 2-pulley mast extension configuration is the most common, and for most sails is ideal. The 3-pulley mast extension configuration is mostly used with race sails that require very high downhaul tensions. The greater mechanical advantage of the 3-pulley configuration means that - in theory - less effort is required to achieve the necessary downhaul setting, and fine-tuning is more precise.

However, you also must consider that pulley friction works against the mechanical advantage of the whole system! And, since there are more turns, there is more friction to overcome in an 8:1 system than in a 6:1 system. Put simply, you have to keep your pulleys rolling smoothly! Good quality rope, and a dash of silicon spray, can greatly reduce friction in the system.

Take note that, in order to use 3 extension pulleys, a sail block with 4 pulleys is required. If the sail block only has 3 pulleys then the most powerful system that can be achieved is 6:1. As noted above, this is probably perfectly adequate. Also, it is of no concern if an 8:1 capable extension is used to rig a 6:1 system (that is, one of the extension's pulleys goes unused).

After use, it is good practise to rinse your mast extension with fresh water. This washes out sand and salt, and helps to inhibit corrosion.

Number of Pulleys in Windsurfing Extension

Aluminium or Carbon Tube

The most noticeable difference between carbon and aluminium extensions is weight. Multiple small gains through weight reduction of rig components have a cumulative effect, resulting in improved overall responsiveness and crisper sensations, allowing you to sail faster and with less fatigue.

Of course, if you are only swapping an aluminium mast extension for a carbon one, that alone will not make a big difference. It is the combined weight reduction that matters: board, mast, boom, extension, footstraps... all the component parts!

Budget-wise, carbon mast extensions are 2-3 times more expensive than aluminium.

Aluminium Or Carbon Windsurfing Extension Tube

From a resilience/safety point of view, aluminium is a better choice than carbon. Unfortunately, nothing is unbreakable, but when an aluminium extension is stressed to failure it will typically bend - meaning that sailing back to shore should be possible and safe. In contrast, when a carbon extension fails, it will typically snap into two pieces - making normal sailing impossible, and potentially leaving you in a compromised situation.

Tube thickness

Mast extension tube wall thickness is the major determinant of resistance to deformation, bending and/or breakage.

RDM extensions have thicker walls than their SDM equivalents. This is because smaller diameter tubes are inherently less rigid than larger diameter tubes, so need thicker-walled tubing to compensate.

The extra wall thickness of RDM extensions means that these are also stronger and more resilient in a general sense: in the kit bag, van, trailer...

The extra material present in the thicker walls also makes them heavier than their SDM equivalents.

Mast extension tube wall thickness

Collar adjustment

A less critical, but still important component to consider, is the collar adjustment mechanism. This part lets you set the mast extension at the correct length. Here we explain the difference among the various options available.

Ring & Pin

This is the most widely used method, being simple and reliable. Just insert the pin at whatever setting is needed then slide the collar down to lock the pin securely in place.

A drawback of this solution is that when the mast extension is not in operation the collar is free to slide and could be lost. To prevent this from happening, some extensions use a plastic end-cap with a flexible "catch" to prevent the collar from sliding off the tube.Extension Collar adjustment - Ring & Pin

Stainless Steel Reinforced Ring &Pin

A stainless steel reinforced Ring & Pin has exactly the same features as Ring & Pin but has additional stainless steel reinforcement to prevent the pin from getting pushed into the plastic collar. It better resists high downhaul loads.Stainless Steel Reinforced Ring &Pin

Hinged Collar

The hinged collar option is the easiest to operate with just one hand.

A minor disadvantage to be aware of is that, if incorrectly closed and used under tension, the hinged part can catch the sail's luff sleeve and/or sustain deformation damage. However, with normal care, this can easily be avoided.

Extension Collar adjustment - Open, Twist, Slide & Lock


The Slide&Lock collar is an innovative but simple system. By pushing the collar up, the collar will open and you can slide it to the desired position. With a little practice you'll be able to adjust the collar with just one hand. 

The collar is strong and reliable. The only downside is that on some sails, on occasion, the sail sleeve might catch when releasing the downhaul.

Extension Collar adjustment - Stainless Steel Open, Twist, Slide & Lock

Pulley Diameter

The greater the pulley diameter the easier it will be to apply downhaul.

Windsurfing Extension Pulley DiameterPulley orientation

There are two types of sail pulley-orientation setup: zero degrees is considered regular; ninety degrees (perpendicular to the mast) is less common.

Threading the downhaul ropes so as to avoid crossing the lines will reduce friction, and therefore make it easier to apply and adjust downhaul. With a correctly-threaded line, you'll be able to downhaul your sail pulley-block to extension-block. Achieving sufficient downhaul when the lines are crossed is difficult or impossible.

Although with most extension/sail combinations it is possible to thread the rope without crossing - in general, it is quicker, easier and more intuitive if the extension is matched to the sail's pulley orientation.
Windsurfing Extension Pulley Orientation

Rope Quality and length

To achieve the required rig tension, many sails need between 200 kg and 450 kg of downhaul force. Accordingly, another important detail you should consider when buying a mast extension is the quality of downhaul rope and the length supplied.

Good quality rope will last much longer, and lower friction will make downhauling the sail much easier.

The downhaul rope should be sufficiently long to allow correct threading through the pulleys and out beyond the cleat of the mast extension. If it is too short it will be difficult to thread the rope without it slipping through your hands, or there may be insufficient rope beyond the cleat to get a good grip on.

Remember to allow for a longer rope run if using a 3-pulley mast extension.

Note that the colour doesn't say much about the type of rope. Although there are visual differences, any material can be painted in any colour. So if you're questioning the rope quality, ask the salesperson in the shop for advice.

Polyester 4.0mm

Most extensions are equipped with a standard quality of 4.0mm polyester rope. Polyester rope functions reasonably for a majority of users.

Rope - Polyester 4.0mm

Pre-stretched Polyester 4.0mm

Pre-stretched polyester rope is less elastic than standard polyester rope. Less elasticity makes for easier downhauling. Pre-stretched polyester rope is usually 2-3 times the price of normal polyester rope.
Rope Pre-stretched Polyester 4.0mm

Dyneema 4.0mm

Dyneema® is the strongest, lightest and toughest rope quality available, making it the best choice for any mast extension. Dyneema® has less friction than polyester or pre-stretched ropes, and a much higher tensile strength. The only downside to Dyneema® is that the price is usually 3-5 times that of polyester rope.

Rope - Dyneema 4.0mm

Reinforcement features

Windsurfers who push their gear hard would do well to consider below-mentioned features. 

Stainless Steel Reinforced U-Pin Socket

This is the part of the mast extension base that receives the U-pin. Most mast extension base parts are produced from Nylon (plastic) and this does, over time, begin to wear. When reinforced with a stainless steel insert, the wear between the U-pin and mast extension base is considerably less, which helps to maintain a solid board / rig connection.

Stainless Steel Reinforced U-Pin Guiding HD Part

Stainless Steel Pulley Block

At the expense of considerably higher weight, a stainless steel pulley block guarantees strength and durability. This part is typically fully stainless steel moulded and houses the extension's pulleys.

Stainless Steel Pulley Block

Base / Tube Connection Reinforcement

To prevent flex between the mast extension base and its tube, additional reinforcing supports may be added. The supports are made of stainless steel or aluminium, depending upon the extension model.

Base / Tube Connection Reinforcement

Tack Strap Edge

Most camber-induced sails are equipped with a tack strap that makes it possible to increase shape (and power) in the foot panel of the sail. But if the tack strap slips up the extension then it loses tension. Very few mast extensions are equipped with a tack strap edge to prevent the tack strap from moving up.

Tack Strap Edge - prevents the tack strap from moving up

Why Choose Unifiber?

At Unifiber we have created a comprehensive range to make sure that all windsurfers’ needs and budgets are catered for. We produce reliable, quality products, that deliver top performance for all sailors and conditions.

We carefully select our materials and components, and keep an extensive stock of spare parts to extend the lifespan of your gear.

Unifiber also offers a comprehensive 1-year unconditional warranty on all mast extensions and 2-years of coverage for manufacturing faults.