Bruntons SigmaDrive is a brand new 21st Century solution that is already an award winner and provides effective anti-noise and anti-vibration solutions of the highest order.

What makes SigmaDrives different is their ability to resist propeller thrust when installed as a standalone coupling, directly from the shaft to the output flange on the engine’s transmission. It reduces and even eliminates vibrations that originate from an imperfect alignment between the propeller shaft and the engine, compensating for up to 3 degrees in all directions. This system can also be installed using thrust bearings so that the engine can be placed utilising the space available ergonomically.

SigmaDrives are designed to fit virtually all boats from yachts to workboats, canal narrow boats to military vessels; in fact pretty much any powered vessel with engines up to 1300hp. They are extremely easy to fit, requiring no modifications to the craft, which can usually be equipped with the drive unit whilst still in the water. Together with its anti-noise and vibration abilities having a SigmaDrive on your vessel also ensures that seals and bearings are always perfectly aligned, reducing wear and guaranteeing a longer trouble-free life for all associated components.



The SigmaDrive brochure describes in some detail the unique benefits that you will obtain after you have fitted one to your vessel.

If, between the brochure and this website, you find yourself still with unanswered questions, please do not hesitate to contact us using any of the methods on the contact page.



Why does a SigmaDrive work so well? Because SigmaDrive is a constant velocity joint which allows the propeller shaft to rotate without transmitting the engines movements and vibrations. Other attempts at solving these solutions rely on rubber couplings or Carden units.

The SigmaDrive requires none of these, is compact and easy to fit, usually without slipping the vessel or requiring modifications to the shaft line. It’ s a premium product manufactured from a special bronze alloy that is maintenance free and its internal components are hard wearing and long lived.

Looking at the image you can see the usual method of connecting an engine with a propeller. The three fixed points, consisting of the propeller mount, the mechanical seal and the engine / gearbox, are individually or collectively capable of creating the two potential causes of noise and vibration. Firstly, any imperfect alignment of the three points can create vibration and noise. Secondly those vibrations and the associated noise are then transmitted directly through to the hull of the vessel and thence throughout the boat.

The simple solution is to fit a SigmaDrive coupling in the place of the standard one. The whole system from gearbox to propeller instantly becomes much more flexible, with the coupling able to correct imperfect co-axial alignment between the prop shaft and the gearbox of as much as 8 degrees. As can be seen in this second image with the SigmaDrive in place the reduction in the rigidity of the whole propulsion system means that the engine vibrations are significantly reduced or eliminated completely, and the prop-shaft can rotate naturally with no vibrations or noise to transmit to the hull.




Mollymawk is a Pan Oceanic 38 cutter, and we are very grateful to her owner for writing us a full report of his experiences with his SigmaDrive. It’s a report that covers so many of the questions a potential SigmaDrive purchaser may be asking that rather than editing it for this page you can read the full article below.


Although it is very early days for SigmaDrive they are already being fitted to a range of vessels. We are delighted that the first testimonial that we have received comes from one of the United Kingdom’s most highly regarded constructors of custom built vessels, Cockwells of Falmouth. Managing Director Dave Cockwell was happy to provide us with the following kind words.

“At Cockwells we have used CV joints for many years but had issues with them, including bad corrosion occurring not long after fitting. This is an issue we do not have with the stainless steel and aluminium bronze constructed SigmaDrives and to date we, and our clients, have been very happy with the performance of them.”


This product is for conventionally driven vessels. The system uses a constant velocity joint to self-align the shaft. Thrust taken up on the engine from the propeller invariably changes the angle of the shaft line, particularly when the engine uses soft rubber mounts. Using a single SigmaDrive replacement coupling will ensure the shaft is correctly aligned at all times, especially under high load. The result, reductions in many cases of around 50% in noise and vibration.

The SD standalone unit that resists the propeller thrust compensating for up to 3 degrees in all directions.

SD 55, 100, 150, 225 and 300


This system incorporates a thrust bearing to isolate the propellers’ thrust to the engine. It uses a combination of three SD units built together. Two of which are incorporated in the thrust bearing and another coupled to the transmission with an intermediate shaft.

Sigma STS Thrust System STS 550, STS 1000, STS 1500, STS 2250, STS 3000


D- Sigma is a replacement Cardan drive also coupled to a pair of constant velocity joints and can replace an existing Cardan shaft for Water jet Drives and Pod Drive propulsion systems.

D Sigma D 55, D 100, D 150, D 250 and D 300


The SD unit is a standalone unit that resists the propeller thrust compensating for up to 3 degrees in all directions and fits all makes of V drive transmissions.

V Drive SDV 55, SDV 100 SDV 150, SDV 225 and SDV 300

Calculation spreadsheet

Discover our calculation spreadsheet. It now includes a link for each configuration. This will take you to the exact configuration on our online shop. You will also have the possibility  to copy and paste the right information directly to the cart on our online shop.


If you have any questions,
please phone us on +44 (0) 1255 420005

UK office available weekdays 9:00 – 18:00