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Allen develop a new mast tapering process

by Ben Harden, Allen 24 Jun 2021 03:05 PDT
Parabolic V Cut Out © Allen

British hardware manufacturer, Allen, has quietly been working on some big projects for the marine industry, one of which is the production of 11-meter tapered masts.

The project to create a new tapered mast for the Dragon fleet came about after sailors and boat builders had started to notice the bend characteristics differed between each mast produced. Meaning, if you broke a mast and replaced it with a new one all the tuning and set up and measurements would no longer be valid. This also affected the continuity within the fleet, as each boat would require its own settings to get the most from its specific mast section.

Mast tapers are needed to get the best shape and performance from a sail. The basic technique to create a tapered mast requires the manufacturer to remove a "v" section from the mast, once removed the section needs to be closed - usually done with an internal mandrel, hammer, or clamp. Once closed it is held together with a weld. Straight forward it would seem, but it proves very difficult to achieve a consistent result. Each process has a possibility for small variation which will result in slightly different bend characteristics.

The British company, Allen, did lots of research into why the slight variations would occur and how it would affect the bend of the spar. Firstly, it was found that the forming (closing) of the section was inconsistent, with the position and amount of pressure varying between each form. Secondly, once formed the welding to close the section would be affected by the amount of pressure from each clamp. Once the clamps were removed the welding would then have a distorted finish and result in an uneven taper.

Before the Allen design team could create a solution for the tapering, they decided to create a 3d CAD model of the desired taper. This would allow the team to utilise their expertise with 3d CAD and machining. The boatbuilder supplied Allen with one of their best tapers and a 3d scan was taken. The design team could then reverse engineer a 3d model and then had a target taper to aim for.

Once the 3d model was created a parabolic cut was established and a template created to cut the "v" shape. With the correct hand tools, the Allen factory team quickly had the "v" cut out and felt they had an operation that was easy and accurate enough to repeat for a consistent cut for future production.

Tom Clayton, product designer at Allen, commented "We had surmised that the forming operation was going to be the most difficult operation to achieve and quickly realised we would need to somehow form the taper from top to bottom to allow us to control the sizes of the taper. Firstly, we tried forming the section using a standard toolroom "v" block as a former in a vertical direction and found that it was possible to close the section by working slowly along the length of the mast. After some further research, we decided to try and develop this idea further."

Using the 3d CAD data the design team manufactured a set of forming tools that replicated the profile of the taper. After some extensive precision engineering, the 2.5m custom press and forming tools had been finalised and assembled.

The mast with the "v" cut out is then inserted into the press tool and starting from the tip of the mast is zipped together by the press. Because the form tools replicate the taper and are so accurate the press can be released without any spring back from the material. This means a weld can now be carried out on the formed taper with little chance of distortion.

The mast is then sent into the machine shop where additional holes and slots are made for sheave boxes, spreader, and forestay hardware but before these additional products are fitted the mast is heat-treated and anodised.

"We aimed to produce a consistent tapered mast. One that would result in the same bend characteristics and make rig tunning easier between the different boats. Now we have produced the first production batch of 20 masts, I believe we have certainly nailed the brief. The taper is identical across all the sections and looks much neater than the previous version." Mentioned Darren Elwell, Design Manager at Allen.

Allen has been building spars for many years, with many of the Topper boats using beams, booms and masts manufactured from the Allen factory in Essex. The company is planning to expand its mast production with several other one design tapered aluminium masts coming soon.

If you would like to find out more about the masts being manufactured by Allen or would like to see if the team can help you with production issues, get in contact with their sales team at or call on +44 1621 774689.

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