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The Low-Down on High-Load Dinghy Blocks from

by Phil Anniss 26 Jun 09:00 PDT
A key element of Allen Brothers marketing strategy is an emphasis on sponsorship of elite sailors © Allen Brothers

At we love looking at the data and comparing products to gain insight. In this blog we look at the rapidly evolving world of high-load dinghy blocks and compare four leading products on the market from Allen Brothers, Harken, Ronstan and Morf Block.

In the last five years dinghy sailing has experienced somewhat of a revolution. New high-tech materials have driven a rapid increase in performance and most notably, in the last two years, the take-off (literally!) of foiling in all corners of the sport has put significant pressure on manufacturers to increase the strength and performance of their hardware.

Allen Brothers 30mm Extreme High Load Block

Allen brothers were one of the first to the market with a small high-load dinghy block which was specifically developed for the trend setting International Moth class, which started using vangs with >50:1 purchase systems. Produced in a range of bright colours, allowing design conscious sailors to personalise their cockpit layout, the Extreme High Load versions from their 20mm and 30mm Dynamic ranges quickly became the go-to high-load dinghy block and dominated for several years.

Harken 29mm Fly Block

In response to the growing popularity and demand for these high load blocks the big-boys, Harken and Ronstan, set out to develop their own. To set themselves apart from the arguably quite traditional technology adopted by the Allen Brothers high-load block (alloy cheeks, and Stainless sheave / bearings) both of them chose composite cheeks. However, Harken then chose to optimise for light-weight, over load, with the use of a Titanium sheave on stainless bearings and race. Ronstan, on the other hand decided to go all out for strength with a stainless sheave on Stainless bearings.

 HarkenAllen BrothersMorfRonstan
CheeksComposite FibreAlloyComposite FibreGRP Reinforced Nylon
BearingStainless / BallsStainless / BalllsComposite / PlainStainless / Balls

When you review the data (below) it would appear that Ronstan have aimed at directly improving on the Allen Brothers original Extreme Load Block. At the 20mm size they have achieved an 18% weight advantage with their GRP reinforced Nylon cheeks but then at the 30mm size they have achieved an impressive 57% improvement in load carrying, for an equivalent weight.

 HarkenAllen BrothersMorfRonstan
 Fly – Soft Attach BlockExtreme High LoadRB1 – High LoadSeries 20 High Load
Sheave Diameter (mm)18202020
Max Line (mm)5556
Safe Working Load (kg)125300225300
Nominal Breaking Load (kg)450900450900
Weight (g)7.2176.214
Strength to Weight Ratio17:417:736:321;4

The combination of the Harken Fly Block's composite cheeks and Titanium sheave delivers 57% and 36% weight savings, over the bench-mark Allen Brothers block, in the 20mm and 30mm sizes respectively. At the 30mm size the Allen safe working load is matched but at the 20mm size Harken have a relative low load of 125kg vs the Allen and Ronstan at 300kg.

 HarkenAllen BrothersMorfRonstan
 Fly – Soft Attach BlockExtreme High LoadRB2 – High LoadSeries 30 High Load
Sheave Diameter (mm)29303030
Max Line (mm)7868
Safe Working Load (kg)350350450550
Nominal Breaking Load (kg)70012509001650
Weight (g)26411642
Strength to Weight Ratio13:58:528:113:1

In the meantime, taking a completely different development route, Morf Block has arrived on the scene, in the last 3-4 years, to shake things up. Morf Blocks whole raison d'etre is based on the use of high-tech materials to deliver an alternative, high performance, yet simple and easy to maintain solution to traditional blocks. Using an alloy thimble running on a modern, high-tech version of an old-fashioned plain bearing, the Morf Block transforms the playing field in terms of strength to weight ratio, compared to the other manufacturers. When they first came out, a lot of traditionalists disputed whether they could be called a "proper block", however, their acceptance and proliferation in control lines of high performance race boats would suggest they have earned their place in this product category.

Morf MB2 High Load Block

The technical compromise that the Morf block has taken is line speed, which will always be less on a plain vs ball bearing block. However, in many of the applications for these blocks (high-load purchases) there is relatively little line movement, which suits the Morf Block very well.

Ronstan Series 30 High Load Block

Manufacturers have really responded to the increasing demands of performance dinghies over the last few years. Allen Brothers was a clear leader into this area and no-doubt is working on their next iteration of blocks to take another step ahead. The revolutionary Morf Block has transformed accepted thinking on strength to weight ratio whilst Ronstan has done a fantastic job with their Series 30 High Load block with an incredible Safe working load in a very compact package.

If you have any questions please contact us at or browse the full range of blocks and sheaves at

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