Tuesday, June 9, 2009

Ultimate Showdown of Ultimate Destiny: Harken Blocks vs. Ronstan Orbit Blocks

This year Ronstan released new smaller (20 and 30 mm) sizes of their Orbit blocks. They're pretty nifty blocks and as with any new introduction into the realm of marine hardware they beg the question - are they better? Our very own Rob Beach set about answering that question and came up with a whole bunch of numbers for us to crunch.

We set about comparing the new 20 and 30mm Orbit blocks with the comparable Harken and older Ronstan blocks. Basically we looked at two main categories - working loads and weights. Rob was very meticulous in his calculating and measuring, there were even spreadsheets involved. In the end we found that the numbers weren't as straight forward as we'd thought they would be and it was difficult to make direct comparisons but we've done our best.

Below is the working load data for the blocks. The main thing we found was that there appears to be no standard safety factor being applied by manufacturers to calculate their MWL (Max or safe working load). They vary from around to 2 to above 6 and it does seem to be the case that Harken's numbers are generally higher than Ronstan's. Even within manufacturers they don't appear to be standardized.

We calculated an average of all the safety factors and then used that to calculate an standardized MWL using the BL (breaking load) of the blocks. We felt this was the best way to compare strengths across the different blocks.

Part #BL #MWL #Manuf.
Max Work Load
Safety Factor = 3.2203
20 mm Singles
RonstanNEW 20 mm Orbit; single lashing20 mmRF2510912105502.20376
Ronstan20 mm Single Loop Top20 mmRF2010112105502.20376
Harken Micro Single22 mmH22412002006.00373
20 mm Doubles
Ronstan20 mm Double20 mmRF2020215407702.00478
HarkenMicro Double22 mmH22612003503.43373
30 mm Singles
Ronstan30 mm Single Swivel30 mmRF3010016506602.50512
RonstanNEW 30 mm Single Swivel Orbit30 mmRF3510013236612.00411
HarkenBullet with Swivel29 mmH16620003006.67621
Harken29mm Carbo Single (w/ swivel)29 mmH34010003303.03311
30 mm Doubles
Ronstan30 mm Double30 mmRF3020220908802.38649
RonstanNEW 30 mm Double Orbit30 mmRF3520219849922.00616
HarkenBullet Double29 mmH08420004005.00621
Harken29 mm Carbo Double29 mmH34216256602.46505

We also looked at the weights of the blocks, both as stated by the manufacturer as well as our own measurements from our postal scale. For the most part they were the same but there were some small variations. We also calculated a strength to weight ratio in two ways. First we used the manufacturers stated MWL and weight and then we used our calculated MWL using the average safety factor and our own measured weight.

ManufacturerBlockSheave DiameterPart #Man. Listed weightStrength to weight ratio based on man. dataWeight per postal scaleStrength to weight ratioMan. Stated Max Diam. Rope
20mm Singles
Ronstan20mm Orbit (Single Lashing)20mmRF251090.318330.312526mm (1/4")
Ronstan20mm Single (Loop Top)20mmRF201010.511000.66266mm (1/4")
Harken Micro Single22mmH2240.54000.66216mm (1/4")
20mm Doubles
Ronstan20mm Double20mmRF202021.55131.53196mm (1/4")
HarkenMicro Double22mmH2261.52331.42666mm (1/4")
30mm Singles
Ronstan30mm Single Swivel30mmRF301001.25501.24278mm (5/16")
Ronstan30mm Single Swivel Orbit30mmRF351001.16011.23428mm (5/16")
HarkenBullet with Swivel29mmH1661.751711.54148mm (5/16")
Harken29mm Carbo Single (w/ swivel)29mmH3400.93670.93458mm (5/16")
30mm Doubles
Ronstan30mm Double30mmRF302022.83142.62508mm (5/16")
Ronstan30mm Double Orbit30mmRF352021.75841.83428mm (5/16")
HarkenBullet Double29mmH0842.51602.42598mm (5/16")
Harken29mm Carbo Double29mmH3421.83671.82808mm (5/16")

So what does all this mean? Well, clearly the Ronstan safety factors are lower than those used by Harken. When we calculated the MWL based on our average safety factor this meant the Ronstan blocks generally saw their MWL reduced while the Harken's increased. This affected the strength to weight ratios in the same way.

Does this make the Harken's better? I don't really think so. The vast majority of dinghy applications see these blocks used at loads far below their MWL let alone their BL. If you are pushing the limits of the loads though, I think the data supports leaning towards the Harken products over the Ronstans.

There's also something to be said for the fact that the Ronstan blocks may just function at a higher percentage of their breaking load than the Harkens. Unfortunately I don't have the technology to test that in house - but if anyone wants to give me a load cell for free I'd gladly break some things.

The new Orbit blocks are definitely a new direction in block technology and it's great to see Ronstan pushing the boundaries of classic hardware. Using the soft loop attachments are a great idea and I think definitely something we'll see a lot more of in the next few years. They don't appear to offer the weight advantages you might expect though - the Harken blocks are the lightest in many of these categories.

If you were expected a "this is the best one" conclusion at the end of this post I'm afraid I'm going to disappoint you. I do think the 20 mm Orbit single is a pretty cool block - it's super lightweight and can be lashed anywhere you need it. I think the 29 mm Harken Carbo blocks are still a great choice for larger diameter lines. Beyond that there's no clear winner here. Each block has advantages and we didn't even cover pricing.


  1. Nice work--can't seem to get the table to render fully though. Anyway, thanks, keep it up!

  2. Okay never mind, before I refreshed the page you guys must've fixed it...

  3. Note that the range in your SF column for the Ronstan product is 2-2.5. If you look at the Harken product you will see that the range is far greater, 2.46-6. It seems as if Harken is putting a bit more work into reporting the exact load at which the block's performance begins to degrade rather than simply breaking them apart on a hydraulic ram/load cell and recommending a MWL that is half of the observed BL. So the question is, are we really comparing apples to apples. Very interesting article though, Thanks!

  4. I think it would be more interesting to do a test of the block's draw a SWL. For me, 1 oz extra doesn't matter as long as it takes less force to move a rope through the block. Anyone else that has a 6x or greater purchase probably has the same opinion.

  5. What he said. The term is rolling resistance. That test would mean a lot to all of us as we pull the lines by hand.


  6. No, rolling resistance refers to the energy loss caused by the deformation of what is rolling. (Hard objects roll better than soft objects.) This is a factor for ball/roller bearings, but it's not what you're looking for.

    You're talking about what people mean when they say block efficiency and friction.

    You also want to check up and down the load range as things can deform at higher loads and suddenly become much less efficient. Some blocks also switch to journal bearings at higher loads.

  7. This comment has been removed by the author.

  8. Cheers! You have really allured me; I have no words to explain my feelings about your post.

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