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| Home >> Class Rules - Queries & Suggestions >> Changing cunningham blocks for larger 20mm block |
25/07/2022 20:20:00
Dunsmall
Posts: 25
My understanding is that your reading of the rule is correct.
I believe it came about because the original fit Harken blocks are not available from other manufacturers, e.g. Allen, Ronstan, in excatly the same sizing for every application in the sub 20 mm category: Kicker Purchase, Outhaul, & Downhaul. And there maybe places in the Aero world where Harken is either not available as a spare, or not preferred.
However if your reason for changing is difficulty pulling Cunningham on then I suspect you are not going to see a meaningful easing in changing from 18 mm to 20 mm blocks; that's only a 10% increase in leverage after all.
In my opinion and experience with an early 2014 Aero you'd be better advised to look at the rope, and your technique 1st.
The method I used to test the suitability of ropes on my early boat for the blocks and radii they had to turn is:-
If you put the Cunningham 2'ry into a loop bak onto itself, and then slide two fingers down toward the tightening loop you should reach a point where you can feel the rope needs more effort to turn tighter. Stop at that point and measure the diamter enclosed. This is the minimum diameter the rope can bend around before taking effort out of your pull, and incidentally weakening itself. If that diameter is greater than the smallest block in the system it works then you should consider changing the rope to a more flexible one.
I also changed the Cunningham 1'ry, the one that passes through the sail Tack eye, for a Vectran rope. But I cannot be categoric that this was a significant improvement. Other than it is the tightest turn in the Cunningham system and it didn't make much sense to me at the time to taper the opposite end.
The other is technique.
The control that bends the Aero mast the most is the main sheet; through the Leech of the sail. Kicker & Cunningham can follow.
Trying to pull either on 1st needs much more effort.
You do not say what size rig you are trying to bend. It is worth bearing in mind that the 9 rig is the easiest to bend, it is the longest, and the 5 the shortest, the hardest. This may seem surprising given all rigs use the same top mast. But one of the secrets of the Aero design is the mast system. Whichever lower mast is paired with the top mast they all bend iprogressively with it. You can see that in the cut of the Luffs of each sail size. There is no 'knee' in the Luff curve where the upper mast becomes suddenly, or discontinuously, more bendy than the lower mast!!
In sailing all three original rigs I have found the 5 noticeably stiffer than the 7 and the 7 somewhat stiffer than the 9.
Reply
I believe it came about because the original fit Harken blocks are not available from other manufacturers, e.g. Allen, Ronstan, in excatly the same sizing for every application in the sub 20 mm category: Kicker Purchase, Outhaul, & Downhaul. And there maybe places in the Aero world where Harken is either not available as a spare, or not preferred.
However if your reason for changing is difficulty pulling Cunningham on then I suspect you are not going to see a meaningful easing in changing from 18 mm to 20 mm blocks; that's only a 10% increase in leverage after all.
In my opinion and experience with an early 2014 Aero you'd be better advised to look at the rope, and your technique 1st.
The method I used to test the suitability of ropes on my early boat for the blocks and radii they had to turn is:-
If you put the Cunningham 2'ry into a loop bak onto itself, and then slide two fingers down toward the tightening loop you should reach a point where you can feel the rope needs more effort to turn tighter. Stop at that point and measure the diamter enclosed. This is the minimum diameter the rope can bend around before taking effort out of your pull, and incidentally weakening itself. If that diameter is greater than the smallest block in the system it works then you should consider changing the rope to a more flexible one.
I also changed the Cunningham 1'ry, the one that passes through the sail Tack eye, for a Vectran rope. But I cannot be categoric that this was a significant improvement. Other than it is the tightest turn in the Cunningham system and it didn't make much sense to me at the time to taper the opposite end.
The other is technique.
The control that bends the Aero mast the most is the main sheet; through the Leech of the sail. Kicker & Cunningham can follow.
Trying to pull either on 1st needs much more effort.
You do not say what size rig you are trying to bend. It is worth bearing in mind that the 9 rig is the easiest to bend, it is the longest, and the 5 the shortest, the hardest. This may seem surprising given all rigs use the same top mast. But one of the secrets of the Aero design is the mast system. Whichever lower mast is paired with the top mast they all bend iprogressively with it. You can see that in the cut of the Luffs of each sail size. There is no 'knee' in the Luff curve where the upper mast becomes suddenly, or discontinuously, more bendy than the lower mast!!
In sailing all three original rigs I have found the 5 noticeably stiffer than the 7 and the 7 somewhat stiffer than the 9.
Reply
25/07/2022 18:19:00
Jonathan Rickels
Posts: 104
Hi, just reading the rules to check on changing the cunningham blocks supplied with slightly larger ones to make it easier to ger more cunningham on. Part C 6.1.3 (X) says blocks supplied at 16 & 18 mm can be changed to similar blocks up to 20 mm. firstly have i read that correclty and secondly does it include the cunningham floating double block and the one on the deck, which can be changed to 2 seoarate 20mm blocks so long as they are attached in the same way. I am aware that the double floating block must remain a double but can it also be increased to 20mm. Thanks Duncan
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24/07/2022 17:47:00
Dunsmall
Posts: 25
