I put the below basic guide & notes together for Andy & Gill Peters who are putting together their new E5. Hopefully it may be of use to others also. It is just my own basic view as I understand it, comments welcome!
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Basic tuning guide & notes for Cherub 2968 Ronin the GT60/B1C - Oct08.
I have; Superspars mast (quite stiff), Hyde sails, Beiker hull
Loos gauge is latest spring version ‘Pro Loos PT1’.
As my Cherub rig is very similar to the RS800 which I am familiar with I have used that as a starting point for tuning wire tensions.
Rig tension & rake
RS800 uses 22L on the forestay but I have increased this to about 24L to compensate for narrower shroud base. This is measured with both lowers and uppers off.
With a spirit level horizontal down Ronin’s deck, this gave a mast head rake of 36cm measured at mast base using a lead line from mast head.
This is normal setting – up to overpowered, say 0-18k.
For a windy setting on the RS800 I would drop the shrouds 0.5 hole and to keep the same rig tension the corresponding forestay movement would be 2-3 holes up. I expect to do the same in the Cherub – but haven’t yet.
Lowers – with the rig tension on, but the uppers slack;
0-6k (drift) slack - to flatten sail as struggling to attach flow. Pin into tightest ‘hand tight’ hole possible without pulling mast or tensioning.
7-13k (underpowered) tight - to create power once windy enough for that flow is established. Should register on loose gauge, say 5-7L. Need to release rig tension or pull mast to pin this. When the uppers come on lowers should increase to 11-14L.
14-18k (full power) slack - but don’t want too much depth. Pin into tightest ‘hand tight’ hole possible without pulling mast or tensioning.
19k+ (overpowered) slackest - need to blade main to depower
So you might find the 0-6 and 14-18 are 0.5 hole looser than 7-13.
19k+ would be 0.5 hole slacker again but if you move the shrouds down 0.5 at this transition then that will give that effect without the lowers actually moving.
The ‘slack’ & ‘slackest’ settings will go tighter once uppers (& kicker) are applied.
(I do not have D2s meeting the mast at spreaders)
Uppers- this is a dark art!
Over tight or over slack and you are depowering. Somewhere in the middle you are powering the rig up by supporting it sideways but not overly bending it.
Use uppers to power up in constant medium breeze.
Consider slacker lowers when gusty (&shifty) to give a responsive rig.
When very windy have them tight to help save the kite puller the mast fwds.
Overly slack uppers will hinder pointing.
Overly tight uppers might hinder leach tension.
RS800s use 10-15L on uppers, measured with rig tension and lowers on. My lucky number is 12L.
Note; the above L numbers relate to 2.5mm wire uppers and 3mm wire lowers, make adjustment if diameters are different. I use 3mm string (Marlow SK78) on uppers and lowers and think I can use a loos gauge on it just like wire (?). The L number difference from 2.5->3mm is add 3 units so my 12L becomes 15L. but; RS800s have much narrower top spreaders than my Cherub, therefore actually need less tension to give the same support? (or maybe I can shorten my top Cherub spreaders?)
