UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: craig_guthrie on June 30, 2008, 02:21:23 PM
-
Most photos I have seen show very clean simple boats with pins on the shrouds and a fixed forestay. What sort of adjustabilty is available on the water with the faster teams? Weight savings makes sense to have things more simple...I like to play with things on the water.
Spreader Deflection. How many degrees and depth of sweep?
Thanks.
Craig
-
Hi Criag,
I keep on saying that adjustable uppers are a good idea - and keep on not putting them on our boats!
I don't think anyone has adjustable shrouds, but I think Pete B may have an adjustable forestay. The norm is definitely that the boat will keep you busy enough with the three sheets, two trapezes, kicker, cunny and T foil, and the extra weight (of which there is lots: Our rope trapezes weigh 800g not including the bungee, so imagine how heavy all those 32:1 cascades are.... and now get them wet...).
Spreaders: a bit greater than 30 degs from athwartships so they push forwards, and the spreader root is held back by the D2's (often called D1's - the shrouds which go to the base of the lower spreaders)
I think ours are 430mm long and displace about 250mm.
-
Thanks for that Will. I think I may end up with adjustable caps and forestay...I thought there looked like plenty to deal with.
Are vangs and cunnos lead to the racks?
Have people congregated to the twist grip for the foil or is a line system run from the rudder/ tiller cassette to the rack effective as well?
Thanks.
Craig
-
Hi Craig,
Yes, most people lead the controls to the racks. Ours are by the shrouds, but half way along is good.
Kevin Ellway now leads the t foil forwards to the shrouds too.
Twisty grips are a moot point. Some have twisty grips, some have string, and some have both!
-
It is mostly keep it simple, have a look at, although they could do with some updating.
Running Rigging (http://www.sailingsource.com/cherub/test/doku.php/tech/running_rigging)
The Rig (http://www.sailingsource.com/cherub/test/doku.php/tech/rigging)
Just about everyone has pinned rigs, with the tension pulled on using a boat breaker and the sails tied up with no haliards.
Adjustable caps are something I would contemplate but there is quite a weight penalty, especially once the rope is wet.
I think that unless you have a way of adjusting your shrouds, possibly 49er style with turnbuckles an adjustable forestay is not much use on the water.
For the T-foil there is a mix of systems and I use rope to the sides but many people are going for twist grip, it lets you be more aggressive with lift when going down wind.
-
The main thing I have gathered about Cherub rigs is that you need quite a bit of tension to stop the winwdard shrouds going slack when both sailors are on the wire. Therefore lengthening the foresaty to rake the mast back say in windy weather will leave you with a floppy mast. pulling more tension on whilst on the water will require 32:1 I expect. How do you deal with D2's? and lowers?
It sounds complex and as Will suggests heavy. Good luck though because you might hit on something that really raises the game.
-
What would be the disadvantage of the windward shroud going slack? Many 600 sailors have this as a base setting.
-
As far as I know, your using the bits oif string (or rope) attahced to your mast for two reasons:
1) To keep it in the shape you want,
2) To keep it upright!
If your shrouds are going slack then surly your mast is bending in a funny way?
-
If you have a mast which
1) is stiffer than a stiff stiffy in Stiffordshire;
2) is heavier than a heavy heave from Heavey;
3) is supported by diamonds;
4) has only one person hanging from it;
5) has only one sail on it;
then sailing with slack shrouds may be a good idea.
Interestingly the 49ers do the windward-shroud-circle thing too, but this is because they have to use the below-hounds section of the mast for gust response due to SMOD-randomness rather than anything intrinsic.
-
The RS600 has dimonds rather than proper spreaders and no jib so the shroud tension is not that important.
When you have shrouds linked to spreaders the tension in the shrouds controls the bend of the middle of the mast. If your windward shroud is getting loose the midle of the mast will be wobbling all over the place loosing power.
Also if you have so little tension on your shrouds your forestay will be sagging off ruining your pointing. the shrouds should be as tight as you dare before things start breaking.
-
Re sytems, I suggest keeping everything as simple as possible. It just has to be effective, efficient....and reliable. No use having something 'clever' if it does not work easily, all the time and without breaking
I bought my boat with adjustable 12:1 forestay (dont see why you would need 32:1) but as my shrouds are pinned there is little benefit except for ease of rigging which is nice. There is not enougth range in the forestay adjuster to rake the shroud pins on the water. By choice I would have a fixed forstay with boat-braker to reduce weight and keep it simple.
I think adjustable uppers are a good idea but I dont get to hung up on the precise setting, it's a dark art, nobody really nows. Adjusters dont have to be heavy as 4:1 will crudly suffice, as per RS800s.
I have D1s, but not D2s, for better or worse(?), might lose some central mast support but if I can get away with it, I save windage and weight.
Definitely need control lines lead to racks so adjustable whilst wiring. Amidships is more convenient and avoids going forwards when it is scary to do so. As long as they are across ther boat and not fore/aft trip hazards then I think that is OK. I have sailed Kevin's SK4 and stepping forward downwind to uncleat the T-foil because the nose is digging in feels a bit unnatural - scary!
In RS600s rig tension is not critical, just like windsurfs dont use it. In Cherubs with spreaders, jib luff, jib slot, it is more so.
I have a string only 6:1 T-foil adjuster with the downside that one of us has to bend to reach it when maybe we least want to. As it is simple and it works I will stick with it. A twist grip you can adjust without moving seems more ideal.
-
Can't remember if this has been covered or not, but If I was putting a boat together I would have a string system for big adjustment (windward and leeward mark roundings) and have a twisty grip for fine tuning. For the bare away at the windward mark, I quite like how Phil has (soon to be had :-[ ) it on Primal Scream. You can just kick the line out of the cleat and have line cut to length where the T-foil is neutral. Negative is for wimps!* Of course, because we're all so stylish ( ;D) we do the 49er style 'helm on the racks while the crew jumps in and hoists' bare aways where this system will become most useful!
*Hoppy and Tim seemed to like the extreme negative T-foil kite runs at carsington.
-
We used to have adjustable shrouds on our fireballs, it worked well on there, but then a fireball is much more stable than a cherub - for on the water changing. Having said that, it did take a bit of effort changing, one person leaning on the trapeze while the other changed it.
I prefer the fact that the cherub is fixed, means your concentrating on your sailing, not faffing about with the rig.
Also, as Will said eailer, have enough to concentrate on anyway, and I just see it as other thing to mess about with - which doesnt always help you go faster
:)
-
my t foil runs 3:1 on a twist grip no problem at all.
must be my manly northern strength
-
I am really happy to see how much chat these questions are generating and can't wait to get my boat building project under way!!!
So, now for another question:
Do folks have one or two sets of sails? One for the light and one for the breeze? I spent some time looking at photos and there seems to be a fair range in the gear. The big square top main looks great for the light and medium breezes but what about when that extra sail is reduced to inverting and drag?
I figure that this is the right line to follow as we have just finished going over the running rigging.
Go for it!
Craig
-
There is nothing to stop you using differnt rigs, as long as they are within the rules (for racing anyway). 15.5m upwind and 21m downwind. Most people just have one as having 2 sets is expensive and having a well set up rig with a decent set of sails, you should be able to depower is all nicely anyway.
-
I am really happy to see how much chat these questions are generating and can't wait to get my boat building project under way!!!
So, now for another question:
Do folks have one or two sets of sails? One for the light and one for the breeze? I spent some time looking at photos and there seems to be a fair range in the gear. The big square top main looks great for the light and medium breezes but what about when that extra sail is reduced to inverting and drag?
I figure that this is the right line to follow as we have just finished going over the running rigging.
Go for it!
Craig
Usually,
people do have a single set of sails across the wind range.
However it's better to have 2 sets not to destroy your premium set.
Ghislain
-
what about when that extra sail is reduced to inverting and drag?
It probably means you have't got enough downhaul on! In the extreme you should be aiming to put on so much downhaul that the topmast bends enough to completely use up the luff round up there and leave the sail flat as a board so that it just feathers rather than inverts. Much less drag, plus provides a useful end plate effect on that part of the sail that is still driving.