UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: john_hamilton on December 23, 2009, 01:21:53 AM
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can anyone see anything glaringly wrong with this system????(http://img705.imageshack.us/img705/1048/spinnysystem.jpg)
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What is the black line for?
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Comments below are based on BS, EJ and the Aunti Dot. The key to a good system is that everything lines up, this reduces friction and halyard twisting.
I'd suggest ensuring the cleat and hoist pulley are in a straight line - or you'll burn through even a cam-cleat in a couple of hoists if not.
The pully at the back wants to lead the take downhaul in a straight line from the bow hoop to fitting (i.e. along the bag)or this will cheesewire the bag. This back pulley does not want to flop about or be at any risk of flipping and jamming. On 2699 the back pulley is on a plate a fair bit forward of the transom, on EJ it is mounted on the rear rack support, about 40cm from the centreline of the boat.
Putting the kite sheet takeup so it draggs the sheets down the tube at the bow is novel. I think the sheets will simply jam against the bag/kite, but it might be a genium. On EJ we elasticated the kite sheet and added a single takeup ring - this drags the middle of the kite sheet forward on elastic (2699 has 2x forward pullers and no elasticated sheet).
Both EJ and Aunti use the motion of the pole to tighten/activate the sheet take up (elastic connects to base of pole, through a pulley at bow, under the mast support structure and then to take-up ring on sheet). The system drawn looks like it supplys a constant pull? Elastic is not needed to bring the pole back in.
We went a bit elastic in rope mad on EJ and did all the control lines. The other bit that works a treat was to elasticate the bit of the spinni halyard that is adjacent to the mast when kite is hoisted (sits between the top of the mast and the kite bag when kite is down). This results in a halyard that always has some tension in it and no need for any other takeups and no tension in the downhaul in light winds. This sounds a bit strange at first, but the key is that as soon as you start to hoist the rope pulls tight and the halyard rope takes over and performs as normal.
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Roland,
that bit about the elastic in rope is pure genius! What type and diameter rope did you use? Also this was only meant as a scetch and i understand the importance of it all being in a straight line. The spinnaker sheet take ups arent inteanded to take the sheets all the way to the tube now but are basically d-rings attached to some elastic that goes to the kite hoop around a block and then to the bas of the pole.
Ross, the black bit is elastic. I have already changed i to a forwArd pull due to suddenly realising i was dealing wih a 12ft boat instead of the 49er that the elastic system is based on.
John
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also roland, what length or halyard have you finally ended up with?#
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here's mine... the floating ring a the transom to turn the rope to the rear block is now a block. Make sure your sock has enough volume.
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daryl,
what is the function of the back-to-back blocks on the pole launcher? iv senn it on the 49er aswell but what does it do?
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John,
Are you asking about the travelling back-back block. It is a 2:1 against your crew that means you get more pole travel from a block that can only move from bow to the block that sends the halyard up the mast. If your crew moans about the loss from the double block, just point out that there is a 2:1 for on one side and the two cancel out (forget that this is meaningless as the pole is a pain to pull anyway :0) ).
It is possible to drop one of these to leave you with a single block and give the crew more purchase, but then only get a much smaller pole travel. Wives tales will also swear blind that this means the kite will bag out early and drop in the water.
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what length or halyard have you finally ended up with?#
21m of D12. If you are kitting out a whole boat there are several friends who can help (Mr Barton included).
We used a huge ammount of 3mm D12 on the last 2 rigs - BMG has now bought a large quantity sucessfully from http://myworld.ebay.co.uk/schoppenpopp/ds (http://myworld.ebay.co.uk/schoppenpopp/ds). Remember to tell him which colour you need.
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ok thanks roland, i was worried because digby is having trouble pulling cheese's pole out fully at the moment and was wondering about losing the block, but i think i will now keep it on the new boat and hope hes bigger by then!!! thanks for the d12 tip. also which mr barton? pete or james?
john
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Hi John,
That system is pretty much how we had Aqua's. The changes we made when putting Atum together were to have a double floating block because Atum needed more pole travel. Doing this also allows you to put the pole-launch rope through a sheave in the heel of the pole and use the same rope as the tack line. This means that you can get the kite in even if the pole jams. However, in late 2006 we changed back over to the system where the tack line is separate because that way the hard bit of hoisting the spin is at a different time to the hard bit of launching the pole. That is, the difficult parts are at opposite ends of the hoist.
Will (on call on Christmas Eve!)
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any tips on keeping friction to a minimum apart from obviously having a few blocks as possible involved
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Thinner rope = less friction.
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Cloth choice for the sock can make a big difference, the stuff I had on Primal was quite sticky, some of the woven stuff also seems quite rough. I have to say I have yet to find anything I am truly happy with. Regularly spraying with Mclube is good
I like to keep a large radius on the chute mouth both at the front and the back, remember to think how the kite goes out of the sock and the interface between sock and chute. i also think that avoiding any internal sharp corners also prevents jambs on the drop. A large radius on the sides is a good idea, to help get it back in when it is full of shrimp.
At the top of the mast I have a stand-off to ensure that the block is not hard against the mast, or it will rub a groove in the mast.
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phil, what is the best material you have found yet then?
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The stuff that Tim put onto PR seems very low friction, however I think that it absorbs a lot of water as it never seems to dry out.
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Atums sock was a modified RS800 one.
Lucy made Antidote's one from cat tramp material which is v slippy. We got it from Grant Piggot sails - v good bloke and friend of the class. He made a set of sails for Loco. http://www.gpsails.com/
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any tips on keeping friction to a minimum apart from obviously having a few blocks as possible involved
It's pretty much all been said. Good quality blocks, thin string and keeping everything as in line as possible will all help. Interesting notes on the sock material choice. I think I am going for a bag kite though.
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Whoah! Unusual!
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any tips on keeping friction to a minimum apart from obviously having a few blocks as possible involved
I think I am going for a bag kite though.
Funny this is something I am actually thinking about. As I think it may be easier for my very small crew, although by the time I get some sails he may be a bit bigger!
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Use Holmenkol Seal and glide stuff to coat your kite. It makes a huge difference to hoists and drops reducing the friction of kite to sock. The stuff is a bit pricy but make do 2 spinnakers. Use a spray lub on the inside of you sock.
We've used a trampoline mesh material for our socks with no problems. We have also coppied ATum and Antidotes spinny sheet elastic take ups which appear to work well.
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I've done a fair bit of bagging in the Woof 12's and also Simon Rs slug at some events. I can tell you that bagging in the Woof is a lot easier than bagging in the slug. With no false floor and a very dished hull shape you keep the CoG very low. Standing 'on top' of the slug makes it quite a bit more tippy.
Saying that, as long as your crew is good at "windmilling" then they should be fine. It didn't take many drops before I was as quick as dropping with a chute, and it does make you a lot more focussed! I think from a point of view of finding a crew for events you might struggle with a bag. Finding someone good enough to crew the cherub is quite difficult as it is, but throwing the spanner in the works of having a bag will make life more difficult still.