Can anyone explain why these ropes run around to the other side?

http://www.merlinrocket.co.uk/gallery/view_photo.asp?folder=gallery/rigging_guide/3683&file=centreboard_case_rear.jpg

I assume they're the rig back / fwd control lines. If they're  cleated on the other side, no rope would run through those blocks.?

Yes, those are the 'one string' lines. You have to uncleat "rig forward" in order to pull on "rig back" and vica versa.

Yes, we know that means two strings overall!

Hi mags,

What I dont undersand, is that the ones running behind the c/b case won't move if they are cleated on the other side. Its less string and blocks to get a 2:1 from a single block with a beckit than to have two blocks (albeit one shared). Cant see what it adds just having a single piece of string to do both sides. ?

Its normally the tails that go across to the other side, to allow a continuous line.
The trick is to avoid pulling all the "rig back" in on one side, while pulling all the "rig forward" on the other (which might be typical on a triangluar course). You would soon run out of adjustment and not be able to control the rig on the side you are sitting.

As it is the tails go across to the other side of the boat, so you can continually adjust forward or backward without running out of string.

Thanks Chris. I can see the utility now. Now to work out how to string it. More fittings!

I've been scribbling on the back of an envelope. 

Assuming you go rig back on one tack, and forward on the other...

Am I right thinkin that the slack on the fwd / back controls is cross-connected behind the centerboard case and that periodically you have to grab hold of the blocks that run along the centerboard case and drag them round a bit so that they dont run out of travel.

 i.e raking back on port, fwd on stbd a couple of times:
2:1 block on the rake fwd line on the port side hits the king post, 
2:1 block on rake back on the port side reaches end of c/b case.

Hi John - I did the full one string conversion on 3386. The two tails on each side are spliced together, with slack under the side deck. So in reality the up / down on both sides is the one length of string. You are correct that the blocks at the back of the case are the cross connections between the port & stbd sides, but these are not the slack in the system.

So to rake, uncleat the up cleat, pull on the back / down rope. To derake, reverse the process. Since the system is one length of string it is self adjusting.

Once you have stretched all the ropes and adjusted the splices, the system shouldn't bottom out.

The strings tend to end up one-sided NOT because you have different rake on each tack(!) but because you tend to go rig back UPWIND and rig forward DOWNWIND.  On a port-hand course this means you are going rig forward after bearing away on STARBOARD at the weather mark, then rig back on PORT after rounding the leeward mark.   

Top tip: before each start (on a port-hand course), pull all the rig-forward string through to the port side and pull the rig-back string through to starboard.  

The same applies to the kicking strap control line, which (on a port-hand course) always goes off on starboard tack at the weather mark and back on on port tack at the leeward mark.

Hi Richard, thanks for the clarification, and tips.

I didnt literally mean on each tack! Just that reverse operations would be occuring on different sides of the boat, at successive upwind/downwind marks.

Its all sorted now, as per Andy's instructions; my raking control lines for forward and back on both sides are one single and continuous piece of string, with elastic takeaways under the side decks. 

In due course my kicker and other lines should be continuous too. 

See progress at:

http://www.facebook.com/album.php?aid=83656&id=564343407&l=5526308762

For convenience