Just added a Hobie 18 with wings to my fleet, anybody got any tuning tips? The P.O. had been sailing it with the diamond wires totally slack, and claimed that was what the manual called for. I'm amazed the rig didin't come down on him with how many broken strands there were on both shrouds...
So any one who wants to share some tips, or just remenisce about how much they loved theirs, let me know...
Phil Berman's book "the Hobie 18 Performance Manual" is a litany of detail (well worth the read for basic 18 theory). My comments are based on racing at or slightly above minimum crew weight (Paul and I weigh 305). The main message I get from Phil is the 18 main is flat and a flat sail means more RPM (speed) which is great for us at a light weight. Or, we don't need to build more power into the sail, which isn't designed primarily for power.
When not racing I, like everyone, am interested in two basic settings to cover everything for "real windy" and "wish there was a little more wind" (besides if we did everything Mr. Berman wanted us to do it would be dark before we got off the beach).
Spreaders are forward medium and heavy. Mast rake as far forward as possible for medium, one hole back for heavy with shrouds adjusted accordingly, tight(med) & tighter(heavy). The diamond wire set "just tight" on the leeward side when going to weather, which must be checked on the water. This is somewhere between the 24" and 36" marks on our mast (since we're light weight we go loose in light air also i.e. towards the 36" mark, heavy crews will go to 12" [tight]in light air). Diamond tension can be easily set by honking in your main and downhaul, while on the beach.
After that the only viable adjustment on the water is downhaul. 8:1 is class legal and cascading with pivoting cams for crew control is best.
Keep the main flat for speed.
Just so you get a different perspective on this, mine would be that with the Hobie 18 Magnum, you need as much power as you can get. You should shove your battens in until the sail looks like a hungry dog. Fuller the better.
We have seen too many people get discouraged and leave sailboat racing because they listened to the flat-sail theory when it is not the best theory for their particular boat and/or their particular weight or the sailing conditions where they normally sail. 
Ditto to Mary's post.
First off, if you're going to race consider taking the wings off. They're great for cruising and fun sailing, I think they're added weight and windage for nothing when racing.
On my 18 I almost always had the mast all the way forward unless it was honking. Even when I put the spinnaker on it. As for the diamonds - the original spec for the 18 called for the loose diamonds, with different settings for different wind ranges to use in concert with different spreader rake settings. I used to spend a lot of time messing that stuff until reading Catsailing for the 90's.
That's when I set my spreaders forward and tightened the diamonds until they were tight but not tight enough to pre-bend the mast on their own. Then I used the downhaul to force the bend and depowering. I got to quit thinking about all that other stuff, and the boat was faster.
Also, my original set of Hobie sails were horrible - to get any consistent shape the battens all had extreme different levels of tension. When I got my new Hobie sails, they were wonderful - only had to tension the battens to take out the wrinkles and the sail had a nice full and consistent shape. Get a new set of rags if the current ones have any age to them.
I really enjoyed the 18, nice boat.
Mary,
I had to think about that one for a minute. So the battens are like the dog's rib bones sticking out? If so thats a great image.
Bill
I thought about it for longer than a minute and still didn't get it! Thanks for the help!
Best description of tuning tip ever i reckon.
Thanks for the feedback, keep it coming...
Okay, with a normal Hobie 18 without wings, for racing in light air, you have to get your crew weight way forward to keep the sterns from dragging.
In the case of a Hobie 18 Magnum, the wings are putting even more weight toward the aft end of the boat, so you have to get the crew weight even MORE forward to compensate (if racing). And there is only so far forward that you can get. Plus, the way the wings are mounted create an obstacle to get over in order to get onto the bows -- knee and shin-banger.
And what is the point of having those nice comfy wings to sit on if the boat is going to go slower? Fine for cruising, but NOT for racing.
On the other hand, in heavy air, the wings can be an advantage, because then you want the weight farther back, and you get better leverage to keep the boat upright by sitting on the wings or trapezing off the wings. Trouble is that most people, at least in the United States, do not sail in enough wind most of the time to make the wings an asset.
And, of course, sailing in heavy air with more weight, width and leverage puts more strain on the standing rigging. I'm sure many of us have seen masts break when somebody takes a beach cat out in strong wind with three or four big guys on it to hold it down. Something has to give, and usually it is the mast.