I have not had much luck with mast rake on my hobie 18. I seem to be better off straight up and down. anyone have any input.
Personally, I'd have to agree with you. Mast rake on the 18 does not play as big of a role as it does on the 16 for example. However, the distance from one hole on the chainplate to another can make a couple degree difference. Just try sailing your boat. Figure out how it is fastest, pointing or footing. I have brand new sails and they were horrible pointing upwind. I tried max. rake and I tried minimum rake. No matter what I still could not point as high. I usually sail (with a new forestay) with two holes sticking out of the bottom of the furler unit. If is is REALLY blowing and I am sailing light I might drop it down so there are none sticking out but that is rare usually I leave at least one. That is just a general reference though. Read Phil Berman's 18 performance manual, although some stuff is out of date most of it is good.
More important than mast rake is mast bend. This is where you will get your power from or not get it from. This is also where you will get your pointing abilitiy from. The tapered comp tip on the 18 is meant to bend and the sail is cut to have it bent. Set the diamonds loose. The comp tip section of the mast is probably one of the biggest (if not the biggest) tuning device and power source on the whole boat. Use that and get a nice adjustable downhaul and you can almost forget about mast rake.
If your just starting out on the boat get the perf. manual and tune the basics. Roughly tune it so you can make coarse adjustments in the tuning and tune it once and a while according to the conditions and crew weight. Learn to sail then boat then worry about the little things.
Sorry for such the long post, kinda got carried away.
-Todd
I'll agree with Todd - I generally run mine with the mast fully forward. I'll rake one forestay adjustment hole at a time for incremental increases in wind, but I don't bother thinking about it until the wind gets near 20kts or I'm sailing really light. My difference is that I have an all-metal mast, and run the diamonds tight, using the downhaul to induce mast bend. I like to try to keep the slot open to avoid backwinding the main.
A lot of pointing issues with the 18 seem to break down into two things - one is making sure your weight is forward/bows are down, the other is to make certain you are not oversheeting the jib.
HOW MUCH PONDAGE ARE YOU RUNNING ON THE DIAMOND WIRES????
No measureable poundage, just tight enough to prevent side-to-side bending.
Generally 18 sailors aren't technical (not as serous ) like some of the 20' cat sailors. I've never seen or heard of anyone using any of the gauges to measure the tension on any of the wires on the 18.
Sailing with loose diamond wires will not result in side to side bending, the shrouds and the tension on the downhaul and main sheet will keep it bending back instead of side to side.
Generally I sail with my diamond wires to the point that they just barely touch the mast about a foot to a foot and a half up the wire. On my solid aluminum mast I sail with them even looser. The aluminum mast does not bend as easily so I sail with them so they are touching about 2 feet up.
The 18 performance manual is outdated to the point that it was printed for tuning an all aluminum mast. Use those measurements for an all aluminum mast and reduce them about half a foot to a foot for a comp tip mast.
I've sailed distance races with my spinnaker with my diamonds tight and I have noticed a huge difference in the amount of bend in the mast, there is NONE. I satarted sailing with a little slack in the wires and really kept my main in tight downwind.
When I say side-to-side I mean on the minor axis of the mast section, not necessarily on the boat, poor choice of words on my part.
A mast using pre-bend has its bend forced into it by the diamonds on the major axis, or front-to-rear, or thick direction of the mast.
A mast using the loose diamond technique (no pre-bend) will bend along both the minor and major axis of the mast section, with the amount on minor axis bending depending on the looseness of the diamonds. Of course the stays and mainsail hold the stick up, but the curve formed by the mast will be along the minor axis of the mast section. Some believe this allows the mast to interfere some with the jib slot (depending on rotation), something to consider with the 18 as the jib overlaps a fair amount. With this technique you run the diamonds looser to depower, tighter to power up. Mast rotation plays a critical role in using the bend allowed by the loose diamonds. On this type of rig you over-rotate to flatten/depower, but when going upwind that presents the flat section of mast to the wind, detrimental when it's really blowing.
There's a section in Catamaran Sailing for the 90's on this I believe, and details the different idea for how to run the diamonds, with pictures illustrating the slot issues. This is almost a technique mid-way between pre-bend and loose. By keeping the wires tight enough to prevent minor axis bending, you are essentially using your sail fully powered up as the default case - something some people (including myself, but I sail heavy) don't mind because they feel that the sails are a little flat by default anyway. When you crank on the downhaul, the mast bends mostly on the major (front-to-rear) axis, giving a pre-bend effect. When you rotate the mast now, the curve of the mast moves away from the slot. Bad thing here is I've noticed that if you over-rotate by accident the top of the mast can bend out of column, giving a wierd shape. When you see this decrease rotation. This also may be a little rough on the luff of the sail, as it is now fully responsible for forcing bend where before the loose diamonds would do a lot of that.
Which is faster? I'm not sure, honestly. I sail mostly against other designs in portsmouth, so I don't have two-boat comparisons to relate. I like the logic of the "stiff" mast approach and that's what I use, mostly because I don't have to mess with diamond wire tension anymore (getting old and lazy...). But I also appreciate the fact that the sails are cut for the loose rig, so maybe that's better. Someday with nothing else to do I'll revisit the loose rig and see if there's a noticeable difference good or bad. But I'll probably just enjoy being out sailing instead! 😉