Hi,
I added a 3' comp tip section onto my Cheshire Cat mast to accomodate a larger mainsail. My question is, should I move my jib,stay attachment higher up also on the mast? Right now, the mainsail dimensions are: luff-23' foot 7.5', and the jib dimensions are: luff 17.5' foot 5'.
Any advice would be greatly appreciated!

Are you changing your jib?? If you are using the same jib why would you change its position on the mast? the only reason to change it would be if you were fitting a different jib with a longer luff and leech.

It makes perfect sense if I am extending the jib luff, I would be getting a taller jib ! We are talking about improvement to performance, but hey, by reading the Cheshire website, I should just sail it out of the box and kick butt, right? The jib luff now is 17.5'. I just don't know how high to put the new luff, on a 25' mast. Any advice would help.

If you are using the "factory" jib and set up, and you were to set the head of the sail at a different (higher) angle on the mast you will change the sheeting angles at the clew which can alter the control and set of the jib i.e. if the angle of the jib sheet is higher then the direction of the "pull" on the sheet is more along the leech of the sail and less along the foot and less "even" through the sail, and you may find that the jib is much more difficult to set so that it works well with out "hooking" the leech, or, having too full an entry at the luff and thereby reducing your ability to point.

Hi,
I am wondering how tall a jib I could add, to accomodate the larger mainsail. My mainsail luff is 3' longer now. The jib attachment on the mast seems way too low. I am looking for some advice on how long the "new" jib luff should be, how high to move it up the mast, but I don't think I should change the foot at all. it is about 5'. That would really change the sheeting angle.
Is there any formula for this, or is there a comparable boat to compare the length/dimensions with?
Sail Plan : main 23'luff - 7.5' foot
Jib ??' luff - 5' foot
Mast is about 25'
boat weighs 170 lbs
Thanks

The jib, on a rotating mast is usually attached, on the mast, at the same location as the hounds, and if you were to attach a new jib higher than that you should really raise the position of the hounds accordingly to give the correct support to the mast. If you start playing around by attaching a "working" jib above the hounds you can get into all sorts of mast bend problems. If you raise the hound position you are left with all sorts of ugly holes in the mast from it's original position which can weaken the mast in a very suspect load point, as well as having to replace all your rigging. By putting on a "taller" jib and keeping the foot length the same you would only be gaining a very minute extra area at the smallest part of the sail and I don' think that you would even notice any performance difference (and potentially if it wasn't all converted correctly, there could be an actual drop in control and performance). Adding to the mainsail area is an entirely different (and easier) situation where there should be a marked improvement in power (particularly more so from its height, and higher aspect ratio than from the extra area)

The hound position depends entirely on the strength of the mast, its bend characteristics, and to a lesser degree, the cut of the mainsail (although a sail is generally cut to suit the mast rather than vice versa). There are all sorts of hound position ratios i.e. 3/4, 7/8 even 2/3, and all percentages in between. The best hound point is set where it fully supports the mast the best taking into consideration how you want the mast to perform and bend with out "S" bending and/or breaking under unacceptable low loadings. If the sail works better when the head twists off early or needs to shed load early due to it being "over powered” for the cat, or the crew is very light, (among other reasons) then the hounds can be positioned lower to allow more bend above the hounds. The reverse IE higher hounds, if the mast is required to stand up straighter under greater loads. There are also other concerns as well IE does the mast have diamonds or not, if it does, how long are the spreaders, and are they raked backwards and if so how much rake, and what tension is on them etc. These are just a few considerations to be taken into account when positioning the hound position on a mast.

Bart,
Why don't you ask Frank Meldau, the designer and manufacturer of the Cheshire Cat? Website is http://www.intl-fiberglass.com/boats.html

What I do know is that there is some reason why sailors go to a lot of trouble to get the tack of their jib down as low as possible, so you probably do not want to mount your current jib higher.

Also, with a sloop rig the main and jib have to be designed as a "team." The draft on a sloop main is graduated progressively farther aft down the sail to accommodate the overlap (or slot effect) of the jib it was designed with. So if you just arbitrarily decide to put a taller jib on the boat, the draft on the main might not be correct at that height, which would totally screw up the air flow over the main.

I'm sure the engineers and sail designers will correct me if I am wrong.

Absolutely correct Mary