g'day im jerry first time user sail A CLASS MK4 at kingston s.e south australia water is generally flat average wind varies between 10kts to 20kts .could anyone advise me on mast set up as im still playing around with prebend and chain plate settings . cheers jerry

Hi Jerry, I also have a Mk IV and other than the downhaul adjustment I have not changed anything on the diamond wire setup. On windy days the mast will start to slap from side to side after hoisting the sail easing the downhaul until launch keeps that to a minimum. Have you asked the guys over at www.ahpc.com.au yet? It might be a local call for you and Im sure they will know the answer. Keep intouch I'm learning more about cats on this site than anywhere else. Great group here!

Jerry,

I've got a decent light air setup on my boat and as soon as I get a chance to extract my notebook from the trailer, I'll list them here.

Jake

Sure ya will, I've heard that before.

thanks every one for replying to my to my questions .sorry about the delay at getting back to you.any imformation on mast rake ,pre bend ,or general set up's is appreciated.


thanks ready

Rake in general, less wind, set up stright, more wind, more rake. As far as prebend goes, I think you will need info from the manufacturer or other owners.

Jerry-
I'm sure you'll love the "A" cat! Very hard to give specifics on these boats as the masts can be different (the older Mk IV's even had aluminum masts though most have upgraded to CF- but could be Saarberg, Hall, Fiberfoam, etc. CF mast) and the sails can be very different materials (Dacron, Pentex, etc.) built by different sailmakers (Goodall, Ashby, Danger, Landenberger, Glaser, Ullman, etc.). Best thing to do in your particular case is to note type of mast (if possible), year of boat (if can't ID mast will at least give a clue), sailmaker and year of sail (if possible) and E-mail the sailmaker for suggestions as to prebend, rake, spreader length, etc.

Enjoy!

Kirt

Jerry,
You are in the right place. Call either Glenn at Ashby Sailcraft or Greg at Australian High performance. Both are very intimate with all of the Boyer and Flyer A cat designs. They will be able to give you basic mast set ups and give you a base rake setting.

thanks guys ill get in touch with boyer or glen ashby
and then start to set things up

Could you leave a post when you have received reply from Glenn? I mailed him about one week ago with a similar question but haven't received any reply yet. May be my message is stuck in his spam-filter ...

However, I would like to understand the subject in general. Right now, I have an average spreader rake but pretty high diamond tension. I guess, I can achieve the same mast bend with higher spreader rake and less tension on the diamonds. How will this affect the performance of the boat, is one option preferable over the other? If somebody could give me advice on this ...

Me too.

How much pre-bend is too much? This thread is about A-Cat stuff but I think the concept is universal.

I have a new main for my H20 and using Mike Krantz's technique of matching the mast bend to the sail luff curve, I was able to make a perfect match.

However, to do that I ended up with 4" of spreader rake and 800# wire tension.

I can find no reference in the various tuning manuals and posts of anyone using more than 2 1/2" of rake. Have I gone too far?

The sail looks great (we will find out this weekend).

Spreader rake will change how your mast reacts to pressures from wind and control lines. More rake will turn loads into mast bend faster than less rake will. Loads include side forces from wind, compression from trapezing weight (additional leverage), downhaul, and mainsheet tension.

I still treat spreader rake as a method to fine tune the mast reaction based on the weight of the sailors on board. Heavy sailors will want the mast to bend less quickly in response to additional pressure (higher wind) so they will want less spreader rake.

My impression of this is changing a little through conversation with some of the a-cat guys but I haven't completely digested what they're doing with tuning spreader rake.

Mast bend is fine tuned with the Cunningham right? I thought the prebend would only be re-set for a sail change. Watching the racing cats video the sail shape changed a lot as the mast came back the sail got fuller there was a mainsheet trim with every Cunningham adjustment. Have to watch that one again I believe it was a Tornado used in the video they covered rake of the spreaders as well. From my limited experiance on the MK IV every adjustment on the water results in a slowdown before speed increases. I was told by another Boyer owner to set the rake using the trap line as a ruler it should be about the same at the back crossbrace and at the forestays you can adjust for heavy or lite wind only on the beach.

Jack, you're talking of Mike Krantz's technique - is there a document or a link you can provide? And Jake, do I understand you right that less crew weight results in higher spreader rake and vice versa?
I have to re-adjust all parameters (spreader-rake, diamond tension, mast-rake, and side stay tension) since I put a pretty recent sail (Ashby 2004) on my A-Kat from 1997. There are so many parameters to gamble with - where to start? With the current set-up I have the feeling that my boat is too sensitive to gusts.

A few years back, Mitch Booth showed Dave and I how to tune our Tiger mast to match the luff curve of the main. He had us flip the boat on it's side, connect the main on the halyard hook, connect the downhaul, and mainsheet and sheet in hard as though you were going up wind. Note - the main is not in the luff track, it is outside the mast. Look at the luff curve of the sail, and compare it to the curve of the mast track. Adjust your diamonds and spreader rake accordingly to get them to match. That is your new "base setting". We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.

Mike Krantz quote

... do I understand this right: 800 - 1000lbs diamond tension? This converts to 360 - 450 kg - this is enormously much! Currently I have 270kg (= 600lbs) and feel already uncomfortably with it. But again, with more spreader rake and less tension I should be able to achieve the same results ...

Jack, you tuned your mast according to Mike Kratz's technique and want to make a try upcoming weekend? Please let me know how it has worked!

We found that we were carrying anywhere from 800 to 1,000 lbs of diamond tension to get some mainsails dialed in.


Seems to me if it takes that much to make it happen you might want to look at having the sail re-cut.

i think that you have mis-understood what the boss was saying. That curve is the MAX mast bend that you want with full down-haul, you just need enough prebend to allow the downhaul to get you to this point.

Question:
If you "overset" your pre-bend so when you max downhauled... you went past "fully flat" ... would that put more draft in your sail and power you up?