Spreader Rake

OK so Sis and I have noticed that in the lighter air we can not get the boat to move while in heavy air we did well as long as we could double trap. I know I am a lot heavier then the previous skipper but the light air problems were dramatic we felt. Well after RTI it was pointed out to me that we had way to much spreader rake. Got home and measured it and found the rake set at 125 mm. Talked to mike borden and found he and Chris are set at 55 or lower. This would explain why we are dying in the light air. So I am wondering what are most of you setting the rake at. We have the 09 Goodall main and together top out around 290 lbs.
Thanks

I've never understood spreader rake. Why does that setting explain why you're dying in light air?

How did you measure your rake?

Pete,
The discussion about spreader rake and all of that could take a board of it's own, especially with all of the varying opinions on this board.

So,
Here are some links that can get you going.....

http://www.ahpc.com.au/PDF/VIPER%20Tuning%20Guide.pdf

That says Viper tuning, but there is some explanation of what spreader rake can and do. So, that would pertain to all boats, even monos....

another.

http://www.landenberger-sailing.com/spip.php?article21

That one takes reading a couple of times to get it, then you need to experiment with it.

The Viper tuning also explains how to measure the spreader rake.

What everyone needs to take in consideration that the bend characteristics of all masts and sails will be different.

Basically,
If boat 1 and 2 have a brand new main from the same manufacturer and the masts are the same(wing masts), the bend characteristics of mast 1 could be different from mast 2. In other words, what rake works on boat 1 might not work on boat 2. But, discussing it with another sailor should start getting you in the ball park.

The ONLY way to REALLY know, go out and sail against another boat.

Mike.

Hi Jody
By all means find out what other peoples settings are but don't forget as Matt pointed out recently no two masts, sails and the way you sail/race is the same.
Your main should have tell tales roughly 2-3 feet above the spreaders and roughly a foot inside the luff, Set your spreaders to keep these tell tales flying as close to 100% as possible. If you don't have these tell tales in the above area you'll never know if you have the correct, matching mast to luff curve.

the way to measure it is to put a sail batten accross the back of the diamons where they exit the spreaders and then measure the distance to the sail track on the mast.

Too much rake means the mast bends more easily and there is less power in the sail.

There are huge differences in sails, especially brand to brand. A lot of the Euro sails tend to use straighter luff curves which may require less prebend. Masts vary and sails change over time.

Spreader rake in combo with tension change the prebend. It has to be smooth and it has to match the sail. Note the diamonds only effectively change about ½ to 2/3 of the mast shape. Knowing your settings for down haul and rotation to properly set the main sail is even more important to maintaining power. Any discontinuity will detract from the sails performance. Having too “fat” a sail, from improper prebend or rotation both will make the boat feel very sluggish and detract from your ability to point and power up in light wind. Beware as I have seen a lot of people feel they have no power in light wind and arbitrarily adjust things that make the problem even worse.

On our web site under support we have a tuning guide which describes what you should be looking for in setting up your mast. That being said I have never seen a sail needing 125mm of rake, that sounds a bit excessive, but to arbitrarily say you need 50 or 75 would likewise not necessarily provide you with a setting that works on your boat.

If 125mm is excessive, what is the normal range?

Jeez Pete, were you not reading the post above?

You have to look at the whole picture. Sailing to somebody’s fixed chart will do you a huge disservice. His 125 was probably set as a result of some post somewhere and although it sounds high it may work fine. 125 and 500 lbs of tension may be way too much prebend – but maybe not. With a lower tension setting it may be great. This though may cause more bending in the mast, so again if you do not adjust your jib trim and rotation to take this into account you will be slow. Is the problem the mast settings, or the other settings.

If you trim properly and drive properly 125 in rake COULD be wicked fast. Screw up any other item on trim and you may not ever know what caused a problem with boat speed if you have one.


(I have seen as much as 90 but the tension is so low for most reputable sails you run a risk of breakage, I have seen some older Euro A class set ups that were around 10)

Normal range as defined in what I see or heared being used over a wide range of F16 masts and sails (see Matt's comments) is :

30 mm to 70 mm spreader rake

I'm running 48 mm myself (superwing mast from 2002 and a 2003 redhead mainsail with a luff curve cut for a 150 kg crew but also with an issue in the very top requiring me to always run lots of downhaul).

Wouter

I have no idea what my spreader rake is. Looks about right though. Have no idea about diamond wire tension either. of course someone else set the mast up prior to me owning the boat. He seems to know what he is doing though so I never messed with it. That was with an Ullman main and I have since changed to a glaser and it works fine... at least other people seem to sail it fast

Jody,
Are you sure it is just a light air problem? You and Joanna seem slow all the time.

THAT'S THE SPIRIT!!! MORE.....

That would be a good one for a book about sail trim, "adjust spreader rake till it looks about right"

theoretically, the "eye ball" method is best if you are trying to match the curve of your mainsail. Unless one is sufficiently able to measure the curve exactly (smacks of higher math and such.... and math and I never got along). I do know, however, from eyeballing, is that my mast has a slight twist in it. Maybe 1cm rotated at the top compared to the bottom. (crap, there just went my resale value

That's why I have been taught to trust in the telltale method. Sail makers don't just stick em any old where. Each tell tale is positioned to guide you to achieve optimum sail shape and control.
Take the very top telltale, middle if you have three in a row what's it telling you?........ If the outside is flying horizontally and the inside isn't you've either sailed off the wind (pinched) or you haven't enough mainsheet tension.
Now you are beating nicely the mainsheet is pulled on as hard as is reasonably practical for the conditions and the top telltale still wont fly horizontally. If you pull more downhaul on from your marked max power setting (we've all marked our downhaul position for max power haven't we). Then the inside top telltale WILL fly horizontally.
And so on, each telltale serves a purpose.

what about leach tales? never been able to figure those out really

You want them flipping- foward, back, forward, back, forward, back.

If they're flying forward too much: oversheated and the sail is hooked. In light air the rememedy is to crank on the cunningham and open the top of the sail up to get a consistant shape.

If they're flying back too to much: Undersheated

or...... I'm talking completely outta my butt.....

I asked glaser about them when I got my new sail and he said something about them only being helpful downwind with the spin???????

You still want them behaving like I said when you are going downwind as the main still thinks its going to weather. You should be playing the main going downwind just as much as going to weather. A bit hard if you're singlehanding though.

CAB how high can a main go up the mast again?

Will have to look at the taletalls again. Have noticed that up wind the one just above the tang area is flying the complete opposite of the others, thought about just taking it off, but reason hits and I think it might be trying to tell me something. Any one got a telltale decoder or a babble fish?

You should not play around with rake and diamond tension, until you have a good understanding of sail trim. E.g. When I bought my boat I sailed around 50 times until I started to understood how it reacts on downhaul, sheet, rotation and batten tension. Then I could understand how the boat reacts on different rake and diamond tension setting.
IMO the best reading is on the landenberger page:
* More rake = more stiffness in the longitudinal axis and more pre bend
* More diamond tension = more pre bend
And as Matt said, rake and tension work in the lower part of the mast/sail.

Once you understand why you are slow (sail to full or flat and where; you need tell tales to see this), you can change rake and diamond tension to adjust.

If you are not sure about all the stuff above, make some pictures of your sail in strong wind and light wind trim upwind and in downwind trim (boat on the side, mast supported at the hounds) and post it here.

Cheers,

Klaus

chris how high does your mainsail go?
mic

sorry see you next saturday.
mic

Chris,

Is that your new ride?
You did a great job of staying away from the camera guy

he's in stealth mode regarding a lot of things it seems!!
"move on, nothing to see here..."

As of last weekend the RR is still under finishing touches per Chris.

you mean his A cat?

No my new ride is still not ready. Jody has named it the RR or Rabid Rabbit. It turns out it is a lot of work to build a boat. I am hoping it will be ready for Juanas in September.

I do have a new uni main that I used at round the island and my friends (I use that word loosely) claim it exceeds max hoist height. That is what Jody and Mic are joking about.

Friends?

Chris, that thing will go a lot faster if you attach the hulls at the END of the beams...

Actually, in very light air he would be smoking as he would be the only one flying a hull!
Jody- You should contact your sailmaker (Goodall, right?) and he will send you the approximate setup for your mast for that sail. Whenever you get a new sail you should always measure your mast first (bend characteristics- see AHPC site- I think they still have the procedure listed there-) and send those measurements to your sailmaker first. My Ashby main came with setup instructions including spreader length, rake and prebend measurements for various windstrength ranges (it changes with these- not surprisingly- with a single sail, other option is to leave mast set up the same and switch sails- this is what the high end monos often do). Sailing in light air is tricky- most people tend to oversheet in general. Cats slow down considerably in maneuvers in light air (especially if it's choppy or you are throwing yourself around on the boat) so after a tack you want a fairly "fat sail" for power but as the boat gets up to speed you want to slowly keep bringing the main in to ideal setting for that speed. The self tacking jibs are quite small and usually quite flat so they don't help as much as the larger, overlapping jibs especially in light air. Try to stay very smooth and "sail" the boat through the tacks in light air, avoiding any powerboat wakes if you can (ie timing your tack), but don't take too long and end up in irons. It takes practice and many cat sailors don't like to sail in light air so don't get the practice.
You have access to 2 boats- you need to compare the masts/sails of both boats. Did Olly set up the rake at 125? Olly was very good (as you know!) and I'm sure had reasons for doing so if so- probably related to crew weight (very light) and sail cut as well as technique. Might have worked great for him but you are dealing with different parameters now-

Hope any of this helps!
Really sucks that Horn Island Hop was cancelled!! That's where I was hoping to be right now!

Kirt