Cal 25 Mast Rake & Shroud Tension

The Cal 25 mast doesn’t bend fore and aft so we only need to concentrate on mast rake and upper & lower shroud tension.

Rake will affect the balance of the boat in regards to the helm. In general, more rake – more weather helm.   Less rake – neutral or potential lee helm. My thinking is the helm should be neutral to favoring a slight weather helm in an 8 mph breeze with little to no heel in the boat. Soon after purchasing my 2013 North sails, I asked Mike and Ian, North Sails, what the Cal 25 rake should be.   You would think this is a simple question, but I was surprised that the answer is not. Due to the construction methods and given the different Cal 25 classes, A, B and C, it is possible that the position of the mast butt, the height of the mast partner – ultimately the height of the mast, the location of the shroud hounds and forestay could vary from boat to boat and mast to mast. So getting a simple measurement that would be the starting point for the class isn’t necessarily straight forward.   I was told that a local sailor who has won numerous National Championships is sailing with a forestay length of 31’ 3 ½“ (measured pin to pin).   Not knowing any better, I figured I’d start with the same measurement. My forestay length is: 31’ 3 5/8” – just to be different ( +1/8”).   We could devise a more scientific method to determine rake taking into account the boat building discrepancies but that would take a lot more thinking – a good topic for another discussion. Guess we’ll have to stick to the forestay length measured pin to pin as a starting point. Note that the backstay will slightly affect your rake as it is trimmed and eased – indeed has a huge effect on luff sag. The backstay is a critical adjustment while under sail – again another great topic for another discussion.

The outer shrouds or uppers keep the mast in column. I show 27 ½ on my uppers as measured with the PT1 Loos Gauge. I’m not positive what the tension of the uppers should be – I simply haven’t done enough testing to determine what the optimal tension is. We seem fast with this setting, so I haven’t changed it. I do believe that changing the tension for different conditions will make a difference, but I just don’t know how much adjustment to make at this time.

I believe the key and secret for consistent speed is with the lowers and the ratio of the tension between the uppers and lowers. I show 12 on the lowers which is tighter than last year’s 8 using the Pt1 Loos gauge. Again, with no fore and aft mast bend, all we really can control is side bend which relates to allowing or disallowing the middle of the mast to pop to windward under load.   In heavy winds, the top of the mast will bend off regardless of the tensioning. When the middle of the mast pops or bends to windward it primarily will do two things. It will open the slot between the headsail and the mainsail and it opens the mainsail leach – all this depends upon the strength of the wind and the amount of tensioning. With the widening of the slot and the leach opening up, you can trim a little tighter which helps with speed and pointability. Too much side bend will result in loss of speed and windward performance will eventually degrade too. With the right amount of side bend you’ll gain in height and be as fast as those around you. With my lowers set to 12 and in winds less than and up to 8 mph mph my mast is pretty much straight. With just a little middle sag in light air it powers up the mainsail. With winds less than 4 mph, the mast is obviously straight and with the lowers loose, I unfortunately experience slop in choppy conditions. In the sloppy conditions, I will sometimes have my crew pinch the windward uppers and lowers by hand to reduce the slop. In winds 8 – 12 mph the top of the mast bends off a little and above 15 mph the mast would as expected pop to windward as the top of the mast bends off to leeward too.

So in summary, with almost two years’ experience in this class sailing with a mast that doesn’t bend fore and aft, I think the key to setting up the mast is the ratio between the two shroud tensions, uppers vs lowers. Hopefully I can get the boat in early next year and do some thorough testing and experimenting. I think my rake is fine but I want to vary the shroud tensions and observe the results. Please share your testing, observations and experience !!!

 

John McAllister
Patriot #466

4 Responses to Cal 25 Mast Rake & Shroud Tension

  1. Admin October 18, 2016 at 2:06 PM #

    My 2016 Measurements using LOOS – Gauge (PT-1)
    measure 66″ up from deck on each stay and affix a piece of tape; attach gauge to wire above tape

    Uppers 30-1/2 (348 lbs)
    Lowers 15

    -John McAllister

  2. Joe Schichtel February 19, 2017 at 12:57 PM #

    My wife’s25-2 has 3/16 cable for the uppers and 5/32 for the lowers. We have a PT-2 Loos gauge because that gauge is the one Loos says is for 3/16. Will the pound settings work for her boat? She races in the China Light series of the Buffalo Harbor Sailing Club. I am trying to find the best base settings for her boat. I don’t expect the crew to experiment with adjustments.

    Joe

    • Admin February 20, 2017 at 9:25 AM #

      Hi Joe

      My measurements are using the PT1 gauge and not the PT2 gauge. Unfortunately, we do not have one Loos gauge that supports measurement tensions for 3/16″ and 5/32″ wire. In the absence of any gauges and tensioning by hand, the uppers should be snug and the lowers looser. With the right tension applied to the lowers you will be able to make about a 3 – 4″ inch circle moving the shroud about its center axis. This is the general rule of thumb for how we setup boats in the Detroit area.

      I used the site below to find that using the PT1 gauge on my uppers reads about 30 and translates to 335 lbs (this might be a little tighter than most of the boats in the area — I used to sail around 27 on the gauge). I also tightened my lowers last summer and the PT1 gauge reads 15. I don’t know what that translates to in lbs. As you know, I would need to measure using the PT2 gauge for the 3/16″ wire.

      I will try and find someone that has a PT2 gauge and measure my lowers this Spring when we setup the boat again (I plan to use 30 on the uppers and 15 on the lowers using PT1, again). I’ll publish the findings…

      http://loosnaples.com/how-to-use-pt-series-tension-gauges

      -John McAllister
      US466 Patriot

  3. Joe Schichtel February 21, 2017 at 4:15 PM #

    Thank you so much for your time. I believe that on the pt-2 around 15 on the scale would be similar to the 30 on the pt-1. I am not much of a sailor (I tell everyone my title on the boat is “cabin boy”) but I am starting to learn what we can do to increase the boat’s performance.
    I didn’t know if there was much difference in the settings for the 25 and the 25-2. Her boat has a roller furler so I will work with the yard manager regarding the forestay length. Do you have any suggestions for tension on the rear stays? We do not have an attachment that squeezes the 2 stays just down from the “y” connection.
    Again, thank you for your help.

    Joe

    p.s. Does this count as my approval for the e-mail?

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