VANCOUVER ISLAND WINDTALK

Do It Yourself IMCS Testing

Have you ever had a rig that just never felt right – too stiff or maybe it was WAY too soft? Ever think that maybe the mast you were running in the rig might not be the ‘right’ match for the sail? One sail manufacturer says (in addition to ‘bad’ matches) there are ‘good’, ‘better’ and ‘best’ mast-sail pairings.

Well I was in the process of switching from one sail brand (brand “A”) to another (brand “B”). I have most of my sails switched over to brand “B”, but was still using mostly masts from brand “A” at the time. I had read some conflicting reports as to how compatible brand “A” masts were in brand “B” sails (everything from ‘not compatible’ to ‘very’ compatible). So I decided to do some IMCS testing of my masts (both brand “A” and brand “B”) to see how different brand “A” was from brand “B” (IMCS and bend curve) and to see if the brand “A” masts I had were within the recommended range for brand “B” sails, or not.

I was able to test 11 mast combinations in about five (5) hours total – from scratch. With this guide and this spreadsheet you should be able to do it in less than half the time.

Theory

There is a very interesting discussion of mast characteristics (stiffness, bend curve, marketing and manufacturing variation) here.

Mast stiffness and bend curve are two different things and even though two masts may have the same IMCS (stiffness) rating there bend curve can be quite different (making for quite different sail performance, one to the other). There is a very interesting description of IMCS (including how to calculate it), stiffness, and bend curve here.

If you want an overview of sail-mast compatibility, there is a useful comparison chart of sail requirements here (unfortunately it does not also include some of the independent masts e.g., Powerex, Nolimits, etc. – as they are competitors).

Some actual test results from IMCS and bend curve can be found here.

Tool List for Testing

• A room with an exposed ceiling (will make measuring a lot easier)
• Four tape measures
> Three to measure bend (soft tapes or hard tape measures that can lock out are best)
> One to measure length
• Two ladders or one ladder and a solid wall that can accept a heavy gauge screw
• A light coloured fine tip marker
• Paper and pen to note bend measurements
• Computer and a copy of the attached “IMCS calculator” spreadsheet (to calculate your results)

Testing

So armed with these instructions noted in the ‘theory’ section above here is what I did:

Step 1 – Constructed a spreadsheet to do the calculations for:

• measuring points (¼, ½, ¾),
• deflection (¼, ½, ¾),
• IMCS (465),
• IMCS (460),
• bottom flex,
• top flex,
• IMCS bend curve, and
• IMCS delta (claimed versus actual).

To save you some time I posted the spreadsheet here so all you have to do is drop in your data and voila – your results will pop up. Note you are responsible for verifying the resulting numbers.

Step 2 – Built Your Test Rig

Note you are responsible for ensuring you apply a safe testing process in a safe manner. What is described below is the method I used, but you are responsible for determining your own testing method including the use of any, products, techniques and safety equipment you deem to be required.

You need a pivot point on either end of the mast for the test to work. I used a heavy gauge screw driven into a stud within a wall (parallel to the floor) on one end and a ladder on the other end. Try and have the test mast lay as level as possible end-to-end. I also used three separate tape measures, one for each measuring point (¼, ½, ¾), suspended from the ceiling to speed up taking measurements and to minimize variation in measurements (under load versus at rest).

Step 3 – Measure Your Masts

1. Calculate your measuring points (¼, ½, ¾) using the attached spreadsheet (one set of measurements for each different mast length).

2. Create a 66 lb weight – make sure this is as accurate as possible as it will affect all of your calculations. I used a construction bucket filed with drain rock measured on a digital floor scale.

3. Create two pivot points. I placed the recess in the tip of the mast over the heavy gauge screw I drove into the vertical stud in the wall.



I then placed the base of the mast over the step on the ladder.I minimized the amount of mast on the ladder step (so as not limit the affect on mast bend/limit the impact the measurements). Be careful, as the mast is loaded it will shorten, so you have to leave adequate length on the ladder rung so it will not drop off the rung once loaded.



4. Secure the mast in place. I used a bungee cord to put a little forward tension on the mast base to help hold it against the wall (and stop it from moving around under load).



5. Mark your measuring points (¼, ½, ¾ - calculated in Step 1) on the mast with the marker.

6. Hang your tape measures, so they are coincident with measuring points (¼, ½, ¾).

7. Load the mast with 30 kg (66 lbs) of weight at the ½ distance on the mast. I used a looped rope with a carabineer so I could attach and unattached the rope securely and quickly.



8. Take your measurements at each of the measuring points (¼, ½, ¾) while the mast is under load and record them.

9. Remove the weight from the mast and repeat your measurements at each of the measuring points (¼, ½, ¾) and record them while the mast is at rest. I found taking the at rest measurements after the mast had been loaded to be more accurate than taken them before (the mast moves less following unloading than it does during loading).

10. Consider doing some mix-and-match testing switching different bases with tops (if the ferrules are compatible) to see the affect.

Step 4 – Review Your Results

Now it is time to take a look at your test results and consider how to apply them.

Here is how I applied my results:
• I shifted masts of the same specification (that had different results) in my quiver – the stiffer 430 was shifted to the larger sail (6.0) and the softer 430 was shifted to the smaller sail (5.2).
• Other masts were targeted for replacement.
• Verified changes with on-water ‘testing’ (this is the really fun part).

I hope this thread is of some use to you.

genius! was the stiffer 430 labelled as such or were they both supposed to be the same?
do older masts measure softer then when they were new?

looks like a good time, anything to keep from sailing out in the snow, that is nuts. now fold some laundry.

very cool and totally time consuming process and investigation, I am sure, wow, thanks for sharing!! There are a few threads on here that comment on this stuff, some with very good input....not sure how useful it all is tho

A couple of very superficial points as I cannot claim to have studied all you have provided but I did read some of the links.

Gaastra, Fiberspar (the longer masts) and Maui Sails masts are all very stiff in the tops (most often placed between 5 and 9). These masts are specifically made for the companies own Vapor (former Nitro and Neutron) and TR sails. The masts are not Constant Curve - in spite of the pretence - and they mostly only fit to the sails mentioned ***).

I can attest to the fact that Gaastra Ignition masts rig both Gaastra and KA's very well. I can also confirm that they rigged the Sailworks sails like crap. I can further enlighten that I was the one who pointed out the flaws in Unifiber's assignment of mast characteristics to the KA sails where they had it totally wrong (and also their comparison between Gaastra and Sailworks).....so their selector list reliablility is questionable. Mind you KA also shifted mast design somewhat in 2010, but not appreciably (Triana, the italian manufacturer..... who apparently also made the Gaastra masts....went bankrupt). They also seem to have too stiff of a top which promotes going to the smaller mast when possible.

As for the science, well, I will have to have some serious down time...maybe after my hip surgery to play with this stuff.....or maybe I will count rocks in a quarry instead for a thrill In the meantime I will strive to always purchase the masts that go with the sails...when you sell your sails, don't you also sell your masts? I would recommend this.

In addition and again rather over simplistic and superficially, if a mast feels too soft, I try to rig the sail on the mast size bigger.....even if it is the same manufacturer. You cannot always achieve this and it is a drag but trying to match another mast manufacturer without actually purchasing it...well, that's not really an option, is it? Ergo if your sail feels like crap even with the same manufacturer's recommended mast....guess what, I am switching brands. Having said this, there seems to always be a "dog" in a full quiver and one that rather excels I can only surmise that you cannot have the perfect match given extensions and floating turbans as well as having different rider shapes/weights that impact how the mast and sail behaves.

Which brings up a last, again perhaps highly unsophisticated point: rider body weight/shape must matter! It impacts what mast or sail brand will work for you better or not, perhaps this is not the all determining factor but nobody makes mention of this in their science, do they We all know that certain body shapes and weights allows riders to hold differently sized sails...and pumping and running fully powered affects sail shape and is governed by mast stiffness....when I need more power and less "light feel" I go to the stiffer mast, the larger size. When I want smooth wave riding, I go to the smaller. Same as I choose a powerwave (onshore, flat water) over a sideshore wavesail. I also have tried sufficient types of brands where I reasonably conclude some don't work for me.

I am waiting for the rider shape/weight/sailing style table that matches up with the sail manufacturer and as for aftermarket masts, they all lie anyways so I do like the ones that:

-don't break
-have nice finishing
-have innovation in their boom/ferrule and base areas to promote longevity
-are as light as possible
-come with a decent bag
-or say "Powerex" on them

I know, I'm a simpleton the science is lost on me

PS:

I placed the recess in the tip of the mast over the heavy gauge screw

I would try to avoid this point strain if you don't have a supporting tip insert you would be unhappy to crack the mast tip, perhaps a supported turban is better

downwind dave wrote:genius! was the stiffer 430 labelled as such or were they both supposed to be the same?
do older masts measure softer then when they were new?

looks like a good time, anything to keep from sailing out in the snow, that is nuts. now fold some laundry.

Both masts were labelled with identifcal generalized specifications (same IMCS and both 'constant curve'), but one was labelleled as a 'freeride' and other 'wave' - if there were manufacturing differences specified, they were not disclosed.

As discussed here there are variables in the manufacturing process seems difficult to control and some companies appear to do a better job of quality control/quaility assurance than others.

I know with my own testing I found significant variation in one brand and hardly any in another brand.

Kus:

Good discussion. Your comments are appreciated (as always).

KUS wrote:...In the meantime I will strive to always purchase the masts that go with the sails...when you sell your sails, don't you also sell your masts? I would recommend this.

In addition and again rather over simplistic and superficially, if a mast feels too soft, I try to rig the sail on the mast size bigger.....even if it is the same manufacturer. You cannot always achieve this and it is a drag but trying to match another mast manufacturer without actually purchasing it...well, that's not really an option, is it? Ergo if your sail feels like crap even with the same manufacturer's recommended mast....guess what, I am switching brands. Having said this, there seems to always be a "dog" in a full quiver and one that rather excels I can only surmise that you cannot have the perfect match given extensions and floating turbans as well as having different rider shapes/weights that impact how the mast and sail behaves.

Which brings up a last, again perhaps highly unsophisticated point: rider body weight/shape must matter! It impacts what mast or sail brand will work for you better or not, perhaps this is not the all determining factor but nobody makes mention of this in their science, do they We all know that certain body shapes and weights allows riders to hold differently sized sails...and pumping and running fully powered affects sail shape and is governed by mast stiffness....when I need more power and less "light feel" I go to the stiffer mast, the larger size. When I want smooth wave riding, I go to the smaller. Same as I choose a powerwave (onshore, flat water) over a sideshore wavesail. I also have tried sufficient types of brands where I reasonably conclude some don't work for me...

Yes I have in the end matched all of my sails/masts brands (now).

On your point on body weight - I totally agree! After using both recommended masts and softer 'optional' mast in each sail - I have gone with a mix of 'recommended' in the larger sails and the softer 'optional mast in the smaller sails.

Here is my current seven (7) sail, six (6) mast current (Ezzy) quiver (excluding formula gear which has been in hibernation for a while):

3.3 Ezzy Wave SE (2006) + Ezzy RDM 340 ~8.3% smaller
3.6 NP NR (1999) + NP SDM 370 ~8.3% smaller
4.0 Ezzy Wave SE (2005) + Ezzy RDM 340* ~10.0% smaller
4.5 Ezzy Wave SE (2005) + Ezzy RDM 370* ~11.1.% smaller
5.2 Ezzy Wave Panther (2009) + Ezzy RDM 400* ~13.3% smaller
6.0 Ezzy Wave Panther (2009) + Ezzy RDM 430** ~13.0% smaller
6.9 Ezzy Wave Panther III (2011) + Ezzy RDM 460 ~31.6 smaller (than my 9.8 formula sail)

* Using 'optional' softer mast in these sails.
** Using 'optional' softer top in this sail.

KUS wrote:...
PS:

I placed the recess in the tip of the mast over the heavy gauge screw

I would try to avoid this point strain if you don't have a supporting tip insert you would be unhappy to crack the mast tip, perhaps a supported turban is better

Good point. All of the masts I tested had a thick-walled plastic insert inside of the tip of the mast (which I would hope would have helped to distribute the point load), but supporting with a turban would likely be a better option.

KUS wrote:As for the science, well, I will have to have some serious down time...maybe after my hip surgery to play with this stuff.....or maybe I will count rocks in a quarry instead for a thrill ..

HEY! What's wrong with counting rocks in a quarry? Sound like fun to me! Well maybe just the first 66 lbs.