I was led to believe that North masts were generally constant curve which is why I have North, Loft and Naish masts to suit my constant curve sails Loft, KA and North.
I am current using a Naish 430 on a North 6.2 E type and it rigs really well.
The older NP 4.9 that Paddles mentioned was a complete pain in the ar$e in an NP RS6 7.8 I have. NP and NP , I thought it should all be sweet, but I was seriously ready to bin the sail. Bought a more modern RSX 4.9 and all of a sudden the sail works perfectly.
I have gotten away with north masts in NP sails if they are 2 cam or less and vice versa. But with race sails and 4 or more cams the correct mast seems to be the only option.
Select to expand quoteMark _australia said..forceten said..
for the poster with the theory that the longer NP masts become more constant curv, as a very general not rule but trend,
No not a general rule, it is fact. Robert Stroj says so and I think he would know.
You have left off the remainder of my post, instead cut and disected , you ignored the size .
Select to expand quoteOrange Whip said..
The sail I was looking at was a 2013 S-Type 8.4m. It is 2,325.8 kms from me to the shop that has it on consignment, so not an option to try it. Goal is to have a sail that sets really well on the mast, if not perfectly. 
this sail has cams
the 490 in this case is a better mast.
what I don't like is the cams on this as a key ingredient. My 2¥ are pass, and look for a user friendly sail.
should you purchase the S, you will need to experiment with settings, not the end of time, I really feel you will lose performance potential, but this could be within acceptable parameters to you, not me.
That mast is probably at least 15 years old. Neil Pryde can't tell you much about their own old masts (somewhat annoying).
I checked out the website, mytrims:
mytrims.com/masts/data.asp?ID=118
"Neil Pryde RacePro
Specifications
Name: RacePro
Season:2000
Curveflex:top
Length:490 cm
Diameter: cm
Weight: kg
Carbon: 95 %
Stiffness: IMCS29 MCS
Additional info: Specific to Neil Pryde RX sails. Top too flexible for most designs"
Please note your call as to whether to run the risk with your proposed purchase, but the preponderance of opinion, as I read this forum is suggesting not run the risk with the mast. Masts are not that expensive these days , provided you buy them secondhand, so if you are wrong just buy a newer matching mast (secondhand there are quite a few around).
Of course if your mast does not work with the North S type it is probably not going to work with anything other than a NP RX sail, unless the "mytrims" source, above, is wrong which is entirely possible. If it does work on other NP sails then perhaps you should be looking at them.
Select to expand quoteforceten said..
Mark _australia said..
forceten said..
for the poster with the theory that the longer NP masts become more constant curv, as a very general not rule but trend,
No not a general rule, it is fact. Robert Stroj says so and I think he would know.
You have left off the remainder of my post, instead cut and disected , you ignored the size .
No, the longer ones are more constant curve and that is the end of the story.
"a very general not rule but trend" is a little confusing and if experienced folk need to clarify that, a noob might struggle with it...
Then, this thread pertains to whether a very old NP SDM will work with a modern North sail.
So talk of whether NP is now constant curve in the longer (race) masts is not so relevant to the North. So the original question is not answered by your post. Then to throw some doubt on NP curves (as you did) may confuse others.
Thus I thought I'd make a simple statement to avoid confusion.
Now reading it for the 3rd time I think you may mean the longer ones are more CC, but 460 is kinda the length where it changes, so they may or may not be CC?
Mark
The 2nd post in this thread starts the constant curve discussion.
To explain my NP mast generalization , NP are soft top. That is a generalization, in longer sizes they become more constant curve, since I have some data to support this, I feel the statement is correct(Peterson dk. ) the cc becomes more pronounced in sizes longer than 460.
Select to expand quoteMark _australia said..
It is interesting I recently asked the same question about whether an old NP SDM has the same bend curve as the newer ones. Nobody really knew for sure, but seems it is probably actually constant curve.
But if we ask about an old NP mast with a North sail then everyone seems to know for sure? 
Given I have a NP sail that sets funny on a NP mast that is only a couple of years older then yeah things change. So unless the North sail is sooo cheap or free and you get to test it plenty AND see it rigged on the correct mast for reference, then I'd give it a miss.
Cos anything, even the same brand on a mast that is 15 years older than the sail, well that is a gamble.
This was your posting right?
That even those with years on of experience don't know?
