A friend of mine recently broke his tendon in big waves so I decided to check mine. Looks fine but I'm going to replace it anyway. Probably use the old tendon in an old base for the 2 times a year I go foiling. Or maybe I should just bin it?
if in doubt chuck it out 
I got cleaned up in big surf, heavy enough to bend the mast extension. The tendon which was almost new broke a couple of sessions later. So I replace every year or after a big crash, whichever comes first
I say change them no matter what discipline
I've had brand new spares just fall in half in storage - they just harden or something with age. Fair enough we see some pretty full on heat here but I say change annually
At the same time change ur goretex vent or the o-ring in a normal vent
Cheap insurance
now do I actually? Ummm 
I change tendons at the start of each season. Find I need to get a new uni about every 18-24 months as they get pretty flogged with the hours I put in in WA.
FYI since getting boards with Gortex valves about 2018-19 I've taken onboard what the doubters say. I've a spray bottle in my kit with fresh water in it, I blast in/around the valve recess regularly, not every sail but when I think about it or if the boards are headed into storage. Seems to be working a treat, get rid of the damaging salt+sand+grit and longevity is improved. My oldest Pyro is going into its 6th summer and I haven't seen any salt crystals of damnation to date.
Same, the Severne mast base (pretty sure most come out of the same factory) seems to get quite a bit of play overtime. It's the bolt that connects to the board and it can't be replaced.
I generally replace the tendon once and the next time the entire base, somewhere after 200-300 sessions. A bit of a shame as otherwise the base is still fine.
Recently started using one of the Chinook Two Bolt Tendon Quick Release mast bases which don't seem to have that issue. So far, I'm impressed. Replacing a tendon is also much easier on those. You know what I mean if you tried to replace a tendon on Severne mast base, oh boy!
If your tendon looks like the cracked one on the left, replace it otherwise be ready for a swim or damaging your board deck if you have to sail back with the one on the right.
Many people including myself have learnt it the hard way. Check your tendon regularly, replace periodically. You have to remove it in order to properly inspect it so as well just replace it.
General rule I run by is:
1. Change tendon after 1 season & assess the failsafe ropes.
2. Change foot after 2 seasons.
3. If it's a NP foot.....change it for a real one straight away.
AB.......
3 rules.
Chinook
chinook
chinook
the one piece machined stainless cups and pin (for Europin) being one bit is the go. The bolts are thick and only need one Allen key to disassemble.. Not WD40 and a wrench and a screwdriver and cursing. It's a pleasure to change the tendon and nothing else on it breaks or gets sloppy
Select to expand quoteMark _australia said..
3 rules.
Chinook
chinook
chinook
the one piece machined stainless cups and pin (for Europin) being one bit is the go. The bolts are thick and only need one Allen key to disassemble.. Not WD40 and a wrench and a screwdriver and cursing. It's a pleasure to change the tendon and nothing else on it breaks or gets sloppy
I switched from Chinook to Duotone (before Covid so since my experience is now > 6 years old, quality may have improved since then) after buying replacement chinook tendons on 3 separate occasions from 2 different retailers and each time having the tendon fail within between a few days and a few months of replacing. Haven't had a Duotone tendon fail on me yet, even though I have pushed replacement past 12 months. Thus I am now of the opinion that the material used in the Duotone tendons lasts longer than material used in the black chinook tendons.
I've stopped using tendons in waves, the Boge style is much better. It last longer and doesn't flip a small board on its side etc.
Tendons are good for slalom and Formula though, where one rarely puts the sail down. Storage also seems important for a long lifetime, dark and cold works best. I've kept spares in the dark but indoors, and these failed very quickly.
Volcano pad is toe & deck insurance . When the sail feels strange it's time to hobble back in for a 5min swappsie , no biggie .Chinook is the gold standard for sure .
Select to expand quoteMark _australia said..
3 rules.
Chinook
chinook
chinook
the one piece machined stainless cups and pin (for Europin) being one bit is the go. The bolts are thick and only need one Allen key to disassemble.. Not WD40 and a wrench and a screwdriver and cursing. It's a pleasure to change the tendon and nothing else on it breaks or gets sloppy
likewise for the streamlined bases
Machined stainless with the bottom cup pivoting thru a metal plate to reduce that slop you get in the plastic bases. Plus a two year warranty, handy if you survive the swim back in
Phil thru did have a bad batch lonnngggg ago so u scored that one I think. I refer to the actual base - just the ease of changing a tendon is a selling point. I've had bases where I simply couldn't change it with a lot of tools and a vice. Skinned knuckles etc.
Chinook comparison is how wonderfully nice to be able to easily change a tendon at the beach with only a Severne sails hex tool
Have used Chinook tendons - happy. Since 2-3 years on Point-7 tendons- very happy, robust and light, never failed, never thinking of changing, only rinsing with fresh water after sessions- thanks for reminding that tendons after all degrade. Another brand making reliable mast bases and tendons is unifiber imho.
I go with inspection. Bend them and see how bad they are, looking right around the pin holes. When it starts cracking it'll look like it's almost coming off.
It helps to use shims and get the tendon really tight in the base. That way there's minimal torque on the pins.
I gave up on streamlined, they seem to not like humidity!?!!?
Chinook last a while (1-2 years) and Bic seem to be working very well in the tropics.
It may vary per climate!
Decided to change my backup tendon too. I think it's only been used once or twice but it's from around covid (or even pre-covid maybe???) so why take a chance even though it still looks good. Doesn't feel at all brittle despite living in a tropical climate.
Well done on getting it apart. I couldn't get the screws out of mine. Any tips?
Select to expand quotelao shi said..
Well done on getting it apart. I couldn't get the screws out of mine. Any tips?
I didn't do anything special. I had 2 torx screwdrivers, one for each side.
What else apart from the tendon breaks on a mast foot? I've got NPs and have only ever broken the tendon. I have seen the pin on a Windsurfter LT break from rust though.
It may be that certain tendons prefer certain climate. Also you want the tendon to fit very tightly in its base, use shims if needed.
I've tried streamlined, bic, chinook and North.
Worst streamlined 3-6 months, crumble apart in high humidity.
Second north, fails no warning.
Third Chinook 1-2 years.
Winner curiously Bic, changed it once in 2 years. Since then not changing it. Got 2 in 2022.
~150 sessions a year, all waves.
