There are at least 3 or 4 choices of brands that all look like they fit the Chinook bases. Which ones do you use and why? Are there any ones to avoid?
I'm new to tendon bases, having always preferred BOGE hourglass joints, but I have been given some Chinook bases that need new tendons. 
(Converting to Europin.)
Not all tendons are the same. Some have 4mm holes and others have 5mm holes for the bolts.
PS , don't get the ones on eBay.
The Severne tendons are great. Clearish so you can easily spot any cracks or hairline splits appearing. They last really well too.
Maybe a boring answer, but once a year I replace mine with the original Chinook tendons. Have not had one fail on me yet.
I use Boges "hourglas" joints. Use it a couple of seasons, never failed
The internets recommend it for wave/bump'n'jump.
I do always what the internets says ; )
It seems that the tendons are less dampening and more direct, but never tried it.
Looking for a baseplate with removable joint/tendon because it will fit in the boardbag with the baseplate...
I had a Chinook tendon fail due to a huge casting void. Since then have gone clear (NS or other). Can't hide a void when they're clear, easy to spot wear, and seem to last longer. It's very easy to shim 4mm to 5mm using the right size copper or stainless tubing.
I use chinook and Severne bases (clear tendon), change tendons every couple of years, don't like the 2 bolt bases because you can't get the base back far enough in the track
Severne base and its original tendon for Formula and slalom.
Hourglass rubber style for waves and small, narrow, speed boards.
The tendon version doesn't last long in waves for me (too much bending I guess, plus the water gets really cold around here), it also flips the board over on its side in water-starts. For Formula and slalom the sail is very rarely put down and the tendon (severne) will last +10 years, in my experience.
Been using the clear severne one in those same chinnook bases. Lots of sailing Still going strong around 5 years.
If it fails there's a rope to stop full separation and get back in and I've always got another spare assembly in my box.
I have been using Streamlined tan-colored tendons for many years. It is easy to spot cracks so you can replace before failure. I use them in Chinook hardware. This requires me to shave 1mm off each end because they are 1 mm too long. Bolt holes and diameters are the same as for Chinook.
I tried Chinook black replacement tendons but stopped using them black when I had a rash of failures. Other people have had good luck with them. I probably got a bad batch.
I use Chinook in my Chinook and havent had a failure yet. I replace them every 12 months or 100 sessions.
I did have one which maybe wasnt Chinook, as I had to add a small shim in the base so the holes lined up. If you mix brands you might have to do this.
I think it depends on your climate.
For tropical humid the Bic has been fantastic 2 years+?
Chinook isn't bad at about a year.
Streamlined 3-6 months, their material falls apart, same as boom bushings.
Always try to shim your tendon for a tight fit.
I use the streamlined (old is better) base with Bic tendon.
Chinook, replaced annually because you cannot fully inspect without disassembly.
I've had multiple breakages with streamlined, which can quickly become brittle and break at the holes without warning. Before i switched to chinook universals i used to use chinook tendons in my streamlined universals.
Chinook, replaced annually because you cannot fully inspect without disassembly.
I've had multiple breakages with streamlined, which can quickly become brittle and break at the holes without warning. Before i switched to chinook universals i used to use chinook tendons in my streamlined universals.
Chinook, replaced annually because you cannot fully inspect without disassembly.
I've had multiple breakages with streamlined, which can quickly become brittle and break at the holes without warning. Before i switched to chinook universals i used to use chinook tendons in my streamlined universals.
Chinook, replaced annually because you cannot fully inspect without disassembly.
I've had multiple breakages with streamlined, which can quickly become brittle and break at the holes without warning. Before i switched to chinook universals i used to use chinook tendons in my streamlined universals.
Chinook, replaced annually because you cannot fully inspect without disassembly.
I've had multiple breakages with streamlined, which can quickly become brittle and break at the holes without warning. Before i switched to chinook universals i used to use chinook tendons in my streamlined universals.
I have just replaced my chinook tendons, i do it minimum once every 2 years, thats about 150 sailing days in wa. No cracks just slight distortion of holes. What i did notice is the new ones were dated and less than 6 months old which has got to be important. I always check tyre manufacture dates for the campervan before buying them. The forces on a uj are huge, this year I had an
alu mast extension peel open in a big wave crash.
Play safe.....??
Tendions:
- a monoblock of rubber with two small holes in that rubber
- those holes are hidden from view
- access to view those holes, depends on the quality of your rusting bolts and whether you can undo them
- the rubber is not reinforced with any composite material
- the holes are elongation-stretched, with the highest forces being applied to the point of least strength
- used in an environment where where a key material of sand, is an abrasive
- the abrasive only needs to create a small nick in the elongated hole, for the least-strength point to continue to tear
- even if you inspect the bolts, they tend to self-undo
What's not to like !
.. ahh but there's more -> since most of the wear is hidden from view, you cant inspect-at-every-session... unbeknownst to you, the tendon has already started to tear. You go out on the water, since the material is already compromised, it takes significantly less effort to continue to tear. It then decides to completely shear. The remaining stub punctures a hole in your board.
Most of those issues _do not_ apply to other shapes/designs, or they are mitigated to a great extent due to being able to simply inspect it at every session.
Its a poor design. Whomever came up with it, didn't really advance the concept of the universal-joint.
Boges:
- the hourglass shape allows full inspection of the narrowest point
- depending on your model, you are likely to be able to see both ends allowing visual inspections
- the holes in the rubber dont proceed through the material
- the fatest point of the material is the location for the joint, this allows for bigger holes, so less stress on weakest point.
- due to their design, webbing (not string) can be used as the backup.
A per "The Board Lady" there is a grading of material to match the densities, when going from bulk-rubber, the glues, the metal connections.
I cannot envisage a better design. Even the webbing somewhat eliminates the hole-punching issue.
Select to expand quotemathew said..
Boges:
- the hourglass shape allows full inspection of the narrowest point
- depending on your model, you are likely to be able to see both ends allowing visual inspections
- the holes in the rubber dont proceed through the material
- the fatest point of the material is the location for the joint, this allows for bigger holes, so less stress on weakest point.
- due to their design, webbing (not string) can be used as the backup.
A per "The Board Lady" there is a grading of material to match the densities, when going from bulk-rubber, the glues, the metal connections.
I cannot envisage a better design. Even the webbing somewhat eliminates the hole-punching issue.
Matt, you forgot to add this to both lists: Sh~t Chinese manufacturing quality control 
I stopped using Boges when Mark Australia made an excellent point once with a photo some time back. What I do like about tendon models is that I can fully strip them down and inspect every 6 months. But yes, you raise very good points, and totally agree with you.
Nb/ Only sail out as far as you're prepared to swim back. I give this advice to everybody, notably for ocean spots. I've had to call the Police a few times over the years for sailors that don't inspect their bases. SAPOL give you a free towel when you get rescued.
I just replace my tendon every year. At Christmas time , so I don't forget . Problem solved. It doesn't matter if you tendon or bogie .Compared to all the other costs involved with windsurfing , an overpriced bit of rubber once a year is good safety value. Never check it and never broke one. It seems silly to me trying to get maximum use out of a very important $30 item . One less thing.
If you use decent emergency cord on your base you wont have a separation from a broken tendon. (dynema)
Thanks to this thread I'm reminded mine is due for a change. I'll get it out so I don't forget.
You cant have a thread on anything to do with UJs without the tendon v boge type debate
This started as a what tendon, but people say use boge. Why?
I say both types can fail, so buy the one most applicable to your sailing. Tendon for slalom/blasting/flatwater, boge for wave/b&j.
Replace tendons regularly, 12-18 months seems normal, and replace boge UJs, the complete unit, maybe every 2-3 years.
I've broken 1 tendon, the short safety cord meant the end rested on the deckplate when sailing back in. No damage to the board. I've had 2 boge failures, the pin broke both times rendering the safety webbing useless and the board separated from rig.
You cant see corrosion inside the boge either. Ive rescued 2 people where the inside of the boge failed because the bottom pin corroded, unseen. Because the pin failed, again the webbing was useless and rigs separated from boards. Both were sailors who hadnt sailed for a while and the corrosion split the plastic inside the boge.
Also note, the cups of a tendon design are difference fit (at least the brands I buy). This is one of my checks. When the bases wear out over time, the tendons become loose in these cups, and what Matt mentioned above about stress points become true - Time to turf it (and not surf it) 
Most of the hourglass failures I have seen have the threaded insert pulled out of the end. Inspection of ggge narrow part won't help with this failure mechanism.
When sailing back with a broken tendon, the safety line may save your rig, but the deck of your bokard where the broken tendon is banging around will be damaged and perhaps destroyed.
Whatever you use, change it annually !
Funny I rescued 2 people with boges as well! Well 1 technically, the other one was just myself.
Super easy to inspect tendons just bend the base ! No need for tools.
Sorry to repeat myself, shim the tendons so they fit tightly. Not sure you can fit a different tendon in the Chinook because the holes are too close to the edge. The other ones yes.
Regarding Boge (Rubber) joint vs tendon. A week ago I sold my board that had a rubber joint from 90s (F2 Bullet), because I got a newer used set. The rubber joint was still in perfect shape after 20+ years. Now I regret of selling. The tendon joint in my new board is a complete **** and requires replacement. I have to spend as much as I got for selling the old set to get similar quality joint. And the tendon seems to be much stiffer than the rubber UJ. The only reason for tendon to exist is that it is cheaper than all other joints and allows higher profit margin. My choice would be either mechanical or boge (rubber) UJ.PS I am still impressed with the quality of F2 from 90s, I had two boards the Bullet and Comet, both with rubber UJ, and never had a single problem. The boards themselves could be dropped on a concrete and survived. My newer Bic from 2012 cracked after a slight impact.
