Extensions

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aeroegnr said..
Yeah if it's bending it's not fatigue. The back and forth loading with the holes on the starboard/port side will eventually fatigue with some stress concentrations of the holes vs. way less loading in the fore/aft direction.

But if some are bending vs. others I wonder if it's just thicker sidewall on some rdm extensions vs. the rest. I don't have a chinook extension to measure with my calipers but I wonder if either there's an alloy difference between that and others or thickness as well. I will say I do like their metallic looking single pin bases, as the safety lines and overall build are much better than the severne and aerons I've used, so I got a couple of those instead. Maybe the newer chinook not only has holes in the fore/aft direction but also have a different alloy/thicker sidewall?

We may also just be running into a limitation of the RDM design and aluminum. You get diminishing returns on thickness vs. diameter on stiffness/strength and it may just be the cost of doing business.

Indeed, extensions do not really suffer from fatigue, neither do good masts really. A well made mast that is 10 years old is just as good as a brand new one. The moving parts of extensions do suffer from wear, depending on the materials.This mast base of Chinook is the only one I trust, sell and use in rental. Nowadays the safety rope is Dyneema as well. I do not replace the tendons untill I see a crack and that takes 2-3 years. I dont know of any other that is of the same quality.

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sheddweller said..

Gestalt said..
I reckon you are onto it aero. The chinook is prob weaker aluminium.

both severne and simmer use heavier grade alloys in their hd models. It's impossible to know but I don't see hd on the chinook site.

So are we adding the severne extensions to the "stronger" category? Does anyone have direct experience of chunky powerful wave use and 30cm extension with bigger than 4.7 sails?

This is a 5.2:


And this a 5.0:

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sheddweller said..
Yes I believe you.
I want to know which other extensions are also strong.

I think the Chinook will also go a long way with the holes turned. That is the biggest difference. Some of the first beefed up extensions I did some 12 years ago still broke because the first series did not have the holes turned yet. I had those made by MaverX masts from their ferrule material, which are fully carbon prepreg plus a thicker wall and thicker diameter. They were definately stronger but a few still broke. Then I turned the holes and since then not one broke and could even reduce the diameter a little. Now we have no fear using 28 or 30cm extension. With regular extensions we always combined different mast pieces to make steps of 15cm in length. So you never needed to extend more than 15-18cm. Still they broke loads. We have lighter winds here so bigger sails combined with good sized waves makes that the sail, mast and extension suffers more than in most places. Ezzy told me years ago that we broke more masts than they did on Maui. And Ezzy masts are amongst the strongest. They were always good with guarantee as well, unlike extension suppliers.

simmer have both standard and HD in alu and carbon so 4 in total. if yours was a gold colour then it was HD.

I sail mostly in strong winds 30-35 knots and above. I use my ext. to the max - 3.7 sail rigged on 310 mast and 42 ext. ( my most extreme settings). I always prefer softer and shorter masts- a matter of taste. But I agree- this might be risky if you use bigger sizes and sail in more than 3 m waves.

I concur there is a rich field for discussing the optimal angular rotation upto 0,001 degree exactitude, but not today

However, following thru that the 90,000 degree rotated hole array is the way to go...why isn't the biggest&baddest hole on the block (locking pin button)not following suit? As well as the metal roller base "cup" sidewalls shape? Are they allowed deviancy for being at the costly contraptions extremity?

Another question i have: what is the insert overlap in mm of the metal cup base & the carbon tube?
As i just bought one of these non-rotated similars from a german brand, Lidl- or Galdisails or something..after Chinook had me swim for ages.

Also, alu can snap cleaner then carbon (Chinook), completely ignoring any "bend phase"...mind. Carbon (Chinook) also snaps clean. Carbon was a wayyyy longer&colder swim then alu, but that may be too contextual. Generally like Chinook.

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Gestalt said..

aeroegnr said..
I was curious and there are "stainless steel" extensions out there...but it's only the pin bottom. They still use an AL tube.

www.unifiber.net/windsurf-gear/mast-extensions/rdm-aluminium/rdm-elite-v2-stainless-steel-mast-extension-609a521724c4f931a21f0000

Also wondering if you don't bend the extension in extreme loading, if you end up breaking something else that otherwise gets deflected...

I made my own extensions from stainless steel years ago but they were way too heavy

Ahh I figured that would likely be the reason. Cool that you tried that.

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sheddweller said..

aeroegnr said..


We may also just be running into a limitation of the RDM design and aluminum. You get diminishing returns on thickness vs. diameter on stiffness/strength and it may just be the cost of doing business.

This is what i suspect and tbh is my experience over the years but before sacking it off (again) and changing things as gestalt says- i want to be sure i cant just buy one that works

If i were breaking HD extensions i would modify a carbon extension by epoxy gluing another carbon tube on the inside. adding thickness and covering up the holes would provide a lot of strength. 2mm thick or so.

not sure what the ID of an sdm extension is. might need to make up the correct diameter with 2 tubes.

i have used this method to fix broken carbon booms and it ends up being stronger than the original boom.

I wonder why sail brands don't manufacture fixed length carbon extension. One size per sail, sold with the sail.
That way, I believe, you could reduce significally the weight of the extension (no extra length, no added thickness to withstand the holes). And it's also very simple when it comes to rigging...

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Nicko29 said..
I wonder why sail brands don't manufacture fixed length carbon extension. One size per sail, sold with the sail.
That way, I believe, you could reduce significally the weight of the extension (no extra length, no added thickness to withstand the holes). And it's also very simple when it comes to rigging...

Yes and no. What would happen if you use a mast of another brand, supplied extension might not work...

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philn said..

Gestalt said..
simmer have both standard and HD in alu and carbon so 4 in total. if yours was a gold colour then it was HD.

HD. Now used for sails needing extension between 2 and 8 cm.

There you go! Good you recycled it.

The carbon ones normally snap when the gear ends up in the washing machine and the board hits the mast/extension as a result of that..... Following a swim to the beach with the gear. The alu ones probably get bent in the same way, but I only find out after when I am safely on the beach. Never broke an alu one though.

The carbon ones always went within a couple of months...

never body impact, always wave/rinse cycle...think shear force also plays its part
again alu breaks clean also, no bend deformation visible afterwards.

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Taavi said..

Doggerland said..
never body impact, always wave/rinse cycle...think shear force also plays its part
again alu breaks clean also, no bend deformation visible afterwards.

But if the extensions would be made super strong, then what would break next? Rip the mast track out of the board right?

haha, sure thing...the Chinook track replacement is going strong.
besides the joys of nagging&ranting about gear...February Northsea swimming (broke my extension this time) is something to cherish, rapid mild hypothermia has wonderful (cognitive) effects i was reminded again.

That bend is from the rinse cycle