Just bent the 3rd Chinook aluminium rdm extension when extended to 30cm ( 400 luff length 370+30 on a 4.7)
Had enough of that now- what brands dont break/bend at that length ?

Have used the regular severne extension quite often at 28/32cm and the cyclops as well for either freeks or foil glides. No breaks of those, but some issues with the mast base/extension button releasing too early (cyclops). There's another thread here somewhere on that issue.

Had loads like that. Carbon, aluminium from different top brands. Even had an AL360 Ergal extension that weighed 740gr bend at 12 cm extention after 3 weeks. No guarantee either. But when examining aluminium extensions, you can see it is always on the holes where it bends. One hole is squashed and the other side stretched. Indicating that the forces bending or breaking extentions is side ways. Off course from the front a wave does not have any area to hit the sail. So we did some calculations how much difference it makes when you turn the extension 90 degrees. Below is the images of such simulations. The applied force and length is the same but when the force is applied at 90 degrees, the force inside the extension is nearly half: 1,4943 N_m2 vs 0,7970 N_m2. So just by turning the extension 90 degrees, it is nearly twice as strong. I told some of these brands this because I had no intention to get into extentions but they did not do anything with it. So I did it myself as it was too big a problem. Since then (2012) not one broken. Off course we now will get the anti angle gestapo on here again saying this is BS because their brand does not do this. But maybe it can help some people.

Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

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aeroegnr said..
Have used the regular severne extension quite often at 28/32cm and the cyclops as well for either freeks or foil glides. No breaks of those, but some issues with the mast base/extension button releasing too early (cyclops). There's another thread here somewhere on that issue.

Are you wave sailing with them?
I have zero issues freeriding, the problem only occurs in chunky waves.

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sheddweller said..

aeroegnr said..
Have used the regular severne extension quite often at 28/32cm and the cyclops as well for either freeks or foil glides. No breaks of those, but some issues with the mast base/extension button releasing too early (cyclops). There's another thread here somewhere on that issue.

Are you wave sailing with them?
I have zero issues freeriding, the problem only occurs in chunky waves.

Not in waves as much as I would like. So, yeah not seeing the same conditions as you.

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sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

Check the new Chinook... they have turned the holes 90deg to the Old... been that way for 2 years...

chinooksailing.com/collections/euro-reduced-diameter/products/carbon-extension-euro-pin-ex-rdm-medium-32cm

Yeah that's why I like using a tip extension instead.
I do use a streamlined at 28cm no problem.

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gorgesailor said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

Check the new Chinook... they have turned the holes 90deg to the Old... been that way for 2 years...

chinooksailing.com/collections/euro-reduced-diameter/products/carbon-extension-euro-pin-ex-rdm-medium-32cm

Ah, good. So they finally listened 10 years later. But better late than never.

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sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage. ?feature=shared

With my 4.5 (403cm luff) regularly use 32-34cm on a 36cm carbon wave grenade + 370 mast, probably 4-5yrs old. Has had the bjesus belted out of it wavesailing and still going. Also have the newer cyclops, seems good. Would simply never go back to ali stuff.

Until carbon snaps
But ali just bends and you still get home. Not going to carbon extensions again....
Never been able to damage a severne ali RDM extension anyway and like 1/3 the price

Snapped a few carbon extensions (various brands) and started to see a pattern there, went back to aluminium ones, some bended but always got back safely on the beach. I now have a Chinook one with the 'Bouke' orientation of the holes and it has stayed in one piece and straight for 2 seasons so far. I guess Bouke has been on to something there!

Never used the extension over 28 cm.

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Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

Select to expand quote

Gestalt said..

Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

269.9 degrees, clockwise.

Here is the test data for anticlockwise

I am on rdm carbon pro ext from point- 7, after abusing lots of chinooks,gaastras, severnes. The smart thing is that the pulley lines are perfectly in line with the sail pulleys, thus minimizing torsional forces whatsoever . No other manufacturer does that to my knowledge. No need to search for the perfect drill.. there are still some smart people on this planet. Cheers!

Select to expand quote

Gestalt said..

Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

Don't be a ****, no need for it.

Select to expand quote

sprayblaze said..
I am on rdm carbon pro ext from point- 7, after abusing lots of chinooks,gaastras, severnes. The smart thing is that the pulley lines are perfectly in line with the sail pulleys, thus minimizing torsional forces whatsoever . No other manufacturer does that to my knowledge. No need to search for the perfect drill.. there are still some smart people on this planet. Cheers!

Yea, I really don't like those small bases. I had streamlined ones for a while and every time I rigged it up it annoyed me. Much prefer the larger area of the Chinook style to put my foot on.
If they don't break I may have to try again.
Do you sail in chunky powerful waves? Are they strong enough for that?

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Mark _australia said..
Until carbon snaps
But ali just bends and you still get home. Not going to carbon extensions again....
Never been able to damage a severne ali RDM extension anyway and like 1/3 the price

Yes and no. Indeed, if you have to choose between a carbon extension and an alu that can both fail, the safest choice is the alu. However Alu is weaker. There is a reason why we dont use alu masts anymore. Another good thing with alu is that you can see what happened, which way the extension bent. With carbon impossible. And I have had an Alu snap, it is the one in the bottom of the picture. It is very rare but it can still happen. And this was only a small selection of the extensions I had in broken. Extensions nearly always tend to fail in waves, which is not too bad because waves are usually close to shore. But a broken extension can cause more damages to the board or sail when getting washed.
And another important issue is how secure the connection with the mast base is. This is a difficult one as there are various ways it can fail and some cant simply be calculated. With some mast bases the screwed on pin can shear off, with the US cups, the nut can pull through the plastic when a wave hits the board, others can release with a combination of a pulling and twisting force. Wear can also play a part.

Select to expand quote

sheddweller said..

Gestalt said..

Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

Don't be a ****, no need for it.

If you think he's above board then buy his extension and enjoy it.

What a surprise he has a bunch of photos of flogged out aluminium extensions and a graph that says a tube with holes in it is stronger when the force is against the side with no holes. No **** Sherlock.

Lets not even question why he's comparing aluminium to carbon or why if he has never had a broken extension he's only offering a 2 year warranty.

anyways, this idea that waves, and the resultant forces only hit at 90 degress to the sail i just don't buy.

lets test that theory. Turns out sails get smashed from the side, the front, behind, the top.
?si=mxjCyz_LvaAe41rb

so if there is a magic angle why not 42.365 degrees

Select to expand quote

Gestalt said..

sheddweller said..

Gestalt said..

Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

Don't be a ****, no need for it.

If you think he's above board then buy his extension and enjoy it.

What a surprise he has a bunch of photos of flogged out aluminium extensions and a graph that says a tube with holes in it is stronger when the force is against the side with no holes. No **** Sherlock.

Lets not even question why he's comparing aluminium to carbon or why if he has never had a broken extension he's only offering a 2 year warranty.

anyways, this idea that waves, and the resultant forces only hit at 90 degress to the sail i just don't buy.

lets test that theory. Turns out sails get smashed from the side, the front, behind, the top.

?si=mxjCyz_LvaAe41rb

so if there is a magic angle why not 42.365 degrees

You ok hun? bad day?


The forces dont really hit, you should think of it more as the loads passing through the rig. Empirically all my extensiosn at 30 cm bent sideways, and this is also true of all the other ones i have seen over the years. , i have never seen one bend fore and aft, so whether you buy it or not, it seems to be the failure mode is predominantly sideways. You are arguing( badly)against observable fact- bit of a fools errand that.

Given that, it makes sense that we need to strengthen the sidewalls I have access to fem modelling, i could make some more pretty pictures for you, but really- booke ( or whoever ) has already done it, and the conclusions look logical.

The bottom line in reality is that RDM masts are great- except, when they were designed noone really thought too much about the extensions , which are just too narrow diameter even with ridiculous thick walls. What about an extension that slides over the RDM instead of inside, i think it could work if it was just for the longer lengths- say 24-34 cm then a normal internal for sub 24cm. hmm might try that.

Interesting video, do you know any of the designers of the kit being used in it? I wonder what they would say?

Im great. Thx for asking.

The weak point of the extension is where the holes are so that's where they fail. It's that simple. It has nothing to do with hole orientation because we can't control the direction of the force on the system during a crash.. Even if we could, there are also torsional forces and orientation of holes has almost no impact on torsional forces.

the only force we can control is downhaul and not surprisingly orientating the holes at 90 degrees to downhaul forces makes sense.

What does have an impact is tube dia, wall thickness, smaller holes, less holes etc.

To be a little more abstract, what if it's actually the board orientation or the clew position or fatigue that caused the breakages above or even a result of torsion. How would we know.,

boukes ideas are always one dimensional and come with evidence that begins with an unproven assumption and ends by magically validating his thoughts. I guess why it's called witchcraft.

Select to expand quote

sheddweller said..

Gestalt said..

sheddweller said..

Gestalt said..

Bouke-Witchcraft said..

sheddweller said..
Do you still do them with the Chinook base? I looked at your website and your extension base pulley thing is of the style I hate with a passion( too small a surface area for rigging, much prefer the larger Chinook style).

You do have me thinking. Maybe I will buy another Chinook , drive the retaining pin out, drill a new one at 90 degrees and see how quick it bends.

No I stopped with the Chinook base after 2 years as the tube only inserts about 12mm into the base and that became the weak spot. Only happened twice but enough to chose one where the tube continues all I the way. I use a tube with a bigger diameter with less play in the mast so I had to sand the end slimmer to make it fit in the base, which was a PITA.Plus the stainless steel split collar is better, stronger. It does not protrude out of the mast so the sail does not get caught when releasing the downhaul and above all does not make dents in the deck when you have to set it right there where it fully hits the deck with a lot of leverage.

?feature=shared

I reckon you should rotate the holes 90.01356784 degrees. that would be even stronger.

Don't be a ****, no need for it.

If you think he's above board then buy his extension and enjoy it.

What a surprise he has a bunch of photos of flogged out aluminium extensions and a graph that says a tube with holes in it is stronger when the force is against the side with no holes. No **** Sherlock.

Lets not even question why he's comparing aluminium to carbon or why if he has never had a broken extension he's only offering a 2 year warranty.

anyways, this idea that waves, and the resultant forces only hit at 90 degress to the sail i just don't buy.

lets test that theory. Turns out sails get smashed from the side, the front, behind, the top.

?si=mxjCyz_LvaAe41rb

so if there is a magic angle why not 42.365 degrees

You ok hun? bad day?


The forces dont really hit, you should think of it more as the loads passing through the rig. Empirically all my extensiosn at 30 cm bent sideways, and this is also true of all the other ones i have seen over the years. , i have never seen one bend fore and aft, so whether you buy it or not, it seems to be the failure mode is predominantly sideways. You are arguing( badly)against observable fact- bit of a fools errand that.

Given that, it makes sense that we need to strengthen the sidewalls I have access to fem modelling, i could make some more pretty pictures for you, but really- booke ( or whoever ) has already done it, and the conclusions look logical.

The bottom line in reality is that RDM masts are great- except, when they were designed noone really thought too much about the extensions , which are just too narrow diameter even with ridiculous thick walls. What about an extension that slides over the RDM instead of inside, i think it could work if it was just for the longer lengths- say 24-34 cm then a normal internal for sub 24cm. hmm might try that.

Interesting video, do you know any of the designers of the kit being used in it? I wonder what they would say?

Perhaps some people should read the forums guidelines again. I bet he would never say those things to my face. Yes, we have high tech prepreg full carbon masts which are about as good as you can possibly make them (the good brands) and then you have to put a thinner tube in the bottom with holes in it. That is bound to be the weak spot. However, the forces on a mast become smaller towards the ends and the forces of a wave in a sail are always sideways. If a wave hits from the front or back, it has far less surface to attack. So with these 2 factors, it is still possible to make it strong enough. Many of the carbon extensions I have seen broken are not full carbon and have a considerable amount of glass fibre in them. Many also have diameter of 31 to 32mm, which gives a considerable amount of play in the mast, which leads to point loads on both mast and extension and makes them weaker. Most or all of the best masts have an inner diameter of 33.2mm (established in the 80s by Powerex and No Limitz, who were the first to come with RDM masts) and I designed my extensions for that diameter with 32.5mm. I do not remember the exact calculation for tubes but in general the strength goes up with the 3rd exponent of the thickness. So from 31 to 32.5mm makes it 15% stronger. But some of the (chinese made?) masts have a thinner diameter and my extensions dont fit.
When RDM masts first came out, it came with a kit to modify normal SDM extensions so you could put the mast inside. It had a plastic bung for the bottom so the mast could stand on the pin and top cap for the extenstion with a hole in it. That indeed never broke but was a PITA downhauling. It also came with a piece of thick hose to fit the boom. At the time I designed my sails to work without extension: a 4.2 on a 385, the 4.6 on 4m, 5.0 on 415, 5.4 on 430 and 5.8 on 445. This was 1997:

And look, its a thruster (still without toe-in;))

Honestly, I would tell you to your face

Select to expand quote

Gestalt said..
Im great. Thx for asking.

The weak point of the extension is where the holes are so that's where they fail. It's that simple. It has nothing to do with hole orientation because we can't control the direction of the force on the system during a crash.. Even if we could, there are also torsional forces and orientation of holes has almost no impact on torsional forces.

the only force we can control is downhaul and not surprisingly orientating the holes at 90 degrees to downhaul forces makes sense.

What does have an impact is tube dia, wall thickness, smaller holes, less holes etc.

To be a little more abstract, what if it's actually the board orientation or the clew position or fatigue that caused the breakages above or even a result of torsion. How would we know.,

boukes ideas are always one dimensional and come with evidence that begins with an unproven assumption and ends by magically validating his thoughts. I guess why it's called witchcraft.

It's not fatigue, 2 of the latest Chinook bent ones had been in my shed for a while so old style but new. Less than 10 sessions for one and the 3rd session for the latest one to bend.

tbh you aren't getting your head around this, it seems to be a bit complex for your level of understanding.

What I really want is a list of extensions that don't bend or break when extended to 32 cm and used/crashed in powerful chunky waves.

Candidates so far-
Witchcraft.
Possibly new Chinook.
Others have been mentioned but I'm not sure if the recommendations were for chunky wave crashes?

Grateful for any more real world feedback.

Select to expand quote

sheddweller said..

Gestalt said..
Im great. Thx for asking.

The weak point of the extension is where the holes are so that's where they fail. It's that simple. It has nothing to do with hole orientation because we can't control the direction of the force on the system during a crash.. Even if we could, there are also torsional forces and orientation of holes has almost no impact on torsional forces.

the only force we can control is downhaul and not surprisingly orientating the holes at 90 degrees to downhaul forces makes sense.

What does have an impact is tube dia, wall thickness, smaller holes, less holes etc.

To be a little more abstract, what if it's actually the board orientation or the clew position or fatigue that caused the breakages above or even a result of torsion. How would we know.,

boukes ideas are always one dimensional and come with evidence that begins with an unproven assumption and ends by magically validating his thoughts. I guess why it's called witchcraft.

It's not fatigue, 2 of the latest Chinook bent ones had been in my shed for a while so old style but new. Less than 10 sessions for one and the 3rd session for the latest one to bend.

tbh you aren't getting your head around this, it seems to be a bit complex for your level of understanding.

What I really want is a list of extensions that don't bend or break when extended to 32 cm and used/crashed in powerful chunky waves.

Candidates so far-
Witchcraft.
Possibly new Chinook.
Others have been mentioned but I'm not sure if the recommendations were for chunky wave crashes?

Grateful for any more real world feedback.

I got my head around it, They all break at some point given wear or conditions because they have holes in them . Carbon Break less than aluminium

some designers design sails to not need more than 24cm extensions to avoid breakage and stop stiff lengths interrupting the mast bend curve.

maybe change sail brand

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.

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.

Select to expand quote

Gestalt said..
some designers design sails to not need more than 24cm extensions to avoid breakage and stop stiff lengths interrupting the mast bend curve.

maybe change sail brand

Yes, that's a valid point. I can use a tip extension, or mix and match the mast or use sails with a mast size that don't need 30cm... BUT that's the tail wagging the dog!
The sweet spot with this sail is a 370 with 30 cm base. The sail is really nice like that ( and the other options quite simply aren't as nice)hence the continued search for an extension that doesn't break/bend at 30cm.
But as you infer, if it isnt possible I will either have to put up with it breaking extensions or change something I dont want to change.

Select to expand quote

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?