Shroud Tension Bavaria 38 2003

[Spirit of Mary]

Nigel: Topic split off from here

Hi Simon,
I was so free to put your pictures on a Dutch Bavaria Forum and asked if there was similar experience. And yes, in 2014 there was a topic on the Forum with a picture not as worse as yours, but with the wear of the mastfoot pin in the frontside of the V groove. The owner of the boat (also a BAV 38) put the question to Selden Holland and they asked the Bavaria specialist of Selden in Sweden. The answer was: (free translated from Dutch) As shown on your picture the dynamic impact of the mastfoot pin at the frontsite caused high wear. This wear happens when the mast is "pumping". This "pumping" happens when the tension in the stay is not high enough. Selden Sweden indicates that the design of this mast is critical for (too) low stay tension. The stay tension needs to be adjusted at 25% of the tensile strength of the stays. This results in a much more stable mast with no or minor pumping and no dynamic impact of the pin in the V groove of the mast foot.
I would verify this with the Selden distributor in the UK or where you are located together with your images.
I am looking forward for your respons on this Forum.
Ger

[Salty]

The posting from Spirit of Mary (Ger) regarding the comment from Selden in Holland and Sweden ties in closely with my own thoughts on this problem. In the past, and shortly after launching at the start of the season, but before I'd had a rigger to tension the stays following a re-installation of the mast, I'd noticed that the mast had tended to flex quite considerably, causing the pumping action that it would seem has damaged the aluminium plate on simonmoore's boat. Once the required tension on the rigging had been achieved, that pumping action stopped, but slacking off the backstay tended for the pumping to be reintroduced. Since then I've always kept a good tension on the backstay of my B36.
One good thing is that the aluminium plate, on my boat and probably on many others similarly fitted, is very largely visible such that cracking should be quite easy to spot, hopefully before it becomes a total disaster.
Next time onboard I'll try and get a measure of the tension on my backstay, and post it here.

[MarkTheBike]

Next time onboard I'll try and get a measure of the tension on my backstay, and post it here.

That would be very useful, Salty. As a newcomer to deck-stepped masts, I was unaware of this flexing so have been slackening off the backstay when the boat is not being used and pulling it in when sailing. Sounds like that may have been a mistake. It was actually a question I was going to raise, i.e. does one let it free when moored, pull it in a little for sailing and more for racing (or getting back to the pub before closing time)? Nothing in the manual about it but I'd be interested in other peoples' views. In the meantime, I'll keep mine tensioned.

[Craig]

The mast set up on my Bav 38 ( 2009) model is also a seldan mast. I don't know if it is the same as the 2003 model.

The Seldan instructions came with the boat. The side stays are tensioned to 15% of breaking strain and should always be left at that tension, even when overwintering. A Loos gauge can measure the tension. At 15% tension you should notice that when beam reaching in strong winds, the lee stays should remain tensioned and not vibrate. 

Backstay tension should always be maintained but should be increased as wind speed increases. This does 2 things. It flattens the main and lessens the risk of the mast pumping.

I'm a bit confused from the discussion as to whether there is a confusion between the tensioning of the side stays and the backstay. If your side stays have less tension, the risk is mostly a risk of breaking the stays. If the back-stay is not tensioned the risk is inverting the mast ( depending on your setup) and breaking the mast.

Poorly tensioned side stays or the backstay will cause some movement of the base of the mast.

One problem I have seen is sailors tensioning the back stay without releasing the headsail halyard. If you tension the backstay without releasing the headsail halyard, it will transfer the tension in the forestay to the headsail. It is easy to stretch the luff or break the halyard in these conditions. 

Many cruisers do not adjust their backstays to the conditions and create more wear in the rigging.

Any area where you have metal to metal contact in the rigging should have Tefgel or something similar applied. It is expensive but well worth it.

Craig
"Shirley Valentine"
Gold Coast
AUSTRALIA

[Spirit of Mary]

The mast set up on my Bav 38 ( 2009) model is also a seldan mast. I don't know if it is the same as the 2003 model.

The Seldan instructions came with the boat. The side stays are tensioned to 15% of breaking strain and should always be left at that tension, even when overwintering. A Loos gauge can measure the tension. At 15% tension you should notice that when beam reaching in strong winds, the lee stays should remain tensioned and not vibrate. 

Backstay tension should always be maintained but should be increased as wind speed increases. This does 2 things. It flattens the main and lessens the risk of the mast pumping.

I'm a bit confused from the discussion as to whether there is a confusion between the tensioning of the side stays and the backstay. If your side stays have less tension, the risk is mostly a risk of breaking the stays. If the back-stay is not tensioned the risk is inverting the mast ( depending on your setup) and breaking the mast.

Poorly tensioned side stays or the backstay will cause some movement of the base of the mast.

One problem I have seen is sailors tensioning the back stay without releasing the headsail halyard. If you tension the backstay without releasing the headsail halyard, it will transfer the tension in the forestay to the headsail. It is easy to stretch the luff or break the halyard in these conditions. 

Many cruisers do not adjust their backstays to the conditions and create more wear in the rigging.

Any area where you have metal to metal contact in the rigging should have Tefgel or something similar applied. It is expensive but well worth it.

Craig
"Shirley Valentine"
Gold Coast
AUSTRALIA

Hi,
I was not complete in the reply.
The reply from Selden Sweden in the Dutch case, also was that the 15% tension of the tensile  stength of the stays, which is  mentioned in the instructions, is not sufficient. I didn't quote this because I didn't verify this value in the Selden Instructions. But now Craig is mentioning this, I have to  complete my reaction.
So for the Bavaria 38 the 15% should be 25%, a value which for most boats is considered as the right tension.
I am very interested in the reply from Selden in the SimonMore case.
Ger

[Craig]

Ger,

I am confused by the response you mention in the Dutch Case. I'm wondering if the 25% mentioned might be a typo.

Seldan clearly state in their on-line material and the manual I received with the boat that stay tension should be 15 - 20 % of breaking strain of the stainless steel wire used. Loos, the manufacturer of the rigging gauges warn that tensioning past 25% will cause damage. The optimal tension in rigging should be the optimal stress for the wire and should be independent of the boat design. The manufacturers of the rigging should select a size of wire appropriate with the expected loads from the design.

I know of one sailor who replaced his side stays with a higher breaking strain wire in the belief that this would be stronger. It was not, it merely transferred the forces to the mast and deck.

My understanding is that changes in stress in highly stressed metal over a period of time will result in metal fatigue. Under-stressing is also a problem as it may cause shock loadings when a stay may go slack..


"Pumping" of a rig generally refers to the forward/aft motion of the mast, particularly when sailing downwind and caused by a slack aft stay, not the side stays. Many designs of boats, particularly fractionally rigged boats ( not Bavarias in my experience) have running back stays to control mast bend. Some have "Check Stays" designed to stop the pumping action. Having been on boats experiencing the "Pumping" when the check stay was not tensioned, I can testify as to the forces. The whole boat was vibrating. Not having the check stay tensioned properly can lead to the mast inverting ( bowing forward) and breaking. My 2009 Bav 38 is 7/8 fractionally rigged. It is almost a cross between the fully fractionally rigged boats, typically 3/4 or possibly even less and a masthead rigged boat.

With 15% tension in the side stays, as the force of the wind increases, the tension in the lee stay decreases as load transfers to the windward stay. The maximum sideways force that may be applied by the wind should be designed to be less than 20% of the breaking strain of the stays, after taking into account the vectors. Your boat will heal over so that a force of this magnitude should never be applied to the mast.  With this force, the windward stay tension would increase to about 25% of the breaking strain and the leeward stay would reduce to about 5%.

Fibreglass along with steel and wood flex under load but fibreglass, being mainly a plastic will not completely return to its original position when load is removed. Bavaria have minimised this by connecting the rig to the Grid and not the hull. Rig tension should be checked yearly to counter this "bending".

The greater the rigging forces, the more the boat will be deformed.

Given that "Pumping" generally refers to backstay tension, I think that the problems with the mast base ( tabernacle) is likely to be from insufficient back-stay tension, not side stay tension.

Craig
"Shirley Valentine"
Gold Coast
AUSTRALIA

[Spirit of Mary]

HI Craig and others,

i only refer to the reply which the Dutch guy got from Selden Sweden. He mentions that the 15% mentioned in the Selden manual is too low according the reply from Selden Sweden. He mentions that it is the tension in the side stays (shrouds, Dutch "want"). Because the spreaders form a V backwards, the tension has a clear influence on the stability (non pumping) of the mast and even with a pretty loose backstay one can sail and backstay tension can be used for sail trimming by mast bending. So Selden Sweden said that increase of the stationary stay tension to 25% is the solution for the wear on the mast foot. A second solution would be increase in the length of the spreaders, which to my opinion is overdone. The Dutch guy increased the side stay tension to 25% (in 2014) and says he has a much more stable mast and no pumping anymore.
In the Simonmoore case the foot shows apart from the wear by the pin also heavy cracking. I don't know if to the opinion of Selden in this case is the same as in the Dutch case. Waiting for the Selden reply?

Ger

[Mirror45184]

Hi
In relation to mast pumping and potential damage; The mast section is designed to allow for a positive bend where the centre of the mast moves forward. Swept back spreaders help to prevent this and can, with sufficient tension, introduce some positive pre-bend. Although the "tree trunk" section used a lot of tension is required. The D stays also control this bending forward as well as providing sideways support. In the mast manual they warn about inverting the mast. This inversion is a negative bend, where the centre of the mast moves backwards. When this occurs the D stays no longer control the side stability of the mast and consequential failure can occur. The most likely scenario for this inversion to occur is when the mainsail is reefed such that the head is below the forestay attachment point. It is at this point when most back stay is required which pulls the top of the mast backwards and helps to hold the centre of the mast forward (positive bend).
The mast pumping occurs when there is insufficient support or coordinated support from the shrouds, D stays and backstay when sailing which allows the mast bend flex in and out excessively. There will always be some dynamic flexing.
The damage found by Simon could certainly be caused by this pumping. An alternate cause from a similar base of insufficient rig tension cold be due to the foot of the mast slamming due to falling off a wave or other similar vertical loadings. Either way I will also be having a close look at the mast base next time I am at the boat.
Cheers
Mark Hutton
SV SYnergy
B40 Cruiser 2009

[Craig]

Mark,

You are spot on.

Reinforces the point that correct shroud ( side stays) tension is required, as is back stay tension, particularly in stronger winds. The back stay should always be tensioned to provide some bend and as wind pressure rises, so too should the back stay tension.

The only concern I now have is whether the 15% tension recommended by Seldan in their on-line manuals and the printed material I received with my boat is the best tension and whether the Loos warning that more than 25% tension is dangerous is correct,  or whether the "Dutch" recommendation of 25% tension mentioned above is better. 

Craig
"Shirley Valentine"
Gold Coast
AUSTRALIA

[suibhne]

Its strange that this happens over winter when the boat is presumably in the water with the sails removed.
I assume this, because if it was 'on the hard' for a lengthy period  the mast should be dropped for all sorts of reasons.
Last sailing season I bought the Loos professional guage and tensioned it to the Selden spec with a noticeable improvement in going to windward.
Over winter my boat a BAV 36 2002/3) was left in the water with sails removed.
I  eased back the cap shroud tensions slightly and the same for the backstay.
I found conflicting information 'out there' in the web on this topic such as 'if you tension to the Selden spec you will not be able to shut the doors' so its best to stick with Loos and Selden as they will be liable for faulty professional advice.

[suibhne]

Craig says

"The only concern I now have is whether the 15% tension recommended by Seldan in their on-line manuals and the printed material I received with my boat is the best tension and whether the Loos warning that more than 25% tension is dangerous is correct,  or whether the "Dutch" recommendation of 25% tension mentioned above is better.  "

I don't see these as incompatible statements.
Take it up to the Selden Spec
Only go beyond this if you feel you want to push it a bit and are happy about all the other non Selden links in the chain such as the hull stiffness.
The Loos limit refers only to the stainless steel wire.

[Spirit of Mary]

Hi,
In the link http://www.riggingandsails.com/pdf/selden-tuning.pdf , you can find the mast tuning guideline from Selden. At page 44 you can find the guideline for the fractional, multi-spreader rig, swept spreaders and deck step mast. This is true for the Bavaria masts. The guideline talks about a first tension of 15% and later increased to 20% all at maximum backstay tension of 20% with backstay loose the tension should not increase to more than 25%.
I will try to get the Original reply of Selden in the Dutch case.
Ger

[ANTREVELL]

I own a Cruiser 33 with 8mm ( I think ) shrouds . Where do I find the breaking strain of an 8mm shround. Can you confirm whether it is 15% or 25%. Has anybody any experience of the different guages .

Regards Tony

[Spirit of Mary]

I own a Cruiser 33 with 8mm ( I think ) shrouds . Where do I find the breaking strain of an 8mm shround. Can you confirm whether it is 15% or 25%. Has anybody any experience of the different guages .

Regards Tony

Please read page 28 and 29 of the Selden tuning guideline. You find the breaking load of different sizes of shrouds. Further you find on page 29 the folding rule method. You stick a 2 m ruler to the shroud and with tensioning every mm elongation (based on a 2m ruler) is 5% of the breaking load.
Ger

[Craig]

I've checked with my local rigger.

He has confirmed that the optimal tension on all stainless steel rigging is 15 - 20%, no matter what make of mast you have.

The 15-20% takes into account the optimal loading and safety factors that the stainless steel shrouds encounter and the tension required to ensure shock loading does not occur. Mast manufacturers calculate the forces on the sail and mast and then calculate the size of stainless steel shrouds required to satisfy those forces. In strong wind conditions where the mast is forced forward or sideways, the side stay tension increases so strains greater than 25% will be reached but these will be within the safety margin. Increasing backstay tension lessens the tension in the shrouds as well. The tension should always be measured without backstay tension. Masts are designed to have some backward bend. The risk is that if the mast inverts ( bends forward) the forces on the mast rise greatly and could lead to failure of the mast. That is why baby stays,running back-stays or check stays are fitted on many racing boats. Back-stay tension also assists with flattening the Main in strong wind conditions.   

He recounted a story of a sailor preparing for an ocean crossing who wanted to "Bomb-proof" his boat. He replaced all the rigging with new rigging at least 1 size more than was recommended. His mast broke the first time he encountered 40kn winds.

Craig
"Shirley Valentine"
Gold Coast
AUSTRALIA

[Spirit of Mary]

Hi,
I promised to try to get the Original reply of Selden in the Dutch case. I got it but it was a reply of the Selden dealer in Brouwershaven (Neth.). So in Dutch language. He got it from Selden Sweden.
Quote translate":

"I have got a good feedback from our "Bavaria" specialist from Selden Sweden.
It proves this rig (Bavaria 38 2003) requires a punctual trim.
For a longitudinal to the ship stability of the mast, the cap shrouds need to have 25% pre-tension to give sufficient forward support to the mast via the spreaders. When now the backstay is tensioned to try to avoid pumping of the mast, the opposite is reached. It creates more compression in the mast and the pretension in the cap shrouds is reduced.
So it will be a combination of correct tuning of the cap shrouds and be carefull with increasing of backstay tension.
We discussed also a small a adeption of the spreaders, but this was a too small advantage compared to the cost involved, because besides this adeption also new shrouds (cap and diagonal) are required.
Advice of the department responsible for the calculations was to look if application of checkstays would be an option."

I want to point out that this was a Selden reaction on the Dutch damage case of the mast foot (see pic in the Topic Start).
Waiting for the reaction of Selden on the SimonMoore case.
Ger