Mast construction for rounding Cape Horn

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  • 22 Dec 2021 20:56
    Reply # 12211219 on 12197206

    One point of argument with Sponberg and Hasler/McCloud. They state that stress reduces linearly from the mast support at deck level to the top of the mast, therefore needing a straight taper for the mast. With a junk rig the stress imposed is not linear but has a concentration at the battens in the top tapered section. This means that most breaks I have seen in junk rig masts occur about 20% down from the top of the mast. I suggest, therefore, that an entasis taper is better for a junk rig mast. This puts a larger diameter of mast in this area of stress concentration.

  • 22 Dec 2021 17:31
    Reply # 12210877 on 12210586
    Anonymous wrote:

    I can't answer that.......... but somebody can.  More than one Freedom yacht has been junk rigged I think, one of which was listed for sale right here in 2018 

    Junk Rigged Freedom 28


    Perhaps I can as my daughter owns that boat now.

    The masts on a Freedom 28 seem to be perfectly suitable for junk rig. Having said that, before Hazel bought the boat, one of the original Freedom masts broke (the aft of the 2). The boat is ketch rigged and hence the forward mast has a larger diameter. The repair was carried out by replacing the aft mast with the original forward mast and fitting a new (second-hand?) Carbon Spars mast forward.

    This current mast arrangement performs splendidly!


    Thank you for posting that........
  • 22 Dec 2021 15:21
    Reply # 12210586 on 12198766

    I can't answer that.......... but somebody can.  More than one Freedom yacht has been junk rigged I think, one of which was listed for sale right here in 2018 

    Junk Rigged Freedom 28


    Perhaps I can as my daughter owns that boat now.

    The masts on a Freedom 28 seem to be perfectly suitable for junk rig. Having said that, before Hazel bought the boat, one of the original Freedom masts broke (the aft of the 2). The boat is ketch rigged and hence the forward mast has a larger diameter. The repair was carried out by replacing the aft mast with the original forward mast and fitting a new (second-hand?) Carbon Spars mast forward.

    This current mast arrangement performs splendidly!

  • 18 Dec 2021 14:38
    Reply # 12200929 on 12200880
    Anonymous wrote:

    Would it not be fairer to say that a mast built to what is considered to be "normal" strength and specification is going to be strong enough to withstand "normal" conditions around Cape Horn at least a few times?  While a mast not built strong enough is likely to fail.  

    Regardless of its material?

    If the wrong circumstances come along, no mast or ship is strong enough to resist them.  Titanic being a case in hand. If you keep hitting heavy storms, it is bound to reduce the life of your mast, though maybe not for quite a long time  


    Aluminium masts are as likely to fail through thousands upon thousands of tiny flexing cycles caused by  thousands and thousands of miles sailing causing metal fatigue and cracking as they are to collapse under the stresses of 1 single enormously powerful event. They may then collapse in a relatively small storm after being fatigued for thousands of miles of easy sailing.   

     Everything wears out in time.  Tree trunks may well be able to flex easily when they are planted in the ground and recover, but when used as a mast in a boat,they are no longer alive and will be dried out and not possess the same ability to recover from excess winds or a rollover or knockdown as when they were alive and rooted to the ground.  

    Again, if if it's built strong enough to start with, it will survive many more cycles than if it was built too weak in the first place. 


    But nothing has infinite strength.  the best you can do is build it to what is considered to be strong enough for the worst conditions you are likely to encounter on a reasonably regular basis, whether its Aluminium, Wood, GRP, Carbon or a combination.   

    I agree completely, the goal will be to go around or go anywhere in the nicest possible weather. I only mentioned the horn to exclude coastal type designs. 
  • 18 Dec 2021 14:27
    Reply # 12200880 on 12197206

    Would it not be fairer to say that a mast built to what is considered to be "normal" strength and specification is going to be strong enough to withstand "normal" conditions around Cape Horn at least a few times?  While a mast not built strong enough is likely to fail.  

    Regardless of its material?

    If the wrong circumstances come along, no mast or ship is strong enough to resist them.  Titanic being a case in hand. If you keep hitting heavy storms, it is bound to reduce the life of your mast, though maybe not for quite a long time  


    Aluminium masts are as likely to fail through thousands upon thousands of tiny flexing cycles caused by  thousands and thousands of miles sailing causing metal fatigue and cracking as they are to collapse under the stresses of 1 single enormously powerful event. They may then collapse in a relatively small storm after being fatigued for thousands of miles of easy sailing.   

     Everything wears out in time.  Tree trunks may well be able to flex easily when they are planted in the ground and recover, but when used as a mast in a boat,they are no longer alive and will be dried out and not possess the same ability to recover from excess winds or a rollover or knockdown as when they were alive and rooted to the ground.  

    Again, if if it's built strong enough to start with, it will survive many more cycles than if it was built too weak in the first place. 


    But nothing has infinite strength.  the best you can do is build it to what is considered to be strong enough for the worst conditions you are likely to encounter on a reasonably regular basis, whether its Aluminium, Wood, GRP, Carbon or a combination.   

  • 17 Dec 2021 20:40
    Reply # 12199476 on 12197206

    For me the easiest free-standing mast construction is a wood glass composite using a similar process to the wing masts built by Gold Coast.Worth checking out.





    2 files
  • 17 Dec 2021 15:40
    Reply # 12198862 on 12198752
     Bruno wrote:

    David Tyler said:

    Long ago, I raced an OK dinghy in the days when their unstayed masts were made of spruce. The usual mode of failure was horizontal compression cracks on the after side.

    David,

    Does this means that on a foreward raked mast these cracks would be on the fore side?

    No, this happens because the OK mast, like the Finn and Laser, is bent backwards to tension the leech and flatten the sail. 
  • 17 Dec 2021 14:50
    Reply # 12198766 on 12198439
    Anonymous wrote:

    Are second hand carbon fiber masts really suitable for a junk rig? I guess at least some of them are designed to fit a wishbone rig. The occurring forces will be quite different i guess?


    E. Sponberg, page86


    I can't answer that.......... but somebody can.  More than one Freedom yacht has been junk rigged I think, one of which was listed for sale right here in 2018 

    Junk Rigged Freedom 28

    I would suspect that the mast, designed for a wishbone rig is probably well suited for a junk rig.  Some apparently have tracks screwed to the mast for an ordinary Bermuda rig, but they are probably equally structurally suitable with the track removed.    The problem with some of the Freedom masts is the way the outer fiberglass is wound over the carbon fiber like thread  on a spool from what I've read. It will develop cracks through the fiberglass as a result of how it is applied.   The glass obviously is merely a protective layer with zero structural role.  This would seem to be a well known issue, and the solution is apparently well established.   The Freedom masts have a very good reputation overall.


                                                  H.W.


  • 17 Dec 2021 14:42
    Reply # 12198752 on 12197206

    David Tyler said:

    Long ago, I raced an OK dinghy in the days when their unstayed masts were made of spruce. The usual mode of failure was horizontal compression cracks on the after side.

    David,

    Does this means that on a foreward raked mast these cracks would be on the fore side?

  • 17 Dec 2021 14:38
    Reply # 12198744 on 12198415
    Anonymous wrote:

    Some anecdotal evidence:

    I got knocked down twice in the S Atlantic and my aluminium masts were undamaged. 
    Galway Blazer lost spruce masts in the same area. 
    Jester and Jester II. both lost spruce masts.
    Badger went to Antarctica without mast trouble. Hers are near-solid, built from many pieces of douglas fir.

    I used to have a mooring near a Freedom 40 that broke at least two “carbon” masts. There was little actual carbon in evidence at the break.

    Long ago, I raced an OK dinghy in the days when their unstayed masts were made of spruce. The usual mode of failure was horizontal compression cracks on the after side.

    For a timber mast, I would be looking for something with high compression strength and fatigue resistance. 

    I loke this^.     

    So Graham said this about aluminum...

    The section should be spun-tapered for a start, not welded, and the wall thickness should be a minimum of 5mm for a mast suitable for your boat.  It should ideally be 6061 alloy with a T6 tempering, for additional hardening.  I don't think my 10.5m mast on Arion was T6 though.  It had a diameter of 200mm at the base and began tapering about four metres up from the base to 100mm at the truck, with a wall thickness of 5mm.  It was the bottom section of a 25m flagpole, made in France.  Setting 35 sq m of sail, I hammered that rig for some 15000 miles of coastal cruising without problems.  It is hard to say if an alloy or timber mast would survive a violent capsize, which is always a possibility in the Southern Ocean.  If I was sailing there with an alloy or timber mast, I'd carry a built in jury rig on deck, like Galway Blazer

     did.

    Is there anything else that should be considered when looking for a aluminum mast. I'm sure there are a number of posts about aluminum mast, I will search those. But is there a post or place where it's all put together, the definitive aluminum mast selection guide?:)

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