Carbon mast with 6,2 meter length ?

  • 08 Aug 2019 11:50
    Reply # 7818107 on 7799739

    Hi,

    Today after 2 sleepless nights because of thoughts about glueing my carbon mast pieces I did it at last and it took very little time. I think building my boat has taught me preparation for any task is the key to easy execution.
    I first stuck on the 2 inserts lots of plastic tape around it like on the first picture in the attachment until it was the same diameter as the long pipes to make sure that it is completely straight lying on the table after gluing and then I mixed 25 grams of epoxy with 14 grams of hardener 3 teaspoons of silica and one spoon of wood flour and brushed first the insides of the long pipes and then the inserts themselves and slid them together wiping any excess epoxy away finished in 10 minutes. The second picture shows both pieces glued into the long pipes. 24 Hours of curing and I know if I did a decent job.

    Greetings from Karl

  • 29 Jul 2019 11:11
    Reply # 7801039 on 7799739

    Hi Graeme and David,

    Thank you so much for your suggestions for my mast. The rotating idea like all my other junk rig wisdom I have of Haslers book Practical Junk Rig but he talks of the whole mast rotating. I think I will glue it in the middle and transport it on top of the cabin roof. Yes Graeme the outside pipe is the one you quoted while for the inside pipe I bought this:

    0371CTPP5046-1 Carbon Rohr 50x46x1000mm
    Außendurchmesse : 50mm
    - Innendurchmesser : 46mm
    Länge : 1 meter- Gewicht : 465g/meter.
    Aufbau : PRE-PREG TECHNOLOGY, Epoxitharz.


    I think the pre-preg technology is the better quality produced carbon pipe as it is also a third more expensive. I will test the bending of the whole mast in my boat shed by putting pressure at the mastheads position and have it fixed at mast partner and shoe position and in addition I will find out the exact bending force specifications from the French supplier. My gut feel so far is that the 3 meter pipes are as stiff as steel and practical the same as my yard and boom which I made myself out of a combination of fiberglass and carbon sleeves and epoxy. Some leftover carbon sleeve I will use at the joins of the mast at the head and in the middle and if I got some left I will strengthen the mast with it at the partner. My next report will hopefully be with pictures of what I have done besides juggling the ideas in my head.

    Greetings from Karl




    Last modified: 03 Aug 2019 11:30 | Anonymous member
  • 29 Jul 2019 00:02
    Reply # 7800705 on 7799739

    Hi Karl it seems that wind surfer masts are usually made from carbon fibre, small diameter tubes with an internal sleeve join. This one is 4.5 metres when assembled.


    Mind you, I think they are supposed to be quite bendy, you won't be wanting that much bend. The point is, the join detail does not seem to be a problem.


    I presume this (below) is your outer tube?

    0372CTW550510-2Carbon tube 55x51x2000mm Outerdiameter: 55 mm-Innerdiameter:51 mmLength: 2 meters- Weight: 533 g / meter.Construction:pultrusion, inner fabric 80 ° + single direction + outer fabric 37 °, epoxy resin.

    Since you have already bought the tubes, why not just give it a go?  If it breaks at the join (or at the partner) you can fix it, and make it stronger.

    Last modified: 29 Jul 2019 00:19 | Anonymous member
  • 28 Jul 2019 23:18
    Reply # 7800670 on 7799739

    Hi Karl,

    carbon fiber tubes are made mostly of unidirectional material with little material binding it together to stop it from bursting. When sleeved over the lower section your upper section of pipe will experience significant pressure that is liable to split the pipe at the join. A glued joint with a binding of CF around it would be much more likely to survive the forces at the joint. I suggest that you contact the supplier and verify the layup of the pipe, and its actual bending strength for the purpose that you are putting it to. I have doubts that it is strong enough where it passes through the deck. A rough calculation of the expected force is the sail area in square meters multiplied by the wind force of approximately 5 kg per square meter at 15 knots of wind, applied at a distance of deck to center of area of the sail plan.  Once you have calculated this force multiply by at least two for a safety factor. Then compare to the bending strength of the pipe. The manufacturer should be able to give figures for this.

    All the best with the project, David.

  • 28 Jul 2019 20:53
    Reply # 7800523 on 7799739

    I think the amount of overlap (bury) is 30cm and therefore within the approximate 10% which is regarded as a minimum for tabernacles, so in theory the join itself should be as strong as the rest of the mast, in bending. However there is still the problem that the halyard and yard will put a rotational force on the top of the mast. It would be interesting if the top section of the mast was able to rotate. I  have never heard of that being done, (though I have seen on other more simple rigs, rotating masts where the entire mast is allowed to rotate in the partner.) I suspect that with all the running rigging which is usually carried on a junk mast that rotation of the top part would be unacceptable, but I don't know from experience. Maybe the top part, if not glued, would need to be secured in some way so as to prevent rotation, but I am not sure the best way for a carbon fibre tube. Hopefully someone else who knows more than me will chime in here. 

    I had a sailing dinghy a few years ago, in which the mast came apart simply, in two parts. It was no problem, quite convenient in fact, but it was a very simple sail.

    My own thought would be to glue the mast fully and just accept that when trailing the boat, the mast will need to be carried over the top of the cabin and will protrude forwards and aft, a little, which is the usual way for a trailer sailer.  However there is room for some other ideas here. Your little boat is very interesting and when you get her sailing, some more photographs and a description would be very good.

    Last modified: 28 Jul 2019 21:30 | Anonymous member
  • 28 Jul 2019 11:54
    Reply # 7800130 on 7799739

    Hi Graeme,

    Thank you for this idea. I want to try not to glue the top half of the mast at all just slide it over the glued in and cured 30 cm sticking out of the lower mast half and put it together for sailing and when the boat is on the trailer I can store both mast parts in the hull. Please do let me know what you think of that.

    Greetings from Karl

  • 28 Jul 2019 09:38
    Reply # 7800097 on 7799739

    Where you are joining two tubes the same diameter, I suppose there needs to be some way of ensuring the smaller diameter tube goes inside the same distance each side of the join and does not slide out of position during assembly. Epoxy glue is slippery stuff. Maybe it might be easiest to glue the smaller diameter tube just into one of the outer tubes first - let that cure, then then glue and slip the other one on the next day. Just a thought.

  • 28 Jul 2019 06:21
    Reply # 7800046 on 7799739

    Hi Graeme,

    Thank you so much I will do it exactly like you described it. My 55 mm diameter carbon pipe is for sure strong enough as it is buried 1,16 m in the 14 foot hull of my boat which is comparable to a dinghy. I got the 3 carbon pipes from www.carbonrohr.net which I think is a producer in France and It was here in Austria within 3 days after  I paid 771 Euros which included 100 Euros for delivery. So the mast cost me actually 671 Euro. Once I have glued it I will post pictures of it.

    Greetings from Karl


  • 27 Jul 2019 23:44
    Reply # 7799799 on 7799739

    For Serendipity I made a three part mast from aluminium tube of different diameters and I presume the gluing principles are the same. Applying the glue and sliding the two tubes together is easy. I found in the past, with aluminium, that a much stronger glue join results if you sand the surfaces and prime with liquid epoxy - then, before it is cured, paint on the epoxy glue and slide the tubes together (making sure the mast is lying straight.) Where there are two different external diameters (as in your top section) the join should be faired with filler and glass tape, to make a smooth transition between the two diameters. I put a bandage of tape over the join itself, also.

    In my opinion (others may not agree) the important role played by the glue join is just to hold the two parts in place, resist twisting and resist the top section being forced down into the lower section. As for bending forces, I do not believe the glue join needs to contribute much, provided the inner tube is sufficiently "buried" in the outer tube - the same principle as applies to a tabernacle. This means, in theory, about 30cm each way (your 60 cm joiner would do it) - but intuitively I would rather double that. With lots of gluing surface and a material which should take kindly to to epoxy, there should be no problem with the join.

    I would leave it to the experts to advise you about whether 50mm carbon fibre tube is strong enough for your mast. I wish I could get some of that tube. 

    Heaving down with the halyard. It puts a bend in the mast, but the join is plenty strong in bending.







    Last modified: 27 Jul 2019 23:48 | Anonymous member
  • 27 Jul 2019 22:15
    Message # 7799739

    Hi,

    I have bought myself 2 three meter long carbon pipes inner diameter 51 mm  and a 1 meter long pipe with an outer diameter of 50 mm. From this I want to use 60 cm to connect the 2 long pipes and 40 cm for the top to reach the required length of 6,2 meter. Can anyone give me an idea how I distribute the epoxy evenly onto the connecting parts ?

    I can only think of brushing the connecting areas with epoxy and push them together. Can it be that easy ?

    The whole exercise I need to do because my alu mast is for my age and strength too heavy even that it weighs dressed only 9 kg while the carbon mast  comes in at 3,8 kg.

    Geetings from Karl

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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