Seeking advice for building an aluminum & cedar mast

  • 30 Dec 2022 04:12
    Reply # 13038757 on 13031450

    Luiz: did you get the email I sent you?


    Annie

  • 27 Dec 2022 18:13
    Reply # 13036470 on 13036303
    Anonymous wrote:
    Anonymous wrote:

    Anyone else have experience using cedar for masts? We get Western Red Cedar here which I think is too brittle for masts. What is available in Brazil and is it used for masts and spars generally?


    I have to say, I don't think cedar is particularly suitable for masts. The tried and tested spruce or doug fir are better options IMHO



    Sorry, I'm going to take that back. I've just been reading about boats built with Thai cedar masts.... Ya lives and ya learns!

  • 27 Dec 2022 15:12
    Reply # 13036303 on 13031786
    Anonymous wrote:

    Anyone else have experience using cedar for masts? We get Western Red Cedar here which I think is too brittle for masts. What is available in Brazil and is it used for masts and spars generally?


    I have to say, I don't think cedar is particularly suitable for masts. The tried and tested spruce or doug fir are better options IMHO

  • 21 Dec 2022 13:10
    Reply # 13031978 on 13031450
    Deleted user

    Thanks Graeme, Frederik and Jan for all the important stuff that I have been learning right now!

    It makes me confident to make my own stuff.

    I will follow up with the results as soon as i get it.

    Cheers



  • 21 Dec 2022 10:02
    Reply # 13031786 on 13031450

    I agree with Frederik about using Tec7, I'm addicted to the stuff. I'm not sure it's widely available outside of the EU though. As far as I know it is very similar to some of the Sikaflex components which are more international. 

    Tec7 has a sister product called Gtec7 (I think) which is phenomenally strong and sticky. Both products form a super strong bond if used to glue two components that are primed with epoxy and the Tec7 is applied when the epoxy is still slightly tacky. 

    Anyone else have experience using cedar for masts? We get Western Red Cedar here which I think is too brittle for masts. What is available in Brazil and is it used for masts and spars generally?

  • 21 Dec 2022 08:38
    Reply # 13031742 on 13031450

    I made a hybrid mast for my previous boat. I glued the wood top piece into the aluminium base using Tec7, a very strong polymer glue, suited for gluing different materials. It stays sort of flexible. Different materials will react differently to temperature swings. No mechanical fastenings. 
    Bury ca. 15%.

    An epoxy lip prevented the topmast from possible “telescoping”.

    I put some water pipe isolation in the alu tube to minimize annoying noise from the cable running up to the masthead lights. 


    3 files
    Last modified: 21 Dec 2022 08:45 | Anonymous member
  • 20 Dec 2022 23:15
    Reply # 13031509 on 13031450
    Anonymous member (Administrator)

    A cute little motor-sailer!

    The two-part mast not unusual these days. I’ve done it (but with two components of aluminium tube – I’ve also done a wooden extension at the heel). It wasn’t difficult. I avoided any mechanical fastenings and just used epoxy for the join – it seems OK but I am persuaded now that a slightly flexible polyurethane rubber “goop” might be better, especially when bonding two dissimilar materials such as wood and aluminium. Other people who know more than me will hopefully chime in here.

    The transition between the two components needs to be faired so the transition from one diameter to the other is smooth. That’s no problem with wood – and you have the chance to make the top part tapered too, which is good.

    I really wanted to comment on your concern about strength. People mostly worry about the bending strength, but if there is sufficient overlap (sufficient bury of the wood into the aluminium pole) that won’t be an issue, and I don’t see the need for any mechanical fastenings (and drilling holes should be avoided anyway).

    The issues that people tend to overlook (at least, in conversations I have had) are two fold: (1) There will be a downward force on the top component, due to the downward pull of the halyard. The fairing which brings the diameter of the top component into line with the lower component means there will probably be a lip at the join and this should be enough to resist that force and prevent the mast wanting to “telescope”. And (2) (surprisingly perhaps) a rotational force on the top component due to the wringing (twisting) effect of the halyard spans as the sail is sheeted in and out. The entire mast has to be fixed against rotational forces, and the top part of the mast must be able to resist rotation with respect to the lower part.

    I think polyurethane rubber glue (such as Simsons which comes in a tube) together with the lip at the point of transition will be enough to take care of all the forces, provided there is enough “bury” and personally I would prefer not to drill holes or add mechanical fastenings. I would be keen to know what others think, as quite a few hybrid masts have been made and all pretty well tested now I should think.

    How much bury is needed? That’s the only real question, I think. I used the old 10% rule but it kind of didn’t seem enough so I added a bit more for good measure. But of course, you don’t want to be adding any more weight than necessary up there.

    I look too forward to reading some advice on that question.


  • 20 Dec 2022 21:59
    Message # 13031450
    Deleted user

    Recently I have taken a 33 feet wailer shallow draft to finish the project.
    The previous owner have planed a motor boat but as soon as I saw the hull I visualized a beautiful junk rig on it.

    After study abou the bird mouth technique I cam across a six meter aluminum tube 168mm ext. diameter.

    My plan is to have the six meter tube as a lower section of the mast and extend about 4 meters of a bird mouth cedar spar.

    My challenge is on how to build a strong joint on those two different materials.
    I  have seen some junk rig spars half aluminum and half wood before.

    I hope to connect to somebody that already done this before to shine some bright on my path.

    Thanks very much,

    Luiz Prado 

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