Stiffening hollow fiberglass masts with foam?

Discussion in 'Fiberglass and Composite Boat Building' started by AlaskanMariner, Nov 8, 2008.

  1. AlaskanMariner
    Joined: Nov 2008
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Oupa, NZ

    AlaskanMariner New Member

    I have two hollow fiberglass unstayed masts about 12 in diam tapering to abt 10 in, abt 50 ft from keel to masthead. These whip like crazy when the boat pitches in steep seas and cause a most uncomfortable (and I suspect dangerous) motion.

    I need to stiffen the masts, or, if that fails, change them to steel poles. So, has anyone injected expandable foam into a mast to stiffen it?

    I'd greatly appreciate any info I can get to help me make this decision.


    Carl Bostek

    PS - the boat is currently a Gallant rigged schooner and I'm converting her to a traditional Chinese lug rig (Junk) with new sails.
  2. Stumble
    Joined: Oct 2008
    Posts: 1,896
    Likes: 71, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    I am just curious how old the masts are, and where the flex is occuring? Do they flex from the base all the way up, or start part of the way?

    I am not at all familure with unstayed masts, but I am thinking that expandable foam is probably a bad idea for a number of reasons:

    1) to my knowledge none of it is really waterproof and will likely degrade over time being exposed to the flexing and water intrusion from mast openings. Plus I would be afraid that the foam holding water against the mast could lead to accellerated delamination of the fiberglass.

    2) how do you run halyards, wires, or electronic cables through the mast if it is full of foam?

    My initial thought is to add external stayes that jump from the top of the mast to about two thirds of the way down. Or to add a layer of carbon fiber, kevlar or fiberglass to beef up the current mast.
  3. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 207, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Foam won't make any difference unfortunately, The problem is the youngs modulus (stiffness) of GRP and the chosen dameter. Stiffness is the reason Carbon-Epoxy is used instead for free standing masts.

    Wood might be a better option but I think there may be stock CF masts available in the US. Watch your COG if adding steel masts.

    Try contacting Eric Sponberg he's expert in free standing masts.

  4. AlaskanMariner
    Joined: Nov 2008
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Oupa, NZ

    AlaskanMariner New Member


    Thanks for the lead. I went to his site and dropped him an email. Hopefully he won't be too busy to jot a short reply..... His work is beautiful!

    I'm actually in Opua, NZ so I don't know if carbon fiber masts are available here. Perhaps in Oz. But the cost of having one custom made and then shipped from the States, or even Oz, would surely exceed my budget. We can get custom steel poles of about 50 ft for about NZ$7500 I'm told. They will need to be treated and painted of course, but the price is right.

    Because of the design of my hull, the masts cannot be moved and conversion to a sloop rig won't work either. So I'm having to convert from the Gallant rig, an airfoil design, to a Junk rig. If I could afford it, I'd seriously look at rotating masts and a Freedom rig. But I can't.


Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.