polypropylene honeycomb vs plywood for wharram

Discussion in 'Materials' started by John Coulson, Jul 2, 2020.

  1. fallguy
    Joined: Dec 2016
    Posts: 6,397
    Likes: 1,305, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Putting foam on battens on a male mold is not ideal. The problem is foam is not strong sans glass and bulkheads. I was advised strongly on this forum to build in a female jig and did. It was pretty fun; except for the bow. A female walk in jig allows you to install the bulkheads so the hull can be removed from the jig. This was a bit complex because the jig needed to be broken to lift out the hull.

    I don't know the shape of the Tiki, but a dev panel hull can be built this way.

    These panels were built on a vac table using wet bag method. If you are using csm and 1708 (more csm), than you would not want to build attached to your dwelling and ought to consider learning infusion. You do not want to hand laminate all 1708 hull.

    We used epoxy and triax and no csm. I am curious about the Lloyd's csm requirement because I had some troubles with air in the table side laminate qualities [sic].

    Anyhow, building a dev panel hull in a female jig is better than male jig because you can fit bulkheads and not worry about hull shape.

    We actually had a couple steps to walk in and finished our way from the bow to the stern. Once the transom was fitted; we broke the jig at a half point and lifted the hull out with a gantry; did the bottom and outside seams and faired and flipped again and applied a deck shoe. Anyhow, here is a picture. I recall sharing this before, but not on this thread. If I could change a thing; the bow nose would be it. I would build the bow jig off the boat cuz my ankles paid dearly to work forward. And my foams forward should have all been higher density for a bow eye..

  2. fallguy
    Joined: Dec 2016
    Posts: 6,397
    Likes: 1,305, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    On my pic, John, you can see darker foam on the left. That is a high density insert where the cockpit loads will land and a beam socket resides. Up in the bow vee, it looks white. That area of the hull is all glass; the white is just paint and release material for releasing the glass later. Green areas are 1708 tapes which I opted to use and pay the weight penalty. Some green forward as the inside of the hull to wl was hand glassed with 22 oz triax.
  3. Rumars
    Joined: Mar 2013
    Posts: 1,496
    Likes: 805, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

  4. Saildog007
    Joined: Nov 2015
    Posts: 6
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Lorain, Ohio

    Saildog007 Junior Member

    But how does ply compare in terms of material cost and labor time to foam when it must be protected by filling edges and applying several layers of epoxy ?
  5. fallguy
    Joined: Dec 2016
    Posts: 6,397
    Likes: 1,305, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    ply is always faster than foam, but ply is not suited for all builds and has a weight penalty

    all developable hulls that can use ply can be built faster with ply; sheathing requirements are less glass and thus less epoxy

    In order to glass on foam, even on a male mould, stations must be doubled. In a dev panel foam build, all the foam is built in a painstaking process on the table; plywood can be vac bagged, but typically is not.

    So, there is no getting around the speed of ply. But as you get to production boats, even ply is slow versus a mould.

    all relative...

  6. gonzo
    Joined: Aug 2002
    Posts: 15,960
    Likes: 1,296, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Wharram catamarans are low tech designs for amateur builders. If you are going to use honeycomb cores and re-engineer the laminates and all the structure, it makes no sense to build one of those designs. There are modern designers that can sell you plans for an ultralight boat with better performance, and definitely higher resale value. Otherwise, plywood is great as originally specified.
    fallguy likes this.
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.