roto-molding motor yachts

Discussion in 'Boat Design' started by capt_jack, Jul 1, 2010.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    Yep, you are right, Jon. There are various materials out there from which to choose. Matching the right stuff to the right mission is interesting, to say the least.

    I'm just about to spend five days taking in all the new boating products at the upcoming Outdoor Retailer Show, here in Salt Lake City. The manufacturers are using wood, composites in several flavors, rotomold, vacu-thermoforming, inflatables and, as you indicated, hybrid mixtures of these, looking for a great final product.

    Should be interesting to check out the boats, take them out on the water at one of the local mountain lakes and then have a solid conversation at the show in the convention center.
  2. capt_jack
    Joined: Jun 2010
    Posts: 30
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    Location: Houston

    capt_jack Junior Member

    According to my limited research the material can be welded using heat or ultrasonic welders - If the welded parts are as strong as claimed it leads to some interesting possibilities.

    Time will tell how Triumph makes out with it. I hope they have better looking designs planned, however. That's one of the ugliest boats I've ever seen and for a pontoon that's quite an accomplishment to lower the bar even further.
  3. Lew Morris
    Joined: Jun 2001
    Posts: 124
    Likes: 4, Points: 18, Legacy Rep: 92
    Location: Pismo Beach, Ca

    Lew Morris Industrial Designer

    >> ...i used to do Rotomoulding of tanks for a Chandlery wholesaler here, i made the moulds, not too difficult, but the ovens are limited in size, so i seriously doubt ANYONE has an oven big enough for a 50 footer, even if someone was silly enough to make the moulds for it...Heating the mould could be done externally of course, but it then becomes a trial and error situation to cook the pellets correctly....trial and error on a 50 foot job would prove economically fatal. <<

    Hello all. It's been awhile since I posted last.

    As an Industrial Designer outside of the "marine industry" I have been involved in a lot of roto-molding projects. In my opinion, roto-molding is at best, a crude process in my opinion.

    From a technical stand point;

    * Roto-molded objects must be rotated 360° in all three axis; which would mean an oven with the internal measurement of something on the order of a 70-80 foot CUBE (to allow for the "spider" that the mold is mounted on).

    * HDPE is highly susceptible to degradation caused by inaccurate process temperature control - in this process the heat is provided by open gas flames directed on the exterior of aluminum molds. Any slowing of the rotation either overheats an area, or allows another to cool.

    * HDPE parts would be substantially heavier than composite structure because its strength determined by its thickness.

    * Fiber reinforcement is essentially impossible by virtue of the process; the mold is opened, and predetermined amount of resin is dumped into the mold, the mold is bolted together, the rotation process is started. The molten resin basically sloshes around on the inside of the mold for a predetermined time and then allowed to cool.

    * HDPE is dimensionally not very precise, and shrink rates are substantial (on the order of .025" per inch (.3" per foot), and are dictated by the physical dimensions of the part, MATERIAL WALL THICKNESS, and density of the particular alloy (blend). Think of it this way; on a 50' vessel, you could expect the part coming out of the mold to shrink approximately 15 inch IN ALL DIRECTIONS

    * The process involves a two-piece mold which is literally bolted together on the parting lines. Imagine the volume of a 50' hull mold.

    * HDPE can be welded, but not to an "engineered" degree. As with aluminum an oxide forms on surfaces being welded and yields unpredictable results. My experience is that the best one can hope for is being able to plug holes.

    Triumph's products withstanding, in my opinion the process is not very practical for anything much over 20' due to material limitations.
  4. Chris Ostlind

    Chris Ostlind Previous Member


    All of the rotomolded boat operations I have witnessed did not have 360 degree rotation on three axes. On the long axis of the hull, 360 is a must, but not fore and aft. The tool only needs to rotate partially... basically tipping the tool to make sure that all the interior surface is being coated.

    It isn't being said all that clearly at the original link site, but I'm inclined to believe that the only major parts that might go a full 50' would be the flotation cells (pontoons) under the superstructure. Everything else there could be formed in smaller pieces and joined in post production. I don't see cylindrical forms as a huge technical problem to overcome, since they could be very simply designed.

    Much of the rest of that boat could be thermo-formed acrylic that is affixed to a sub structure and finished off with hardware as needed. That makes for a simple boat to touch-up with a redesign in a few years as the skelton is easy to adjust and thermo-formed parts are fairly cheap to produce. Some inspired design work, some CNC cutting of a set of new temp tools in stacked sheet goods and voila, you have a freshened-up boat with a whole new look and color scheme. Then, settle-in on a final design choice and make some more permanent tools for longer production life.

    My 2 cents
  5. apex1

    apex1 Guest

    Kenia Dollar cents Chris............................
  6. Chris Ostlind

    Chris Ostlind Previous Member

    So, where, pray tell, is Kenia?

    If it's supposed to be Kenya, then ... well, enough said about the value of the slur.

  7. apex1

    apex1 Guest

    Well Chris,

    .if you cannot contradict the pro´s you contradict yourself. Doesn´t matter.....

    keep on chasing Ad Hoc and me, to the very extend...if YOU feel better, who cares?

    In commercial boatbuilding is NO place for HDPE, Bamboo, ...esthers on wood, so named "ferro cement", and the like.

    Not that you would not know that, but you like to contradict and indoctrinate.

    Feel fine Chris!

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