Boston Whaler type construction

Discussion in 'Boat Design' started by Saqa, Dec 19, 2014.

  1. Saqa
    Joined: Oct 2013
    Posts: 482
    Likes: 9, Points: 18, Legacy Rep: 75
    Location: Hervey Bay

    Saqa Senior Member

    I came across this on the Whaler site, it seems to be similar to my current interest of 'solid' foam core hull. What are the pros and cons about this type of construction?

    Boston Whaler Construction
    Boston Whaler was thrust into the national limelight in 1961 when Life magazine pictured founder Richard T. Fisher as he sawed a 13-footer in half and drove off in the half with the engine. Thanks to Whaler's unique Unibond construction, you can still do that today. And nowhere is that more valuable than in commercial and governmental applications.

    In more common scenarios, commercial Whalers are subject to repeated intentional groundings, punctures by submerged objects, and even impact from collisions in dense fog. There are literally hundreds of stories where Whalers have remained afloat with significant damage- a 3' hole in the bottom, the bow crushed, etc. - and returned their crew safely to shore.

    This remarkable Unibond construction provides up to 2-1/2 times the flotation required by the US Coast Guard. Here's how it works.

    Unlike most molds, the Whaler hull mold is comprised of two pieces. Each is coated with gelcoat and a skin coat of fiberglass before multiple layers of bi- and tri-directional fiberglass material is applied. The two molds are then latched together and a precise amount of liquid closed-cell foam is poured into the area between the hull molds.

    The foam expands and fills the space between the molds permanently bonding the halves into a single, inseparable unit. This results in an extremely strong and unsinkable hull. Pound your fist on the side of a Whaler versus another boat and you'll see what we mean


    A 23' Whaler is listed as just over 1300kg dry weight
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,553
    Likes: 500, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    So far as I know, the poured foam in the void between the inner and outer skins expands in a closed environment, which requires extremely strong moulds. What the density of the cured foam is, I know not. You could do something similar in a less robust mould set-up, with the provision of relief holes, and a suitable foam density formulation. You would not trust 2 lbs/ cu ft foam to be adequate, imo. You have the advantages of virtual unsinkabilty, a very stiff structure, and good insulation properties. But it isn't going to be real cheap.
     
  3. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 109, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    For a one off the multiple mold costs would be excessive.

    If you need 5000 , why not?

    A good foam core construction (Airex) will have the strength required . and flotation foam can be added where it will help the boat float upright.
     
  4. Saqa
    Joined: Oct 2013
    Posts: 482
    Likes: 9, Points: 18, Legacy Rep: 75
    Location: Hervey Bay

    Saqa Senior Member

    Really its just a feasibility exercise at the moment. PVC sheet foam and two part pourable PU foam are the two options I am looking at. PVC is pretty mainstream but PU is proving to be very difficult to find information or help on. PU is attractive as there are a lot of logs and such floating around after the weekly floods in the wet season for a moored boat and prevailing 30kn or so winds with frequent storms

    Will be interesting to figure out the cost comparison with the two mediums, 8lb PU vs Airex

    Hey Efficient one, thanks for pointing out those pros. Any ideas as to the durability qualities and long term structural integrity due to cyclic loads and fatigue and such of the boston type construction?
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 474, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A Boston Whaler type of build wouldn't be possible, given the reasons sited, besides they're well know to delaminate their core from the shells.
     
  6. Saqa
    Joined: Oct 2013
    Posts: 482
    Likes: 9, Points: 18, Legacy Rep: 75
    Location: Hervey Bay

    Saqa Senior Member

    Hey Par, thanks for that, I wasnt aware that they had issues with delamination. Do you think that would still be the case with a more rigid cigar type plug rather then a regular boat shaped core?
     
  7. Flomanse
    Joined: Dec 2014
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Florida

    Flomanse New Member

    Boston Whaler likely does not use foam poured into molds but foam blocks machined with a 5 axis CNC Router.
    The Density required these days by the USCG is 4# per cu. ft. for floatation but structural areas are likely 8-16 pounds.
    I have read a lot of suppositions on other threads that knock foam cores because "eventually they will get wet and absorb water". This is 100% incorrect if the foam used is the proper material which is Closed Cell Polyurethane. It simply does not absorb water unless damaged and left un-repaired. Any damage left un-repaired is a no brainer route to failure regardless of the construction material.
    Whether you build your boat with a Foam or Balsa core is a personal choice that should not weigh a complete lack of PM and inspection of the boat by the owner. Balsa tends to be cheaper right now but for some structural areas denser foam may be preferable. Both are good materials and a hull made with material that floats in my opinion is much preferable to one that sinks if the worst case scenario ever does happen on the water.
     
  8. Flomanse
    Joined: Dec 2014
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Florida

    Flomanse New Member

    I would stress that attention should be paid to the use of the correct material for structural areas , the direction of stress loads in those areas and whether or not flexibility is needed. A combination of cores is almost always a better choice build for large hulls to keep cost reasonable and have the proper core capabilities in the proper areas of the hull.
     
  9. meren
    Joined: Sep 2005
    Posts: 51
    Likes: 7, Points: 0, Legacy Rep: 83
    Location: Northern shore of The Baltic Sea

    meren Junior Member

  10. upchurchmr
    Joined: Feb 2011
    Posts: 2,993
    Likes: 138, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    The entire issue with water is that if the foam was really closed cell, it would not be a problem. The closed cells would not allow water beyond the damage.

    If you have to worry about water due to damage it is NOT closed cell.

    Get a piece of Airex and see if it sucks up any water besides the outside cut cells.

    Expanding foam cannot be guaranteed to be a certain weight. That depends on if the foam can freely rise. If it is contained it will weight more than advertised, because it didn't expand. If the top of the rising foam "crusts over" the mass will be higher density. Even the cells next to the structure you pour it in will be more dense.

    Isn't ABS PU a contradiction?
    ABS = acrylonitrile-butadiene-styrene
    PU = polyurethane

    So one is styrene and one is urethane.
    Perhaps I don't understand chemistry anymore.
     
  11. gonzo
    Joined: Aug 2002
    Posts: 14,338
    Likes: 618, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The expanding foam density is for an open condition. Otherwise, it will depend on the final volume.
     
  12. Flomanse
    Joined: Dec 2014
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Florida

    Flomanse New Member

    ABS has no place in hull construction. It is susceptible to chemical attack, delamination and degradation.
    PVC Foam is more economical than Pour PU and more uniform in density.
    But it is certainly possible to control the density of 2 part pourable PU if you control the environment the shape of your pour and do not pour too much at a time. It will collapse while expanding under it's own weight when poured too deep.
    Also PU can not cure properly if it is not open to the air when poured. IE you should not pour it in a mold at all if you want a reliable cure.

    PVC, Airex and PU all have their pro's and cons and it depends on where in the hull as well as the specific design shapes .
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,553
    Likes: 500, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Can you explain a little more about they are actually built ? The foam shaped by the router is attached to the inner and outer skins, with what ?
     
  14. Pericles
    Joined: Sep 2006
    Posts: 1,997
    Likes: 129, Points: 63, Legacy Rep: 1307
    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member


  15. SamSam
    Joined: Feb 2005
    Posts: 3,856
    Likes: 178, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    Here's a video of how the BWs are made. Since the molds have to withstand the pressure of all the expanding foam, they are of pretty heavy construction and it's nothing you would want to do for a few hulls.

    https://www.youtube.com/watch?v=WNGx77-2WWI

     
Loading...
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.