Cylinder Mold Hulls

[great white]

Does anyone have any experience/opinion regarding cylinder mold hulls? I question things like speed of construction and cost.

[JimConlin]

I assume you're talking about Kurt Hughes's technique for laminating curved, but not compounded, plywood panels, then building a boat. I think that even the designer is tending toward composite construction using strips (of some material) these days. He's written some good how-to stuff on the topic.

[Paul Scheuer]

I'm confused. Is this what is called "constant camber" ?

[JimConlin]

'Constant Camber' is a technique developed by Dick Newick (http://www.wingo.com/newick/) and Jim Brown (IIRC) where compound-curved cold-molded panels were laid up on a mold. All panels for a hull would be done on the same mold. This greatly reduced the labor in building molds but limited the shapes of the finished hulls.

'Cylinder Molding' is a technique developed by
Kurt Hughes (http://www.multihulldesigns.com) in which curved, but not compounded, panels are laminated of thin plywood on a mold. The panels had the form of part of a cylinder, hence the name. This technique made it easier to build 'developable', but more sharply curved, hulls, particularly multihulls.

Both techniques were originally developed with multihulls in mind.

[ 12-20-2003, 11:30 AM: Message edited by: JimConlin ]

[Aramas]

There was an article in Australian Amateur Boatbuilder about a decade ago about a guy in Perth that built a Hughes cat using that method. His comment was that yes, it really works and it's really fast. However, planking a hull is only a small proportion of the work to build a finished hull, so even a 90% labour saving on the planking might only be 10% or less saving overall.

You still have to build a mould, albeit a simple one, and there's a lot of scarfing and vacuum bagging involved. You essentially end up with a plywood extrusion of the midship section which you then cut to shape and 'torture' into a hull shape It's then stitched up with wire twists or plastic ties, then taped up with glass reinforced snot. I gather there's a rather lot of bogging and sanding involved to get a fair hull that matches the other one smile.gif

I have a Hughes plan catalogue from the same period that goes into a lot of detail on the method. Hughes' commented in it that it's not suited for people that are too fussy about it turning out exactly like the plans - lol. It's more suited to the 'do it by eye, and if it looks right it is right' school of boatbuilding.

The problem with most of the 'quick and easy' clever building methods is that, as previously stated, it places limitations on the shapes that can be used.

[ 12-20-2003, 11:34 AM: Message edited by: Aramas ]

[Ian McColgin]

The cylinder mold approach has been the normal approach to developed metal surfaces for a couple of hundred years now.

I never really understood the math of how the plating schedule is creating, but it makes for a nice hull. Beiser's large Alden ketch (see "A Proper Yacht") was done that way.

[JimConlin]

I just looked a little deeper in the Kurt Hughes site and found THIS (http://www.multihulldesigns.com/pdf/cm33.pdf)

[ 12-21-2003, 12:39 AM: Message edited by: JimConlin ]

[JimConlin]

I came across another cylinder molding project HERE (http://groups.yahoo.com/group/multihull_boatbuilder/message/6394)

[Tom Speer]

I think you'll find that both cylinder mold and constant camber hulls have compound curvature. In the case of cylinder molding, the compounding is not as severe as a typical tortured ply hull because you're starting with a single-curved material to start with instead of a flat sheet.

The compound curvature of the constant camber hull is built-in when the ply is molded.

[bainbridgeisland]

Originally posted by JimConlin:
I came across another cylinder molding project HERE (http://groups.yahoo.com/group/multihull_boatbuilder/message/6394)I notice this fellow had trouble with voids when laminating sheets of ply together. Drilling 1/8" dia holes every 6"x6" or so in all but the first layer eliminates this problem. Try it. It is not part of the process that Kurt normaly uses but it has worked for me.