Hull Construction

[Emerald]

Hi All,

I've always been fascinated with how boats are built, and the whole idea of joining two halves is way up the list with questions. So,anyone out there with some solid knowledge on how Ericson joined the two halves together on the boats constructed that way? For example,the schedule on the Independence 31 (from
brochure on this site) is as follows:

Below Waterline:
3 oz matte
7.5 oz cloth
3 oz matte
18 oz roving
18 oz roving
3 oz matte
18 oz roving

On Centerline:
Same as below waterline
4 alternating layers of 3 oz matte and 18 oz roving

The text with this continues, "This schedule provides a hull thickness of 1" in the centerline area and 1/2" in other below-waterline areas."

so for my boat, does this really indicate that the schedule for the centerline is the material used to join the two halves together? Is that 8 layers total (4) 3oz and (4) 18 oz alternating? Am I correct that in almost all cases, the predominant forces at work on the two sides in a hull, regardless of construction, is compression? Other things that come into play?

Just for the record, I am not worried about my hull splitting in half. Just want to learn more about how it all goes together.

Thanks!

 

[Russell Skinner]

Hull

David,

I'm not sure about the exact layup, but that sounds about right. A sailboat hull is exposed to all sorts of forces. General compression for sure, but also alot for tensile forces, particularly at the chainplates, point loads at mast base and engine mounts, bulkheads, and groundings- and also all kings of other racking, twisting, shearing and moment forces are at work as the boat moves through the waves. Frieghters have been know to break in half while either in the trough or on top of a wave with both ends cantalevered out in the air.

The good news is your 31 is built like a rock.

 

[Randy Rutledge]

Russell, are you saying a sailboat in rough conditions goes through about the same thing as a frog in a blender?
The water presses in on the hull the shrouds try to pull it apart and the mast tries to drive the compression post through the hull with the aid of the running rigging. A wave to the side of the bow loads the rudder and keel while twisting the hull.

Yet the surest flotation is a bottle and that is not far from the shape of a sailboat.

Gotta love these E boats.

 

[exoduse35]

just about right

that discriptoin while crude and nasty sounding is pretty close. kinda elevates Bruce King to even higher god like status doesn't it? as for the construction of mating the two halves, the halves are trimmed at the matting edges coated librraly with adhiseave/sealant layers and stuck together. then the layers described are bonded in. the reason for the diferent types of fabric is that they have unique strength charictoristics. the cloth has fair strength in the direction of the strands, great strength diagnal to them, and provvides the smoothest finish to start or finish a lay up. it doesn't show as badly through gel coat, and the fibers lay flat. the mat is made of long fibers that are glued together. when wetted out this glue is released, and as the fiber is layed randomly the strength is also distributed randomly [or in all directions] it does however want to rise off the plane it is being aplied to, leaving the surface rough in texture and sucessive layers compount this. roveng is kind of a comprimise, or hybred of the two. it is esencialy a cloth on steroyeds. instead of individual strands weaved together, bundels of strands are. this is akin to a rope verses a string. roving has superior strength to either cloth or mat in a single layer, however in multiple layers large air voids are created by the coarseness of the weave. the resin is used to capture the strand fiber and hold them in a fixed position. the resin itsetf has very little strength and is brittle. air of course has no strength. the lay up order is designed to minimize air, and maximizr the fiber held by the resin. the mat layers in addition to providing strength at their own layer also expand into the weave of the roving layers above and below, filling the void of the coarse weave with fiber and thus removing air and resin, making the most solid build up possible. hope this brief tutorial answers the original question