MonoCoque Construction...

Hi,
Is it possible to build a boat as one solid piece of hull and deck?

Are there any benefits?

Is it pointless compared to traditional construction of hull and deck?

 

You might say that aluminum and steel boats already are built this way.

In a fibreglass boat, the hull/deck joint is a major weakness and is often underdesigned and poorly fabricated. I have seen some on 20-30 footers that were secured by nothing more than self-tapping screws every 8" or so- and this at a boat show. These vessels had never hit the water and the joint was already splitting open.

The nature of moulded fibreglass construction is such that there must be joints. There are basically two ways of building a joint that works. One is to build it strong and rigid enough that loads are shared across the joint. For example: through-bolting the hull/deck joint, then injecting Plexus into the gap, then laminating fibreglass overtop. The other is to build a completely flexible joint that moves independently and shares almost no load. For example, the expansion joints in a bridge, the silicone sealant around a window frame, or the adhesive joint holding a car windshield to the body.

Fibreglass boat hull/deck joints often end up somewhere in between- not strong enough to share all loads, but not flexible enough to yield and recover without damage. Both the hull and deck of a fibreglass boat are structural elements, and loads have to be transferred between them. The joint often becomes fatigued, it works open, water gets in, and things start to disintegrate.

So in short, a PROPERLY ENGINEERED solution that either eliminates joints or effectively fuses them into one piece, can be a very good thing if you can pull it off properly.

 

Epoxied, directionally fiber(glassed mostly), wood/foam cored hulls often are just that.
It's either lighter, cheaper, faster or stronger (maybe bit of this and that) depending what's been the main considerations of the boat..

 

Technically, a hull, regardless of how many pieces are bonded to it, (stringers, bulkheads, etc.) is one giant molecule after it's cured. So in this sense it's monocoque.

From a practical stand point you can easily under stand why you'd want an accessible (no deck) hull shell to install the interior, electrical, plumbing, tanks, engine, etc.

Many roto molded boats are in fact one continuous piece of plastic, hull deck, seats, the whole bit. These boats typically are so simple in nature they can be built like this. More complex shapes and boat's with a fair amount of equipment need to have a way of installing it, before it's entombed in a cocoon like shell.

 

Thanks all.
Asever invaluable comments