Marine Engineering 104: What keeps what’s inside my boat, inside my boat?

What is it with interiors? Those inner, untalked-about bits of boats that never seem to see the light of nautical-chat day. Does anybody, anywhere brag about the size of their cabin sole? Or compare the space-age materials in their staterooms or galleys? Has anybody ever said “High-performance head” on any boat in any century, ever? We doubt it. 

Meet the interior of a boat. In this case, “Anna” in construction at Lyman-Morse Boatbuilding. Thanks to Alison Langley Photography

“Interior denial” is a sort of sad fact of boat-design life. That’s too bad because what’s going on inside your boat is a driving factor for what’s going on outside your boat: How long she is; how beamy; how big the sails and engine, all are subject to the volume and demands of a floating vessel’s interior. And when it comes time to build that boat, watch out! Interior construction is probably the major factor in how a boat gets made. What interior parts are built into the hull? What parts are prefab-ed and dropped in later? A big part of the yard’s job is to machine, massage and mechanize the construction of interior detail and features. Yet, so little is known as to why an interior is built the way it is.

What fortune then, that we are in the final interior-details push done on our latest: the 66-foot Anna. She’s just coming together nicely over at Lyman-Morse Boatbuilding, in Thomaston, ME. And as we’re cranking the interior drawings out, the production design staff at LM are turning our interior into reality.  This is quite a process worth going into further, later, yet we’re realizing now it’s a great — and rare — opportunity to open up the inner details of interior construction to the outer boat world.

If you’ve ever wanted to take a fantastic voyage down through what keeps what’s inside your boat, inside your boat, buckle on up:

Here’s why what’s below is what it is.

The Interior-Structure Brothers.

The big “know” in nautical interiors is that all the stuff inside a boat is made either one of two ways. It is either hand-installed piece by piece by craftspeople down inside the boat, usually as custom elements carefully designed to extend the structural needs of the hull to serve a human functional purpose. Or the interior structures of a boat are part of larger modular units that are pre-assembled outside the boat; and then dropped into place in one step, like a pre-fab home.

Interiors come in two flavors: They’re either hand-installed elements finessed to do structural work …

Modular pre-built units speed assembly, offer ease-of-construction and allow the full intelligence of modern team manufacturing technologies to come to bear.

What’s groovy with Anna’s interior is she uses both approaches. Depending on where you are looking inside her, some bits are hand-constructed. Some are modular. And examining the different engineering passages in her explains why those choices were made. 

Let’s start in one of our favorite inner rhythms on this boat: the forward master bedroom. This area is seriously engineered to bear the burden of slamming into big bad seas. Every square foot of this part of the hull needs to resist more than 1,200 pounds of pressure. That’s right, every frame bay here needs to support an elephant. Whoa! To handle that load, we installed, between the forward bulkhead and the cabinets at the foot of the bed, four frame bays; each is divided into two or three sections by stringers. If you’re scoring at home, that grosses up to between ten and twelve elephants per side. You are doing the math right: Anna is built to feel a herd of between 20 to 24 elephants standing around grazing on her. That’s a lot of elephants.

This high level of primary structural integrity comes from the laminated frames or  “ribs” of the hull. But see how the cabinet-work also helps add strength? They play a crucial role in dividing the frames into lengths that are small enough to resist the deflection the elephant-herd of wave stress. Those frames are rugged enough to let us sneak in a queen-size bed on centerline, so its sides form longitudinal stringers that go right down to the hull skin and support those frames. It’s simple once you see it.

… Or they’re pre-built units, dropped in essentially fully complete. Like a really well made mobile home.

Notice how the bed-side tables run the length of the bunk each side and are integrated into yet more stringers hidden under the decorative teak top? Further, storage in drawers and for hanging garments demands specialty cabinets; these integrate to the structure engineered in transverse and horizontal cabinet surfaces to add yet more stiffening where both are bonded to the frames and the hull’s skin. It’s all delicate to get just right: The cabinet-work must be strong enough to support the hull, and that strength can’t suddenly stop in random a “hard spot,” where stresses coagulate, spike and cause failure.

It’s strange to get your brain around. But with custom-installed load-bearing interior furnishings, if you screw up the wrong night table, she’ll sink.

Exposing Anna’s Mod Side.

What makes Anna a terrific interiors lesson is how other sections of her insides turned out to be better manufactured as drop-in modules. Parts of this most-unique custom yacht really are  bespoke quality, though the production method could compare conceptually to any high-output trailer home. But instead of using those interior construction efficiencies to drive costs down, we turn those resources into better features, higher performance and richer design.

Here is the starboard galley and head module just as it’s flown in and installed.

The 3D rendering  shows what’s possible with pre-built modules. There is the port unit that features a cabin, a small sitting area, a head and some serious storage. And then a starboard unit with larger master bathroom and shower, the complete galley. Both pre-fabricated sections made on the shop floor, by craftsman who get to work in utter luxury of standing and doing their jobs upright. Once dropped into the hull, both units are essentially finished. (Keep in mind, the cabin sole absolutely adds structure to this and all parts of the boat. But we hid it, for the most part, in this drawing to show the engineering detail. )

The entire starboard galley and master head is held in place by just a few attachment points, and “floats” off the hull its own egg-crate “skin.”

Notice how the starboard module, above is flying over the boat, just as it might be just before it would be dropped into the hull. See how it’s pre-built to a high level of completion? All but final paint and varnish is applied. All systems like heating and cooling ducts, plumbing and cooking gear, etc, are installed. Just a few key connection points are needed to mate the unit to the boat’s structure. In this case, it’s where the bulkheads meet frames and the sole substrate to special support structure built into the bottom of the hull. Most of the interior partitions and shelves are kept “floating.” That means, there is space between the unit and the hull skin. That way, the units do not require careful fitting. Why waste the time?

The port unit uses a similar approach. It too was pre-made with all but the final finish, comes with plumbing, HVAC and storage. For the record, the deckhouse that goes over top both these modules will be built more like the forward cabin. It will mate up with the engine compartment after it is installed into the larger deck module, that closes the hull off to outside elements.

Anna’s Insides Are Happy to Meet you!

We asked. And Anna told us, because she likes us, that she would be thrilled to have you and your family stop on down and take a look at her interior work for yourself, at any time her shop is open. Her maker, Lyman-Morse Boatbuilding, is happy to introduce you to this newly coming-together lady.

Plus, there’s this an awesome bistro called The Slipway right over on the next dock from Anna’s yard. What better day trip could there be? A fantastic voyage outside to this lovely Maine town to see the world’s best craftspeople finish off the inside of this marvelous boat, followed by lunch.

Let us know if you come. We may join you. We can sit over a crabmeat roll and joke about how all those smart people, working so hard, make us designers look really good!