The first thing to decide before any renovation is, what to leave in and what to throw away.

I've never regretted tearing out an interior. if in doubt, tear it out! You'll be happy for it later.

Don't let metal get in your way; I've seen lots of boats where the interior design was compromised by old steel parts that would have been easy to cut away before the wood went in.

With rare exceptions, you don't need those steel bulkheads [walls] unless you're planning to sail the ship. If you have a steel cabin and roof welded over where the opening of the hold was, then the ship is much stronger than it was when in service, loaded down to the decks. Just cut them away. If you have a wooden roof with no steel across the top, you should leave some of the bulkheads in. Just cut doorways through.

You can rent a cutting torch [snijbrander] or have it done; but believe me, you'll never regret the metal you took out, just the metal you left behind.

Obviously, be careful! Have water available to put out any fires immediately before they get away. I like to have a bucket and a scoop of some kind to throw the water with, and a hose, ready and close by. And a fire extinguisher standing by as well, just in case. Don't cut metal if there's wood behind it, or a cavity you can't reach with the hose. There's often debris and grease that can burn.

Rusty metal is hard to cut with a torch, On heavily rusted steel, use a disk grinder if possible. Wear goggles to protect your eyes and ear protection so you can't hear the neighbors complaining about the noise.

Windows and doors;

Leaky windows and doors have to be replaced or repaired; double glazing is highly recommended. Heat is expensive these days, you don't want it bleeding away.

Windows and doors are very expensive to have made, because it's time consuming. There are plenty of companies that supply them, check around for the best price.

For wood in steel, I prefer to use a steel frame and hang the window or door directly into it. the difficulty is that the person who does the steel work rarely does the wood work as well.

 In this diagram, a T steel window or door frame is welded into the hull. The blind ear of the frame is handy for attaching the interior wood. I use a cartridge hammer to shoot a nail straight through 6mm steel. the hinge is screwed to the wooden door or window with wood screws, and to the steel frame with machine screws. I use a rubber sealing strip between the metal frame and wooden opening section, and finish with a tightly fitted strip of hardwood. Note that this is an outward opening window, not the norm in European houses. It saves interior space, but could be a problem if another boat comes alongside and damages it.

Insulation, vapor, and condensation;

Condensation is the hardest thing to avoid in a steel skinned living space. To prevent it, first we have to understand how it forms.

Water will condense, or form, out of warm wet air when it is cooled. That's how rain works. In a ship, condensation will form on cold metal inside when wet interior air from your living space flows over it when the outside temperature is low. The only way to avoid it is to keep the interior air from the hull. This isn't easy.

Grease the inside of the steel, and fill the wall cavity with insulation. I favor Rockwool in 2  45mm layers. Then lay a membrane of impermeable plastic [bouwfolie], then add the interior wood.

I try to make the overlaps between the plastic sheets fall along a beam so that the seam is sandwiched between the beam and the interior wood.

I'm not a fan of the 'niposol' bubble foil insulation. In my experience, it doesn't work half as well as claimed. Also, contrary to manufacturers claims, it will burn [A friend of mine found out the hard way]. On top of that, it offers no sound absorption [which is very important].

 Also, it creates a condensation trap between itself and the metal. I've taken it out of where I'd installed it, and put in rockwool.

Attaching wood to metal;

There are as many ways of doing this as there are people who work on boats!

I use a cartridge hammer [Sheithamer in Dutch]. It uses an explosive .22 cartridge [like a gun] to push a piston that pushes a specially hard nail right through the wood and on through the steel. I've routinely penetrated 45mm wood and 7mm steel. It's fast and very secure, but expensive at around €0.40 per nail with cartridge. Also it only works if you have a solid piece of steel in the right position to nail into, usually this means only the new part of the boat. Obviously you can't attach to the outer sheet; the nail will stick out! The tool can be rented. Contrary to common belief, you don't need any special license or permit to use the tool.

Another system I use is very simple; drill a 5.2mm hole right through the wood and the steel, then use a 6mm possidrive wood screw [spaanplaat screw]. Sometimes I put a little soap or grease on the screw. It slides right in, is secure, removable, and adjustable. The only trouble is, you have to drill the holes. On a big job, there are thousands of them.

Also available are "self drilling self tapping" screws made just for this. I'm not at all impressed with them; you have to push really hard to get them to drill through. Try that overhead a couple of hundred times. And they aren't cheap either.

Several people I know use "clamping"; hold a piece of plywood behind the wooden beam, then screw through the beam and into the strip so that it tightens behind the ear of the steel, holding it all in place. I don't really like this system as it gets in the way when insulating, and I'm not sure how well it will hold over time. I build ships to last for 50 years or more. But my friends report no problems with the system, so maybe I'm just over cautious.

Windows;

The choice of windows is really an architectural or design decision, but I hate those porthole or boat windows.

You pay a huge amount for a poor window; they're small and have metal frames. the metal is always cold in winter, since it's bleeding your heat away. If you're going to sea, use proper boat windows, but if you're permanently moored, use double glaze units that let light in. Those metal frames drip condensation inside all winter long, causing the wood below them to be stained and wet.

I've nearly always made my own windows from hardwood and steel, but that's not for everyone. You can order regular window units made for houses in whatever size you want. Fitting them in a steel hull will mean a trip the the shipyard most likely, a hole cut [from the inside], and steel strip welded in to form a frame for the window unit.

Windows in the hull;

A lot of people are hesitant to cut holes in the hull, but there's no reason not to. Insurance companies say the bottom of the cut has to be at least 20cm above the waterline, and I prefer a bit more in case your boat gains weight some day. Non opening windows 25-30cm above the water [and I use extra heavy glass for those just so I feel better], and opening windows from 40 cm above the water.

Don't worry, if the boat wants to be returned to freight service in the year 2525, the hull can easily be welded shut again.

Roof windows or skylights;

They usually leak. They're usually insecure. They let in little direct sunlight in winter [when you want it], but lots in summer [when you don't]. If you want to bake like a fish in an oven all summer, and you like cold drafts in winter, install skylights.