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Changing Cabin Headroom

On August 26, 2011, in Designer Articles, by Glen L. Witt

Headroom in the cabin of a boat is all important to many. Granted, having a generous space above your head when you’re inside is great, but let’s be sensible.

Full headroom on a boat under 20’ is mostly impractical. Yes, there are a few exceptions. A houseboat and some displacement hulls with deep bilges may come close to full headroom.

However, most trailerable boats under 20’ will look top heavy, and well may be, if the cabin structure provides full headroom. The closer the length approaches 30’, the more full headroom becomes practical.
Just what is “full headroom”? For years 6’ under the cabin beams to the sole (floor) was considered full headroom. But, let’s be practical; six foot people are quite common. Then too, can you walk comfortably with only an inch or so above your head?  Nope, you will automatically duck or walk stooped over.

Do you really need full standing room in a boat cabin? Of course not: small boats don’t have much room for walking around. And is it so bad to duck your head?

The above not withstanding. many will insist on more headroom than the plans indicate. Simple–just boost the cabin roof six inches. If it were that easy don’t you think the designer would have done it?

When a person buys a set of plans they do so because they like the looks. Increasing the cabin height to any extent usually makes the hull look and may actually be top heavy.

If contemplating such a change, take the profile view of the boat, lay a white sheet of paper over the cabin, and sketch in the contemplated increase in height.

Chances are, if you increase very much, the pleasing appearance you liked vanishes. And, you may have a craft that nobody else wants when it’s time to sell.

There are a few ways to “cheat” a little more headroom without lousing everything up. Increasing the crown or arc of the cabin roof will gain a little. Eliminating the cross cabin beams is another. Beams can be run lengthwise and the cross beams eliminated providing a clear pathway along the center of the cabin.

Eliminating the beams entirely and making a “sandwich” cabin roof is a method we’ve used on a few of our designs. This requires building a removable framework to the required cabin arc, either with longitudinals or athwartship beams.

Plywood in sheet form is bent over the structure in at least three epoxy glued laminations. A similar approach is to use the temporary framework and bend a single layer of plywood over the surface and fasten around the perimeter.

Athwartship beams about 1” x 1 ½” are bent over the plywood fastening in place from the underside and outer perimeter. Spacing of the bent beams varies, seldom more than 24” apart.

Sheet foam insulation can be optionally used between the athwartship bent beams followed with an outer lamination of sheet plywood seldom less than ¼” in thickness. Both of these methods eliminate permanent cabin beams and gain valuable headroom.

The sole can be lowered between frames to bear on the boat bottom or battens and keel. However, the raised frame makes a nasty stumbling block. Often, a frame can be cut away along the passageway.

The ends of the sawn off frames are then supported with longitudinals, usually the cabinetry will suffice. Sister frames are used one on either side of the removed frame portion; these extend across the centerline (keel) and preferably two battens past the cut off frame.

The sister frames can be bent in place from at least three laminations of plywood about 1 ½” wide and at least 1/4” thick; obviously the size would be increased on larger craft.

It all boils down to that important word “think”. Investigate all aspects before major alterations of the cabin height to gain more headroom.

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