Part One - Part Two - Part Three - Part Four
For this installment of Reading Plans I thought we'd look at interior plans. I could not find any real help on the internet for cabin plans, so this will be quite general. The issue is easy to recognize. Plans are in two dimensions - lengths and heights and widths. But the builder has to create in 3 dimensions.
These are the two dimensions, by Francis Herreshoff, one of his little gems, the H-28. It is 28 feet overall. The cabin space is in the shaded area, the cabin roof is in red and the cabin sole planking is in blue. I've shown the two dimensional views, since that is what plans look like. They do so that the builder can put down exact dimensions on the flat. But when the designer and owner sit down to talk about the cabin layout, they will need to look at it in three dimensions, as I have drawn it in at the bottom.
I would imagine the no. 1 priority is, how much space is there - really - in it? We can first look for the designer's headroom, remembering headroom is usually at the galley near the cabin's rear only. What you have to see is if the cabin sole changes height. But that's only one dimension. The width has to be taken into account. That's usually simple enough to determine at the boat's beam. But then how much room is cut into by frames? And is there an interior wall, called a ceiling on big ships, which would cut into the interior volume even more? And what about where the hull narrows? Usually, a bulkhead sits where the hull narrows so that beds or storage are in front of the bulkhead. That makes some room below unusable for a family.
And then there is the nebulous subject of headroom. The Atkins didn't believe that most cruiser-owners needed 6 feet, or even 5. They liked low cabins for low windage and fairly shallow keels. The idea many had before 1960 was, the less room the more the cockpit is the area of choice.
And then along came Philip Bolger with the Birdwatcher. He showed a taller structure could still sail well, and owners would use the boat more often, in a variety of settings. The compromise is the flat bottom is where you sit. The arrival of the lug sail really helped the sail rig from being astronomically tall.
So, do owners like the headroom they specify, or do they end up wanting more than the original plans showed? I don't know, but I think it would make an interesting survey. I know of one designer who believes owners actually need less headroom than they request.
This is a motorboat named Kittiwake, a sensible 24 feet, 8 3/4 feet wide with a 2 foot draft. It is a simple build if you have around 35 feet by 15 feet. When the designer Sam Rabl built it, he put it together in his back yard.
You can see the keel, stem and stern are fairly simple with the frames from keel to sheer numerous but not hard to install. Sam would probably say frame both sides at the same time.
The mainframes hold the interior, so the frame dimensions are substantial. Sam likes to draw his mainframes from top left to bottom right. The side and bottom frame pieces are connected with carriage bolts, which we might not do these days. The mainframes are 1 1/4 x 3".
This is the cabin framing page. This gives you the dimensions of the bunks, the location of the motor box, the floor joists on the forward side of the frames (except for the one furthest aft), the distance between bunks and other measurements. Once you agree that this is how you want the interior to be, or that this is enough space for you, this page is not really helpful except that it is clearly drawn. I do like the way Sam has the water closet well away from the galley.
However this page doesn't specify the methods of construction we need. For that we need another page.
Here we have the three mainframes which constitute the cabin with a detail. The detail shows you how the beds are tied to the frames, how the frames are used for support and the reinforcement pieces at joints. Sam assumes you will use the same method on all three cabin frames.
So you see the method is to frame from the keel to the coaming with each frame and knees. Then the main frames come in, from stern to stem. With Kittiwake there are no 'bulkheads,' since the main frames take that role. Then the cabin details. On some designs the bunk will not end and be secured to a main frame or bulkhead. An additional bulkhead will be drawn in, sometimes on one side of the keel only. You can see how much space the bunk takes up.
By the time you finish with the frames, mainframes and interior joinery, Kittiwake will be as stiff as Elvis.
Paul is also publishing his books on Amazon.