Forward Hatch Measurement

[Hull376]

I know that the factory forward hatch opening on the Ariel is about 18" X 18". But does anyone know the more esoteric measurement of the camber of the front side and the backside lips to the sides? I think the opening is straight on the sides, but the front and back are curved a little to match the cabintop and the shape of the original hatch cover. I'm looking for the delta from the midpoint highest point on the front lip to the sides. It should be something like 1/4" or 1/2"?

I can't get down to my boat to get this measurement, so if someone has it, it would help me out!:)

[ebb]

Kent,
These are measurements taken across the bottom of the lid that was on A338.

The front opening side is 19 1/4" outside to outside.
We assume the curve to be fair and from the center of the curve to a strate edge held across from side to side measures: 7/8" minus 1/32".

Thus if the lid was placed on a flat table, that would be the height of its curve at the center.

The back hinged side at the mast measures 19 5/16" across, outside edge to outside edge.
The curve from the center to a strate edge is 5/8". But notice below in this post that the lid is not snug to the deck on the hinge side. About an 1/8" space more-or-less in the middle (probably an original cutting mistake.. So you could add that to the 5/8" and get 3/4".


The length of the hatch from front to back measures 19 1/2".



Sometime in the past I laid out the curve of the cabin deck at the mast step - on the floor - with a string, nail & pencil to find the radius of the curve. Naturally, I can't remember what that radius was: a number of feet, like maybe 5 or 6. BUT it is on A338 a true radius camber. Which often the mast has flattened.
If you want to generate that circle, the state edge above is a chord. So if you have a floor space large enough you could lay out the actual curve by experiment with a long stick, tape measure or string.
Lay out the 19 5/16" chord with a long 90 degree axis running thru the center of the chord. Using the axis, move radius line or stick up or down the axis until a circumference line (made by a pencil at the end of the stick) hits both ends of the chord. It should match the height in the center above the chord we have on the lid. Actually the height of the curve you draw above the chord is the true height and could be a little different than the curve in the hatch.

This is to say that springing a batten between two nails will probably not get you a radius curve
if you are laying out lines for a new hatch.


Since I cut out this original hatch out with an allround larger hole to fit a Bomar I could get me shoulders through, I still have the hatch, the camber of the deck and the coaming in one piece. The lid fits the camber very well in front but 1/8" shy on the hinge side. Large discrepancy. However the hatch is right there where the mast is and stuff must have got bent out of shape over the years. And the guy who trimed out the hatch lid after it was laid up might have wandered off his cut lines.
I would ballpark the height at 3/4", can always trim the lid to fit a slightly deeper curve.

Also the front of the hatch is out on the 'nose' of the cabin. I did not check the fairness out there, only under the mast at the time. We might assume the curves get artistic out there.
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For the record: these fore-hatches of ours show a good deal of craftsmanship. A338's is precisely made, nicely finished lid with the top left without gellcoating. There are signs that a non-skid pattern was molded on top.
Two traditional 'knuckle' hatch hinges, three inches on the bases but cast in aluminum. These hinges have a little wiggle-room and allow the closely fitted hatch to be tightened down on U-shaped weather stripping around the coaming.
As a system the hatch was made to be watertight.

[Hull376]

ebb,

As always, you're the champ. Exactly what I needed. And more. People really appreciate your help!!!!!