Bushwacker |
05-10-2012 10:28 PM |
Quote:
Originally Posted by Blue_Heron
(Post 202306)
Regardless whether it's a Moesly or a Potter, the original transom would have been alternating layers of mat and roving. That's definitely not the original outer skin. Only an inexperienced and poorly informed amateur would use an all mat layup on a transom laminate.
Dave
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I agree, that's not the original transom, it's a lousy repair job! Look at the first picture and you'll see that the core didn't even follow the contour of the bottom. If those big gaps were filled with water, it's easy to see how a freeze would have busted through that weak mat! Here's the original laminate schedule thats described on page 2 of the 1969 Boating magazine test of the 20' Seafari:
1. 2 layers of 1 oz. mat against the gel coat (to prevent print through of the roving in gel coat.)
2. one layer of 18 oz. roving.
3. 4 more alternating layers of 1 oz. mat and 18 oz. roving, for a total of 7 layers of glass, and .221" total thickness.
4. Additional lay-ups in highly stressed areas bring thickness up to about 0.345".
5. Bottom is stiffened by 4 pre-molded fiberglass inverted U-section stringers located in way of bottom jogs. Stringers backed by 4 alternate layers of 1 oz. mat and 18 oz. roving and taped in place with similar layup.
If you look at the sketch on the last page of that Boating Magazine article in the Literature section, it clearly shows how the stringers were taped in with 4 additional alternating layers of mat and roving. The thickness distribution in the bottom design is a brilliant use of material from a stiffness perspective . . . the hull is naturally very stiff at the vertical steps, but having a stiff section with a thin section on either side of it would be asking for trouble. So Moesly straddled that vertical step with a VERY tall (and stiff) stringer, so what you have is a stiff section supported by a much stiffer section on either side of it! Then in between the stringers, there a couple more 0.345" thick "mini-stringers" created by the overlap of the 4 extra layers of material where the big stringers are taped in to the hull. The very stiff area of the stringers is then surrounded by material that's over 50% thicker than the nominal hull thickness.
The thinking that went into this design is typical of that seen in the aerospace business, where everything must be very strong but extremely light . . . wait a minute, that's how race boats are built too!
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