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View Full Version : lets talk about those deck beams....



redbopeep
09-01-2007, 02:02 AM
Ok, I'm a'staring at the beams that will need replacing (rotted) and wondering about what I see.

The boat is 54' on deck so there's plenty of deck beams to stare at. Now, from the stem back to frame 17 there's the foredeck, then at 17 on back we have a flush deck (raised deck). What I'm wondering about is how the deck beams are "supposed to be set" on the shear clamp. Looking at the plans of this boat I see that the deck beams are drawn parallel to the frames, in other words, they're "vertical" and don't follow the shear. However, what's the "as built" state is that the deck beams are vertical from about frame 14 on back but they're set at a slight angle averaging about halfway between parallel to the frames and perpendicular to the shear clamp from frame 13 forward. This includes the deck beams around the foremast (schooner rig) which have some lovely blocking between the deck beams that I wish to retain and reuse.

It seems a bit interesting that they're set this way. The shear line (and thus shear clamp, too) is noticeably coming up from about frame 15 forward. Frame 13 deck beam "starts" being a little bit off of vertical and has a small cut in so that it rests properly on top the shear clamp. By the time we get to frame 9, its a bigger cut (the shear is rising faster) to make it fit properly at an angle and it seems to have made it to that "halfway between parallel to the frames and perpendicular to the shear clamp" position. By frame 6, the deck beams are really quite "canted" but still have a cut into the shear clamp because they're not quite as "canted" as they'd be if purely perpendicular to the shear clamp.

I hope you can understand this.

So, what's "normal" in the world of Crocker schooners? Or boats of the 1920's-1940 era? We're tending towards just going with what's there already but wonder if what's "right". I see no mention of this is Steward or any other reference books I own.

As always, I appreciate your input!

Jim Ledger
09-01-2007, 05:29 AM
It was probably a lot easier and faster to install them canted. there would be a lot less wood to remove under the seat and on the top when beveling the beams fair.

outofthenorm
09-01-2007, 06:58 AM
If I understand you correctly, it sounds like the cant was built in originally rather than being from long term distortion like sag or hog. If it was original, I'd be tempted to put it back the same way, unless there was some other VERY good reason to change it. According to Mystic Seaport, Crosby built their catboats with canted frames, and by inference, canted beams as well. They were just small boats, but it seems pretty certain that big boat yards did the same thing now and then, for exactly the reason Jim said. But I'm puzzled by your comment about the shear line "coming up" - is that a design feature or a distortion?

- Norm

redbopeep
09-01-2007, 10:28 AM
If I understand you correctly, it sounds like the cant was built in originally rather than being from long term distortion like sag or hog. If it was original, I'd be tempted to put it back the same way, unless there was some other VERY good reason to change it. According to Mystic Seaport, Crosby built their catboats with canted frames, and by inference, canted beams as well. They were just small boats, but it seems pretty certain that big boat yards did the same thing now and then, for exactly the reason Jim said. But I'm puzzled by your comment about the shear line "coming up" - is that a design feature or a distortion?

- Norm

I probably am not doing a good job of describing the shear. No distortion, its a normal looking shear, not "linear" but instead is more or less flat for a bit in the middle of the boat and curving upwards towards the bow in a a pleasing shear line.

When you're looking at the shear plank (and the clamp) "locally" in the boat's midsection, you see that it is perpendicular to the frames, (and deck beams) but as you go forward, it becomes clear that the shear is rising and the clamp is no longer perpendicular to the frames. Nothing special about it, I'm just probably not describing it very well. I was very interested in the fact that the "cant" of the deckbeams seems to be halfway between a "full cant"that they would have if it remained perpendicular to the shear and full-on vertical that they would be if remaining parallel to the deck beams.

Since the frames themselves are not canted, we didn't expect the deck beams to be canted either.