Bilge Stringers, sheer clamps & Beam shelf

[cs]

So as not to add unnecessary stuff to the dragonship thread, I thought I would come here and show my ignorance and ask just what are these.

Chad

[crawdaddyjim50]

Bilge stringers run for and aft like butt lines perpendicular to the frames. A sheer clamp is the part of the outside edge of the boat where the deck meets the hull. Not sure of Beam shelf.

[Ken Hutchins]

These are internal structural members running fore and aft, in this photo the bilge stringer (or clamp) is the lower one with some of the dust removed on the lower end it is riveted thru the frames and the planks. The shear clamp is the upper one which is cross bolted to the deck beams and riveted thru the frames and the planks. A beam shelf would be a thinner additional piece inboard of the shear clamp and secured to the beck beams and the shear clamp.
http://www.imagestation.com/picture/sraid192/p1c37cdb4b786b6a5a6d002963dc90856/f1bd9e67.jpg

[crawdaddyjim50]

So you would use a Beam shelf if your sheer clamp was not wide enough to accomadate the deck beams and cross bolts?

[Ken Hutchins]

A beam shelf would be required with a smaller, thinner (weaker) shear clamp, all these components add strength and stiffness to the hull.

[crawdaddyjim50]

Thanks, I think I have it now. Those are some pretty good sized scantlings on the boat in the pic. How big is she?

[mmd]

http://i32.photobucket.com/albums/d19/mmd_ns/sectionJPG.jpg

The sheer clamp provides longitudinal strength to the entire hull, as well as local strength to resist banging against wharves & stuff. The beam shelf adds to th elongitudinal strength plus provides a greater bearing surface for beam ends. The bilge stringerprovides longitudinal strength to the hull, local strength to the flatter areas of the bilge, and halves the unsupported span of the frames.

[formerlyknownasprince]

Plenty of stringers here:

http://www.imagestation.com/picture/sraid105/p7723121659c7c5d1570f12b30f433303/f9725644.jpg

That's a five gallon jug of West system for scale - and 2" diameter shafts

Ian

[Ken Hutchins]

The photo is my TALLY HO II, 36'LOD do the search thing for more photos and also our web site.

[cs]

Thanks guys. Michael your image was rather helpful. I now understand and can continue on.

I'm learning more about boats by design (thanks to all those how are guiding me) than I could ever learn by just reading.

Chad

[seo]

The shelf is a fairly recent addition to marine construction. I believe its primary purpose is to increase panel stiffness of the deck.
Hull constructiion changed with the introduction of bent (as opposed to sawn) frames, outside ballast, and also when the ceiling ceased to be a structural element.
In the old days of freight carrying wooden hulls, the ceiling was nearly as thick as the planking, and added greatly to the stiffness of the hull.
This is still seen in historical vessels like the Maine schooners, some old big draggers, and some replicas. Some older construction did not have a sheer clamps either, but instead used a hanging knee at every frame, with lodging knees to provide panel stiffness to the deck. Yarghh! me hearties!!
I wonder if the need for a shelf has been effected by the almost universal use of plywood for deck sheathing. That made deck strapping obsolete, as well as the tie-rod bolts that were necesary to keep a laid and caulked deck from pushing the grub beams/coamings and carlines off the end of the deck beams.
Lots of these changes were made by the various Herreshofs. LF in particular started out before the age of plywood, and continued designing and innovating after decks and bulkheads were made out of plywood.
seo

[bainbridgeisland]

Seo, even within western boat building, structure is not cast in stone. You probably realize that structural features vary with the availability of material. So, on the Pacific Coast of North America, a classic structure uses a 'harpin' instead of a sheer clamp or sheer clamp and shelf assembly. This was done because very large timbers were available and the method produces a strong hull that is easier to build (at least sometimes). This is only one example of many possible variations. The marine press in the USA has concentrated primarily on the structural methods of the North Eastern part of the country (they are getting better about this but the classic texts in this country have this perspective). So many folks think the methods used in the North East are the only 'right' methods to build boats. I think the correct way to view variations is to enjoy the ideas and recognize that there is not a singular right path to boat building.

By the way Seo, I agree with you that we don't see a 'shelf' as often as we used to. I think MMD's illustration is a very good place to start from though.

[Alan D. Hyde]

That's an excellent illustration, Michael.

It's way above average for that sort of thing.

Why not (in your spare time, of course :D ) author a short but profusely illustrated book on Understanding Traditional Boats??? I'll promise to buy a dozen copies... smile.gif

Alan

[mmd]

The section that I posted above is the 'midship section of Herreshoff's "Bounty". I did a re-make of the interior at the client's request, but the hull is as Mr. Herreshoff drew it with the exception of the bilge stringers, which I added in the illustration just for this posting.

A short course in the structural elements of a small wooden sailing boat can be had for a pittance by purchasing the poster by Sam Manning shown below from our host's on-line store.

http://www.woodenboatstore.com/images/710008.JPG

[ 11-29-2005, 03:47 PM: Message edited by: mmd ]

[Jay Greer]

L.Francis Herreshoff, like his father Nathaniel, usually left the bilge stringers out of his designs as he was of the opinion that,"They are too close to the center of gyration to be of any use or have any practical effect."

My own opinion is that leaving out the stringers but sealing a hull from cabin sole to one ceiling strake below the sheer clamp has two positive effects. First it strengthens the hull without creating hard spots that strain and crack frames. Additionaly, it creates a chimney effect that circulates air from the bilge and out the sheer clamp area by thermal convection and effectively keeps the inner hull freer of dampness than an unsealed hull.
JG

[Bob Cleek]

Remember, though, that the Herreshoff's boats were built lightly in general and had rather flat runs where the bilge stringer would lay. Different hulls might benefit from stringers more than theirs. Also, the bilge stringer, as much of a pain as stringers are to install, is a very useful attachment piece for cabin furniture.

[seo]

Bainbridgeis, I hope that I didn't sound doctrinaire on construction. What works, does. In the early 80's I worked on a couple of big 80'+ Alaska salmon tenders, and the differences in construction from east coast practice was interesting. In some ways they were more similar to scandanavian boats of the same size and type, which isn't surprising, given who built them.
Certainly the availability of great long Douglas Fir timbers for cheap must have effected design. I read somewhere that Dougfir was the only wood that you could build an entire vessel out of, from keel to topmast truck. Maybe it was even true...
For myself, I do not like bilge stringers, and don't much care for ceiling. I've seen lots of frames broken right at the stringer, and think that there's a cause/effect. As for ceiling, I like to be able to see as much of the hull as possible. I like the look of frames and buttblocks. My current boat is all ceiled in, but I don't have the courage to remove it.
My favorite wooden hull construction innovation was the elimination of carlines under cabin trunks. This is done in LF Herreshof's H-28, and is simple and neat, with no rotting timbers buried in there, bolted six ways to Sunday.
The LFH method was to simply let the deck halfbeams end on the inboard side, and lay plywood over them, then canvas, then set the cabin trunk sides down directly on top of the plywood. Bolts went up through the ends of the half beams, through the plywood, and up through the trunk sides. Regular planking screws went up through the plywood into the trunk side in between the beams.
By making use of the great stiffness of the cabin trunk side, LFH eliminated a part (the carline), simplified things, and made full use of the panel stiffness of the plywood deck by fastening it to the trunk sides.
After all, the carlin is just left over from old ways of building hatches, with carlins, grub beams, and tie rods.
Years ago I surveyed a Derektor Gulfsteam 30 (maybe Bob D's personal boat?) It had a very clever improvement, with each deck half-beam protruding about an inch inboard of the cabin trunk, all of them capped off with a varnished longitudinal piece that looked good, made a great handhold, and perfect for hanging dishtowels.
seo

[Billy Bones]

Originally posted by mmd:
A short course in the structural elements of a small wooden sailing boat can be had for a pittance by purchasing the poster by Sam Manning shown below from our host's on-line store.

http://www.woodenboatstore.com/images/710008.JPG...And those very same illustrations along with an extrordinarily good essay explaining them is available in the back of "Forty Wooden Boats" also available from our host. If you had to buy just one of the WB design books, I'd make it "40". Still, "30" has a great essay on boat design theory by Joel White. Great stuff, both.

[seo]

For what it's worth, both "Sensible Cruisng Designs" and "Commonsense of Yacht Design" (both by LF Herreshoff) offer great drawing, incredibly good drafting, and lots of original thinking. Some of the ideas weren't all that good, but he did get up in the morning and start thinking...
seo