Chine development

I am looking for single chine development info, as relating to sailing craft . I see many different examples of chine development , going from straight at the waterline to arching way up at the bow. I have been trying to simplify some designs , and wonder about the implications of these chine lines .

There are two issues to deal with, one is hydrostatics , and the other is construction . In most cases the solution that offers the simplest construction with the least compromises in good hydrostatics would be best .

I have been looking all over and cant find any explanations for what I see , and that includes chines .

F

 

Chine shape can't be separated from side shape and bottom shape with regards to hydrostatics and construction.

 

Frank.......

Sorry it doesn't work that way.......

Simplest construction equals biggest compromise in form, most complex construction equals least compromise of form. Between these opposite poles lie endless compromises......

The form is altered to suit the use and performance objectives, generally speaking simplifying the form will degrade performance in certain conditions.

The parent of offshore sailing vee bottoms is probably the 1901 CD Mower designed SeaBird, below is a close relation the Gulfweed by JG Hanna. These hulls are reasonably simple, very able, and emphasize low speed (fine entry and exit) light-air sailing ability with good reserve buoyancy in the overhangs. Waterline is short, interior volume low, initial stability is low, prismatic is also low so top speed is low.

 

Here we have a much more modern shape, even though it's obviously related the previous form above. This is the 1958 Black Soo designed by EG van de Stadt. In this case the designer has created a hull with a longer waterline, much more immersed chine, less deadrise and a overall shallower and flatter form. Prismatic is higher, initial (low angle) stability may be higher even though the hull is proportionately narrower because of the wider waterline. Speed potential is much higher than the deep-deadrise Hanna form, and coupled with light displacement a high-performance in heavy air (North Sea racing) boat is the result. She will also have high wetted surface compared to the Hanna hull and will suffer in light air.

 

Someone could draw the wrong, unintended, conclusion from that statement. More complex construction does not always equal less compromise of form. It's quite possible to make bad decisions and have a complex construction with a compromised form. A somewhat extreme example, but one I'm sure has been at least contemplated by someone: a flat bottom, hard chine shape with double diagonal planking over laminated frames and a built down keel/skeg.

For conventional wood or metal fabricated hulls there may well be a correlation between required construction complexity as form compromises are reduced. For fiberglass/composite construction I wouldn't be surprised if the correlation is weaker.

Perhaps another way to say what Tad intended is that reducing form compromises may require increasing construction complexity. More complex construction may enable improved form but does not guarantee it.

 

I like the Guffweed better than the Seabird. Most Seabirds I have seen are overloaded
and the chine is well immersed and I think they would be sluggish. Black Soo , is a nice example of the type and reminds me of John Spenser's work . I wonder how it would be with the bow chine parallel to the water line?

I can see that in a conversion of a round hull to chine , an increase of length is necessary,... not a bad thing if possible .

I am interested in stringer on bulk head construction , and possibly stitch and glue.

Anyway that info is a help.

F

 

I think this would sound better if the word "construction" was replaced with "shape" and it's as true a statement as it gets. The complexity comes from conforming to the least amount of conflicts. Once you introduce unnecessary variables, such as building ease, material choice compromises, multiple concessions to satisfy comfort, safety, preformance, etc. you end up with an end product that does some things fairly well, but nothing exceptionally so. If you only have a preformance profile to target, then you can optimize the hull, rig and appendages to suit. This results in a highly refined hull, rig and appendage package, which by it's nature, will be a very complex set of shapes.

 

I think the statement would be all right and generally true if it were reversed. Least compromise of hull form (usually) equals most complex construction. Being that nothing in boat design is ever always true, I stuck in the "usually" caveat.

 

Some compromise between performance and ease of construction is permissible and possible IMHO, but the finished boat may have reduced performance or be non-compliant with one-design requirements. There should be no compromise with safety, but in most performance-oriented designs there is already a measure of compromise in place.

Some designs and boat types lend themselves more readily than others. For example after I finished a canoe I took a look at the plank developments and realized that they could have straight edges with very little change to them; the effect on hydrostatics/dynamics were concerned according to FreeShip and when built it was an attractive boat. I made similar changes to a small sailing rowboat design which had less than 1/2 inch change to the lines and virtually none underwater, which saved time developing the planks and lofting or alternatively constructing a more complex building mold.

However, those were all fortuitous and minor changes; major changes to plank developments will completely change the hull shape and the boat may not even go together. Designs with lots of rocker, highly curved chines and severe flare would not allow this shortcut, designs with gentle chine curves are more amenable. Of course, it only applies to some planks - usually the sheer planks - but in my case I start with those and subsequent planks are cut to fit - particularly easy for a flat-bottomed design.

Construction method is going to have an impact on what can be done. Stitch and glue will let you get away with this if the developments for all planks are updated. If a boat is to be built over a full mold or is fully framed then the planks are cut to fit there is absolutely no point in messing with the chines. It works particularly well with my construction method which is illustrated in my blog (see public profile).

 

Here are 2 exaggerated iterations of bows . Both are the same from mid ships back.
The construction complexity of the first is greater , but not much so.
the Cp. of the first is lower by , .01 . The first is about .55 and the later is .56

what other implications are there of one shape to the other?

 

I'm not sure I buy the construction complexity.....you have the same parts to make, just a harder bend in that bottom panel.

For a given entry angle (waterplane) the higher chine can have a fuller deck line (in plan) and more volume (buoyancy) up high.

 

The bottom planks of the left hand design (#1) are more severely curved, how much more will determine the degree of building difficulty. The buttocks show that the sheer and bottom planks become parallel near the bow, in effect the chine edge disappears. This means the sheer and bottom planks meet edge-to-edge here which will make it hard to close the seam using stitches which will be pulling in the same plane as the planks. If they do not fit perfectly they will not fit at all, since a ply plank will not bend in its own plane.

In the #2 design the planks meet at a relatively sharp angle along the entire chine so they can be pulled together easier using stitches even if there are slight cutting errors. If sheer planks are laid down before the bottom, it allows the bottom planks to overlap the sheer planks and the edges trimmed precisely in one pass using a router, eliminating the stitches.

It particularly suits my own method in which chine logs are glued to the edge of the sheer planks while they are flat. After the sheer planks are bent around a mold and the keel added, the keel and chine logs can easily be bevelled to accept the bottom planks using a plane (hand or power) equipped with a guide to keep the blade in the plane of the bottom plank for accurate bevelling. This method best suits small boats where the smaller scantlings result in a sheer plank and chine log assembly that will bend easily.

 

One factor which can complicate construction of hard chine boats if sheet material is desired for the planking is whether the surfaces are developable. If the surfaces are developable then it should be possible to use large sheets of plywood, metal, etc for the planking. If the surface shapes are not developable then other methods of planking, probably more complex, will be needed.

There is no guarantee that the surfaces of an arbitrary hard chine shape are developable. One way to ensure the surfaces will be developable is to have the all section lines parallel but that is very restrictive of shape. Considerably more complex shapes can be developable but they need to be designed as such. This is one area where the use of appropriate 3-D computer software can really speed up the design process, and even make feasible the design of developable shapes which would be extremely tedious at best to do manually.

 

Are there particular complications when strip-planking a single chine hull?

Thanks - Gary

 

A non-developable plate is simply one in which the multidirectional strains on the sheet material exceed the stretching and compression capability of the material. Dividing such a plate into two usually solves the problem. A new edge or chine may result from this if the original plate was convex or concave in which case the original hull shape will not be exactly reproduced. Alternatively the as-designed plate may turn out too wide to conform to a twisted shape, or lead to a contorted-looking development that is obviously going to be a problem in assembly. I ran into that problem in a design; the two new plates are parallel throughout (i.e., no new chine) and the stresses from using two plates were greatly reduced.

Dividing a plate into many narrow planks is common. Strip-building is one method, older designs often had lumber planks laid diagonally which generates a hollow plate, and of course cold-molding is an extreme example. If such a method is adopted for a chine hull originally intended for ply construction the building complexity and hours will be increased, although cost may not. Strip planking will require some way to provide cross-grain strength, such as ribs or glass fiber inside and out and a more complex mold will be needed since the thinner material is less able to define a fair curve between widely spaced station molds than the original ply. However, if stripbuilding is intended it makes far more sense to start with a design intended for that method of construction which can take advantage of the design flexibility it provides.

Note that I use the term "plate" here for the whole development. A plate may be a single piece of ply or a number of planks. For plywood boats the terms plate and plank are, I believe, synonymous.