Chine development

So if a chine hull surface is shaped so that it can't be planked with simple large sheets but has to be divided into smaller pieces the shape the construction will be more complex and/or the shape will have to be changed.

 

There are cases were a small part of the hull may have to be diagonally planked with ply .
This should be no big deal if the construction is stringer on bulkhead .

In the case of strip plank , I think a chine design may lose its value unless there are other reasons for the use of a chine in the design. But as far as cost , it may be easier and less costly for the home builder to find quality material for strip planking than for ply.

Construction aside, I wonder how to determine the amount of drag is caused by the chine.

 

Thinking about chine hulls because I grew up in NC and have an affinity for deadrise boats of all colors. I have a 20' spritsail skiff of that genre that gets sailed 5 days a year.

And strip plank - I want a wooden boat easy - not plywood and goo.

Gary

 

Do you mean narrow strips which are glued to each other when you say "strip plank"? Lots of goo in that type of construction.

Or do you mean traditional carvel planking as used in the North Carolina boats?

Or ???

 

I was thinking glue, not epoxy. I can deal with glue.

Gary

 

There's a great deal less goo in my plywood boats than in a typical stripper.

Typically in a stripper the strips are glued using carpenters glue or similar. After hull assembly the hull is covered both sides with glass and epoxied; this creates cross-grain strength and seals the wood; the glue type is no longer relevant.

In my current build ribs provide cross-grain strength so fiberglass is not needed, but this ultralight boat must be removed from the water and dry-docked between trips. I use a "water-proof" glue like Titebond III but I don't trust it to withstand prolonged immersion. I used no epoxy.

Related methods include riveting the strips to ribs and carvel construction where the plank to plank seams are caulked with cotton, covered with stopper before painting and the expansion of the planks when wet aids the sealing process.

 

It is much harder to design a good single chine hull that a rounder form but it can be done but you need to understand all the variables and compromises in hull design. Once you develop a decent hullform you will need to tweak it to get the coefficients you desire.

Look to cross chine flow and turbulence, I've found that swept up chines forward have more resistance than chines that run parallel to the waterline forward. Whether that suits the boat you are trying to design is another matter. With a deeper forefoot you can even completely eliminate the chine forward for the first few stations .

Chines are better kept more or less aligned with the flow and at the exit keep the waterplane intersect to above a minimum angle then you won't add noticeable drag. The figure appears to be around 135 degrees per chine and is a good reason to soften the chine aft on some hullforms.

A test model will show you a lot very quickly about chine placement.

Unfortunately you won't find much literature on this and there are a lot of abysmal conversions of round bilge designs to single chine.

Some recent tests on heavy displacement vessels indicated that well placed chines can even reduce resistance through their affect on the overall flow field around the hull.

 

Mike , That reinforces my thought that using a round hull as the parent model is wrong from the start.

Ben Seaborn when designing the Thunderbird , said that he rapped sheet material around a round hull, and it looked OK . I think he must have started with a narrow ,relatively flat floored , hard bilge boat .

From what I see there is no standard way to do this "conversion", and it is better to start the design with the chine in mind .

There are many good chine hull examples to get hints from. But other than from Bolger , not much discussion about their design and hydrostatics. Although many designs that today would be called poor , did perform well as intended .

 

Frank
Yes the style and form of a vessels hull is dictated by the construction. If you are going to use developable sheet material then the style needs to be chosen to suit.
A lot of designers design a round bilge classic lines hullform to their chosen coefficients, and then force a sheet developable shape onto that hullform as a chined option for that particular design. The resulting change of the coefficients ensures a result somewhat less than ideal form.

It's quite unrealistic to pick a style and then to try and fit the material to it. If you play with card and scissors or a 3d cad package you'll quickly see the forms that lend themselves well to sheet construction that are close to your requirements for the desired sweep of the chines. Then take the lines and transform them to get the coefficients you desire.

 

Developable surfaces

This is a rowboat that I designed to a customer.
It has a trapezoidal midship section and is well rounded fore and aft.
The trapzoidal midship section is much more eficient than the V-bottom, higher stability and less wetted surface.
It has only developable surfaces and can therefore be built in plywood.
The upper chine aft is in this case also an asset to get better performance.
This basic form can be used for all type of boats.

JS

 

HJS, very nice and creative design.

 

Did you use an application for the developments - and if so which one?

 

Developments

I design my boats in Delftship Pro.
There can I check the development and move the panels around untill they fit together in the way I want to have it. It is simple if you know what you want and have the skills.

JS

 

Considering the drag associated with chines parallel to the waterplane versus sweeping upward toward the sheer; if the hull experiences pitch, such as in waves, the parallel chine may have greater drag due to vertical motion of plunging into then withdrawing from the water surface. Of course, many other factors already discussed also influence what chine shape is preferred. For a developable hull form, I always design the chine first (with some iteration). Unless you are willing to accept some knuckle in the forefoot, the bottom and sheer are related in the upsweep at the bow. Increased upsweep in the forward keel (and chine) is needed to create a more vertical bow shape. Lowering the chine reduces upsweep in the keel and produces a more slanted bow angle with more resulting flare in the topsides. Mathematically almost any shape can be "developed", but the question is whether you have materials that can conform to very tight curvatures. Your choice may be to either accept a simpler shape or abandon developable methods and use one of the alternatives previously mentioned in this thread.

 

I doubt drag from a chine parallel to the waterflow is significant. I have noticed my chined canoe has a preferred speed which, perhaps, is where the wave is best aligned to the chine. The chines noticeably dampen out rolling, compared with a similar-sized molded boat. I am working on a round bilge canoe of virtually identical dimensions, it will be interesting to compare the two, with and without chines.