Chine Discussion

I'm currently working on my Westlawn degree and have a quick question regarding chines. I have been doing some reading and understand that chines are primarily used in providing lift and also spraying off the water. However, I do have a rather interesting question, "How does one know what size the chine is suppose to be?"

What makes the difference between a 30' boot and 60' boat in regards only to the chine. Does the width of the chine change directly with the beam of the boat or is there a set width for a chine? Answer to these questions will help me determine what can be applied to the design I have in the works. Thanks, for everyones suggestions.

 

By size of chine, do you mean the beam of the boat across the chine, or do you mean the size of a protruding object or flat at the chine.

In the former case, use a planing simulation program to optimize the breadth vs speed, weight and LCG. If you have access to a Zarnick program, you can also look at seakeeping. Also look at some typical model series.

In the latter case, calculate the thickness of the spray root, and make sure you are intercepting all of it, but not much more.

 

I am looking for the amount that a chine protrudes from the side of the boat.

 

How do you calculate the thickness of the spray root? Does the calculation change when there are strakes?

 

I worked for a builder/designer of sportfish and when younger raed the Daytona boats he claimed that on a 44' and 52'ters no more than 4" at the transom to nothing fwd. as far as the angle he said 5 degrees at STA.1 2 1/2 degrees at amidships and flat at the transom. He helds records from the Miami to New York runs in a sportfish. When I designed my boat he looked at the lines plan and that was an area he told me to change, I had my chines at 3" aft and he said they were too large to decrease them to 2". I'm no designer and am in the process of getting back into Westlawn but I can only tell you what I have been taught in the feild.

 

So called "deep V" bowriders often have extra wide chines to allow them to get away with modest power. The same company may put chines on their cheapest 18 footer meant for a 3L motor that are twice as wide as on their premium 18 footer with 4.3L motor. For small sport boats it's as much about lift as spray control.

Kelly Cook

 

Chine surface areas are usually determined as a function of the plan form area of the running surface of the hull at it's design speed. There are a few rule-of-thumbs out there, but I think SNAME has some papers on the subject, I'd start your research there. If I remember, Don Blount had somthing published on this. SNAME is also coming out with a searchable compilation of small boat papers on CD that I'm sure would be useful to you.
There are pleny of issues to consider in designing a planing hull form, and your chine geometry is going to be influenced by many of them : Will there be lifting strakes on the hull bottom? At what piont fore and aft does the chine cross the waterline? etc. You'll need to look further into the design considerations here. There isn't a "4 inches wide at the transom, taper to nothing" answer that works in the real world.
The people that design these hulls every day have a mountain of emperical data from modeling, tank testing and sea trialing thier designs, these people may have rules of thumb for there own offices that work because they approach the other variables involved in a predictable way. If I was a student, I'd be looking into the principles of chine design, and I'd be wary of quick-and-dirty answers.

 

Interesting definitions, the "Chine" in itself is just the corner between the planing surface and the hull-side. A "Chine-flat" is the small bit of laminate parallel to the water-line in front view. It's purpose is to deflect spray away from the deck, rather than to produce any significant lift. It will have some effect if immersed (the boat may get stiffer in roll) but that is a fairly minor consideration. Think of the surface-area of the planing surface (ie. the bottom) relative to the area of the chine-flat. the chine-flat is really very small.

Tim B.

 

This may be a difference in design practices between the US and other parts of the world. One popular bowrider here has a beam of 93" and the chines are each 5.75". So on each side of the hull you have 40.75" at a 21deg angle plus 5.75" at a zero deg angle. I would say that generates some lift.

Kelly

 

In response to Tim B: We are indeed discussing the geometry of "chine flat" designs. Obviously, for a simple hard chine hull form, the chine itself is merely a knuckle, and would have no surface area. It is totally inaccurate to dismiss a working chine as nothing more than a spray management tool. Chine geometry is used to (among other things) manipulate deadrise angles, control volumetric geometry, and provide substantial amounts of dynamic lift. Modern planing powerboat performance and handling properties are greatly effected by hull bottom surfaces including chines and lifting strakes. My point was this: There is no need for opinions on this topic, there is plenty of research, published findings, and empirical data available, all of which would be better studied than this thread.

 

KFB

If you would kindly point me in the direction of the appropriate resources on this subject that would be helpful. Which papers can I download or which books can I buy?

Chase

 

All these answers and no one asks what type of hull, speed and designed for what conditions....