Single or Double Chine?

Here are a couple of options from a 5m daysailer I am working on. Instinctively the double chine would seem to make a fairer and slipery-er shape, but is that really true? It is a bit more work to build the extra hull panels but it might be worth it? If anyone has any viewpoints I'd be grateful to read them.

 

Welcome to the Forum Shifu.

I think I would be inclined to have just the single chine on the hull bottom, rather than the double chine - I am not convinced that the extra effort (and materials - lots more epoxy for the joints) will be worth the slight (if any) increase in performance.

Changing tack, what CAD program are you using for your drawing?

 

Hi. Thanks. That's actually Plyboats, which I purchased in back 1996, and have managed to keep going through all my computer upgrades since then.

 

I was taught that the double chine should be designed to match the angle of heel when sailing to give the best surface for planing performance and so forth. Personally, I'm inclined to look as those fast single chined boats, like the Windmill and the flat bottomed super fast sailboards and think, 'that is what fast sailing looks like'.

 

I thought it looked familiar - I also bought a copy of Plyboats back then, and I used it to design and build a few boats, but I lost it when my old DOS computer finally died.
I couldn't get it to work on newer Windows programmes - how did you manage it?

 

May I ask a question?

Would it be better to design the bottom with some reserve buoyancy? If you miss at all on weight or loading, isn't the chine underwater? Or is some heel always planned? I think the chine would best finish a bit above water, but I am not certain.

I prefer the double chine adjusted to @Will Gilmore comment on angle. The second chine would also make the boat stiffer I'd say.

Further, does the chine provide more than just ease of build in a sailboat? i.e. Would the boat be faster with properly placed chine(s)?

my thoughts as a non-sailor

 

Not so.
The closer you get to a rounded bilge, the less stiff the boat will feel. Think about where the buoyancy is located in relationship to the center of gravity. Also, factor in the counter weight of the lifted side.

The new high performance mono hulls are all getting flatter and wider. Those are very stiff boats.

 

I'm running it in DOSBox in Windows 7, which itself is running inside a virtual machine inside MXLinux. It's an elaborate setup but it works well and DOSBox, Virtualbox and MXLinux are all free. If you have a windows computer all you would need is DOSBox.

 

The chine is just touching the water line at the boat's current designed weight of 320kg. As I fine tune the design and the weight I will be able to adjust it along the way. A small boat like this will always react dramatically to weight changes just in putting extra passengers aboard so It likely won't be perfect most of the time.

 

Especially as no boat floats on its static lines once it is moving...

 

Aesthetically the extra chine looks more refined and in the context of building the entire boat just a small bit of extra work.

 

Stupid question, but is there a definite way to count chines?
On wikipedia it counts the keel as a chine and counts both sides. Like a deep V shape is a single chine hull and a box shape is double chine.
In a research paper I've seen them not count the keel and only one side.
And in Shifu example, shouldn't it at least be double chine vs triple chine?

 

It looks to me like Shifu's first boat has one chine with the CAD software trying to render the camber of the curved bottom. Not a great job of it, but curves require a lot of information processing to render, so they often end up looking like polygons.

 

But....did he mean stiffer structurally, or stiffer in stability terms ?

 

Ah! I get it now.