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Old 06-12-2010, 05:59   #1
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Hard vs Multi vs Radius vs Round Bilge Chine

Can someone please tell me the good and bad about each bottom type.

I posted a few days ago asking about Dix Designe but had no responders so I guess I will ask a more general question.

Thanks
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Old 07-12-2010, 00:46   #2
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Quote:
Originally Posted by dreamer38851 View Post
Can someone please tell me the good and bad about each bottom type.

I posted a few days ago asking about Dix Designe but had no responders so I guess I will ask a more general question.

Thanks
Hi dreamer. I suppose hard chine is the same as single chine (or just chine) but I don't know what is meant with radius chine.

It also depends much on the size of the boat. At 40+ foot I would look at multi-chine and round bilge. For smaller boats I would look at hard chine too.

They all have their advantages and disadvantages and there are many factors involved. I have an 1,800 page book about it so not much can be achieved discussing it here.

I think it's better to look at the reputation of the designer and the builder. There are good, solid boats for every construction method you mention.

cheers,
Nick.
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Old 07-12-2010, 01:26   #3
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Material, time and aesthetic dependent...

From my viewpoint the differences between hard chine and round bilge are more related to the hull material, construction time available and the aesthetics.

From the tone of your question I'm guessing that you're not a serious racer (not one of the carbon fibre/foam core crowd?).

There are a few trawlers built with hard chine, maybe to get every last bit of stability, and to help planning but these are not often major considerations in a cruising sail boat.

Plywood, steel and aluminium are well suited to hard chine, and a hull can be built relatively quickly.

Fibreglass is one of the better materials for round bilge as is ferro cement.

I went for a hard chine steel boat as the lower cost translated into a much bigger boat (44') for my buck.
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Old 07-12-2010, 01:39   #4
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I think that harder chine gives a little more initial stability.
Have seen a "radiused chine = curved hard chine" done in steel quite cheaply - build was cheap and quick but looked like round bilge. Round bilge steel maybe sl higher resale value (perhaps cos is usually done by professional builders?)
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Old 07-12-2010, 02:12   #5
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Ted Brewer (claims to have) introduced the radius chine into the North American market. There may have been others before him and I think it was more common in Europe but he has surely popularized it.

IMHO there are differences between the types of hulls that you are referencing but unless you are either going to the extremes of each design type or if you are looking to racing I don't think that they matter much.

What you are essentially looking at is the rate at which you heel in order to develop an off setting displacement change to the force applied to the mast, kinda. With a roundish hull the transition is smoother than with a stepped or chin hull.

There are very successful cruising boats designed in all of these fashions. A flat bottom boat, such as Annie Hill's Badger is one extreme, yet they successfully cruised that boat in many interesting locations for many years. I have two hard chine steel boats. A Murray 33 by Ted Brewer with three plates per side, and a SteelMaid 44 by Alan Pape with four plates per side. I don't notice any unusual handling characteristics on either. If anything they are surprisingly tender. From a practical point of view I don't think there is a noticeable difference, unless you are really looking for it or racing.

Brewer has written on these differences in his book on metal boat building. There may even be a copy of that chapter on the internet if you look him up. He wrote a series of articles for Good Old Boat and it may have been covered there.
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Old 07-12-2010, 03:31   #6
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This is a question handled in most books on boat design, usually in the opening pages as it describes hull forms, shapes and common practices.

Single chine hulls (hard or soft or radius) are the most simple form of hull shape. Of these the flat bottom boats are also the most prevalent. The advantage is simple construction, the disadvantage more drag and displaced volume compared to other hull forms. The V bottom and arc bottom fall into this category as well. Each refines the underwater shape slightly to improve efficiency and displaced volume.

Multi chines hulls are nothing more then attempts to make a round bilge hull form with sheet goods (plywood, sheet metal, foam, etc.). This is because sheet materials can only bend in one direction at a time. Since round bilge boats have "compound" curves, sheet goods can't easily bend around it without kinking, a set of conically or cylindrical "developed" shapes is used in the hull design. These shapes permit the flat sheets to wrap around the hull and sort of simulate a round bilge shape. Naturally the more facets or chines, the more it resembles a round bilge hull form.

The round bilge shapes are the holy grail of boat shapes at slow to moderate speeds, which is what most boats travel at. They offer the best looks, ride and comfort underway as a rule. The round shapes do have limitations, but generally only as higher speeds.

The term "radius chine" is what is done on sheet goods builds, to reduce the hard chine look and improve induced drag issues along a hard chine. It's a technique that's been used for generations (long before Ted Brewer was born). It was begun in metal hulls (early 19th century) to increase panel stiffness and "soften" the chine for decreased displaced volume and improved efficiency.

In a nut shell, the hard chine is the easiest to build, but the least efficient, unless you want to travel at high speed, where the chine then becomes necessary. The radius chine is a hard chine, with it's chines rounded over for a slight efficiency improvement as well as looks. Dix is well known for his radiused hull shapes. A multi chine hull is just one approach to using sheet goods and simulating a round shape. Personally, I'd rather use a molded, lapstrake or tortured method and actually have the round shape then a bunch of chines, but to each his own. Lastly, the round shape is the bee's knees and the most desired in looks and in terms of efficiency. It's also the most difficult to build generally.
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Old 07-12-2010, 04:23   #7
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Thanks all!

We have never sailed a steel boat but are looking at a Dix 45' pilot house. We are going to see it Friday. One of OUR blue water deal busters is a pilot house. It must have one in other words.

Do they need more heel when sailing? We don't care about speed at all but we don't want something that rides weird.

BTW I have been posting from my iPhone so sorry for any typos.
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Old 07-12-2010, 05:35   #8
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Here is a site that gives characteristics of many specific boats. It also has a calculator for more customized analysis.

Sail Calculator Pro v3.53 - 2000+ boats

In Part 2 of this page you can get an explanation of terms such as motion comfort, capsize ratio, etc.

The downside of information like this is that it won't mean much unless you have experienced it, and one person's "initial stability" may be another person's sea sickness, in a sea.
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Old 07-12-2010, 11:58   #9
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Quote:
Do they need more heel when sailing?
If both the radius chine and hard chine designs are the same hull, then yes, there is a measurable difference in heel angle in the same wind strengths, if sailing side by side. How much of a difference? Not enough to get concerned about, it's a slight, but measurable amount, maybe an extra degree or so. Not enough to spill your beer over, which is all that counts.
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Old 07-12-2010, 12:30   #10
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best way to answer this is to sail as many as you can and find out what it is you like and dislike about each one. each will have a slightly different motion thru seas--is what YOU like that matters. is what YOU like and dont like that will affect your comfort and purchase--sail as many s possible before yu buy--isnt easy to sell the results of poor planning anymore. what someone else likes may be reallly not tolerable to you.
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Old 07-12-2010, 12:48   #11
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There is a simple explanation.
skin friction increases geometrically with speed. More skin, more friction; more speed, much more drag. So this discussion is less important on slower power boats, but important to all sailboats.
The least surface area is found on a perfect circle. There is a lot more surface on a box of the same volume. Adding more sides, or facets, or chines gets closer to the least surface area of a circular cross section. A box has greater initial lateral stability (it leans less at first) so adding a few more flats gets closer to a circle, which doesn't have any form stability; sailboats have keels and ballast to get that. Circular form hulls rely on their ballasted keels exclusively to keep the mast pointing up. It works quite well.
Hard chined boats that rely on form stability have a limit to how far they can lean over and come back up. Depending on your alliegence, you can insert numerous pro and anti- catamaran comments here. As above, circular forms on boats (which are compound curves, bending in two or more directions, are far more difficult to build from flat materials. I think that is the most important difference; cost. You can spend a LOT of money getting a perfect hull that delivers 5 or 6% more performance.
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Old 07-12-2010, 14:53   #12
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Boy, you guys make things so complicated.
Thank God they are not or I would be out of business.
My advice is for you to stop generalizing about chines. Some chine boats are great and some are POS. It's all about how you handle the chine. Then radius chine method, and I have done several, was just a way of disguising the chine.

There is some really weird information on this thread.
But what would I know?
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Old 07-12-2010, 16:32   #13
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Great answer Bob.

I hope I didn't add to the confusion and complication.
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Old 07-12-2010, 16:49   #14
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hpeer:
No I think you were essentially right.

A chine on its own can help stabilty or hurt stability dependant on where it is and how you define "stability". Do you want stability at 10 degrees of heel or 30 degrees of heel?
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Old 07-12-2010, 17:15   #15
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now with stability if you have a hard chine vertical side boat it will have a lot of initial stability, but push a bit too far and you get wet, now have a flared side it will be tender as anything to start but it will take a whole lot to get the side under.
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