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Old 31-07-2011, 07:07   #1
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Hull Design - Terminology and Pros / Cons

Hi

I'm a newbie and am currently doing my skippers and trying to learn as much as possible to help make an educated purchase.

Below is a little drawing I mocked up. What are the 3 'designs' called?



One thing I've noticed is that older hull designs (60s, 70s, 80s) tend to be C's and newer hulls tend to be B's. A's tend to be quite rare?

What are the advantages/disadvantages of the various "designs"? What happened in the 80s that made designers start using C's? Surely it can't simply be a question of fashion?

Thanks in advance, I look forward to being schooled.

Regards,
Jonathan.
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Old 31-07-2011, 07:48   #2
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Re: Hull Design - Terminology and Pros/Cons

Greetings and welcome aboard the CF, Jonathon.

You might be interested in Ted Brewer’s Primer on Yacht Design
http://www.tedbrewer.com/yachtdesign.html
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Old 31-07-2011, 07:49   #3
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Re: Hull Design - Terminology and Pros/Cons

Sorry, typo. Should read:

"What happened in the 80s that made designers start using B's?"

J.
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Old 31-07-2011, 07:52   #4
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Re: Hull Design - Terminology and Pros/Cons

I found this article which describes other types of sterns as well.
http://www.jordanyachts.com/archives/135

In addition to a raked stern, C. is also called a counter stern.
http://www.history.navy.mil/photos/g...c/cnt-strn.htm
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Old 31-07-2011, 08:14   #5
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Re: Hull Design - Terminology and Pros/Cons

Arbitrary,

Just a quick and dirty answer to your question.

Basically, what you show are A) a flat transom, B) a "sugar scoop" transom and C) an overhanging transom. The sugar scoop became popular in the mid 80s because it allowed for the use of a integrated swim platform, which was very popular in the areas where swimming off the boat could be done, especially with the charter companies in the Caribbean. By integrating into the hull form, it could be made as part of the hull when it was molded, rather than bolting on a wooden swim platform after market.

The overhang is a holdover from the period where the designers needed to meet "ocean racing" rules, but wanted more deck space and hull interior. The flat transome was easy to build, although not particulalry efficient.
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Old 01-08-2011, 01:30   #6
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Re: Hull Design - Terminology and Pros/Cons

Hi All

Thanks for all the great replies, I have learnt a lot.

So, in summary, (please correct me if I'm wrong), flat transoms are simple to build. Counter sterns increase deck area while keeping the LWL down for handicap reasons and reverse (sugar scoops) sterns are fashionable and nice for swimming.

If the speed of a hull is a factor of it's length, and assuming you didn't care about handicaps or LWL, would that mean that a sugar scoop was the way to go?

Is any one of the designs faster than the other?

Thanks again,
J.
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Old 01-08-2011, 02:40   #7
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Reducing pitch?

One other point is that the "sugar scoop" stern and plumb bow, other than maximizing waterline length also minimizes weight above the centre of effort or centre of buoyancy.

It would also reduce the sail area for a given LOA.

Should be helpful in reducing pitching and rolling. Same idea as cored decks.

For mine, the most interesting modern boat to use these features is the Beneteau Oceanis 41 with a LOA of 12,38 m - 407 and a LWL of 11,97 m - 393.

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Old 01-08-2011, 04:33   #8
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Re: Hull Design - Terminology and Pros/Cons

Quote:
Originally Posted by arbitrarysailor View Post
If the speed of a hull is a factor of it's length, and assuming you didn't care about handicaps or LWL, would that mean that a sugar scoop was the way to go?

Is any one of the designs faster than the other?
Arbitary, since you are a noob, you are excused from knowing this, but NEVER ask if one boat is "better" than another!! You will start a flame war that can annihilate the board!!!

Seriously, though, the question about whether a sugar scoop is better depends on where you want to go sailing and how you want to use the boat. For example, in coastal sailing and gunkholing, the scoop would be great since it would allow you access to a lot of fun places. If you were going to do a lot of ocean sailing, particularly downwind, it's not as good, since any sort of following sea - where the waves are coming from directly behind you - can result in the waves coming up the scoop and into the cockpit. In extreme cases, they can push the stern underwater. Other shapes can have other problems with following seas, of course.

Transom shape makes very little difference to boat speed, although a finer exit from the water (one where there is little turbulence) is preferable. That's why most boats tend to have their widest spots forward of the stern, so that the water flow can come back together aft of the boat. More important to speed is hull shape and amount of "wetted surface."
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Old 01-08-2011, 06:59   #9
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Re: Hull Design - Terminology and Pros / Cons

Another possible reason for 'B': space. Customers have demanded more space down below in the last couple decades. That style transom tends to premit the widening of the stern to get more space below.
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