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  #1  
Old 03-13-2008
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Long versus short overhangs

I was recently reading a piece on the Nor'Sea 27 by Ted Brewer (http://www.norseayachts.com/goodoldboat/Brewer.html) and he mentioned something that caught my attention.

Here's what he said: "Many sailors will argue that some of the old CCA-influenced, narrow-beam yachts, such as the Cape Dory 25D and the Bristol 27, are trailerable bluewater boats, but these vessels, with their relatively long overhangs, were not specifically designed for ocean work."

I've never thought (or read) about the length of a boat's overhang as it relates to seaworthiness and ocean-going capability. I suppose it makes sense that short overhangs with sharp entries would cut the waves better. But still, I've never heard this discussed among all of "bluewater" threads on this forum.

Any opinions, thoughts, or random ramblings?
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Old 03-13-2008
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Obviously you have not been reading my comments. If you go back to yacht design texts, working water craft histories and cruising books that predate the CCA era, there was a strong concensus that the CCA driven narrow beam, and long overhang designs have no place offshore. If you read CCA era design critiques, there was a real outcry against CCA type boats as being 'unwholesome' for offshore work. If you read some of the post Fastnet research and some of the pre- CE directive research on suitable offshore vessels, the short waterline lengths and long overhangs come into the crossfire for their negative impact on motion comfort, lack of stability, and poor carrying capacity.

At least amoung the current crop of offshore vessel designers there seems to be a near unanimous sense that long waterline/ short over hangs are the way to go from all perspectives; ease of handling, sea keeping, motion comfort, carrying capacity, not to mention overall performance.

Which also brings up a related issue. When you look at idealized values for such surrogate formulas as L/D, Motion Comfort Index, and Capsize Screen Formula, the numbers that we all are used to were based on CCA era short-waterline, long overhang designs.

If you look at an equal length on deck boat from the CCA era vs one from today, you'd be surprised that the overall weights of these boats are not all that different, but the waterline lengths of the newer boat is typically as much as a third longer than those of the CCA era boat. The newer boats also often have greater depth and higher ballast ratios as well, meaning lower VCG's relative to the Vert center of Buoyancy)

What this 1/3 longer waterline does is make the equal weight modern boat seem overly light (in other words, what we would consider a moderate displacement boat of today with an L/D of 170 would be the same weight and length on deck as a CCA era boat with an L/D of roughly 350 which would have been considered quite heavy)

Historically a LD of 170 would be considerd too light for offshore work, unable top carry adequate supplies, and the other formulas would suggesting less stable/ seaworthy, and prone to a less comfortable motion, when in fact the longer waterline/equal weight boat should actually be less prone to capsize, have a more comfortable motion and have greater carrying capacity.

But beyond that these CCA era almost by necessity are sailed at very high heel angles, and compared to more modern designs tend to scoop up a whole lot of water over the bow and be pooped over the stern making them miserable to sail in heavy going.

It is for that very reason that I cringe whenever I see someone suggest that boats like the Alberg's, Ariels, Bristol 32 and to a lesser extent 40, Triton, Vanguards and the like make any sense of offshore work.

Respectfully,
Jeff
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Old 03-13-2008
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Jeff is correct of course, but they sure do look pretty when they splash around before they sink.

Just enough overhang so the anchor doesn't hit the bow going up or coming down. More than that and it's like a pot belly on a 50 year old. Saddly overdone and past it's prime.
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Old 03-13-2008
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I love these old boat bashes. Here are some numbers from my CCA hull.

LOA 35.0 LWL 26.6 Beam 10.0 Displacement 14,500 Sail Area 675
Derived quantities. (Click on each box for an explanation in the box below.)
Displacement to LWL 344 Hull Speed 6.91 Sail Area to Displacement 18.16
LWL to Beam 2.66 Motion Comfort 35.56 Capsize Ratio 1.64
Sailing Category Racer/Cruiser Pounds/Inch 950

Seeing as how I actively and CURRENTLY sail this design in all kinds of weather, I think that qualifies me to comment that this particular design is great in the slop and actually more comfortable in heavy weather than newer boats I have sailed. The only complaint I have is the increased tendency to yaw in a quartering sea, due to the placement of the rudder on the back of the full keel.

Ok, here's a comparison between a Catalina 380 (a newer boat I happen to like) and my boat.

LOA Catalina 380 38.66 Knutson 35 38.4 (incl. bowsprit)
LWL Catalina 380 32.45 Knutson 35 26.6
Beam Catalina 380 12.33 Knutson 35 10
Disp. Catalina 380 19500 Knutson 35 14000
Sail Area Catalina 380 725 Knutson 35 675
Capsize Ratio Catalina 380 1.83 Knutson 35 1.66
Hull Speed Catalina 380 7.63 Knutson 35 6.91
Sail Area to Disp. Catalina 380 16.01 Knutson 35 18.16
Disp. to LWL Catalina 380 255 Knutson 35 344
LWL to Beam Catalina 380 2.63 Knutson 35 2.66
Motion Comfort Catalina 380 30.69 Knutson 35 35.56
Pounds/Inch Catalina 380 1430 Knutson 35 893

Last edited by CharlieCobra; 03-13-2008 at 03:33 PM.
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Old 03-13-2008
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You're taking the comment out of context. He's discussing trailerable boats. The four main ones are not CCA designs. He states that some would say the two CCA's are trailerable. He's drawing the distinction between the two CCA's having long overhangs, as opposed to the others not having that setup. He is not saying that because they have long overhangs they are not suited to bluewater work, though his sentence structure would seem to point that way. He is pointing out that they have a different design than the other four designs he's discussing. Read more of Brewer's work and you will see what I mean. He's very fond of the CCA rule and often writes of their superior seaworthy characteristics (his words). "All good things come to an end, though, and so did the CCA Rule." To be fair, he also credits the newer designs with greater speed potential in racing, as well as providing for greater below-deck space.
What he is saying is that he cannot include those two examples (or other CCA cruiser/racers) in that particular comparison. Case in point: I submit to you that there are many, many examples of modern sailboats with plumb bows and sterns (virtually no overhang) that are also not "specifically designed for ocean work".

Last edited by seabreeze_97; 03-13-2008 at 04:07 PM.
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Old 03-13-2008
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Oops! My bad. I was up playing on the sail calculator site for these numbers. The stock numbers they have there for the K-35 don't match my boat because of modifications done to it. Their numbers for the WL are off as well. They list the WL as 25' when it's actually 26'6". Not much diff but good for .2's of a knot HS. Also Oh Joy has 715 sq ft of sail instead of 600 and a 4' bowsprit. It's fun to compare various boats.


I tried to put the link in here but Sailnet's logic keeps screwing it up.

Last edited by CharlieCobra; 03-13-2008 at 04:05 PM.
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Old 03-13-2008
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Charlie's numbers are a good example of what I was saying, if you adjust Charlie's displacement from the way it was calculated during CCA (tanks full, and with normal gear and supplies aboard) vs the way it is done today, dead empty, and look a more modern design, something like a Hanse 350, or Beneteau 36.7, there are probably only a few hundred pounds difference (maybe as much as 4-500 lbs) between Charlie's boat's displacement and the more modern designs. But when you look at the waterline lengths of approximately 31.5 and 30.6 feet respectively, you can quickly see why they have L/D's of 181 and 209 respectively vs Charlie's 344 and that it has little to do with the overall weights of the boat.

And as Charlie says he actively owns and sails his boat in a range of weather and he likes his boat. I seem to spend a lot of time jumping back and forth onto boats that represent a broad spectrum of sailing history, CCA to IRC. The heavy weather liability of the old CCA long overhang, narrow beam designs becomes quickly aparent after you do that for a while.

One other minor point, Charlie's boat has comparatively long waterline length for a CCA era boat (LOD/LWL=.76) as compared to more typical designs like the Black Watch 37 (.69), HinckleyPilot 35 (.71), Bristol 32 (.68), Triton (.7), or Ariel (.71). She is also a proportionately beamy for a 35 footer from that era as compared to a more normal CCA boat like a Pilot with a beam of 9.5' vs Charlie's 10'.

Respectfully,
Jeff
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Old 03-13-2008
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While we have the experts talking, and not to hijack a thread too much:

What's the scoop on the scoop, sugar scoop transom that is?

Good or bad as a speed vs stability issue. Almost all modern catamarans have them and my understanding of the seawind 1100 is it's basically a 1000 with a longer scoop added to increase bouyancy aft and speed potential.

One more question if you feel like answering it - there is a post of a Gunboat 62 passing a RP 80 in the 'where's jody' thread - it's almost flying a hull.
Gemini's - my boat - does heel 7-10 degrees when I'm cooking. Is it beneficial for me to get up on a hull as it reduces drag or is the 'equal' submersion of the other hull canceling that out.
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Old 03-13-2008
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I personally know of the use of a 4' sugar scoop on a Mac65 named "Joss" which held the Ensenada record for a long, long time. The wife of the previous owner stated that it minimized rudder turbulence, which was considerable at over 20 knots. She also said it helped with following seas.
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Old 03-13-2008
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Quote:
Originally Posted by Jeff_H View Post
Obviously you have not been reading my comments. If you go back to yacht design texts, working water craft histories and cruising books that predate the CCA era, there was a strong concensus that the CCA driven narrow beam, and long overhang designs have no place offshore. If you read CCA era design critiques, there was a real outcry against CCA type boats as being 'unwholesome' for offshore work. If you read some of the post Fastnet research and some of the pre- CE directive research on suitable offshore vessels, the short waterline lengths and long overhangs come into the crossfire for their negative impact on motion comfort, lack of stability, and poor carrying capacity.

At least amoung the current crop of offshore vessel designers there seems to be a near unanimous sense that long waterline/ short over hangs are the way to go from all perspectives; ease of handling, sea keeping, motion comfort, carrying capacity, not to mention overall performance.

Which also brings up a related issue. When you look at idealized values for such surrogate formulas as L/D, Motion Comfort Index, and Capsize Screen Formula, the numbers that we all are used to were based on CCA era short-waterline, long overhang designs.

If you look at an equal length on deck boat from the CCA era vs one from today, you'd be surprised that the overall weights of these boats are not all that different, but the waterline lengths of the newer boat is typically as much as a third longer than those of the CCA era boat. The newer boats also often have greater depth and higher ballast ratios as well, meaning lower VCG's relative to the Vert center of Buoyancy)

What this 1/3 longer waterline does is make the equal weight modern boat seem overly light (in other words, what we would consider a moderate displacement boat of today with an L/D of 170 would be the same weight and length on deck as a CCA era boat with an L/D of roughly 350 which would have been considered quite heavy)

Historically a LD of 170 would be considerd too light for offshore work, unable top carry adequate supplies, and the other formulas would suggesting less stable/ seaworthy, and prone to a less comfortable motion, when in fact the longer waterline/equal weight boat should actually be less prone to capsize, have a more comfortable motion and have greater carrying capacity.

But beyond that these CCA era almost by necessity are sailed at very high heel angles, and compared to more modern designs tend to scoop up a whole lot of water over the bow and be pooped over the stern making them miserable to sail in heavy going.

It is for that very reason that I cringe whenever I see someone suggest that boats like the Alberg's, Ariels, Bristol 32 and to a lesser extent 40, Triton, Vanguards and the like make any sense of offshore work.

Respectfully,
Jeff
So how do you explain the fact the ships aren't built with plumb bows? At what point does the traditional overhanging bow become correct again? 30', 50', 100'?

I suggest that if everything you say here is true then modern ships (especially warships) would have plumb bows and sterns. We know the age of the Dreadnought is long over.

Specifically, the negative trend toward CCA boats was because they were designed to fit a racing rule instead of seaworthiness, so many aspects of the design contributed to their poor seaworthiness not just overhangs. Contrary to your argument, most of todays offshore cruisers do have overhangs. They are not as big as more traditional designs but they are there. The overhang provides a drier ride not a wetter one. It is plumb bowed boats that have a tendency to drive through the waves rather than over them.

Regarding your claims of L/D ratios, your assumption that if the waterline length approaches the LOD then the L/D drops making it a boat as safe as an older boat with a higher L/D is flawed. The point is that as the boat with the shorter water line length (and consequently higher L/D) gets over run by a wave, the extra boat above the waterline comes into play and lifts the bow up. There is a reason why submarines don't have long overhangs.

The real reason some modern boats are built with plumb bows is for boat speed and interior room. A plumb bow boat better meets the demands for "Floating Condos" in a shorter hull than does the boat with graceful overhangs. They are also faster with longer waterlines. Proper modern bluewater cruisers still have overhanging bows if for no other reason than to prevent the anchor from flailing the hull and to sweep aside that log that you don't see....
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Last edited by Plumper; 03-13-2008 at 06:08 PM.
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