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Old 16-05-2008, 19:51   #1
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benefit of long overhang

I saw a 35' boat with a 24' waterline. If a longer waterline gives more speed and better ride then why make a boat with such long overhangs?
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Old 16-05-2008, 20:05   #2
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Just for starters...

Long bow sprit allows larger sails.

Forward raked bow helps cut through the water. (edit: keeps more water off the boat)

Fantail stern helps with following seas.
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Old 16-05-2008, 20:11   #3
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There are more issues than just speed
You don't live at the waterline...you live on deck. If the boat is nicely balanced and comfortable then it is a joy to sail
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Old 16-05-2008, 22:39   #4
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Aloha Aqua,
The faster you sail the more your boat sinks in between the waves generated by traveling through the water and with longer overhangs increases your LWL. Also some of the boats with extreme overhangs when sailing heeled to extreme increases waterline. I really like the looks of them and there was an ancient reason when certain rules for racing favored shorter LWL when at a standstill. All of these things have been forgotten but maybe will be revived if we rediscover our Sailing Yoda.
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Old 16-05-2008, 23:04   #5
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The "Clipper" bows had spare bouancy when dove into the water: Deeper she goes, more updraft she got.

Also more sail area and less water-line for less hull speed...

Strange world, but looks good.

The most efficient boats these days have the same length as the waterline. Perhaps even less.

"Cutty Sark" was ever so good looking and as fast as most of them..
19 knots she did under full sail, Clipper Bow and all.
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Old 18-05-2008, 09:28   #6
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So, if I'm reading this correctly then its primarily for looks?

As far as space on deck, I was curious why they wouldn't extend the LWL to near LOD, not the other way around.

On a related note, I see many of the older boats have the stern tapering up almost to a point sometimes. What is the purpose in this? It seems like the big flat stern gives you alot more space inside and and great place to mount a fold up swim platform. But what is the trade-off?
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Old 18-05-2008, 10:43   #7
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Originally Posted by Aquah0lic View Post
So, if I'm reading this correctly then its primarily for looks?
It is about looks, race ratings, tradition, and (perhaps) having a drier foredeck when under way in big seas.

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As far as space on deck, I was curious why they wouldn't extend the LWL to near LOD, not the other way around.
Cost, and the factors noted above. Most modern boat designs do have a more square entry.

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On a related note, I see many of the older boats have the stern tapering up almost to a point sometimes. What is the purpose in this? It seems like the big flat stern gives you alot more space inside and and great place to mount a fold up swim platform. But what is the trade-off?
The wide stern is very functional -- it gives you area on deck, more "form stability" and buoyancy, and more space below. Look at most modern racing monohulls; they have very wide sterns.

The wide stern does create issues when the boat is heeled, though. The underwater profile becomes asymmetrical, and can cause loss of control (sometimes called the "tricycle effect"). In these modern racing monohulls they quite often have dual rudders, because otherwise when heeled a central single rudder would lift out of the water and the boat would spin out of control. Having dual rudders also lets them angle the rudders outboard so they remain somewhat vertical when the boat is heeled. A wide stern may also be more vulnerable to being pushed around by following seas.

A narrow stern (with a reasonably narrow hull) remains immersed when heeled so the rudder remains in the water, and the underwater hull shape can remain consistant, so the boat doesn't suffer from as much weather helm.

VALIS is one of those long-overhang, narrow-stern boats. I have to admit that for me it's perhaps as much about aesthetics as performance.
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Old 18-05-2008, 11:20   #8
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Overhang, especially at the bow, is not simply about looks. Rather, as Robert Perry pointed out (in Robert Badham and Robby Robertson, Sailor's Secrets, International Marine, Camden Maine, 1999 at p. 193:

"Some things, though, begin to look better the heavier the weather gets. Plumb stems are a modern trend. They obviously maximize waterline length, but in a cruising boat do you want to give up a foredeck and make your boat into a submarine for an extra little boost in top end speed? Traditional elements like overhang are traditional because they work. Overhang keeps people dry and provides space to do what foredeck work you have to do."

To his I would add the importance of front overhand in anchoring - have any of you tried to retrieve an anchor in a boat with a plum bow? It is virtually impossible, in most conditions, to avoid banging the anchor into the topsides - even with an anchor roller that extends a short distance past the bow.

The same can also be said about the current trend towards wide transoms and relatively flat underbody shapes. Yes, the flatter hull form can increase speed potential in relatively flat water, but it does so at the expense of a sea-kindly motion: the boat will tend to slam when sailing to windward.

Further, boats with such an underbody design have significantly greater inverse stability - VERY bad in a monohull. Consider the recommendations concerning seaworthiness made in the aftermath of the Fastnet disaster. Witness also various of the original Open 60's that, when capsized, stayed inverted. As you may recall, this forced a rule change that led to canting keels.

Finally, this 'modern' hull form, while having increased initial form stability, also has a tendancy to increase weather helm under heeling once the rather sharp turn of the bilge is sufficiently submerged on the leeward side.

In the result, it is often the purchasers of these more 'modern' hull forms who are slaves to fashion: they want a boat that looks like a modern racing boat; they want the increased interior volume that is created below (they want huge aft doubles and could care less about proper sea berths); they want the home-like look of a wide cabin sole. For this they are prepared to sacrifice a degree (and sometimes a significant degree) of seaworthiness and actual sailing comfort and praciticality.

Brad
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Old 18-05-2008, 13:22   #9
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waves generated by traveling through the water and with longer overhangs increases your LWL.
Some great info above. I am not fully clued in this subject. But I can comment on this part,
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waves generated by traveling through the water and with longer overhangs increases your LWL.
That is not always totally true. There is a big "depends on the design" in that one. Just like Paul Elliot stated that wide sterns cause
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The wide stern does create issues when the boat is heeled, though. The underwater profile becomes asymmetrical, and can cause loss of control
Similar can be said of the WLL adding speed. It often doesn't. It has to do with what creates the wave in the first place and how the hull continues to alter that shape as it sinks lower in the water. Depending on the shape and depth the extra hull has, will greatly influence whether the boat can go faster or not. Certainly the side profile has an enormous influence on speed as the boat heels.
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Old 18-05-2008, 16:21   #10
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It comes down to a (long gone) rating system. There was a time where waterline length was one of the crucial measurments for a boat's rating (because, as has been mentioned, hull speed was proportional to w/l length). Therefore it was beneficial for designers to minimise a boat's waterline length in measurement trim. Boats were generally measured upright, but as a rule, sail on a heel. So a boat with 32 deck length ans 24' waterline would be measured with a 24' waterline, but heeled at 15 degrees might have a a 30' waterline.
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Old 19-05-2008, 06:20   #11
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Weyalan, what you say is partially correct - a great number of racer/cruisers and racing boats were designed to take benefit of the CCA and IOR measurment rules that penalized LWL. But that does not change the fact that traditionally, most cruising sailboats were designed with some overhang, particularly at the stem - and this had absoutely nothing to do with ratings for racing.

As Perry points out, there are some real world advantages to front overhang. Apart from anchoring advantages, foredeck space and less spray, the volume (and therewith bouyancy) of a bow with some overhang increases in 3 dimensions and not merely two (hence, Perry's reference to turning your boat into a submarine - which is admittedly an overstatement).

There are also some real world benefits to narrower sections aft, rocker and relatively 'slack' bilges - and yes, even moderate to higher displacement. Every boat design is a compromise, but it is inaccurate to suggest that plum bows, wide transoms and relatively flat bottoms are now popular because they are in all respects an improvement over more 'traditional' hull forms. Nor is it accurate to suggest that those hull forms were solely the result of efforts to beat measurement rules.

For an inland or coastal cruiser where the owners wish to put a premium on space, or for a circumnavigator designed almost exclusively for speed while going with the prevailing winds, the now popular hull forms are the way to go. For an offshore cruising boat - let us just say that many are prepared to sacrifice maximum hull speed and some space for the advantages of better balance, a more sea-kindly motion, and a drier foredeck.

Brad
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Old 19-05-2008, 15:53   #12
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I bow to your superior knowledge Brad.

another not so well known advantage to a long front overhang is, when approaching a floating marina berth, and upon having your reverse gear fail completely, being unable to stop your forward momentum in time, the leading edge of the bow slides nicely up the marina berth, doing minimal damage to bow and boat. With a plumb bow, the result would have been far more destructive. How do I know this? Well, Umm, cough, lookoeverthere (runs away)....
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Old 19-05-2008, 19:02   #13
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Well said, many older designers had it just right. Much fun as it is to roar around the race course in a carbon fiber, plumb stem, big assed rocket it is not the boat I want to go cruising in. There is something elegent about a boat with over hangs and a modest beam. They ride soft and the hook doesn't bang the knuckle when you pull it up.

Balance, beauty, and sailing comfort are loosing out to palatial saloons and one more LCD tv.

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Weyalan, what you say is partially correct - a great number of racer/cruisers and racing boats were designed to take benefit of the CCA and IOR measurment rules that penalized LWL. But that does not change the fact that traditionally, most cruising sailboats were designed with some overhang, particularly at the stem - and this had absoutely nothing to do with ratings for racing.

As Perry points out, there are some real world advantages to front overhang. Apart from anchoring advantages, foredeck space and less spray, the volume (and therewith bouyancy) of a bow with some overhang increases in 3 dimensions and not merely two (hence, Perry's reference to turning your boat into a submarine - which is admittedly an overstatement).

There are also some real world benefits to narrower sections aft, rocker and relatively 'slack' bilges - and yes, even moderate to higher displacement. Every boat design is a compromise, but it is inaccurate to suggest that plum bows, wide transoms and relatively flat bottoms are now popular because they are in all respects an improvement over more 'traditional' hull forms. Nor is it accurate to suggest that those hull forms were solely the result of efforts to beat measurement rules.

For an inland or coastal cruiser where the owners wish to put a premium on space, or for a circumnavigator designed almost exclusively for speed while going with the prevailing winds, the now popular hull forms are the way to go. For an offshore cruising boat - let us just say that many are prepared to sacrifice maximum hull speed and some space for the advantages of better balance, a more sea-kindly motion, and a drier foredeck.

Brad
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Old 20-05-2008, 01:17   #14
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Moderate overhangs had all the benefits mentioned above. Taken to extremes they became a matter of style over substance , something that sells boats , while it is in style.
Moderation produces better cruising boats.
Clipper bows , as Hereshoff stated, are a mistake in boats under 50 ft, as they drop into a trough, then the sudden buildup of buoyancy stops the boat cold , if it isn't big enough to have enough momentum to push on thru. This becomes obvious when you take a BC ferry accoss Georgia Strait on a summer day. When the small boats with clipper bows hit the ferry wash, they stop dead, while those with fuller , more buoyant bows simply glide on thru without losing much speed.
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Old 20-05-2008, 15:38   #15
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There is no doubt that hull shape is, to a lesser or greater extent, driven by rating rules and the need for speed at the point end of yacht racing. The current propensity for plumb bows (maximum w/l length for o/a length) and wide, flat, rear ends (for planing) and hard chines often seems to offend a conservative yachting public's sensibilities. Nevertheless, the benefits of the yachting arms race do trickle down to us, and since we aren't at the leading edge of yacht racing, we all amke the best of what we have. Whether our beloved boats's hull shape is optimal or even close to it is largely irrelevent because it is, in general, bought & paid for and we are out there having fun.
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