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Topic Review (Newest First)
09-23-2003 07:17 PM
Jeff_H
Confused about overhangs...

I wanted to reply to VIEXILE post above. From the perspective of sailing vessel history, the term ''traditional'' usually refers to vessels that developed through an often vernacular evolutionary process in response to local sea conditions and uses. In most cases these are working watercraft or yachts that evolved from working watercraft.

I would not consider racing yacht designs which are contrived to take advantage of loop holes to be ''traditional'' no matter how old that loop hole happened to be. Long overhangs/short waterlines were strictly a response to a series of rating rules that over penalized the importance of waterline length. While it is true that such measurement rules encouraging short waterline lengths go back to the late 19th century and the CCA rule was preceeded by such rules as the Universal Rule and International Rule (not to be mistaken for the IOR) which produced racing vessels with extremely short waterlines,I would not consider any of the designs produced to beat these types of racing rules to be ''traditional'' watercraft, only older designs produced to obsolete racing rules. That said, I still consider boats produced on the International and Universal Rules to be some of the most beautiful boats of all time and get a kick out of sailing them as long as I don''t need to be anywhere quickly and have a sheltered harbor to duck into when things get dicey.

VIEXILE is right in say that some of the rule beaters that preceded the CCA rule had waterline lengths that were barely over 50% of their length overall, but these boats rarely had fine entries. In fact they often had extremely blunt entry as the wave making impact of a blunt entry would help them increase their waterline length more dramatically when heeled. Even with this increase in heeled waterline length they were no where near as fast as equal length, longer waterline designs of similar weight.

Respectfully,
Jeff
09-19-2003 06:09 AM
msl
Confused about overhangs...

You are correct about the M in MORC. Sorry. What the author (Britton Chance) actually wrote was that the T34C was a "larger version" of the Tartan 27 which is a MORC design.
The Tartan 27 has such a great reputation. Apparently, so does the T34C. Anyway, I probably should pay less attention to old promotional literature. It is fun to read though.
Thanks,
Mark L.
09-18-2003 08:19 PM
sailingfool
Confused about overhangs...

Mark,
Check http://www.tartanowners.org/modeldata/t34profile.htm for the T34C CCa history. Note the T34C waterline is almost 10 feet less than the length overall, giving you a lot of "overhang", although perhaps not extreme..
To understand the performance of such designs, the T34C rates PHRF 168, the same as ''70s C&C and Tartan 30s, but I didn''t see the T34C deliver to that rating...
FWIW the "M" in MORC is for "midget", meaning 30'' or less, so a 34'' wouldn''t be a MORC design...
09-18-2003 07:47 PM
msl
Confused about overhangs...

An article about the Tartan T34C, written by Briton Chance mentioned an "estimated CCA rating" for this boat. What confuses me is how little this design seems to resemble what we have been discussing here... no long overhangs etc. etc.
Am I correct in assuming that the T34 (and others similar to it) is a MORC design described by the builder as having a CCA rating to meet changes in what the "market" wanted to buy at the time of the article''s publication (1969)?
Thanks,
Mark L.

09-16-2003 07:26 AM
JohnDrake
Confused about overhangs...

I wanted to add a comment about my experiences to this very interesting discussion.

I have a 1985 Wauquiez Hood 38 and was actually out in the same conditions as Jeff H in the same waters on the same day we got 30knot winds. My 38 footer is not light at 22,000 lbs and does not have plumb bow or flat aft section of the hull. But at 31ft LWL and a PHRF of 129 she is also not a traditional design. Quite moderate in all respects.

First, regarding the flat hull sections aft and slapping at anchor. I have also found that true, especially for boats that have rather thin inner liners. I have slept aboard boats like that and just could not get to sleep, even in a quiet anchorage. The Hood 38 has moderate overhangs and a nice curve aft, she is very quiet at anchor.

She also has a wonderful motion in a seaway. The bow has a good balance of reserve bouyancy, in my simple estimation. She has none of the bad qualities that Jeff mentions and she also does not submarine at all. IMHO that is an important feature, as it keeps her dry.

As I mentioned, I was also out in a 30knot blow the day Jeff was, last season. Big swells. It was a terrific ride. I was experimenting with different sail configurations and at one point was reaching under reefed jib alone (which I would not normally do), 8.5 knots by GPS, no water over the bow, only 15 degrees of heel, very comfy ride...in fact had two fairweather boats napping aboard, one in the cockpit, the other below.

The Hood 38 design sacrifices some beam and adds a good deal of ballast to get its stability and speed. But with an 11''9" beam, it is not much and unnoticable below. She can roll more than wider beam boats but only under power, not under sail.

In looking at the hull forms of boats I was considering (and emailing Jeff for his much appreciated advice), I decided that two things were important to me, among the myriad to consider in the price range I had: NOT slapping at anchor and having a good amount of reserve bouyancy. I am pleased on both accounts.

The message is that there are a number of more moderate design''s from the 80''s that are a good compromise between the new flat/plumb boats being built now and the older CCA and IOR boats from a while ago. These moderate designs can be visually beautiful, somewhat fast and quite secure in a seaway.

My best to all

John
s/v Invictus
Hood 38
09-16-2003 06:40 AM
VIEXILE
Confused about overhangs...

I guess I don''t get the implication that the word "traditional" doesn''t apply, but really the overhangs result only from CCA rule-beating attempts in the ''60''s. Paul Luke, John Alden, the old Hinckleys, Albergs, etc., and NOT the CCA age plastic boats, but boats built going back to the early 1900''s (J-Class America''s Cup boats, Ranger) etc., all had long overhangs with fine entries. Look at the International Class wooden boats. Narrow, pointy. They make up their waterline on heel, and drag ass running before the wind for obvious reasons - you maximize by reaching. Some of the oldest wooden boats in Maine - I remember a couple of big fancy ones - looked like they had as little as 50% waterline with long, long, LONG overhangs. When did the CCA rule beating concept come into play? Were the old builders focused on that, or did they have some other design concept when laying out such a craft? Interesting.
09-15-2003 08:03 PM
Jeff_H
Confused about overhangs...

Folks,

I think this is an excellent discussion. There are a lot of good ideas being floated that I would like to add to, starting with the other "resident amateur physicist", Allen''s comments. I somewhat disagree with the idea that weight in and of itself is good for motion comfort. That is a bit of an outdated idea. While overall weight does come into play when considering motion comfort due to linear accellerations (heave, surge and sideward accelerations) linear acceleration tend to be of lower magnitude on sailboat that rotary accelerations. Here the sheer amount of weight has far less of an important role than its distribution. (The Cadillac''s boulevard ride came not so much from the weight of these cars but from the design of their dampening systems and the weight distribution that came from placing a cast iron straight or V- 8 that far forward in the chaisis. SUV''s generally weigh far more than the boulevard cruisers of yore, yet have considerably harsher rides than a modern lighter weight sedan.)

When dealing with rotational motion, weight that occurs high in the boat can actually result in a less comfortable motion and contribute to excitation rolling (and pitching) which is the harmonic rolling anbd pitching that Allen mentioned above.

I somewhat disagree with Allen''s statement, "it seems the primary job of damping pitch and roll falls to the hulls, a task for which they are not particularly well suited." This is one of those areas where magnatude of the dependence on the hull for dampening very much depends on the design of the boat. In most traditional watercraft and also modern IMS typeform offshore designs, the hull plays a very small role in dampening rotational motion. While both types would have small amounts of form stability, roll dampening generally came from rotating the large area of a full keel sideward through the water on a traditional design, or rotating the deep fin of a modern design sidewards through the water. In the case of pitch, it is the bouyancy distribution on both modern and traditional designs that really dampens pitch. Turbulence and wave making really do not come into play here as this is pure Aristotle (buoyancy) and Newton (inertia and impact) physics.

"Long, slender hulls may be resistant to pitching, for example, but shorter, wider planform hulls will resist rolling better." Again this deals with form stability issues and as such with buoyancy distribution. In a strict sense, a long slender hull may not be expecially resistant if the ends are very fine and the bouyancy is clustered amidships where it provides little help with pitching (late IOR type form).

In evaluating motion comfort there is always a need to balance quick accelerations with large rotational angles. If we look at the long narrow model, too much buoyancy in the ends will result in too quick a motion, and too little buoyancy in the ends will result in too much pitching. This is also the problem with using beam as a way of dampening roll. "shorter, wider planform hulls will resist rolling better" and so will roll through narrower angles, but will have much faster accelerations. If you look at traditional watercraft that are intended to work offshore or at modern IMS typeform designs, you will note that neither are especially beamy.

I also want to touch on the points raised by Chad. I thought that Chad raised a very good point about how boats sit at anchor. In a bouncy anchorage a boat that tends to pitch will be harder on its anchor rode when it comes up short as it rears upward against its rode. Again this makes sleeping aboard a longer overhang boat somewhat less comfortable at anchor. The other point that Chad raises about slapping and slamming is an important one. Flatter cross sectional shapes tend to slap or pound more than deeper Vee''d shaped sections. When you look at the counters on many long ended boats these will often pound in much the same way the flat stern sections of many production cruisers. Unfortunately fairly flat aft sections are important for reaching performance so that there is a trade off between a quiet stern and performance. It does help to have shorter ends so that there is less area above the waterline for waves to hit.

The other issue that Chad raised has to do with reserve buoyancy in the bow. As mentioned above, the amount of buoyancy in the bow needs to be balanced against the amount of momentum it needs to resist. Too much resistance and the boat has a corky ride and collides violently with each wave, and too little buoyancy and you are sailing a submarine with a mast. Some flair to the topsides forward is a helpful thing. Of course the wettest boats in terms of blue water over the decks that I have ever sailed were old short waterline boats whose bows extended far forward of their waterline plane.

That said, I have noticed that on more modern designs you sometimes really need to slow down a little or bear off in a steep chop. I think that I told this story here before, but last fall my wife and I were beating out of the Chester River in Maryland on a day where there were gusts reported into the mid to high 30 knot range. I was under a reefed mainsail and kevlar blade. We were going upwind at somewhere just below 9 knots. At first I was pointing quite high. This was right after I had gotten my boat and so I was really trying to sort out what she was about. I was really surprised at her motion. Instead of coliding with waves she tended to knife through in much the same manner as cahd mentioned. There was little slowing and none of the harsh collisions with each wave that I would have expected out of a 10,500 lb. 38 footer. I was having a ball and the boat was amazingly dry until we punched into a wave that was a foot or so above the stem. I was stunned to watch a foot or so of water roll aft across the deck, and still there was no feeling of a collision with the wave and minimal slowing in speed. The water rolled aft but went off the deck to leeward before it reached the cabin. After several more of those, I dropped the traveler a little and eased jib sheet and moved the lead forward just a tick and bore off a bit. The speed went up nearly half a knot but we were no longer knifing the tops off of waves. I think that a more traditional design would not have been moving at that speed or that close winded but I also think that a more traditional design would have been more tolerant of the angle to the waves.

Regards,
Jeff
09-15-2003 03:24 PM
dpboatnut
Confused about overhangs...

One additional consideration regarding boat motion and overhangs is how they effect the boat''s motion at anchor. A cruising boat spends a lot of time anchored. Even a cruiser/racer is likely to spend a lot of time anchored. In any kind of chop, the flat sterned "sugar scoop transom" is an abomination to those who intend to sleep onboard. I''ve had this experience with friends'' Catalina 320 and Beneteau 36. It''s like being in Shamu''s belly during an all night belly-flop contest. Sometimes, you can here the stern slap from another of these boats from a couple hundred yards away. An example of a boat that behaves nicely at anchor as another friend''s 80''s Ericson 32. The boat has moderate overhangs, is usually considered to be initially tender, but when anchored with the nose into the chop, it acts like an elevator car. There was minimal, soft rolling, very litle pithching, and no bone-jarring slaps.

Another observation not directly related to boat motion is reserve buoyancy, especially at the bow. Many of the go fast boats today have fine entries and plumb bows which are fast and good for the boat''s motion, as has been mentioned. But they are also largely wave piercing. It''s a staple of sailing magazine covers to show a fast boat head-on, the bowman getting ready for the windward mark, just as the boat punches through a wave, which is now blasted up and over the foredeck crew. Not just spray, but practically the entire wave!

There are trade-offs, and deciding which is appropriate for your needs is why you should, as has already been mentioned, sail lots of boats. And anchor them, too.

All best,
Chad
09-15-2003 10:35 AM
aflanigan
Confused about overhangs...

I think Jeff H is in serious contention to capture the "resident amateur physicist" title here on the board (which I had aspired to)! ; > }

If you think about automobile ride comfort, inertia is a big component in perceived comfort, hence Jeff''s discussion of inertia is quite appropriate. In layman''s terms, a big boulevard cruiser weighing a couple of tons (think Cadillac) will ride over washboard and small potholes more comfortably than a little one ton econocar, because it''s inertia will resist the deflecting input fed to the car''s suspension (springs) by a bump. The other important component for that cushy "boulevard ride" that car enthusiast magazines sneered at back when I had time to read them is damping, as Jeff points out: Sooner or later, the Caddy will hit a bump or series of bumps that get its stiff springs bouncing; if not damped, you''ll be "hobby horsing". Hence shock absorbers connected between the wheels and the car frame.

So how is a monohull''s motion damped? Aside from the damping action of the sails motion during rolling or pitching, and the keel resistance to rolling that Jeff mentioned, it seems the primary job of damping pitch and roll falls to the hulls, a task for which they are not particularly well suited. There are probably two effective mechanisms that could potentially damp the energy of a pitching hull: vortex generation (turbulence generatation) and wave generation (pushing a hull section up and down in the water will generate waves, which requires energy). Sharp edges can generate turbulence, but tend to do it also when you don''t want it (moving through the water under sail). Tapered hull shapes probably generate waves better than flat sided hulls. In terms of damping, Jeff''s experience with "overhang" boats is reminiscent of attempts to damp pitching motions using bulbous formations on the bow. Overall, though, there''s probably not a lot of potential for motion damping in a monohull form, unless you''re designing a houseboat that''s not meant to go anywhere.

Another aspect of seakeeping/seakindliness which needs to be mentioned is resonance. Any harmonic system (like Jeff''s pendulum) can be driven to resonance with input at the right frequency. Like a parent pushing their child on a swing, if you have a boat whose natural pitch frequency is close to the typical frequency of waves you encounter in the waters you frequent, you are going to have a hard time of it. Various add-on systems (anti-roll tanks, bilge keels) have been designed to try and supplement the minimal resistance to rolling that a hydrodynamically efficient hull shape offers.

There''s a good basic discussion of seakeeping and various attempts to improve seakindliness by John Waterhouse at:

http://www.unols.org/SBCompendium/06Seakeeping.pdf

See also the preceding chapter on "stability" which contains the Figures Waterhouse refers to in his article:

http://www.unols.org/SBCompendium/05Stability.pdf

So what sort of design would be most comfortable for you? Ultimately, you are wading into a compromise situation when considering sailboat hull design no matter what direction you approach it from (sailing speed and efficiency, motion comfort, economy, cargo capacity, ergonomics, etc.) Long, slender hulls may be resistant to pitching, for example, but shorter, wider planform hulls will resist rolling better.

Regarding the Nonesuch, I haven''t sailed on one, but as Waterhouse says, "vessel mass is a key factor in the equation. For a given wave height a heavy vessel will have
lower accelerations, or move less, than a light weight vessel." Comparing the Nonesuch 26 to my Helms 25, for example, the waterline length is comparable, but the Nonesuch has more than twice the displacement, and a very substantial ballast keel weight of almost 3000 lbs., which will keep the vertical center of gravity low. I have no doubt that this design would be more seakindly than my lightweight, centerboard coastal cruiser in many conditions.

As Jeff notes, some people have more intolerance of acceleration (quick motion), others of amplitude (big, slow rolling or pitching). Perhaps the best thing to do would be to crew on some deliveries to get real world experience of how different hull shapes make you feel out on the open water.

Allen Flanigan
Alexandria, VA
09-15-2003 10:27 AM
Jeff_H
Confused about overhangs...

Thank you for your kind words. To answer Silmaril''s questions, my post above was written specifically to answer the question being asked. I often write answers to questions that are likely to come up again using MS Word. (I am a little dyslexic and so left to my own devices my spelling ability is a bit nightmare.) I have kept these as a file and will sometimes pull out an answer that had been used before. I also wrote articles for a local sailing club newsletter and occasionally will grab one of these articles or a part of one of these articles and will use them to answer a relevant question.

As to the Nonsuch, I basically like these boats for coastal cruising. They are quite a clever design in a lot of ways and I am always pleasantly surprised at how well they sail. There is a lot to like about these boats.

On the other hand while loosely based on the Cape Cod Catboats, there is very little that is really ''traditional'' about the design of these boats. Cape Cod Catboats were really not intended to be all weather offshore boats. They were the sailing equivelient of a center console fishing boat. Literally dozens of these hearty little boats would be lost when a squall line would go through the fleet.

Cape Cod Cats were an extreeme example of form stability. Form stability is a bad idea when it comes to motion comfort. Nonsuch''s are also major league form stability dependant but are a bit finer than a Cape Cod Cat. As such they really do not have a very comfortable motion. Because of the weight of the mast at the stem of the boat, they carry a lot of fulness forward, this means a jerk pitching motion that was also typical of the Cape Cod Cats for the same reason. They also have a prett quick side to side motion which results from their extreme beam.

The best motion comfort comes from boats with comparatively small inertias and well balanced dampening.

Regards
Jeff
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