Long versus short overhangs

[Jeff_H]

Triton185:

I would say that you are correct that in my opinion CCA boats were inferior sailers to as compared to modern boats in terms of motion comfort, seaworthiness, and the ability to adapt to changing conditions. But I did not pull that opinion out of thin air.

I grew up sailing, owning, and racing CCA era boats and still sail and race on them routinely to this day. I also have owned, sailed and raced on boats from most of the design periods that preceded and followed. I sometimes get to sail on CCA era boats back to back with boats from the IOR,IMS and IRC eras. My opinion (and I do readily acknowledge that it is an opinion) has been shaped by 47 years of comparative experience of sailing different types in varying conditions.

But beyond that I have been trained by and worked as a yacht designer with guys who actually worked with Alden, Rhodes, S&S, and Alberg, and listened to them unanimously decry the excesses brought on by the CCA rule and the negatives of the boats that it produced.

My opinion is shaped by the theortical world as well. I have attended yacht design symposium for most of my life and have listened to the papers describing test results on models and real boats, and talked to the actual presenters as they discussed issues that were important to me. Motion comfort and seaworthiness have always been important issues to me, and the compromises made to beat the CCA rule compromised both seaworthiness and motion comfort, plus produced rigs that are less efficient and much harder to handle than the rigs that preceded and eventually followed the CCA/IOR eras.

I also have an interest in sailing and yachting history. Again, as I look the most seaworthy and seakindly working watercraft, or look at offshore cruising boats designed during the CCA era and compare them to the aberations of CCA rule beaters, I come away believing that the CCA hullforms, keel forms, and rigs are the antithesis of what I would consider ideal or even suitable for offshore work.

Further more even back in the 1960's when the CCA boats were the norm, while they were a revelation in terms of being fast compared to the boats that preceded them, even in that era, there were editorials by yacht designers and experienced cruisers decrying their poor heavy air characteristics compared to the longer water line boats that proceded them.

So, yes it is fair that say that I do not like the results of the design compromises made beat the CCA, but fortunely for me, my dislike of the CCA rule is consistent with traditional design principals, designers from that era and today, with theorists from that period and today, and with my own experience sailing and owning CCA era boats.

As to Ted Brewer, even during the late CCA era, his boats typically lacked the extreme short waterlines and extreme short keel length/attached rudder designs that made them such poor designs. And while I have tremendous respect for his body of work, he is also a designer states that he refuses to even look at the merits of IMS/IRC boats even though they are the results of a return to a more wholesome hullforms, and interest in motion comfort. His comments on their seaworthiness were in relation to middle period IOR boats, which I think few designers would deny was a period that a real lowpoint in yacht design history.

And to touch on RTBates question, "Albergs are NOT offshore worthy????"

I would put it this way, I keep seeing people suggest that Alberg's designs make good seaboats. In my experience they are barely passible. With luck, skill and pluck, they make be acceptable cruising boats, but for the dollar there are much better boats, boats that are easier to sail, more forgiving, more copmfortable in heavy going and generally better boats in all ways. Many of these boats are 40-50 years old and have been weaked by fatique and a life of use. So while people can, and people do take these boats cruising, I would suggest that there are much better choices out there.

And more to the point, some years back, I was at an Alberg 30 post race party. This was a group of experienced sailors, some of whom have owned their boats for 30 or more years and had sailed them all over the place. There was also former Triton owners in the group who had bought Alberg 30's when Triton class racing pretty much died on the Chesapeake. The discussion turned to the fact that on the internet there seemed to be an opinion that Albergs and Tritons were good offshore cruisers. Nearly to the man, there was a unimous agreement that without big crews and a lot of upgrading and re-structuring, almost none of these folks considered either class suitable for serious offshore work. All seemed to agree for the money and effort that it would take to make these old boats capable of reliably withstanding the rigors of offshore use, there were much better suited boats out there, by which the discussion focused on issues with the rig design, hullform, poor tracking, heavy weather helm, and pitch and roll characteristics.

And yes I agree with Triton that boats should be taken on their individual design merits and that within the CCA era there were better and worse designs.

Respectfully,
Jeff

[rtbates]

Jeff:

So where would that place Cape Dories, another Alberg design?
From everything I can gather these narrow slack bilged boats have very good righting moments as well as good 'comfort' quotient. All of the 'offshore' numbers appear to favor the narrow hulled, slacked bilged, long overhang vessel. What am I missing??

[Jeff_H]

It depends on the specific Cape Dory, but most of Carl's Capes are not very good sea boats when viewed against similar displacement designs that are intended for offshore use.

Here's what you are missing, the reality of narrow, slack bilged boats is that they tend to have pretty good limits of positive stability, but compared to the lower vertical center, moderate form stability (not high or low form stability), shallower canoe body, longer waterline designs now advocated for seakindliness, motion comfort and ultimate seaworthiness, narrow, slack bilged boats have pretty poor stability, which also means that they are also more likely to approach their limits of positive stability. When you add short waterline to the equation you deepen the canoe body increasing the tendency toward larger roll angles and a sharper snap at the ends of the roll. And of course, with a short waterline and long overhangs you increase the likelihood of a harsher collisions with waves, broaches and pitchpoling.

As to arriving at seemingly good Comfort Index and Capsize screen formulas on long overhang boats, the point that I was explaining in one of my earliest posts above, is that long overhangs distort the results in a manner that is counter to reality. In other words, if you consider two equal length boats, with equal displacement, one with short overhangs and the other with long, all other things being equal, the boat with short overhangs would have a gentler motion and be more seaworthy, yet the formulas would suggest the contary.

And as I have pointed out before, neither the Comfort Index nor the Capsize Screen formula, really tell you a thing about the motion comfort or likelihood of capsize. Both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats that otherwise are very similar. Neither formula contains almost any of the real factors that control motion comfort or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution, and neither contains any data on dampening, all of which are the major factors that control motion comfort or the likelihood of capsize.

I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. That is why I see these formulas as being worse than useless. This is especially true in the case of boats with long overhangs as explained above.

Respectfully,
Jeff

[seabreeze_97]

The one thing I do not see in your explanation is about those short waterlines. On the CCA boats, their waterlines lengthen with heeling (easily equaling conventional short-overhang boats' waterlines), so as they roll, their lengthening waterlines would tend to decrease, not increase, harshness, and when heeling, impose gradual, increasing resistance to the roll angles. Basically opposite of what you are saying.
On your example of having a 500lb weight on the mast, high above the boat, technically speaking, the capsize ratio and motion comfort scales are correct. Why? The added weight at the high end of that mast requires greater energy to induce roll. Thus, the boat is slower to respond to external force, meaning, it has a gentler motion and greater initial resistance to roll and capsize. The extra 500lbs has a greater inertia that must be overcome to induce roll motion, or, for that matter motion fore/aft. Then, the reversal of the roll is also gentler, as that inertia has to be overcome again to right the boat. The slower response makes the boat gentler, and more resistant to capsize from wave influence. It will heel over longer, and recover more slowly, i.e., more gently. The term "wallow" comes to mind if weight aloft is too great. As stated, practicality must be factored in. In a sterile lab, this would seem to be an ideal solution, but in reality, this can be taken only so far, because if taken to extremes, the boat would be easily rolled if the weight was too great. Weight aloft must be considered with all other factors. Again, opposite of what you are saying. Glass half full/half empty. We're never gonna agree on this.

[Plumper]

Originally Posted by Jeff_H

I typically give this example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. That is why I see these formulas as being worse than useless. This is especially true in the case of boats with long overhangs as explained above.

Respectfully,
Jeff

That is a pretty self serving example. The formulas were developed to give some relative comparison between boats that are properly (or close to it) designed. Any designer or owner who puts 500lbs at the top of the mast is a fool. You could pull many tricks like that out of thin air and use it to fool a formula. That sort of stuff does not lend weight to your argument at all. Quite the contrary.

The fact is that those various formulas are still very much in use. Their usefulness has been demonstrated. Of course they don't work for oddities like your example. They also don't work for multihulls, dinghies or sailing rafts but that doesn't make them wrong. They must be used with common sense.

[CharlieCobra]

Hiss hiss snarl.....


Ya'll behave now...

[Valiente]

OK, before this gets into a bunfight, I would like to state that I respect Jeff H's opinion (and his essays are thought-provoking) and did not realize he had the depth of experience he's stated above. It certainly entitles him to a better-informed opinion than most of us.

I will say this: Good sailors can sail bad boats better than bad sailors can sail good boats. I will also note that many boats of any era, after being subjected to extreme conditions, are washed ashore or found more or less intact after being abandoned by their crews. There's aren't many widow-makers out there, unless you consider those who take manifestly coastal/fair-weather cruisers on fool's errands.

Having said that, I would enjoy Jeff's opinion of what exemplified his ideals of seaworthiness, offshore-appropriate, seakindly motion, resistance to capsize and other "desirable traits" from each decade between 1960 and now...which would be six boats, if you count this present decade as mostly done.

Let's say boats between 35-45 feet, as 35 feet is considered near the low end for offshore (these days) and 45 feet is close to the limit a fit couple can handle.

I want to see if Jeff's scrapbook of boat crushes reveals consistencies or traits that are definitive...if he will oblige me!

[KeelHaulin]

I think the discussion should take into consideration that many of the CCA and IOR era boats were not designed to be "bluewater" cruisers. Most were designed to out-perform their competition on a race course with plenty of crew. Now that they are no longer competitive many have been converted over to dedicated cruisers; some being more well suited to it than others. It really depends on the particular boat you are talking about. I think motion comfort index is a good indicator of how well suited a boat is to extended cruising. If the boat is stiff and pounds it's way through the chop you are going to get fatigued long before you make your destination. Many of the "bluewater" designed boats are heavy displacement and full keeled to resist pounding and awkward rolling motions.

Capsize ratio seems to be less relevant in terms of overall "seaworthiness" than you might think. A big breaking wave is bad news regardless of the hull form; as described below. Does that mean I want a boat that has a low capsize ratio? No; but a high number does not mean you boat won't capsize in certain conditions.

There is some good information on the US Sailing website here are a few quotes:

US Sailing Website

According to Andrew Claughton in Heavy Weather Sailing 30th ed. p 21 "This (the test data presented in the chapter) suggests that alterations in form (of a sailboat) that improves capsize resistance may be rendered ineffective by a relatively small increase in breaking wave height."

If a boat is positioned into a breaking wave, most boats (wide and narrow beamed) can survive a 55% LOA (overall boat length) breaking wave. However, a 35% LOA breaking wave hitting a wide-beamed boat beam-on can easily capsize the boat. All yachts tested rolled to 130 degrees. No yacht, no matter how stable, could consistently resist capsizing when hit, beam-on, with a 55% LOA breaking wave. (K. Adlard Coles' and Peter Bruce's (editors) Adlard Coles' Heavy Weather Sailing (30th edition) Stability of Yachts in large breaking waves. Chapter 2 pp11-23 International marine, Camden, Maine)

Putting this in perspective in a 40 foot (LOA) sailboat: In a highly stable boat wave survivability would increase by 8 feet, if hit beam-on by a breaking wave. A 40 foot sailboat no matter how stable will not consistently survive a 22 foot breaking wave. Thus, in a strong gale with 22 foot seas and breaking waves, a 40 foot sailboat is at risk of capsizing no matter how stable.


Most important factor is an experienced crew: Of all the factors, it is far more beneficial to have an experienced crew that can either avoid or position the boat into large breaking waves.

The 1998 Sydney - Hobart race was one of the worst sailing disasters in recent maritime history. And from it many lessons were learned regarding the functioning of boats and crews in heavy weather. 115 boats left Sydney and were hit by an unexpected typhoon. Seven boats were abandon and five were lost. The 1998 Sydney to Hobart Race Review Committee report, summarized by Peter Bush, committee chair, reported the following as one of the significant findings: "There is no evidence that any particular style or design of boat fared better or worse in the conditions. The age of yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement, or rig type were not determining factors. Whether or not a yacht was hit by an extreme wave was a matter of chance." (Ref: Rob Mundle in Fatal Storm, Publisher's Afterward p 249. International Marine/McGraw-Hill Camden, Maine.)

[KeelHaulin]

"Big" overhangs are always preferable to small:

http://www.sailnet.com/photogallery/....php?file=3587

[Jeff_H]

The ‘Doubting Thomases’ are out in out in full force, ……but more seriously, members of the jury I will try to make a case, which addresses the issues raised by my esteemed colleagues. (I apologize but this is way too long, but that’s what happens when I try to bang something like this out during lunch hour and don’t have time to edit.)

I’ll start with the issues raised by Seabreeze 97. To quote the heart of Seabreeze’s first point, “On the CCA boats, their waterlines lengthen with heeling (easily equaling conventional short-overhang boats' waterlines), so as they roll, their lengthening waterlines would tend to decrease, not increase, harshness..” (I amtempted to ignore the parenthetical “easily equaling conventional short-overhang boats' waterlines” which ignores the fact that the waterlines on short overhang boats also lengthen with heeling and so the long overhang boat never does catch up with the waterline length of the short overhang boat)

To explain why the long overhangs when coupled result in a more harshness rather than less at large roll angles we need to start by looking at the real shape of the stability curve which plots the righting force against heel angle. We all are used to seeing illustrations of stability curves that loosely appear to be smooth sine curves with ideally the portion of the curve representing positive stability being larger than the portion representing inverted stability. In reality, if you plot the actual point righting force against heel angle for any given boat, there will be a series of humps and shelves that relate to the shape of the boat that is in the water at any given point. Most noticeably for example, typically there is a shelf that occurs between the point that the deck edge hits the water, and the point at which the cabin side hits the water (while it varies considerably with the design of the boat, that shelf is typically occurs around 45 to 60 or so degrees of heel).

When we look at a stability curve for the typical slack bilged, with long overhangs, CCA era hull form, these boats develop very little initial stability and build increased stability very slowly until a heel angle where a large proportion of the counter begins to immerse (typically at a heel angle between 25 and 35 degrees). Anyone who has spent much time sailing typical CCA era boats, will say something to the effect that these boats may be tender at first but at some heel angle they harden up and don’t heel much further. That heel angle where the CCA era boats harden up occurs at s the steep portion of their stability curve. Because of the geometry of the hull and overhangs that point of rapidly increasing stability happens pretty suddenly.

This was done on purpose, because in order to get unrated speed at from the overhangs, CCA era boats needed to be sailed at larger heel angles than se sail more modern designs and designer of that era wanted these boats to heel quickly to that point an not much further. In creating this point at which low initial stability quickly increases, the CCA boats initially roll easily but fetch up sharply as they hit this steep increase in stability.

IOR era boats had a similar lurch in their rolling motion but for other reasons. Although IOR boats had shorter overhangs, they typically were purposely tender at small heel angles and carried close to their max beam at a point about a third of the topsides height above the waterline, and had a topside shape that flared out from a substantially narrower waterline beam to that point. When that bulge hit the water, the roll would stop short with a very noticeable lurch.

Both Seabreeze and Plumper question my choice of the example of putting 500 lbs at the top of the mast to illustrate why the Capsize Screen and Motion Comfort Index is being dismissed as misleading. I chose that example because it was so graphic that I assumed it would easily make the point that if a formula is going to screen for capsize or motion comfort it needs to contain at least some of the critical elements that control capsize.

But to further explain my earlier post, I will start with an example which is more likely to occur in real life than someone bolting 500 lbs perhaps a more normal type of example. We have two owners going to the same manufacturer and buying the same model boat. One plans to go offshore, and the other plans to simply do coastal cruising, but do so elegantly. The Offshore cruiser, opts for the lead keel and the carbon fiber mast hoping to keep the vertical center of gravity low and a non-skid fiberglass deck and a barebones painted plywood with simple varnished mahogany trim for ease of maintenance.

The elegant coastal cruiser, decides he doesn’t need the lead keel and carbon fiber mast and so opts for a cast iron keel, and an aluminum spar. He decides that he wants teak decks and he wants the teak interior which includes solid teak cabinet fronts and raised panel doors.

If we compare the examples and assume that the lead keel has the same shape as the iron keel, and we assume that the boat in question is say a 42 footer which had something like 9,000 lbs of ballast with the lead keel, the iron keel of the same shape would only weight roughly 6,200 lbs. And if for the sake of this example, I suggest that we assume that the boats have an equal displacement, with 2,800 lbs saved on the keel being used up as 1200 lbs of increased interior appointment weight, 1,200 lbs on the teak deck, and the remaining 400 lbs in the heavier rig.

If we looked at the plot of the righting force vs. heel for the offshore vs. coastal cruiser, we would see similar shaped curves because the shape of the curve is predominantly controlled by the shape of the boat in the water at various heel angles. But the offshore boat would have a significantly higher maximum right moment (force) and would have much more area under its curve, and would have a much higher (perhaps as much as 10-15 degrees) limit of positive stability. In other words, the offshore version would be much harder to knock down and if knocked down by a wave, more likely to right than turn turtle than the elegant coastal boat.

Which gets us back to the capsize screen formula. If the capsize screen formula is to have any utility, it should be able to give us some clue as to which boat would be more stable and in this, close to a very real life example, the capsize screen formula fails to give any indication that one boat is far more prone to capsize than the other.

Which is where we begin to hit against theory and the application of theory. In looking at studies of model testing and actual heavy weather conditions, the current theories seem to identify primary and secondary factors as follows: The STIX study group that looked at the various race disasters concluded that the single determinant of the likelihood was waterline length, in other words the longer your water line the less likely you were to be capsized.

Beam came next. But here capsize screen (which only looks at only beam and displacement) seems to get it wrong. The capsize screen formula thinks that the narrower the beam the less likely you are to be capsized while the results of the studies of actual experience suggested that within reason that wider beam translated to less likelihood to be capsized basically stating that it took a wave half the waterline length and twice the beam of the boat to capsize it.

The forces involved are so huge that displacement was seen as having little or no bearing. Then there were as series of other lesser and perhaps more controversial factors. Since in large enough waves to capsize a boat, (again because the forces of a breaking wave is so huge, boats of equal beam were seen as being rolled to roughly the same angle. Here is where roll moment of inertia and VCG come into play. A boat with a larger roll moment of inertia will start to roll a little later than a boat with a lesser roll moment but it will also store more kinetic energy and so will tend to roll further at the ends of the roll than a boat with a lesser roll moment of inertia. That over roll takes place at the end of the slide and so is more likely to keep the boat knocked down longer and potentially allow the boat to stick a spar in the water, which will knock it over further and even potentially induce a roll over. In the case of a boat where the high moment of inertia comes from a heavy keel and light spar, the weight of the keel is trying to right the boat and somewhat offsets the tendency to over roll at the bottom of the wave. But in the case where the high moment of inertia comes from weight up carried up high, the tendency to over-roll is increased and the likelihood of a capsize is increased. But not only would the boat with the higher VCG tend to heel to a larger angle, it has a smaller limit of positive stability making it more prone to rolling over than coming back

Which brings us full circle back to Seabreeze 97’s objection to my earlier example, a boat with a 500 lb weight up its mast would have a tendency to roll further in the wave, and would have less of a tendency to right itself.

I agree that the impact on motion comfort of a 500 lb weight up the mast is more complex than that example suggest which is precisely what Seabreeze 97 is pointing out.

But again, the simpliest way to debunk the Comfort index is by comparing comparing two boats. If we start with a CCA era 40 footer with an LWL =30ft, Beam=12 and Displacement= 20,000lbs we come up with a MCI of 33.94. If we compare that to a 44 footer LWL =39ft, Beam=13ft and Displacement= 24,000lbs we come up with a MCI of 29.8. If weight distribution and VCG, cross sectional shapes, etc were similar, the bigger, proportionately slightly narrower, heavier boat would have a significantly more comfortable motion, yet Brewer’s MCI suggests just the opposite. And missing from the formula is such critical motion impacting elements as VCG or even Ballast to displacement ratio, dampening or even draft, and height of mast and so on. Which comes back to my central point being that the MCI produces such inaccurate results as to be worse than useless as a real comparative tool.

Respectfully,
Jeff