Steve Dashew, over at setsail.com, just published a post about being offshore in a short-lived but very nasty blow earlier this summer.
The super interesting thing is that Steve and Linda had just fitted their 78-foot motorboat Cochise with continuously running video cameras. The result is a uniquely useful set of photo-observations, coupled with written analysis, from a guy with a uniquely deep understanding of hull forms.
Doesn’t matter what kind of boat you sail or motor (or aspire to), I highly recommend you read Steve’s post. There is just too much good information about how hull forms work, and don’t work, in big and dangerous waves to let this one pass you by.
Here are two of my takeaways:
Buoyancy needs to be balanced fore and aft
I have long ranted against overly-wide sterns for a whole bunch of reasons. But in Steve’s article we see graphically how vital it is that the stern does not have too much buoyancy, particularly in relationship to the bow.
For if the stern is too wide and big, as we see so often these days, then in heavy weather bad stuff will happen:
- When running downwind in big seas, the stern will rise excessively on the back side of a wave and so stuff the bow, potentially causing the bow to lock in, resulting in loss of steering control, untimely leading to a broach.
- When pushing into waves, the stern must be able to immerse well into the back of the last wave so that it does not drive the bow hard down into the front of the next wave by lifting too much, and in so doing bring tons of potentially boat wrecking green water aboard.
On displacement hulls—planing hulls like Open 60s are different—these two requirements are fundamental and immutable for safe offshore voyaging, as I can attest from having spent literally thousands of hours over the last 25 years watching how Jim McCurdy’s perfectly balanced bow and stern buoyancy react to waves.
Reserve Buoyancy Matters
Another interesting thing from the photos is the way that the flare in her bow sections, together with the resistance of the large anchor and associated platform, helps to stop Cochise from burying her bow excessively.
On Morgan’s Cloud, McCurdy achieved the same thing by carefully flaring the bow and adding moderate overhangs that gently, but firmly, prevent the bow from completely burying in the face of a sea, but still don’t provide excessive buoyancy that would cause slamming and/or excessive pitching.
This same reserve buoyancy prevents Morgan’s Cloud‘s comparatively deep forefoot from locking in when running hard off the wind.
Bottomline
It’s hard to imagine two boats more different than Cochise and Morgan’s Cloud, and yet the fundamentals of good hull design, which makes them safe offshore, are the same, and include balancing the bow and stern so that they work together, instead of drawing a design to accommodate a palatial interior. We ignore these fundamentals at our peril.
Artnautica LRC 58
Before I leave the subject, reading Steve’s post and studying the photos have got me thinking about the LRC 58 again. I always said that the court was out on what her heavy weather performance would be like, and Matt Marsh, AAC Engineering Correspondent, wrote:
When outrunning a following sea, she should be fine, but I suspect that when waves are overtaking her from astern, the seas will tend to lift the stern and stuff the bow. It looks like she has enough reserve buoyancy up front to handle this, but it’d make for a wet ride, and she’ll need a big rudder and strong autopilot to avoid any tendency to broach or bow steer if there’s a real nasty storm coming up from astern.
I also note that in his latest design being built in Turkey, it seems (from a cursory look at these photos) that Dennis has made major changes to the hull form, including making the stern narrower and less buoyant than the LRC 58.
Steve’s article reinforces my thinking that anyone taking an LRC 58 into harm’s way fit her with a series drogue to Don Jordon’s design and, in addition, dispense with the large cockpit (as discussed in this post) since I’m not at all sure that keeping going in bad weather, either upwind or down, would be a good idea.
Hi John.
Good points, as always. You mention that these issues are different on planing hulls, like the Open 60 class. I think it might be interesting to look a bit more at that point, since it seems to be linked to how monohull cruisers are developing these days.
The reason that extreme racers behave differently is complex of course, but I think two elements are interesting:
– Very large hull volume compared to total weight and a speed that gives dynamic lift. Meaning they float/plane “on top of” the water, and they don’t easily get pushed properly under. They do, of course, get a lot of water on deck, but that is mostly water sliced off the sea surface rather than the bow digging into the sea.
– They are sailed by elite sailors who are on non stop maximum attention level, and they accept a very high risk of serious trouble.
No present day cruising boat is able to operate sufficiently on top of the surface, no matter how they’re designed. No cruiser, with a decent mental health, wants the work, stress and risks of pushing as hard as the racers. The obvious conclusion is that using core elements of the hull shape of an ultralight racer for a cruiser will have some problems. Why then do the boat wharfs do it?
The first and obvious reason is that a fat transom gives a lot more space inside, which makes the boat easier to sell and nice in a marina. This item is the logical one. Then there is the other reason, which I think might be just as important:
Racers innovate non stop. A top level racer from today looks radically different from and is dramatically faster than the same from a couple of decades back. We see every visual element of the newest racers as identifiers of speed and power. What that is has changed just as much as fashion in clothes. The extremely long overhangs, bow and stern, of the R-Class (12 meters etc) were defining cruisers, even though the overhangs are very bad for speed but were there to fit the R rule. Moving forward, we got the straight bows. Wow, that looked mean! Now it’s old. Now we need a negative bow! That’s the proof your boat is fast and modern! And, yeah, of course a crazy fat ass belongs in there!
So we willingly accept that we design boats to fool ourselves. We buy boats because we want to satisfy our feelings. I’m a complete nerd, but I never let my emotional decisions be disturbed by annoying logic! Yes, it looks like a joke, but for me, and probably every human, it’s plain truth. The best use for logic is to use it to influence my emotional decisions into something that will last longer than just outside of the shop door. But no logic can make me do anything my emotions don’t like.
So will the fat ass boats become a nightmare shortly after the boat is bought? No, mostly the buyers will love them for years. These boats do an awesome job for most of their owners, who sail very few or no ocean passages and close to never experience seriously bad weather. Their interiors are easily worth losing the big wave behavior they will almost never need. The readers of this site should probably look a bit more thoroughly at those priorities.
So, am I writing all this just to say the obvious “different types of sailors need different types of boats”? Well…. yes… But I think some of the words on the way there might be worth it.
I’m really bothered by how features that start as a rule tweak in a specific race class becomes standard issue in most sailing boats. I would love it if it was possible to go away from “how it was always done” (for some obscure reason) and rather look at what is the main need and what is the smartest compromise to get that. For long distance cruisers, I can safely say that negative bows should not be on the list. Neither should a long list of other features of normal cruising boats.
PS
In the near future, negative bows will be found on some cruisers.
I’d be willing to bet a lot of money on that.
Hi Stein,
Very good analysis, thank you.
I would add one more thought to why taking ideas from extreme race boats like Open 60 and grafting them onto cruising boats is a bad idea:
Because Open 60s and Volvo 65s are very fast and have elite navigators, they actually almost never experience the worst waves in a storm. Rather, they are fast enough to stay ahead of depressions and then veer off into less dangerous sea states before they get rolled by the depression and fall into the really dangerous areas on the back side with sudden violent wind shifts. Not saying they don’t sail in a lot of wind, they do, but they are generally not in anything like the worst sea state.
No cruising boat can do this kind of sea state avoidance.
(I didn’t figure this out myself, but rather learned it from Skip Novak who was talking about how much worse their weather experience was in the old Whitbread race where they were racing IOR Maxis capable of maybe 250 miles in a day, so they got rolled repeatedly.)
The importance of fore/aft balance is certainly neglected in many naval architecture circles, and – perhaps crucially – it’s neglected by the people who create the design tools.
Most designers are aware of the need to get the form coefficients (most relevant here are Cp and Cwp) correct for the boat’s intended speed. There is surprisingly little room for variation here; if the correct Cp is 0.59, then designing the hull with Cp = 0.56 (visually indistinguishable to most eyes, until you overlay the two lines plans) will result in poor performance, and Cp = 0.53 will yield a lame dog.
Only a handful of naval architects, Steve Dashew among them, clearly understand that it’s not just the whole-hull Cp that matters, but that forebody and afterbody Cp and Cwp must be considered separately as well. If the relationship between the two is not correct for both the speed *and* the intended sea state capability, the boat will have performance and handling issues in poor conditions. Most CAD software will not split them out automatically; you have to manually cut up the hull and hack the calculations a bit. Seakeeping calculation methods, too, exist but are often tedious to configure and not easy to use correctly.
When there’s a strong push from marketing to maximize “boat per unit length” rather than “boat per unit mass” or “boat per dollar”, engineering generally isn’t going to push back without good quantitative data. That means both a better understanding of the characteristics that matter, and tools that are designed to reflect and enhance that understanding.
Hi Matt,
That’s really interesting, particularly that the readily available tools don’t support this kind of refinement for sea keeping. As you say, and I had not thought of, makes it really hard for a designer to push back against marketing pressure to do something poor.
Hi John,
Agreed, this is definitely a good article. When I first read it I was surprised by the date on the images and checked in our log the next time I was on our boat and found that I had been about 80nm northwest of them with ~20-25 knots from the northeast and ~6-8′ waves (I anchored up around dark and got underway early the next morning so wasn’t actually underway at the exact time the pictures were taken). To me, this once again shows how small changes in location can have big effects, I was out there for fun and enjoyed myself while it would have been very different had I been where the Dashews were. Being north of the Cape, I had no SW swell so I didn’t have different wave trains interfering and the wind strength was also much more pleasant. I like the comparison they make to the 100 mile entrance pass, the ones that are only a mile are bad enough, I really don’t like the idea of a 100 mile one.
I found his comments on loss of maneuverability interesting. They clearly had given thought to the possibility of a loss of steering and had wisely thought through the backup system. The seatbelts comment suggests that he feels the boat would have definitely made it through but also that they would have been incapable of accomplishing most tasks. For many boats where loss of propulsion or steering would present a truly dangerous situation if not dealt with quickly, it becomes crucial to be able to quickly switch tactics to the JSD or whatever the backup plan is both because of the vulnerability when beam on and also the horrendous motion that increases the length of time in that position.
We saw Cochise underway for the first time earlier this summer in the calm waters of Penobscot Bay and it was definitely impressive how well it appeared to be moving through the water. In 2011, I was taking a 30′ ketch north in a strong afternoon southerly along the southern Maine coast and approached a boat that I just couldn’t figure out what it was until I saw it more in profile and realized it was Wind Horse. They were moving at a good clip going into a significant chop and what really drove home to me how well they were going was when someone stepped out on deck with an enormous camera lens to take pictures of the silly guy who was rolling his way north.
Eric
Hi Eric,
Very good point that even with all redundancy he has at his disposal in his boats, Steve is still constantly thinking and planning for the wild card event (like total power or steering failure) that can lead to disaster.
I think each of us need to take the same approach to having a backup plan. For us it’s having a JSD ready to go whenever we go to sea: https://www.morganscloud.com/2013/06/01/jordan-series-drogue-launch-system/
Fascinating. But would also ask what impact gyradius and rocker have on boat behavior. I’ve sailed my beloved Outbound and have had opportunity to compare its ride to the current crop of production boats. Note less pounding upwind and less wandering downwind in difficult seas on the older Schumacher design than those with the flat, wide stern, slice of pizza boats. Have thought this is not only due to footprint but also relative lack of rocker and induced asymmetry of immersed hull when at heel in the newer offerings.
Also note some hulls are more tolerant of weight in the ends and the slice of pizza boats seem particularly intolerant. Race boats seem quite diligent in keeping the ends light but this is often difficult for a cruising boat to do.
All good points, both in the articles and the comments. As for Cochise, she’s the size of ( and nearly as ugly as) a small warship so you’d expect her to handle a bit of weather!
As for hull forms, did Colin Archer get it right?
Sure, Colin Archer got it right…the same way Steve did: balanced ends.
Not that I can do much about the boat we have, but our steel motorsailer has a relatively short WL of 31 feet and an LOA of 42, with a cutaway forefoot, relatively bluff bows and a relatively narrow stern (about 6′ 6″ compared to 12′ 6″ maximum beam). These strike me as desirable traits in light of the discussion, even though I am resigned to heaving to (or running off with a JSD) when others might make a break for it in approaching bad weather. I endeavour to be careful about weight in the ends, even though my eye and our experience plowing down wave fronts suggests we have reserve buoyancy to spare, but we haven’t really tested conditions where stern buoyancy might come into play. So this is an interesting discussion in terms of “best tactics”.