Seaworthiness

The time during which the max force is applied is irrelevant.wrong
The time during which the min energy is present will determine the speed of the roll.

 

In a nut shell:

Masses far from the rotation axis require more force to accelerate. Once they are moving they require more force to stop.

The heavy rig resists initial roll better than a light rig. Once the rotation is started it takes an equally large force to stop the roll. If the event that starts the roll imparts enough momentum to the rig, that momentum can carry the rig past the AVS even though the force that started the roll has passed.

Heavy rigs are described as imparting roll stability and in the case that the event that could roll the boat is of short duration, the hope is that the rig's inertia will prevent a knock down.

Heavy rigs also reduce static stability. One has to count on the reduced RM being large enough to overcome the inertia of the rig and right the boat. Of course once the motion is reversed, the rigs inertia will roll the boat further in the other direction before the RM can start it back to centre.

Once rolling, heavy rigs tend to continue to roll.

Light rigs start to roll with less energy and less energy is required to stop the roll. This motion is characterized as violent or snappy by those that are pushing an agenda of heavy boats and rigs.

That same heavy rig causes the boat to pitch to greater extremes also. The rig resists the bow lifting over waves and once the boat pitches up it pitches up further. Next the boat pitches down after the wave crest has passed, the high inertia of the heavy rig forces the bow down further ... just in time for it to bury into the next wave.

Now we have a heavy rig that is causing the boat to roll through greater angles (at lower frequency) and pitch through greater angles (also at lower frequency).

What is attached to this fine rig are the sails that are trying to drive the boat. Anyone that has ever sailed knows that reducing roll and pitch keeps the drive from the sails at a more constant value (faster on the race course).

So now you have the heavy rig "stable" boat rolling and pitching so badly that the sails are backed some or most of the time during each cycle. Drive is lost and the dynamic stability of the sails is lost, in some cases the backing and filling of the sails makes the rolling and pitching worse ... time to heave-to, the boat has stopped sailing.

I can only speak for myself. I have been on such boats, the motion is not friendly (IMO). They may score well in the MCR ratio formula, but they don't sail well in a seaway. The gyrations of the rig make the boats hard to steer, and prone to broaching ... setting them up quite nicely for an inversion test.

Yes, the accelerations are higher, but the excursions are smaller in a boat with a light rig. That is one of the reasons that large amounts of money are spent to save weight aloft. Saving weight aloft even at the expense of greater windage (PBO rigging is 30% of the weight and 120% of the windage compared to SS rod).

In simply amazes me that the boats that are designed to sail oceans in any conditions (as racers must) are thought to be unseaworthy. As anyone knows, to win, you must finish.

Just because a boat is able to sail at 20+ knots under control does not mean you have to sail it that way. If it is strong enough to handle 20 knots, it has to be very lightly stressed at lower speeds. A boat like the Pogo 40 could be sailed at the same speed as the Valiant. At those speeds it has a great reserve of stability and speed. Faced with a poor forecast, the Pogo could be sailed hard (perhaps with uncomfortable motion) to avoid the worst of the weather. The Valiant will have fewer choices, the Valiant will see worse conditions and the motion will be much more violent than the Pogo during it's dash out of the impending storm. This is how ocean races are won. I submit that cruising in a boat that is able to pick her weather to a greater extent than the Valiant will be much more enjoyable. The skipper of the Pogo will be there to help with the dock lines as the battered Valiant with it's dehydrated, seasick crew crawls off the boat.

Yep, heavy is better. How can you possibly be a sailor unless you've weathered storms while hove-to or spent hours lying ahull hoping the boat doesn't roll. A design that doesn't require these time honoured skills must be the work of the devil! Being able to sail in Force 9 on autopilot while sleeping must be cheating. No respectable cruising boat should be able to do that. Yes, the Pogo must be a bad boat.

No amount of argument will sway those that have read a book and know that you have to have a full keel, heavy displacement, and a heavy rig to sail oceans safely. If you want to sail a house, I have to agree. You need a boat that can hold all the crap you have convinced yourself that life requires. The high windage and low AR keel was never very weatherly anyway, so that big dodger, bimini, and dinghy on davits are not a concern. We have that big diesel and 300 gallons of fuel and motorsail anyway.

Seaworhy means different things to different people.

 

To take into account dynamic effects due to wind induced heeling and rolling, what we have to study are energies and works. To exemplify the thing I attach here a Word document that may be of help. It has been taken from NSCV-Subsection 6A about criteria to be applied to commercial vessels (Australia. Something very similar can be found in all regulatory bodies, as follows IMO reccomendations). This an example of how dynamic movements are studied based on the static GZ stability curves.
Cheers.

 

A nice compilation of videos from races:
http://www.elportaldelosbarcos.com/sistema/pagina_submenu.php?opcion=451&id_menus=70&id_submenu=451

From there, this nice broach at the Volvo race:
http://www.youtube.com/watch?v=6rvf_SPfx1Y

Cheers.

 

Tom, the reason I am pretty sure of this, and I mean the last part (the energy required to capsize a boat = value behind the positive part of the RM curve) is because I don’t need to think about it. I have seen that being said by very knowledgeable NAs.

For instance Dave Gerr in an article published in 2004 about “Ultimate Stability” on “Sail Magazine”:

…The curve shows other important things. The area under the positive portion of the stability curve represents the energy required to capsize the boat. The more energy required, the stronger the wind and wave action required to capsize the boat. Similarly, the area under the negative side of the curve represents the energy required to right a boat once it’s been capsized. The energy under this curves is measured in units called degree feet".


Or Leif Angermark Marin, the Na that designs Malo yachts:

“Every wave contains a certain amount of energy and every vessel requires a certain amount of energy to be turned over. The energy required to capsize a ship is represented by the area of curve above the baseline, and energy needed to return it to an upright position is represented by the area below the baseline. NOTE: This is only valid for the curve representing the righting moment, NOT the G-Z curve.”

http://www.maloyachts.se/Portals/0/STABILIT.PDF

 

Many have not finished, and that happens almost at any oceanic race, as you know. What I find unseaworthy is the undue bringing of extreme racing criteria to family cruising boats, which is what we are supposed to be discussing from the very post 1 of this thread.

Absolutely.
Let's quote Marchaj: "The problem is that the true meaning of the term seaworthy can be found only by observing what a man does with it, not what he says about it"

Cheers.

 

That's the problem with narrow boats

 

That statement is not correct . Let's see an specific example:

Modern cruising boat design characteristics:
Lh = 11.98 m
Lwl = 10.57
Bh = 4.10 m
Bwl = 3.27 m
T = 2.38 m
SA = 77.4 sqm
DSPL = 5.16 T (MOC)
DSPL/L = 122
SA/DSPL = 25.9

STIX at MOC condition: 38.371
STIX at MTL condition: 41.722

(Almost a 9% difference)

Pogo 40 cruising version's official STIX figure may not be the one you have posted, if the one at the MOC condition is lower than that. And it could very well be even sensibly lower, not only as per the example above, but also because I supect MTL condition most probably includes the 750 kg of water ballast. If I understood you well, a 2.2 tons difference between MOC (5.3 t) and MTL (7.5 t) seems to be a really big one. That difference for the boat considered upwards (quite similar to Pogo), is of only 1025 kg. And her MTL against lightship condition (just in case 5.3 tons is in fact the lightship mass for the Pogo and not the MOC) is only 1690 kg. So we have either 1175 kg or 510 kg of difference between the loading ability of the two boats. Mmmmm....

On honesty and the like: You posted that 44.7 STIX figure and stated:
"About the POGO40 STIX, I will post the relevant part of the official document that certifies the boat. No need to make any calculations. They have already been made correctly and ISO certified."
As it seems now, you are not totally sure about it. If so, this demonstrates, leaving honesty aside, a lack of knowledge on STIX matters, in my opinion.

Cheers.

 

Here we have another debate ... maybe ...

I do not find the the Pogo extreme. It has a moderate design compared to many outright racers.

If you wish to define as extreme the boats with ratios as poor as the C30, you will be arguing with almost every sailor on the planet.

I seriously doubt that you will ever see a Pogo 40 type hull marketed with several thousand kilos of "luxury interior" and the systems that are installed on many 40 foot "ocean boats". For all the reasons that have been stated here, the majority of cruising families will never even consider the Pogo 40 or other Class 40 cruiser. They have read the same books, they "know" the Pogo 40 doesn't fit what the books say, so they won't consider the boat. I find that to be a pity.

What are "extreme racing criteria"?

Strong rigs?
Crash bulkheads?
Unsinkability?
Directionally stable hulls that are easy to steer?
5:1 stability area ratios?
High AVS?
Weather ability in gale winds?

What exact racing criteria makes a cruising boat less seaworthy?

I agree on extreme beam forced by a static stability rule.
I personally don't care for the canting keel system, but I cannot make a scientific case against it. I just don't like big holes in the bottom of boats.

I would argue that any boat that does not meet Offshore Cat 1 safety standards is automatically not seaworthy. I can assure you that most "blue water" boats do not.

I really think the future of cruising will come from the lessons learned by single and short handed racers. What works for them should work for a typical short-handed cruiser.

Many of the cruising boats today follow the influence of fully crewed ocean racers. A family does not benefit from a design that requires 6-8 crew on the rail to perform. That family would be better served by a design that was intended for it's ultimate use.

If cruising is living as a sea gypsy with all your worldly goods aboard and staying in each port long enough to become unwelcome after people tire of looking at your laundry hung on the rigging to dry, then you need a big heavy boat. Something that won't break often, since you don't have a job and can't afford to fit it properly when it does break.

Somewhere between ill suited fully crewed offshore designs, ocean hot rods like the Pogo 40, and the homebuilt steel cruisers that met the book's criteria (before the builder made it 10,000 pounds too heavy), there are a wide variety of sound cruising designs.

No one has come up with a set of measurable criteria that makes the Pogo look like a bad cruiser to me.

Much is made over loading. Consider the Pogo 40 has D/L 81.33 at 11,660# (5300 kg) displacement. Add 500 pounds of stuff I can't live without, assume I'll need 50 pounds a day for me and my crew. 30 days is 3000 pounds, the total load is 3500 pounds for 30 days at sea. That only brings the D/L up to just over 100. You need to load over 6000 pounds of junk to the boat to take in out of the "ultra-light" category. I have no reason to doubt Paulo's number for the Pogo, he puts the load limit at over 4500 pounds.

If your family cannot get by on 4500 pounds of stuff to cross an ocean, you life style is alien to me. I just cannot comprehend *needing* that much gear. 4500 pounds is a small car full of gear lashed to the deck. It's 10 55 gallon drums of water. No one can be serious in thinking that 2 people or a small family *need* that much "stuff".

I just don't get it, surely I don't.

What is an extreme cruiser anyway?

 

Originally Posted by Vega :

....in this kind of boats there is not a big difference in the STIX at MinSalCondition and in MaxSailCondition. For example, for the RM1200, that difference is from 38.33 and 38.7.

You are really incorrigible. After having miscalculated by a large margin the RM 1200 STIX (32,9 to 38.3) , now you say that the difference between the RM1200 STIX in MinSailingCondition and Maxsailing condition is not the one that the designer has calculated? The Min STIX of the RM1200 is 38.33 and the Max STIX is 38,70. These are the designer data, the data that was been certified and that’s it.

We have already seen that your STIX calculations have to be improved.

About the Pogo, what I have said is true. I have posted only the relevant part of the official document and the reason for doing that was that I wanted to avoid another scene like the one of the RM1200, with wild calculations of your part, more incorrect numbers and more apologizes.

The data I have posted specifies clearly that it is a MaxsailingCondition STIX and I never said otherwise. I have posted that one and not the MinSailingCondition STIX, because it was the only STIX data that had been sent to me.

This discussion is quite meaningless, because the stability curve is more important than the STIX and the one I used in the comparison is the one in Minsailcondition, as it should be, because the one from the Valiant is also in Minsailcondition. I have not compared the Pogo STIX with the Valiant STIX, so I really don’t see your point.

 

Good description of an extreme cruiser RHough.

What is the definition of an extreme racer?
A stripped out skimming dish.

An extreme racer is at one end of the scale, and an extreme cruiser is at the other end of the scale.

I abhor both extremes, and regard them as unseaworthy.
Most people can understand the problems of an extreme cruiser.
However groupies of extreme racers, are unable to acknowledge the trade offs that produced their beloved hull form.

Cruising the oceans requires more than the Pogo has to offer.
Cruising the coast would be fun, but that is the most it has to offer cruisers.

Racing does not produce the ultimate hull form for all boats.
Speed came at the expense of some other qualities.

What does the Pogo sacrifice to go flat out fast:?:

 

I am afraid I will have to disagree with those knowledgeable NA’s. I don’t mean to be disrespectful, but at the same time let me not extol another human being to such an elevation that I cease to call into question his reasoning.

First: of all the formula that calculates the areas above and below the curve do not include the mass moment of inertia in their calculation (radius of gyration of mass about an axis). If you think this is insignificant, take your car out on the road, and wait for a passing car to be even with you, and floor it! You will see that no matter how slow the other car is moving, you still have to expend large amounts of energy just to catch up. That is on a 1 or 2 ton car; how much energy do you think it takes to start a 6 to 50 ton vessel to roll. I certainly don’t know, and I guaranty if you ask a knowledgeable NA to look at a stability curve and give you the answer, he won’t be able to.

Second: there is no function that includes damping effect of rig and appendages; I would think this alone would cause an eyebrow to lift.

Third: There is no function in the formula that accounts for positive and negative displacement effect of a vessel in sinusoidal wave patterns. Consider your stability curve; do you think that it is a constant rule that can be followed when a boat is thrusts upwards until it crests at the top of a wave. At this moment, all the mass of the boat is accelerating upward at the very moment that the wave and its associated buoyancy, drops from under the boat. And conversely the boat then descends down the wave until it bottoms in the trough, again the mass of the dropping boat being decelerated, by the buoyant forces. How does the same curve apply to both situations?

Fourth: there is no way to determine the roll period of the boat or the effects of synchronous wave periods by simply looking at the stability curve.

I think the stability curve should be fairly accurate if you are in a protected marina with little or no wave action. The stability curve should be used as a design tool to highlight initial tendencies of a design early in the design process, and to compare form stability with ballast stability for the same vessel. It should be regarded as a starting point that leads into deeper analysis of dynamic forces that the vessel is expected to handle. It may be able to be used a probability indicator to capsize and re-righting, but if so, it certainly should not be used as a final analysis on stability.

It by no means even comes close to quantifying the amount of energy that it takes to roll a boat.
There are a great many professionals who either do not articulate there thoughts conclusively and accurately, or in some cases, they are simply wrong.

 

Yards of teak that need varnish?
24% lead crystal glasses?
Two ice-makers?
A wet bar?
A cozy cabin that my in-laws would find attractive?
Top Hamper?
A head in every cabin?
Two holding tanks?
Road hugging weight? ... oh wait ... that's Buick ...
A chain locker and windless?
Six anchors?

In short, I can't think of anything the Pogo lacks that would exceed the design limits of the boat if installed. 4500 pounds is a LOT of stuff.

In keeping with my title of "Retro Dude" I would like to join the naysayers but the darn boat is just too good. Every objective measure I know of gives the Pogo high marks. Subjectively, I think it is a darn fine looking boat. The style of form following fuction looks odd to me at the Mini and 8.5 size. The Open Rule boats I agree are too extreme. 40 feet and 10,000-15,000 pounds is what I consider a perfect size. Until I heard of the Pogo, I was considering two boats; a Cal 40 or a Catalina 42. The Cal is a known good boat, I like the way they sail, but they are getting to be 40 years old and have not much more interior room than my C30. The Catalina 42 has a good Nelson-Mareck (sp?) hull, an interior layout that I really like, and a good track record. At 15,500 the Cal is close to my upper displacement limit but the boat has only a 30 foot waterline. The C42 at 18,000 pounds is getting a bit big although I like the boat very much. I considered a Dix 38, a Shearwater 45, and a Shannon 43. Wench has decided that she really doesn't want to go ocean cruising, coastal daysails and a week here and there gunkholing are what she's into. That frees up the choice of boat considerably. I no longer have to worry about a boat that she likes.

I think high performance cruisers are a new type. I think that traditionalists want to be able to show how unsafe they are but cannot. I am very seriously considering ordering a Pogo. I plan to visit the shipyard in July to see what I think of the build quality. After that, we shall see.

What do you think the Pogo gives up? Can you back up your statement that "Cruising the oceans requires more than the Pogo has to offer." Just what do you base your opinion on?

 

If you want to buy a Pogo you are going to have a good long wait I'm afraid. Last I heard all the build slots were filled until 2009? The Jumbo and others are enjoying the same popularity. Good luck finding one.

 

Yup, there are a couple of used boats on the market and as of last week I could have a boat September 2008. By July they may well be booking 2009 and beyond. I guess the buyers don't read this thread and don't know how unsuited they are for the ocean?

I already have two volunteer crew for the delivery sail from France ... LOL! One of them is waiting for his Tam Tam Mini in May. There is talk of a Vic-Maui in the boat's future.

Oh ... can I even mention a Mini in a seaworthiness thread?