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  #121  
Old 01-17-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by johnnyquest37;977111...
You are saying the ultimate stability describes stiffness. ... Regardless, it is clear that ultimate stability is the criterion that sail area is based upon. As I understand it, the area under the postive part of the curve defines this.
Hi Johnny,

No, what is called ultimate stability is the one that is not used for sailing but for boat safety. The area under the positive RM stability curve defines the energy needed to capsize the boat.

Stiffness in what regards a stability curve (a GZ one) regards only the part that is used to sail, till the first 30║ of heel. This guy explains it well:

" "stiffness", - the ability of the sailboat to resist the heeling force of the sails. The stiffness, as it will be called in the following, is afforded by the righting moment. Enhancing the stiffness brings significant extra power to the sails and, furthermore, increases the equilibrium and the safety of boats in general. Good stiffness enables a ship to have all sails set wind abeam, whilst maintaining the boat at angles of about a normal heeling (the first 30 degrees of heeling). The greater the stiffness (or righting ability) of the boat, the more powerful the sails can be and the faster the boat can be."

EP 2197734 A1


If you read the French article on wikipedia you will see they are talking about the GZ and not the RM. That is just because if you have an heavier boat with a bigger RM, and a lighter one with a smaller RM (both boats with the same lenght) the less heavy one can be more stiff because it needs to carry less sail. The Stiffness is related with that relation between wet surface and available RM. The GZ curve is a good indication of that while the RM curve will not take in consideration that difference in weight (and wet surface) between the two boats.

Of course you can call stiffness to what you want. I am referring only to a technical use of the term in what refers sailing boats and naval architecture.

By your definition a racing America's cup monohull would have to be considered a tender boat and that will not make any sense in what regards NA.

Stiffness is directly related with power to carry sails in a sailboat, in proportion with its wet surface. It is directly related with boat speed. That's why I am saying from the beginning that it makes no sense to compare the stiffness of a First 40 with the one of the Catalina. Their difference will be almost as big as their difference of PHRF.

What you call stiffness is just initial stability (that will be bigger on the Catalina 40) and should not be confused with stiffness.

Regards

Paulo

Last edited by PCP; 01-17-2013 at 02:00 PM.
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  #122  
Old 01-17-2013
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Re: Blue Jacket 40 (new racer/cruiser)

I have been dipping into this thread from time to time, and have noted this debate about the terms 'Stiff' and tender. I think that the problem in this case is one of lingusitics. Term 'stiff' has a very specific meaning as used in North American English speaking naval architectural jargon. I understand that this term of use does not translate literally into the terms used on other language naval architectural jargon, which may in part be complicating the discussion here. Compounding the issue further is historic useage and colloquial usage. In this case, the disagreement seems to be about a difference in definitions.

I hope this is helpful, but as used within the world of ship and yacht design, stiffness is very narrowly defined as initial stability (i.e. form stability). A boat which is stiff has a lot of form stability. The opposite to stiff is tender, and again, this is solely about the lack of form stability.

But as a boat heels, ultimate stability (also sometimes called secondary stability, gravitational stability, or weight distribution stability) becomes increasingly effective taking over as form stability eventually begins to decrease.

The combination of the form stability and ultimate stability are what describes the overall stability behavior of the vessel and stability is evaluated absent of heeling forces.

As does seemed to be agreed upon here, the statically calculated force required to overturn a vessel at any angle of heel is the righting moment, and this can be plotted over all heeling angles to get the righting moment curve which is a pretty good indicator of a boat's resistance to heel, but not a complete indicator of whether the boat is likely to heel or be rolled since it does not account for overturning forces.

Ultimate stability often gets confused with angle of vanishing stability (AVS) or the term I prefer LPS (limit of positive stability) which is the heel angle at which a boat would rather turn turtle than right itself. This is a tough one to generalize on because it is often said that a boat with a lot of form stability will also have a small angle vanishing stability, or a boat with a wide beam would have a small LPS. That is not necessarily true. There is a whole lot more to it than that.

AVS is also sometimes confused with the angle of maximum stability, AKA the limit of increasing stability. There is a point at which any boat hits its maximum stability. After that point the amount of stability starts to decrease, but the boat still has positive stability and wants to right itself until it reaches its LPS and no longer does want to stand right side up. On some boats the decrease is very rapid and so the boat can seem very stable one moment and seemingly have no stability the next.

LPS is very hard to calculate since you need to model the entire volume of the hull, deck and rig and all weights and their positions. There are simplied calculations for the hull only, but in reality, the cabin trunk and cockpit is usually in the water before a boat reaches its LPS, these contribute or detract from stability by moving the center of buoyancy further from or nearer to the center of gravity at large heel angles, thereby increasing or decreasing the angle of vanishing stability. The higher the freeboard, and bigger the volume of the cabin, coamings and the like, and the smaller the cockpit, the larger the LPS.

Of course increasing the height of the cabin and freeboard decreases stability in the normal sailing angle range, but that is another story for another day.

When Brian (Cruisingdad) talks about using a single term for the tendency for a boat to heel, Brian is referring way more than simple stability. The tendency for a boat toward large heel angles is created by a whole range of factors;

• The side force of the sails as a product of overall sail area, rig proportion (high vs. low aspect mainly) and sail shape (full vs. flat)
• Drag- since the ability of a boat to accelerate allows some of the force of the wind to be disbursed as greater speed.
• Stability- since the simple ability of the boat to withstand rotating under any given side force is obviously very important.
• Lateral resistance, since the side forces can be in part disbursed through sliding sidewards and creating leeway.

Now then, it is not uncommon to hear someone in common 'layperson' type usage refer to a boat as stiff or tender by which they mean the boat heels easily or not. And that colloquial useage is what often confuses these conversations.

As to the America's Cup mono-hulls, these boats have a huge amount of stability, really huge, but they are also tender under the classic yacht design definition of tender, which I know sounds like a contridiction in terms.

Jeff
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Last edited by Jeff_H; 01-18-2013 at 12:07 PM.
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  #123  
Old 01-18-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by PCP View Post
Yes, that First 40.7 is their boat of choice and yes it is a fast boat and yes they travel light and yes, they are circumnavigating.

You insist in not understanding that other sailors can have an idea different of yours in what regards a cruising boat. Yes there are many sailors to whom sailing pleasure is a very important part of cruising.

What I think or not is irrelevant to the way other sailors like to cruise and the sailboat they chose according with that. Believe me like you I know very well the boat I want and you can be sure that is not the boat you would want and vice-verse. There is not a perfect cruising boat but many different types of cruising boats for cruisers with different tastes, even for circumnavigating.

You prefer to sail a relatively slow boat (by modern standards) full of stuff inside. Ok, that's your type of pleasure, your type of cruising but I am amazed at your incapacity to understand that some would prefer a slower and heavier boat (some would even prefer an heavy old design) but others will prefer a faster and more enjoyable boat to sail.

On the interesting sailboat we have been following the circumnavigation of Capado, a small and very light cruiser boat. The crew is a young couple, they are top sailors, much better than you or I and I am quite sure that was the boat they wanted. They have the hull made and finish the rest but for the money they spend on a new boat they would have enough money to buy a used 40ft Catalina.

I am quite sure if I would suggest such a boat to them they would laugh at me, the same way you would laugh if I had suggested such boat to you for doing a circumnavigation.

Here some pictures of their boat:





Regards

Paulo

Paulo, my friend, with all due respect, I wonder if we are having a translational issue here. To be perfectly clear, I understand (completely) that what I consider to be a good ccruising boat and wht others like may be very different. On that, we most certainly boat agree. What we do not seem to be communicating well on is that a J122, or First, or similar boat will have what I consider considerable issues for long distance cruising.

I will go back to reality. Here is reality:

In order for a person to live, they must breathe, eat, drink, and crap. Period. You don't do one of those for a long enough period of time and you will die. I don't care if you are in a Tayana, a First, a TP52, a Catalina, etc. Anything outside of that is luxury.

A person will create, with MINIMAL flushing, 1-3 gallons of waste a day. I know because I am measuring all of these for our book on living aboard. Now there are ways to decrease this (pee off the side, bucket, go to town, etc), but there are also a lot of ways to increase this (sea sick, bad food, too much beer, etc). Let's just say the typical, cautious cruiser will go through 2 gallons on average a day/person. The holding tanks of many of these boats are what... 18g or 22? I cannot remember. They may be less that that, but that seems about right. So two people on that boat have maybe 5 days (if they are lucky) before they have a full tank. Where does that go? Now if you are offshore, you can dump. But in the US, it is 7 miles off in the gulf, no discharge in the keys at all, and no discharge in many other areas (and none anywhere withing 3 miles). That is a real restriction with these boats. Can you increase tankage? Yes. But as we have both bween on these boats, where are you going to put it and at what cost in space? It is alreaedy at a premium.

Where do you put the gas cans on this boat?

Where do you put the tender or do you swim to shore? Without a tender, how do you do laundry in port, refill your water, get groceries, spare parts, etc? In many areas, you have to go via tender to do this.

WHat is the draft on these boats? Any boat with a draft over 6' on the west coast of FL will have to be very careful. at 7', you will likely have entire coves and entrances you cannot get into. I bumped on the ICW (in the channel) at 6. Anything over 7 is rediculous for this area at least, much of the keys, and many other areas I have sailed.

The J122 for example has a 45g water tank and a 35g fuel tank. I think you can increase the water, but where and at what cost in space?

Quote:
Originally Posted by PCP View Post
You prefer to sail a relatively slow boat (by modern standards) full of stuff inside.
You have no idea what I have on my boat, but let me tell you. Now I will leave off the toys and children's related stuff. That is unfair to the discussion. But here is a list of some of the "full of stuff" I carry:

Tools and spare parts:

I carry a full complement of tools, including a wide variety of electrical, screw drivers, jig saw, drill, bolt cuttters, plumbing, etc. I have a complete list (yes, complete) I wrote for my book. It is very long. Everything (everything) in that tool kit has been used at one time or another. When you have done this for as long as I have (cruising since circa 2000), you learn things you should have and the ones you can make do without and leave along the way.

I also carry a wide variety of filters, extra belts, strainers, hoses, lots of extra clamps, spare pumps, etc. I can list thouse out too. It is not nearly as long as my other list, but hopefully extensive enough.

I assume you agree that cruising without a full complement of tools and spare parts is foolish? You must be self sufficient. In fact, the reason I am just now writing to you is that my bilge pump swith failed yesterday (and I blew a valve on my propane tank) - both of which are immediate fixes. It just happens. That's why you carry spares or have a variety of other things for emergency break-fix.

All these items take space. On my boat, stuffed and tightly fitting, they take up a 5x2x3 space. In reality, they take larger than that as some things (like a wet vac) are too large to fit in my tool compartment. All these things must go below the waterline, but not in the bilge. Where are you going to put them on that boat? Well, under the settee, of course. You just lost that space for other things.

My other settee is filled with a pressure cooker, rice, vacuseal machine, lots of galley stuff (flour, sugar, etc). It is also where I put my large and heavy cast iron skillet - to keep weight low.

In the bilge I keep my canned goods (lots of veges, soups, tuna, etc) which are heavy. THis also takes up the rest of my low dry storage. WIth that, my boat is filled below the waterline. We keep enough reserves for a comfortable month. We do not drink colas, incidentally, but I do enjoy beer which is having to be tapered because of space.

THe galley is filled with pots and pans, toaster, plates, glassware, and my dry storage is completely filled with dry goods (pasta, beans, some breads, etc).

THe salon and nav station is filled with charts and all navigational items. The salon is filled with paper items (paper towels, some paper plates, kleenex, etc). I do carry DVD's and a PS3 for the kids that takes up a cabinet, but outside of that, everything we have is what we need for basic living.

In each stateroom, all we have are clothes and many paper items (USCG docs, technical parts information, Yanmar manual, personal checking items), a small printer/scanner, a very small radio, several marine related books that are critical to me for reference, my guitar and a keyboard. THat's it.

I have a complete list of every item on this boat for the book. I wrote all of these out because I felt it was important for others to know what we carry, what works, and what doesn't. THe concept of going lean and mean just isn't reality because most people will look at my list and say, "well, I never thought about that and I will have to make a spot for it." This is information I have gathered over doing this since 1995, and cruising on/off since 2000 (really 1999). I would LOVE to know which of these things you feel is "all this stuff" that you are going to do without?

All these items take up space. Where are you going to put them on these boats? I will tell you: YOu will fill up every crevice, you will toss them into the quarter berths, and you will stuff that boat from bow to stern. Have you ever been on a F/T cruisers, liveaboard boat? Not a weekender or a vacationer - a fulltime cruisers boat? They are typically spilling over with all this junk. Believe me, as live aboards, we dump everything we can that is not essential (within reason)!!!! WHat you consider a performance cruiser (and I consider a weekend racer) simple is very short on cabinetry and places to stuff these things. That is for a good thing for a racing boat (your performance cruiser): it takes up weight and costs momey where most people would not use it. You fill a BF40 with the same cabinetry as a Tayana, for example, I bet you just lost a LOT of its compeitivness. But quite candidly, that is a silly discussion because that much cabinetry would never even fit on a BF40.

Now, once again, am I saying you cannot make a j122 or BF40 work as a cruiser? Absolutely not. You most certainly can MAKE it work. But unless cruising is marina hopping and short jaunts, to populated areas, these are the realities you have to deal with. You CAN make a J122 work... but it comes at a cost. And when you have loaded that boat "with all that stuff", you may find the great sailing charachteristics you bought that boat for are quickly lost. You may find your first storm offshore that those things that are not in cabinets are flying around like bullets (or you are slipping on them). How stiff is that boat now? WHat is its NEW RM? Because everyone of those items you stick above the waterline decreases it AVS, if not countered with an equally heavy item below.

You CAN make those boats work. Your friends in Antarctica are a prime example. There was a family I think that sailed on their First 40 around the world, IIRC. You CAN make it work. But, for the reasons I explained, I believe there are better boats for that use.


My opinions.

Brian
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  #124  
Old 01-18-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by Cruisingdad View Post
Paulo, my friend, with all due respect, I wonder if we are having a translational issue here. To be perfectly clear, I understand (completely) that what I consider to be a good ccruising boat and wht others like may be very different. On that, we most certainly boat agree. What we do not seem to be communicating well on is that a J122, or First, or similar boat will have what I consider considerable issues for long distance cruising.

I will go back to reality. Here is reality:

In order for a person to live, they must breathe, eat, drink, and crap. Period. You don't do one of those for a long enough period of time and you will die. I don't care if you are in a Tayana, a First, a TP52, a Catalina, etc. Anything outside of that is luxury.

A person will create, with MINIMAL flushing, 1-3 gallons of waste a day. I know because I am measuring all of these for our book on living aboard. Now there are ways to decrease this (pee off the side, bucket, go to town, etc), but there are also a lot of ways to increase this (sea sick, bad food, too much beer, etc). Let's just say the typical, cautious cruiser will go through 2 gallons on average a day/person. The holding tanks of many of these boats are what... 18g or 22? I cannot remember. They may be less that that, but that seems about right. So two people on that boat have maybe 5 days (if they are lucky) before they have a full tank. Where does that go? Now if you are offshore, you can dump. But in the US, it is 7 miles off in the gulf, no discharge in the keys at all, and no discharge in many other areas (and none anywhere withing 3 miles). That is a real restriction with these boats. Can you increase tankage? Yes. But as we have both bween on these boats, where are you going to put it and at what cost in space? It is alreaedy at a premium.

Where do you put the gas cans on this boat?

Where do you put the tender or do you swim to shore? Without a tender, how do you do laundry in port, refill your water, get groceries, spare parts, etc? In many areas, you have to go via tender to do this.

WHat is the draft on these boats? Any boat with a draft over 6' on the west coast of FL will have to be very careful. at 7', you will likely have entire coves and entrances you cannot get into. I bumped on the ICW (in the channel) at 6. Anything over 7 is rediculous for this area at least, much of the keys, and many other areas I have sailed.

The J122 for example has a 45g water tank and a 35g fuel tank. I think you can increase the water, but where and at what cost in space?



You have no idea what I have on my boat, but let me tell you. Now I will leave off the toys and children's related stuff. That is unfair to the discussion. But here is a list of some of the "full of stuff" I carry:

Tools and spare parts:

I carry a full complement of tools, including a wide variety of electrical, screw drivers, jig saw, drill, bolt cuttters, plumbing, etc. I have a complete list (yes, complete) I wrote for my book. It is very long. Everything (everything) in that tool kit has been used at one time or another. When you have done this for as long as I have (cruising since circa 2000), you learn things you should have and the ones you can make do without and leave along the way.

I also carry a wide variety of filters, extra belts, strainers, hoses, lots of extra clamps, spare pumps, etc. I can list thouse out too. It is not nearly as long as my other list, but hopefully extensive enough.

I assume you agree that cruising without a full complement of tools and spare parts is foolish? You must be self sufficient. In fact, the reason I am just now writing to you is that my bilge pump swith failed yesterday (and I blew a valve on my propane tank) - both of which are immediate fixes. It just happens. That's why you carry spares or have a variety of other things for emergency break-fix.

All these items take space. On my boat, stuffed and tightly fitting, they take up a 5x2x3 space. In reality, they take larger than that as some things (like a wet vac) are too large to fit in my tool compartment. All these things must go below the waterline, but not in the bilge. Where are you going to put them on that boat? Well, under the settee, of course. You just lost that space for other things.

My other settee is filled with a pressure cooker, rice, vacuseal machine, lots of galley stuff (flour, sugar, etc). It is also where I put my large and heavy cast iron skillet - to keep weight low.

In the bilge I keep my canned goods (lots of veges, soups, tuna, etc) which are heavy. THis also takes up the rest of my low dry storage. WIth that, my boat is filled below the waterline. We keep enough reserves for a comfortable month. We do not drink colas, incidentally, but I do enjoy beer which is having to be tapered because of space.

THe galley is filled with pots and pans, toaster, plates, glassware, and my dry storage is completely filled with dry goods (pasta, beans, some breads, etc).

THe salon and nav station is filled with charts and all navigational items. The salon is filled with paper items (paper towels, some paper plates, kleenex, etc). I do carry DVD's and a PS3 for the kids that takes up a cabinet, but outside of that, everything we have is what we need for basic living.

In each stateroom, all we have are clothes and many paper items (USCG docs, technical parts information, Yanmar manual, personal checking items), a small printer/scanner, a very small radio, several marine related books that are critical to me for reference, my guitar and a keyboard. THat's it.

I have a complete list of every item on this boat for the book. I wrote all of these out because I felt it was important for others to know what we carry, what works, and what doesn't. THe concept of going lean and mean just isn't reality because most people will look at my list and say, "well, I never thought about that and I will have to make a spot for it." This is information I have gathered over doing this since 1995, and cruising on/off since 2000 (really 1999). I would LOVE to know which of these things you feel is "all this stuff" that you are going to do without?

All these items take up space. Where are you going to put them on these boats? I will tell you: YOu will fill up every crevice, you will toss them into the quarter berths, and you will stuff that boat from bow to stern. Have you ever been on a F/T cruisers, liveaboard boat? Not a weekender or a vacationer - a fulltime cruisers boat? They are typically spilling over with all this junk. Believe me, as live aboards, we dump everything we can that is not essential (within reason)!!!! WHat you consider a performance cruiser (and I consider a weekend racer) simple is very short on cabinetry and places to stuff these things. That is for a good thing for a racing boat (your performance cruiser): it takes up weight and costs momey where most people would not use it. You fill a BF40 with the same cabinetry as a Tayana, for example, I bet you just lost a LOT of its compeitivness. But quite candidly, that is a silly discussion because that much cabinetry would never even fit on a BF40.

Now, once again, am I saying you cannot make a j122 or BF40 work as a cruiser? Absolutely not. You most certainly can MAKE it work. But unless cruising is marina hopping and short jaunts, to populated areas, these are the realities you have to deal with. You CAN make a J122 work... but it comes at a cost. And when you have loaded that boat "with all that stuff", you may find the great sailing charachteristics you bought that boat for are quickly lost. You may find your first storm offshore that those things that are not in cabinets are flying around like bullets (or you are slipping on them). How stiff is that boat now? WHat is its NEW RM? Because everyone of those items you stick above the waterline decreases it AVS, if not countered with an equally heavy item below.

You CAN make those boats work. Your friends in Antarctica are a prime example. There was a family I think that sailed on their First 40 around the world, IIRC. You CAN make it work. But, for the reasons I explained, I believe there are better boats for that use.


My opinions.

Brian
Without getting in the crossfire here, because I think I have a foot in both your worlds, I am wondering about your list.

I would love to see it compared to a similar list of lets say Cinderella ( Wingnwing/Dan) who also went crusing as a couple for 6 months and do it every year. They have far less volume in tankage in thier CSY 33, but have incrediable storage space. They go in relative comfort knowing them and are not minimalists.

I wonder what their requirements are in terms of fuel. water waste etc.

The argument about which boat you want for a cruising boat will be a forever one and a lot has to do with personal tastes as well as how you sail your boat also.

Some cruisers I know will never go underway when the wind pipes up to 25+...their philosophy is we can just sit and wait till the weather improves, we are retired and dont want to stress our boat. Whats the rush

Others of our friends will look at 25+ and say wee hhee...and go somewhere at breakneack speed enjoying the elements safely and get to their destination quickly, anchor and enjoy where they are in a new place.

We are of the second variety. Safety rules of course, but I dont want to buy a boat that will get stressed repeating days of winds 20+ over time. This I see as my biggest factor,

So where do you go to figure that out. Where do you figure the longevity of a boat out, afterall I want my last boat to last another 25 years without falling apart/ cracking etc. till i am 82 anyway. And at that point I dont want it to be worth nothing becaused I have used it up.

Where I go to look for this is not a scientific as speed, RM, etc. I look online at the boats that have already stood the test of time. The boats that right now were built 25 yeras ago and stiil have some worth left to them or are not beat to crap because of usage. To me this is the best indicator of the build quality of a manufacturer and thier philosphy in building a boat. All boats look great and shiney in the first 10 years, but I am not trading it away in 10 years. To me this is the biggest comparison in buying my last boat and has been all along. You wonder why people bought Tartans, Sabres, C&Cs, Calbers, Irwins in the 80s over the production boats and why they cost more and do you want to pay more for them, look how many are still aorund sailing percentage wise to the number produced and look at their sale value 25 years later to the production boats. Theres you answer. You can laugh, but of the 90 C&C MKIII produced. Well over 70 are still sailed obviously. ( I did a seach on the onwer forum for owners.) My boat is 3
years old this year. I know 2 other on this forum of SN who have the exact same model ( Hillnme and JSAronson). 80% of this model with very little research are still active. Wonder what the % of Hunters/ Bene/ Catalinas are? This is an important point to me in terms of build quality....longevity

Lets undertand that I am in no way denigrating or putting down the production boats at all. People sail them and have a great time on them and can do many of the same things we can do and even more. But will they be aorund in 25 years and in what condition. This uis a factor in buying. Many are willing and want to replace their boats before 25 more years. Maybe on of the reasons I like the teak, interiors is that in 25 years I think they will still look similar where the laminate will not. The white will fade and scratch and the teak will just need some polish.

When I see people question why would you spend almost twice as much for the same size Tartan, Sabre than corresponding Hunter. Catalina, Beneteau, thats the reason. The Tartan Sabre owers may be keeping those boats longer, and when the resell, would get less of a % devaluation than the others.

Do you want the space and obviously better cost point today, knowing you wont keep it 15 years when it wont be worth as much, or do you go a little more expensive, older, less bling and get something which will hold its value a little better. The figures on YW dont lie...compare them.

The reason a Sabre costs more than a Catalina, Hynter, Benetau is not some contrived figure. Same with a larger cruiser like a Moody, HR, Caliber, Taswell, etc.

Does one sail better and faster than the other. To a small degree probably, but which one will be sailing the same way in 30 years?

Dave
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Old 01-21-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Got my February?!?!? issue of Sailing in the mail the other day, The maestro did review of the bluejacket 40. Not sure if it is on the sailing website as of yet. He did a good ob os reviewing it as normal. Altho personally, not sure he was enamored with it. A Hunter 40 on the page before seemed to get better remarks on how well it might do etc.

I'm still trying to figure out how he considers the BJ40 narrow, where as the Hunter was wide being 2" narrower! Granted the Hunter was literally 2' less in length....not sure 12'2" vs 12'4" is a big deal on a 40'ish foot boat!

Worth a gamble read for those that get the rag, and look up BP's reviews on the site when it is put on there.

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Old 01-23-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by Jeff_H View Post
.. I think that the problem in this case is one of lingusitics. Term 'stiff' has a very specific meaning as used in North American English speaking naval architectural jargon. I understand that this term of use does not translate literally into the terms used on other language naval architectural jargon, which may in part be complicating the discussion here. Compounding the issue further is historic useage and colloquial usage. In this case, the disagreement seems to be about a difference in definitions.
Hi Jeff. I agree on that. Things are what we call them and it seems that on colloquial terms the term Stiff in the US is used concerning a boat that sails with little heel (like a beamy boat compared with a narrow boat). But what matters to us is the proper use of the term in technical language. In fact in Europe there is no divergence in the colloquial use of the term and the technical meaning.

Quote:
Originally Posted by Jeff_H View Post
I hope this is helpful, but as used within the world of ship and yacht design, stiffness is very narrowly defined as initial stability (i.e. form stability). A boat which is stiff has a lot of form stability. The opposite to stiff is tender, and again, this is solely about the lack of form stability.

But as a boat heels, ultimate stability (also sometimes called secondary stability, gravitational stability, or weight distribution stability) becomes increasingly effective taking over as form stability eventually begins to decrease.

The combination of the form stability and ultimate stability are what describes the overall stability behavior of the vessel and stability is evaluated absent of heeling forces.
….
Ultimate stability often gets confused with angle of vanishing stability (AVS) or the term I prefer LPS (limit of positive stability) which is the heel angle at which a boat would rather turn turtle than right itself. ..
I guess you are talking about ships were initial stability has probably another meaning. I am talking only about sailing boats that probably have a different definition of initial stability since the boats use heeling as a mean to increase the GZ (arm) and to make the ballast effective. Not any heeling but one that is smaller than 30║.

That part of the stability curve, the one that is used for sailing is the one that is called initial stability on a sailing boat.

That initial stability can come from two ways: From form stability (that is more important at lower angles of heel and where beam is a major factor) and from stability that is generated by the ballast/Draft (with heeling) providing a lower CG to the boat.

The initial stability on a sailing boat is determined basically by the addition of those two factors. Boats that are narrower have to rely more on ballast (and have or a bigger B/D ratio, or a more efficient keel or more draft and many times the three factors together), beamier boats can rely more on form stability and have the above factors more reduced.

Anyway on beamy or narrow monohul sailboats initial stability is always the addiction of the RM provided by the two factors.

Beamier boats tend to sail with less heel, narrower boats tend to sail with more heel (they need to have more heel to put the ballast working) but that does not mean that a narrow boat, even a very narrow one like the last monohul from the America’s cup is less stiff than a beamier boat, in fact those America’s cup monohuls are massively stiff.

Stiffness in a sailboat has not to do with the heel the boat is designed to sail to (that in some beamy boats can be really small and in some narrow sailing boats can go to 30║) but with the resistance the boat provides to heeling, in proportion with its wet surface and not only on the first degrees but on all heeling that is used for sailing (30║)

The better definition that I know is from Finot that says simply (quoting freely):

Between two sailboats with the same wet surface the stiffest boat is the one that can carry more sail.

As all the good definitions it is very simple and accurate. The RM to carry the sail can come from two sides: Hull form and ballast. On a multihull it comes only from hull form on a sailboat will come always from two sides: Hull form and Ballast, in different proportions on beamy boats and narrower boats.

Only one more word about stiffness in a sailboat:

We can consider Stiffness in absolute terms, meaning the sail area that the boat can carry regarding its wet surface and in relative terms, meaning the sail area the boat effectively carries regarding its RM.

I was obviously talking about the first one. A sailboat can be relatively tender in absolute terms and be relatively stiff regarding the proportion of sail it carries regarding its RM. For that it is only needed that the sail area that he carries is a small one regarding the wet surface. That of course means also that the boat is slow.

Stiffness in absolute terms means power in a sailboat and that’s why I said that the PHRF from the Catalina (WK 120) and the First (36) is a good indication of the huge difference in stiffness between the two boats.

Regarding stiffness meaning different things in what regards sailing Naval Architecture in Europe and US I don’t think so and I can find the same meaning on the use of Stiffness as defined by reference sailing US Naval Architects.

Referring ultimate stability also called reserve stability it is simply the one that it is not used for sailing but needed for safety purposes (over 30║).

As I have said previously it is the one that will bring the boat back from a knock down and it is as important as the initial stability (for safety) even if does not reflect itself directly on the boat performance.

The same thing I have being saying referring initial stability and ultimate stability on the words of some reference American sailing Naval Architects:

David Gerr:
Director of the Westlawn Institute of Marine Technology Board of Directors

Initial stability or sail-carryng power, the stability that directly affects performance.

The initial stability can be thought of as sail-carrying power and thus performance. The greater the initial stability the more sail a boat can fly upwind in heavier air with a taller rig and the faster the boat can go. This is so important that initial stability is sometimes just termed “power…Initial stability is also termed “stiffness”.

There’s a great deal of misinformation about initial stability. In fact initial stability is generated by the boat’s water plane area, combined with how far above or below the waterplane the boat’s center of gravity is.

Reserve or ultimate stability is every bit of essential, but for safety.


Journal of the Westlawn Institute of Marine Technology, 2007.


Rodney S. Johnstone, the long time designer of Jboats:

Where does performance come from? ...

A cruising sailboat’s performance also depends on stability, or "stiffness"-the ability of the boat to resist the heeling force of the sails. Good all-around speed is possible only if the boat is stiff; a stiff boat can carry more sail... If stiffness comes from a wide waterline beam, the boat’s motion tends to be bouncy and abrupt in waves; as soon as this type of boat heels, it usually exhibits excessive weather helm and may be difficult to steer. ..
The most important characteristic of a performance cruiser is that its stiffness be derived from a low center of gravity. ...

The preponderance of heavy-displacement boats ... reflects a modern trend in cruising sailboats toward increased accommodations and decreased ballast/displacement ratios-a trend that has raised the height of the center of gravity of this type of boat. ...

.. Whether light or heavy, a narrow boat with a low center of gravity will have a rock solid feel, an easy motion, and positive control-the unmistakable aura of power, stability, and passagemaking speed.



Michael Kasten from Kasten Marine

Initial stability, or the power to carry sail

.. more ballast lowers the center of gravity, and … it is obvious that for sail carrying, more ballast is beneficial.….A light weight vessel having a large concentration of ballast will have greater stiffness (initial stability)

In a completely separate category is a vessel's ultimate stability. .. Ultimate stability, i.e. the ability to resist or to recover from a large angle roll, ordinarily is enhanced by the addition of ballast.


http://www.kastenyachtdesign.com/
http://www.kastenmarine.com/

Quote:
Originally Posted by Jeff_H View Post
As to the America's Cup mono-hulls, these boats have a huge amount of stability, really huge, but they are also tender under the classic yacht design definition of tender, which I know sounds like a contridiction in terms.
Jeff
Of course the America’s cup monohuls would only be tender if we applied the definition of stiffness that probably is used on ships (I know very little about it), if we use the one that is used technically in Naval Architecture regarding sailboats, the boats will be massively stiff.

You have talked about contradiction of terms and you are right. Just imagine an Open 60 that has lost its keel. Nothing new, last Vendee edition Marc crossed the Atlantic sailing without one. Some days ago, on this edition, Jean-Pierre Dick had just lost his keel, has not abandoned the race and he is trying to sail the boat back to the finish line.

If we apply that Ship definition of initial stability, then his boat is as stiff as before and still hugely more stiff than an America cup monohul and that makes no sense at all.

In fact he is sailing now a very tender boat and a boat that will only be capable of carrying reefed sails, a fraction of what was able to carry before when to the actual hull form stability was added the stability provided by the canting keel and ballast, making it a very stiff boat.

Regards

Paulo

Last edited by PCP; 01-23-2013 at 12:13 PM.
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  #127  
Old 01-23-2013
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by PCP View Post
I guess you are talking about ships were initial stability has probably another meaning. I am talking only about sailing boats that probably have a different definition of initial stability since the boats use heeling as a mean to increase the GZ (arm) and to make the ballast effective. Not any heeling but one that is smaller than 30║.

[Regards

Paulo
We are somewhat in agreement but not fully. To have been more accurate in my earlier post, I probably should have said that the definition for 'stiff' is vertually the same in all texts whether you are talking about ships or yachts. And that definition of stiffness in any vessel applies to the range of angles at which form stability is the primary righting moment with secondary stability being less of the source of stability. That angle with vary from design to design. As a practical matter 30 degrees of heel would certainly fall within the range of initial stability on most boats.

Whether a boat is stiff or not is not defined by GZ alone since displacement is the other key component in determining the righting moment curve for any vessel, and stiffness as it is used in Naval Architecture applies to the relative stability of the vessel through the the range the form stability is the primary source of stability.

The quotes about importance of stiffness to a sailboat are mostly accurate in that the greater the stiffness of a vessel the greater the sail area a boat can carry, but there have been designs like the old English lead mine cutters which have very little initial stability, in other words are not very stiff, but which can carry a huge amount of sail because they do have a huge amount of ballasted stability.

The difference in the PHRF ratings between a Catalina 400 and the First 40 is the result of a wide range of factors, relative drag, rig and foil efficiency, and relative drag to stability certainly come to mind.

Respectfully,
Jeff
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  #128  
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Re: Blue Jacket 40 (new racer/cruiser)

Quote:
Originally Posted by Jeff_H View Post
...
Whether a boat is stiff or not is not defined by GZ alone since displacement is the other key component in determining the righting moment curve for any vessel, and stiffness as it is used in Naval Architecture applies to the relative stability of the vessel through the the range the form stability is the primary source of stability.

The quotes about importance of stiffness to a sailboat are mostly accurate in that the greater the stiffness of a vessel the greater the sail area a boat can carry, but there have been designs like the old English lead mine cutters which have very little initial stability, in other words are not very stiff, but which can carry a huge amount of sail because they do have a huge amount of ballasted stability.

...
Exchanging opinions in this way is not the best way to reach quickly an agreement. My dificulty in explaining complex things in English does not help either. I hope you read French. They explain it well and they are talking about the GZ curve.


Why?
Because if you have a very heavy boat you will have necessarily a big righting moment since the RM is the mass multiplied by the GZ but if you have a low GZ curve you will have a tender boat.

Why?
Because that heavy boat will have a big wet surface and on account of that it will be needed a big sail area to get a decent performance out of it. The RM will be big, but the needed sail area can be even bigger in proportion to the RM and if that is the case the boat will be tender.

The indication if the needed sailing area will be easily supported by the available RM (stiff boat) or not (tender boat) is given by the GZ values because the weight that you are multiplying by the GZ values to obtain the RM values, in a well designed boat relates, with the wet surface.

Take again a look at Finot definition of stiffness that is very accurate and simple:

Between two sailboats with the same wet surface the stiffest boat is the one that can carry more sail.

If both boats have different weights then they will have different wet surfaces and as the weight is proportional to the wet surface (on well designed boats) you can take the weight away and remain with the GZ values that will give you a pretty good idea of the stiffness of each boats meaning the proportion of sail area available for a given wet surface.

That is why David Gerr says that “power…... is also termed “stiffness” and is not the only one. Normally we refer to powerful boats as stiff.

The power in a sailboat is the relation between the wet surface and the sail carried by the boat and that is why you can make a relation between the boat power or stiffness and its speed.

That's why those PHRF values on the Catalina and the First are a pretty good indication between the difference in stiffness (or power) between the two boats.

Regards

Paulo
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Old 01-23-2013
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Re: Blue Jacket 40 (new racer/cruiser)

R' = 610-8.36*(SA/Disp^.333)+0.0000511*(SA^2)-55*(P/(J+E)) -30.8*(LWL^.5)-602*(DR^2/SA)


Guys, quit using the PFRF formula incorrectly. As you can see, the only variables are sail area, displacement, the P,J and E dimensions, waterline length and draft. You need Beam and Ballast if you want to calculate something like the stability index. If you want to do an interesting exercise, set up this formula in your computer, load it with the initial values for your own boat, then “tweak” them to see what you have to do to get a faster boat (hint: displacement). The one thing not mentioned is what the builders do to come up with their initial PHRF numbers. Builders of race boats (like Johnson) are pretty good at building boats at or close to their designed displacements – after all, they would go out of business pretty quickly if their boats couldn’t sail to their rating. Builders of cruising boats aren’t so careful as they know their business isn’t dependent upon winning races but rather, the perceived notion that they have a “fast” boat. They do this by understating the displacement by weighing a prototype boat without interiors, deck hardware or other furnishings. I know this as I’ve been personally involved in appealing a PHRF base rating based on an understated displacement number.
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Re: Blue Jacket 40 (new racer/cruiser)

It all has to do with your definition of stiffness. Define the terms "fine entry" or "salty." It is fairly easy to say this one is "finer" or "saltier" than that one, but it is not easy to define these terms on their own. Sometimes universally accepted objective definitions of some terms are not available.

It is clear to me that the definition Paulo is using to define stiffness (i.e. stiffness = stability), even though shared by many persons of note, is not the only acceptable definition. Paulo, however, is unable to accept that others can have different defintions for the term.

I read the link provided for "Raideur a la toile." This definition of stiffness is mathematically described as the ratio between heeling moment (or is it "capsizing" moment? - my French is not that good) and RM. Also, it states that by definition, the Raideur a la toile changes with the angle of heel (Par dÚfinition, la raideur Ó la toile Úvolue suivant la gţte.), which makes sense, since GZ (and therefore RM) changes as a function of heel angle. Heeling moment would also change, although capsize moment would be fixed at the point of vanishing stability.

So, if this definition of stiffness is used, what heel angles are we talking about? Low angles of heel? Angles above 30? Angles approaching 90? Capsize angles of around 130? In all cases, the ratio of the heel angle to RM changes for any given boat.

So, it is clear that stability is the factor that determines maximum sail area. The designer limits the sail area so that force in the sails alone will not capsize the boat. Greater ultimate stability results in that design being able to carry more sail. But does stability equal stiffness. Not by the definition that I chose to use.
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