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Old 12-10-2016, 11:43 AM   #21
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I do not see that such factual information is at least no disadvantage?
Perhaps not, but I still don't grasp what you would use more precise information for. Are you intending to go take a boat to it's very limits? Might even be a disadvantage if one made an assumption based on stability tests at the time of build and then were loaded much differently.

You know that an A likely can handle more than a B and would be more comfortable in rough seas. We have a classed boat with all the stability testing and charts, so we know it's built to a certain standard, but beyond that we don't use the exact information. We don't tilt to the maximum it will handle just because we can. We aim for the least we can achieve.

We're not going to try to cross an ocean in a CE-B but never seen one with the range anyway, and the boat likely would be able to take far more than the crew could. The weakest points in ocean travel of pleasure boats are not the stability. It's a lot of other construction factors that could doom one first. Windows, engine room vents, hull fittings, shafts, propulsion, fuel.

Back to your Nordic Tug. It has many areas problems would surface before stability would be an issue. You say you found it to be very good in rough weather. How rough? I would not consider it a boat for rough seas. It's CE category doesn't indicate it is. Now, is it fine for what it's owners will put it in? Yes. 6-8', even 10' it can handle fine but it would be miserable and I don't know anyone who would take it into 10' wind waves intentionally. It's a great boat. It's not a passage maker or ocean crossing boat. Tad pointed out the issues that would surface long before stability.

Very few ocean tragedies or sinkings have anything to do with stability. El Faro didn't go down because of instability. It went down because of lack of propulsion and taking on water. Now, Baden had a stability problem, but it never made it off the ramp.

You don't want to find out the stability limits of a Nordic Tug. Fact is, you won't ever find that out, because some other serious issue would surface before stability would. Stability and seaworthiness are not synonymous. It's just one factor.

Now the only available stability numbers would be from the factory. But they would only be accurate for the tested boat or designed boat under those conditions, not necessarily for your boat or any other actually on the water.
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Old 12-10-2016, 12:24 PM   #22
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Nordig Tug 37 stability

http://www.dma.dk/Policy/EUStrategyB...20Services.pdf

https://www.shipownersclub.com/media...ty-booklet.pdf

https://www.uscg.mil/hq/cgcvc/cvc3/r...ence_Guide.pdf

http://www.rina.org.uk/hres/1996-3%2...ity%20Data.pdf

Here is a bit of light reading to get you started on the subject. The last link is a 50 page simplified version for smaller boats from RINA

A stability book can be created for your specific vessel by any competent naval architect. Search the subject on this forum and look specifically for any posts by a member named Tad Roberts. He has posted some extremely well written easy to follow posts that can get the very basic information to calculate the entry level info most recreational boaters may desire.
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Old 12-10-2016, 01:15 PM   #23
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Here are a couple tidbits emailed to me....

A USCG publication....


NAVIGATION AND VESSEL INSPECTION CIRCULAR NO. 4-82

A lack of knowledge of stability problems and damage control procedures may be another
cause. Capsizings had the highest fatality rate of all accident categories, 45% of the
capsizings resulted in a death. A better understanding of vessel stability might have
prevented some of the accidents, especially if the vessel capsized because of improper
loading or topside icing.

Stability is a moving target...no pun intended...but ultimately the skipper has to decide how to alter the stability BEFORE the concept is really needed. Or decide not to enter conditions that may exist that would exceed the vessels abilities including but not limited to stability.


The Australian Naval Architect From the Division President

Editorial

In this issue I want to talk about recreational craft safety. A survey conducted for the National Marine Safety Committee (NMSC) a couple of years ago showed that roughly 90% of recreational-craft users wanted recreational craft built to some kind of standard. Roughly the same percentage also thought that they were in fact built to some kind of standard. This is interesting, particularly as there is no obligation on
the builders of recreational craft to meet any kind of standard. AS1799, Small Pleasure Boats Code, provides a standard for the design and construction of recreational craft up to 15 metres in length but it is not mandatory and it appears that any compliance with the Code in many cases is accidental rather than intentional. In my view, this is an unsatisfactory state of affairs. Commercial craft must meet strictly defined requirements
for their design and construction, particularly in the areas of stability, subdivision, damaged stability and hull construction. Similar-sized pleasure craft on the other hand are not obliged to meet any specific design requirements. This implies that the lives of recreational craft users and passengers are worth less than those of commercial craft passengers and crew. The ultimate demonstration of the inadequacies of the present state of affairs must surely be the case quoted to me of a builder who is marketing effectively the same vessel as both a commercial and recreational vessel. The major difference between the two is that the commercial craft is fitted with ballast while the recreational craft is not!

I won't even begin to touch on the losses of merchant ships due to stability problems. The Koreans have a great deal of recent experience with one of these "very few" events that took the lives of hundreds of people Sewol, Namyoung,Seahoe ... the list of stability related sinkings and deaths is nearly unbelievable. I disgusts me that someone like B would post such garbage to the people who need valid information most..
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Old 12-11-2016, 02:34 AM   #24
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Perhaps not, but I still don't grasp what you would use more precise information for. Are you intending to go take a boat to it's very limits? Might even be a disadvantage if one made an assumption based on stability tests at the time of build and then were loaded much differently.

You know that an A likely can handle more than a B and would be more comfortable in rough seas. We have a classed boat with all the stability testing and charts, so we know it's built to a certain standard, but beyond that we don't use the exact information. We don't tilt to the maximum it will handle just because we can. We aim for the least we can achieve.

We're not going to try to cross an ocean in a CE-B but never seen one with the range anyway, and the boat likely would be able to take far more than the crew could. The weakest points in ocean travel of pleasure boats are not the stability. It's a lot of other construction factors that could doom one first. Windows, engine room vents, hull fittings, shafts, propulsion, fuel.

Back to your Nordic Tug. It has many areas problems would surface before stability would be an issue. You say you found it to be very good in rough weather. How rough? I would not consider it a boat for rough seas. It's CE category doesn't indicate it is. Now, is it fine for what it's owners will put it in? Yes. 6-8', even 10' it can handle fine but it would be miserable and I don't know anyone who would take it into 10' wind waves intentionally. It's a great boat. It's not a passage maker or ocean crossing boat. Tad pointed out the issues that would surface long before stability.

Very few ocean tragedies or sinkings have anything to do with stability. El Faro didn't go down because of instability. It went down because of lack of propulsion and taking on water. Now, Baden had a stability problem, but it never made it off the ramp.

You don't want to find out the stability limits of a Nordic Tug. Fact is, you won't ever find that out, because some other serious issue would surface before stability would. Stability and seaworthiness are not synonymous. It's just one factor.

Now the only available stability numbers would be from the factory. But they would only be accurate for the tested boat or designed boat under those conditions, not necessarily for your boat or any other actually on the water.
I ask you to take a look at this link point with 4 pieces of the same weight and length of various shapes can be found in boat hulls A, B, C, D. below GZ-curves for these boats. Explore the behavior of various boats Curves, for me, this explains the behavior of the ship's lateral swell all how the vessel would behave and what they can expect before it's too late liiana, to sink or fall over.


Understanding monohull sailboat stability curves | M.B. Marsh Marine Design



an example of how quickly and unexpectedly severity will be lost
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Old 12-11-2016, 03:57 AM   #25
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Originally Posted by CPseudonym View Post
http://www.dma.dk/Policy/EUStrategyB...20Services.pdf

https://www.shipownersclub.com/media...ty-booklet.pdf

https://www.uscg.mil/hq/cgcvc/cvc3/r...ence_Guide.pdf

http://www.rina.org.uk/hres/1996-3%2...ity%20Data.pdf

Here is a bit of light reading to get you started on the subject. The last link is a 50 page simplified version for smaller boats from RINA

A stability book can be created for your specific vessel by any competent naval architect. Search the subject on this forum and look specifically for any posts by a member named Tad Roberts. He has posted some extremely well written easy to follow posts that can get the very basic information to calculate the entry level info most recreational boaters may desire.

Thank you or answers and links, A lot of lessons to be learned from each!
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Old 12-11-2016, 08:19 AM   #26
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You appear to know boats well, and do surveys but I am confused by this statement. I have 0 training in naval architecture, but I would think any extra weight added to an upper area of a boat like a dinghy and outboard will change the boats meta center, and have an adverse affect.

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Maybe .... sometimes weight added high will slow the roll but this is something to be discussed with an NA.
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Old 12-11-2016, 08:28 AM   #27
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You appear to know boats well, and do surveys but I am confused by this statement. I have 0 training in naval architecture, but I would think any extra weight added to an upper area of a boat like a dinghy and outboard will change the boats meta center, and have an adverse affect.
He said that weight up high will slow the roll. The slower roll may impact comfort in a positive way at the cost of a reduction in the angle of no return where a boat rolls over.
A great example of this is a sailboat. When a sailboat looses a rig (say in a storm?) people who are aboard speak of the awful motion that results. The weight of the rig up high slows the rocking/rolling motion way down.
Am I making this any clearer?
I tried...
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Old 12-11-2016, 09:18 AM   #28
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An over ballasted boat may roll so quickly from port to starboard and back again that it can throw crew around inside the vessel (i've been on such a boat). Weight added high can slow that roll period but like everything else it's a compromise .... to get something, you give something. You may gain some initial stability but give up some ultimate stability.
It's not something I would suggest without an NA involved.
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Old 12-11-2016, 09:26 AM   #29
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BB

F500 raises the meta center question -- no pun intended.

Don't you think the possible initial stability benefits of added weight up top to a furled and ballasted sail boat is a bit different than an NT? CPs nice attachments in Post 22 discusses the weight placement advisements of the Danish authorities and USCG for MVs. Of note are details for stability and dynamometer tests. Interesting stuff.

But, since the NT is a wonderful coastal cruiser, the dinghy up top with a big outboard should hardly be an issue for the prudent fair weather skipper. Having sailed out of Helsinki and heard from the skipper about putting weight from up top lower into the cabin to lower the CG during a big blow, those waters can turn very unfriendly to coastal cruisers.
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Old 12-11-2016, 10:02 AM   #30
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I haven't read every word here but an interesting comparison could be made ....

The AT and NT are very similar both being "tugs" but they differ greatly in their proportions. The length to beam ratios would suggest that the AT has considerably more stability .. at least from looking at them. I haven't looked at the numbers. It would be interesting to know if how they look is not how they are. Most everybody that looks at the NT or the AT brobably does a lot of comparing the two. Has anyone compared the stability numbers of thesen boats and ... how do they compare?
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Old 12-11-2016, 10:46 AM   #31
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I haven't read every word here but an interesting comparison could be made ....

The AT and NT are very similar both being "tugs" but they differ greatly in their proportions. The length to beam ratios would suggest that the AT has considerably more stability .. at least from looking at them. I haven't looked at the numbers. It would be interesting to know if how they look is not how they are. Most everybody that looks at the NT or the AT brobably does a lot of comparing the two. Has anyone compared the stability numbers of thesen boats and ... how do they compare?
I have my homework assignment.
I would like to make the record clear on this subject. We have traded our storm sails in on comfy storm pillows to be used in harbor when it is blowing!!!
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Old 12-11-2016, 01:38 PM   #32
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Obviously the AT and NT are simply hard chine semi-planing hulls intended for coastal cruising and bare no resemblance to full displacement tugboat hulls. Calling them a Tug is just a name the marketing department came up with.
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Old 12-11-2016, 02:10 PM   #33
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Obviously the AT and NT are simply hard chine semi-planing hulls intended for coastal cruising and bare no resemblance to full displacement tugboat hulls. Calling them a Tug is just a name the marketing department came up with.
Yup ! pretty much a Bayliner MY in disguise.
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Old 12-11-2016, 06:17 PM   #34
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Of coures ... the "tug" handle is just a pleasure boat style. Or style-type of recreational trawler.

And some indeed have planing hulls .. like the Rangers. I don't think the AT has any rocker and a straight run aft makes a planing hull IMO. Especially w no quarter beam angle. With that length to bean ratio, weight and keel planing will be unlikely but w enough power ......
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Old 12-11-2016, 09:40 PM   #35
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To say the AT is not a planing hull is just baffling. These are nearly 20kt boats.

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Of coures ... the "tug" handle is just a pleasure boat style. Or style-type of recreational trawler.

And some indeed have planing hulls .. like the Rangers. I don't think the AT has any rocker and a straight run aft makes a planing hull IMO. Especially w no quarter beam angle. With that length to bean ratio, weight and keel planing will be unlikely but w enough power ......
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Old 12-11-2016, 11:15 PM   #36
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"Makes a planing hull"

I agree.

This is a bigger difference than the L to B ratio. But most will cruise at the same speed (8 knots) so it's not that big a deal for most people. I like them both but the SD hull of the NT makes them much more desirable to me. I wish for two things that won't come to pass. A NT 32 w a smaller (80hp approx) and a stern a bit more like a FD hull.

Interestingly because of it's greater beam and height the AT may make a better 26' boat than the existing NT. That would make a really big 26' boat. Flash thought.
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Old 12-11-2016, 11:22 PM   #37
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"makes a planing hull"

Me too.
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Old 12-11-2016, 11:58 PM   #38
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At one time I queried whether the local NT club would accept my participation. The answer was "NO" because my boat can't exceed hull speed. NTs and ATs are definitely not recreational trawlers in the pure sense.

Well, they at least give me a toot!

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Old 12-12-2016, 12:43 AM   #39
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I strongly disagree with planing hull, 1. planing hull becomes very Stabil crossing the frame rate of about 3 knots, NT wobbles increasingly, if alto should be on the long side. 2. planing hull will only start to function properly 22 knots this size vessels, NT loses stability when driving 18 knots, I have this experience when surfing wave at about 20 knots, but the hull does not act with such speed rises due to excess water, the hull works best with up to 15 knots, . I know what I am talking about the old boat was the same size fly bridge max speed of 36 knots, the comparison is easy because the time in the same waters comparable to the same weather.




AT vs NT (I have never seen a live AT. because there seem to be imported from Europe?)


the initial stability is certainly better than AT wider because only two of the GZ-curve comparison of open up at the end. Width can bring faster acceleration roll movement vs narrower, this of course depends on how the weight is distributed from the center line. I have already stated on several occasions why the manufacturers can not publish openly Stability information about the boats that sell?


Another very interesting comparison would be to see the stability of the facts SD vs FD hull. Here there are so many opinions and a long tradition that it would be nice to compare. Manufacturers should be more transparent with respect to these matters, why Stability data is encrypted? all commercial vessels, regardless of the size found on board the stability of the documents, because the captain may change and a new captain has to be able to know what the ship can you reach up and how it behaves at sea, in theory, by knowing these the captain can plan your trip safe for people, cargo and the ship, simple as that.


Can someone give me a US concept of coastal cruising, whether it's roads distance from the coast or travel distance to the point a to b, or all boating which does not exceed oceans, or the other?
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Old 12-12-2016, 07:15 AM   #40
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NT wobbles increasingly, if alto should be on the long side.
NT loses stability when driving 18 knots
Maybe it's just a bad design.
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