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!!!
Bruce
Nordig Tug 37 stability
- Thread starter North Baltic sea
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If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
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!!!
Bruce
sean9c
Guru
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.
Nomad Willy
Guru
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 ......
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 ......
sean9c
Guru
To say the AT is not a planing hull is just baffling. These are nearly 20kt boats.
Nomad Willy
Guru
"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.
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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markpierce
Master and Commander
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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!
Well, they at least give me a toot!
OP
OP
North Baltic sea
Guru
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?
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?
Maybe it's just a bad design.
There was a thread on exactly this subject and there are some very good answers here.
Bruce
http://www.trawlerforum.com/forums/s3/coastal-vs-offshore-21848.html
OP
OP
North Baltic sea
Guru
Thank you link
Unfortunately, my head is certainly a pea when I could not find an answer
That is, there are no facts which is Costal cruising, there are no facts about the seaworthiness of the vessel, but there is a lot of reviews that are not facts. Probably due to the culture that I love more hard facts than vague stories and images of things seaworthiness of different boat models.
OP
OP
North Baltic sea
Guru
100% agree, I purchased a planing boat but the SD. I believe that NT is also not a submarine very well, because it is designed to work under water. do not understand the answer wrong, a little humor.
Roger Long
Senior Member
I wrote this a few years ago for people like you. It is sail oriented but the basic principles are the same and I should give you a working understanding of stability.
Stability of Boats and Ships
CPseudonym
Moderator Emeritus
Great information as always Roger. Thank you for the link.
waddenkruiser
Senior Member
There is a lot of generic information available about boat stability. One I found very handy and which describes the basic rules and aspects to be considered is here:
http://www.fao.org/3/a-i0625e.pdf
However I wasn't able to find a specific stability curve for our boat (what a pity for an engineer like me). But which additional value would I gain with such a curve describing only the static stability? In practice the dynamic stability gives the limit!
What we really have to avoid is periodic roll and are braking waves equal to or higher than our beam ...
Most of our trawler yacht hulls have an AVS (heeling angle of vanishing stability) quite below 90 while flooding starts already at a heel angle which is typically in the range of 50 (or even lower). And we know that most of our hulls are reasonably stiff (e.g. roll Eigenperiod in seconds is typically lower than beam in meter), i.e. they have a reasonable metacentric height.
If you really want to you can calculate the metacentric height of your boat based on the results of a heel test (performed at your dock) and correlate this with your roll Eigenperiod measured at the same time.
Doing so you would be able later to check whether metacentric height / roll Eigenperiod have been influenced negatively due to a changed weight distribution, a new heavy antenna in the mast top, ice on deck, added heavy load on the cabin roof or whatever.
http://www.fao.org/3/a-i0625e.pdf
However I wasn't able to find a specific stability curve for our boat (what a pity for an engineer like me). But which additional value would I gain with such a curve describing only the static stability? In practice the dynamic stability gives the limit!
What we really have to avoid is periodic roll and are braking waves equal to or higher than our beam ...
Most of our trawler yacht hulls have an AVS (heeling angle of vanishing stability) quite below 90 while flooding starts already at a heel angle which is typically in the range of 50 (or even lower). And we know that most of our hulls are reasonably stiff (e.g. roll Eigenperiod in seconds is typically lower than beam in meter), i.e. they have a reasonable metacentric height.
If you really want to you can calculate the metacentric height of your boat based on the results of a heel test (performed at your dock) and correlate this with your roll Eigenperiod measured at the same time.
Doing so you would be able later to check whether metacentric height / roll Eigenperiod have been influenced negatively due to a changed weight distribution, a new heavy antenna in the mast top, ice on deck, added heavy load on the cabin roof or whatever.
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sunchaser
Guru
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Wadden
Did you read post 44 and thoughts on megacentric height? Other true professionals with requisite NA chops may step forward but the two NAs that peek at this forum are Tad Roberts and Roger Long. Lots to learn from them.
waddenkruiser
Senior Member
sunchaser
Yes, did so and found it valuable. E.g. Roger gives some hints how to establish a fair approximation of the GZ curve based on metacentric height and two heel angles. Certainly that will satisfy the engineer inside me
OP
OP
North Baltic sea
Guru
I asked the factory to the stability of NT facts and the answer was negative. apparently a big secret, I can not understand such a policy. Thanks for all the responses and thoughts!
Roger Long
Senior Member
I doubt they have a clue, not because of anything specific I know about the company but just recreational vessel industry practice.
The low freeboard of these boats would likely make them look pretty poor according to the criteria used for USCG inspected passenger vessels. This doesn't necessarily make them unsafe for their intended use but would not encourage a builder to even do the calculations comparing them with commercial passenger vessel standards.
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