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Old 08-18-2015, 10:28 PM   #1
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Snap Roll

The better half asked a little while ago, "what's that snap roll thing?"
Try as I did, I don't think I did a great job of explaining it to her, so......

I realize it's not the time to be doing videography, but does anyone happen to have a you tube or other video of a boat doing a snap roll?

TIA

OD
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Old 08-18-2015, 10:49 PM   #2
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Originally Posted by Off Duty View Post
The better half asked a little while ago, "what's that snap roll thing?"
Try as I did, I don't think I did a great job of explaining it to her, so......

I realize it's not the time to be doing videography, but does anyone happen to have a you tube or other video of a boat doing a snap roll?

TIA

OD
If you're talking about a snap roll, that's an aviation maneuver. We have film in our library of our legendary test pilot Tex Johnson doing snap rolls in B-47s (it was an experimental nuclear weapon release technique).

If you're talking about what boats with semi-planing hulls and hard chines often tend to do in beam seas, I've typically seen that referred to as a snap-back roll, which is the term I use.
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Old 08-18-2015, 11:03 PM   #3
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If you're talking about a snap roll, that's an aviation maneuver. We have film in our library of our legendary test pilot Tex Johnson doing snap rolls in B-47s (it was an experimental nuclear weapon release technique).

If you're talking about what boats with semi-planing hulls and hard chines often tend to do in beam seas, I've typically seen that referred to as a snap-back roll, which is the term I use.
Thank you.

Yes, I'm familiar with the aviation term/maneuver. The conversation actually started over the thread about living in Panama on a 25 Albin.

Manyboats happened to mention that "The Albin is very good in the rough weather w the exception of a nasty snap roll."

I was just trying to explain it to the boss lady :-)
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Old 08-18-2015, 11:38 PM   #4
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My own explanation, which Eric would probably be able to express much more accurately than I can, is that a boat with a fairly flat afterbody like our Grand Banks rolls, but as it rolls that flat underside aft rapidly builds up resistance to the roll because it's got a lot of surface area pushing down on the water. This resistance is sufficient to bring the roll to a fairly abrupt stop, at which point is starts rolling back the other way. Thus the "snap-back" roll.

If you look up "snap back roll" in the dictionary I suspect there is a drawing of a Grand Banks with the definition. Our boat is the poster child for the snap-back roll. We're used to it and it we don't find it particularly annoying, but a lot of people do. The boat doesn't roll as far as one with a more rounded bottom configuration, or a displacement boat which generally has a quite round underbody.

The tradeoffs are, with the semi-planing, hard-chine hull, less rolling in terms of angle but a faster, snappier change of roll direction. Some people find this uncomfortable. With the rounder hull, or a displacement hull, the roll is slower and the reversal more gentle, but the roll angle will be greater. Some people find this makes them seasick.

Pick your poison.
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Old 08-19-2015, 12:11 AM   #5
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Quote:
Originally Posted by Off Duty View Post
The better half asked a little while ago, "what's that snap roll thing?"
Try as I did, I don't think I did a great job of explaining it to her, so......

I realize it's not the time to be doing videography, but does anyone happen to have a you tube or other video of a boat doing a snap roll?

TIA

OD
Here's one in pictures.
Dockwalk - The Essential Site For Captains And Crew - DockTalk


And the one where he actually goes over
http://www.downrange.tv/forum/index.php?topic=14206.0
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Old 08-19-2015, 12:17 AM   #6
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And here I thought snap rolls were limited to submarines...
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Old 08-19-2015, 07:27 AM   #7
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No strict nautical definition..just like trawler...


My experience is that instead of a more uniform roll, a snap roll is one where there is uneaqual acceleration throughout the period and less predictable as on flat bottom vessels than a slow roll more common for round bottom vessels.


Pretty noticeable on ice breakers (slow roll) or small deep keeled sailboat.... 378s snap roll unless at speed or on a something like an old Boston Whaler or Carolina Skiff..
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Old 08-19-2015, 08:04 AM   #8
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Thanks Gentlemen
Your explanations, links and photos were exactly what I needed.

I've experienced the event a time or two over the years (we always just called it a snap roll as well, but now I know the proper terminology, thanks Marin), but was having a difficult time explaining it to her. The pics, and your explanation of "why" will help for sure.

Thanks again.

OD
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Old 08-19-2015, 08:52 AM   #9
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I think of a snap roll as if 2 very strong springs are righting your boat, while a soft chined boat has 2 soft springs bringing it back to the vertical position. The "strong springs" will keep it steadier in most conditions, but the correction can be more violent.
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Old 08-20-2015, 08:57 PM   #10
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Our previous trawler had a full concrete keel which made the correction of the beam sea roll very quick.....it was nauseating for sure!!
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