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

Off Duty said:

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

Click to expand...

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.

Marin said:

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.

Click to expand...

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

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.

Off Duty said:

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

Click to expand...

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

And here I thought snap rolls were limited to submarines...

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..

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

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.

Our previous trawler had a full concrete keel which made the correction of the beam sea roll very quick.....it was nauseating for sure!!