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Old 24-10-2018, 19:10   #1
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yacht roll at anchor

Hello all. I am a new member
I am between boats and now looking for a boat for a live on cruise for 1 year.

I observed 2 Yachts on moorings from my motel window a few months ago. Strong wind and a rough sea in the bay. Near Auckland NZ.
Boat 'A' rocked hugely from side to side. Boat 'B' rocked at least 60% less!
Both boats were approx. 40ft.
What are the design causes for this.
I would like to avoid buying a boat and then finding I have 'boat A'
Many thanks
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Old 24-10-2018, 21:03   #2
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Re: yacht roll at anchor

Quote:
Originally Posted by David56 View Post
Hello all. I am a new member
I am between boats and now looking for a boat for a live on cruise for 1 year.

I observed 2 Yachts on moorings from my motel window a few months ago. Strong wind and a rough sea in the bay. Near Auckland NZ.
Boat 'A' rocked hugely from side to side. Boat 'B' rocked at least 60% less!
Both boats were approx. 40ft.
What are the design causes for this.
I would like to avoid buying a boat and then finding I have 'boat A'
Many thanks
A complicated and not easy question to answer, and like every boat design question out there, there are always tradeoffs.

Sometimes it is just the frequency of the waves matches with a particular boat's natural roll frequency. Boat "A" might be the winner today, and the loser tomorrow.

But... in general... boats with wider, flatter hulls roll less than narrow, rounder boats. Deeper draft boats will roll less than shallow draft boats. Heavier boats roll less than lighter boats.

Every one of those statements needs to be predicated with "all other things being equal" but they never are.

And you can design a boat that will roll very little, and either not sail well at all, or be VERY uncomfortable while sailing. For example, a wide, flat, light boat with a very deep keel might roll very little but will pound your brains out going into the wind.
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Old 24-10-2018, 21:10   #3
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Re: yacht roll at anchor

IIRC, assuming a reasonable size chop (as opposed to a big swell), all else being equal:

- sailboats will roll less than boats without a mast
- wide boats will roll less than narrow boats
- large boats will roll less than smaller boats
- flat-bottom boats will roll less than round-bilged boats
- heavy boats will roll less than light boats
- catamarans will roll less than monohulls
- boats with more ballast roll less than boats with less ballast
- a lower center of gravity rolls less than a high center of gravity

Note that this is just for the magnitude of the roll. The roll period is also very important for comfort.
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Old 24-10-2018, 21:36   #4
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Re: yacht roll at anchor

Hmmm.. I think better to buy a boat because it has the kind of performance you seek, and then buy a couple of flopper-stoppers just in case.

I was surprised to see a Hans Christian (heavy displacement) roll quite well a little while back because apparently, as billknny says, the wave period just matched the hull's natural resonant frequency.

BTW welcome aboard, David!
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Old 24-10-2018, 21:37   #5
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Re: yacht roll at anchor

Install one or two flopper stoppers.
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Old 24-10-2018, 21:58   #6
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Re: yacht roll at anchor

I haven't tried it yet but my suspicion is the the "flopstopper" is the best of the bunch. It's still a little too pricey for my particular budget. Though after our last trip when we had some long lost hurricane swells roll in, I think my wife would be glad to buy two or three of them before the next trip...
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Old 24-10-2018, 23:20   #7
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Re: yacht roll at anchor

In a lot of anchorages the swell rolls round a sheltering headland and comes in at close to right angles to the wind direction, so beam on to anchored boats.

Often a stern anchor can, by holding the boat off that 90' angle, make a huge difference.
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Old 25-10-2018, 00:47   #8
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Re: yacht roll at anchor

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Originally Posted by Don C L View Post
I haven't tried it yet but my suspicion is the the "flopstopper" is the best of the bunch. It's still a little too pricey for my particular budget. Though after our last trip when we had some long lost hurricane swells roll in, I think my wife would be glad to buy two or three of them before the next trip...
After a lot of research, Flopstoppers was the only serious choice for us. Plus as I learned, the guy who runs flopstoppers is AWESOME. Haven't used them yet (had it delivered to one of my mother-in-laws' house in the US to avoid customs and shipping), but I absolutely cannot wait to try them on as soon as my wife brings it back to the boat in a few weeks! Eventually I will be posting a (probably redundant) report here about how they perform for sure...
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Old 25-10-2018, 03:26   #9
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Re: yacht roll at anchor

The traditional method to point the boat into the swell is to use a spring on the anchor cable. Only works when there is wind though.
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Old 25-10-2018, 03:49   #10
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Re: yacht roll at anchor

Greetings and welcome aboard the CF, David.
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Old 25-10-2018, 08:46   #11
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Re: yacht roll at anchor

Stern anchor will usually work if space permits, but you can't set one if others near you don't have theirs set. I have always used home-made rocker-stoppers. Strong piece of plywood about 2' square, tie lines to all four corners and then together at top to make a bridle. Add very heavy weight tied to center which will hang below. Hang on end of spinnaker pole. If your boat isn't too big, it works like a charm.
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Old 25-10-2018, 09:00   #12
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Re: yacht roll at anchor

For my friends on a budget - I've made flopperstoppers for 2 of my boats and although they won't win any beauty prizes they work pretty well. And besides - you can't see them once they're deployed!

I made mine based on the instructions in Lin and Larry Pardey's book "The Cost Conscious Cruiser" chapter 13, "Improving Life at Anchor". I just looked it up and the instructions begin about page 156. It involves a milk crate and some line so very low tech, low cost.

I got just as much enjoyment rigging this up as I did after we put it over the side and found it worked.
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Old 25-10-2018, 09:51   #13
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Re: yacht roll at anchor

My SPRAY replica, with a 38 Ft. deck length, 14 Ft. two Inch beam and four and one half draft does not roll, however it also doesn't go to windward.
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Old 25-10-2018, 10:09   #14
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Re: yacht roll at anchor

Knowing that wine was expensive in the Carribean we took up the cabin sole and laid down 400 bottles of wine in Spain. She sure rolled at anchor then, but the more we drank the less the boat rolled.
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Old 25-10-2018, 10:47   #15
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Re: yacht roll at anchor

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Originally Posted by Kenomac View Post
Install one or two flopper stoppers.
Forgive a novice's question, but aren't these devices a little hard on the rigging? I've watched a couple youtube videos of both home-made and manufactured. It seems like it would put a tremendous amount of strain on the shrouds and masthead. One manufactured one was snapping the line it was attached to pretty hard. It looked like there wasn't enough weight to pull it back down far enough before the next roll tried to pull it back up again.
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