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Old 28-02-2016, 18:24   #16
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Re: At anchor

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Originally Posted by Lunita View Post
Perhaps a second hull might reduce rolling........
And this answers the OP's question about the monohulls behaviour how?

I was recently on a cat; very different movements but not half as comfy as some would have people believe. Probably takes some getting used to too.
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Old 28-02-2016, 18:25   #17
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Re: At anchor

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My Force 50, full keel boat usually sits very well at anchor and on its mooring. I notice other boats rocking quite a bit also and thought my comfort was simply because of the 52,000 lbs of weight.

Then I pulled both wood masts out for refinishing and put it back on it's mooring. It is almost unbearable now. Without the weight of the masts to counteract the keel it rocks beam to beam horribly with the wake of a passing boat. I began to wonder if I were if I were to replace the wood masts with lighter aluminum ones if I would create a boat I couldn't stand to be on at anchor.

Maybe this effect has something to do with what you were noticing.
This is something to consider. The classic book "Desireable and Undesirable Characteristics of Offshore Yachts" speaks specifically of the difference that mast(s) and standing rigging make on the movement of a boat.

It's on the desk in front of me and I'll look up the specific reference if someone wants it (probably tomorrow because it's almost bedtime).
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Old 28-02-2016, 21:12   #18
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Re: At anchor

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Originally Posted by AnglaisInHull View Post
This is something to consider. The classic book "Desireable and Undesirable Characteristics of Offshore Yachts" speaks specifically of the difference that mast(s) and standing rigging make on the movement of a boat.

It's on the desk in front of me and I'll look up the specific reference if someone wants it (probably tomorrow because it's almost bedtime).
Yes, I'd be really curious to hear. I'm just starting to research stability. There is a street smart sense of what is sea kindly but the actual logistics of why has been fascinating me lately.
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Old 29-02-2016, 06:39   #19
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Re: At anchor

“Desirable and Undesirable Characteristics of Offshore Yachts”
Ed. John Rousmaniere, Norton 1987

The research described in the book was intended to explain why boats capsize in heavy weather, but the concepts are likely relevant to stability in general.

To briefly summarize a chapter of the book, stability is a function of various forces, but one that is very significant is the “roll moment of inertia”, or the resistance to rolling movement caused by the weight and placement of the various boat components. Inertia contributed by a given component is related to both its weight and its distance from the fore and aft axis of the boat; in practical terms this means that the keel has less effect than you might guess (it’s heavy but close to the axis) and the mast, sails and rigging have more (lighter but farther from the axis). A dismasted boat will roll more and is more likely to be capsized by wave action.

It seems reasonable that the same forces affect the way the boat behaves at anchor. To extrapolate (and this is just my speculation based on the above), a long fin keel might actually be better for this - even if it’s not resting on the bottom - than a shorter full keel.

Interesting anecdote in the book: this was discovered almost by accident. Researchers were doing tests on a model hull in a wave tank when someone decided to add a mast to make it look more like a sailboat. They then found that the model had completely different characteristics than previously observed.
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Old 29-02-2016, 17:38   #20
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Re: At anchor

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Originally Posted by Lizzy Belle View Post
And this answers the OP's question about the monohulls behaviour how?

I was recently on a cat; very different movements but not half as comfy as some would have people believe. Probably takes some getting used to too.
The OP did not actually pose his question with regard to mono hulls. ( although we assume this)
My opinion was that a multihull would have a better motion at anchor. They certainly do not engage in the type of rolling motion mentioned. They have a different motion for sure, but one which I prefer, at anchor or underway. I think back to a night at a rolly anchorage locally. We were in fits of laughter at 3am just trying to stay in our berths!
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Old 29-02-2016, 17:43   #21
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Re: At anchor

Resonant frequency. Hulls respond to waves at a certain frequency. Different hulls, different frequencies.
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Old 29-02-2016, 17:45   #22
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Re: At anchor

All the other boats look like they rock more than the one I'm in. Esp after a few drinks.

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Old 29-02-2016, 17:46   #23
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Re: At anchor

I can't explain it.



Someone tell the left-side sailboat he's moored in the wrong direction, according to State of California instructions.
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Old 29-02-2016, 17:55   #24
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Re: At anchor

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If a cruising boat is at anchor for the majority of the time, what determines how comfortable we are at anchor? What would you most look for in a boat you were going to live at anchor in for an extended time?
Its little to do with the boat and a lot to do with the people on it.

In my current anchorage lots of people complain about the roll and go inside the lagoon to still but dirty water that's not swimable.

I don't even notice the roll, not at all.

To me a boat with no movement is a dead boat. Like being on the hard Sea Life is not a person anymore just an expensive pile of fibreglass.
As soon as she is in the water she feels better and when she gets into a nice anchorage she feels 'herself'.

The only greater moment my boat has is when I pull that pick up and her bow goes into the first wave. Then she's alive!


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Old 29-02-2016, 18:01   #25
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Re: At anchor

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Originally Posted by markpierce View Post
I can't explain it.

Someone tell the left-side sailboat he's moored in the wrong direction, according to State of California instructions.
He'll find out soon enough...
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Old 29-02-2016, 18:08   #26
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Re: At anchor

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To me a boat with no movement is a dead boat.
Haha, I thought it was just me

Years ago I was anchored near my dad's boat - 65' of steel. That boat (zeetjalk) didn't move. At all. I raided his fridge and walked back to the dinghy to get back to my own little home.

My dad: "Why go back to your boat? Look at her rolling!"
Me: "Exactly."

True story.
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Old 29-02-2016, 18:18   #27
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pirate Re: At anchor

The only rolling that pisses me off is the rolling of day tripper motor boat twats who pass too close and too fast in an anchorage..
and in Marigot Bay the twat tour guides who take group after group of Cruise ship Lobsters though the anchored boats on jet bikes they can barely control..
Amazed no ones been killed yet when swimming off the boat..
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Old 29-02-2016, 19:22   #28
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Re: At anchor

Windage and freeboard impact yawing at anchor. A fractional rig will also yaw more because the location of the windage from the mast.. too far forward. Full keel will yaw less and it also doesn't tack as well!
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Old 03-03-2016, 04:36   #29
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Re: At anchor

Did I miss it or has nobody yet mentioned a flopper stopper?
Suppose some don't know, so - it's a simple roll-damping device made from a triangle of plywood, a rope bridle and a weight. Extended over a side deck on a short strong pole, it's dangled in the water. As that side rolls downward the weight makes the board tilt and dive, low resistance. Stays horizontal on the upward roll, high resistance, and slows the roll right down.
Very effective, very cheap. Strong support needed though.

Hadn't thought about it before reading this thread but is it possible that, when there are a number of nearby boats on pontoons - not anchored obviously - movement of boats might be affected by waves reflecting from others nearby as well as from fixed structures?
Like reflected waves from headlands, moles etc.?

If so presumably some would have their movement amplified and others have it suppressed - some boats causing others to reach their resonant period of roll and others prevented from achieving resonance.

At anchor I imagine contour of the ground in a tideway might have unusual effects sometimes.

This was just a passing curiosity - no way to measure, predict or improve anything anyway... waste of time posting it really
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Old 03-03-2016, 05:12   #30
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Re: At anchor

I am sure has to do with many factors, the shape of keel being irrelevant, but depth of ballast, turn of bilges, and waterline beam weight of mast. My old full keel Luders 33 was a much rollier boat than my fin keeled Tarten 40 in most conditions. I think this was due to slack bilges which also let it heel more. That said, the luders also tracked true at 0 degrees and 35 degrees of heel which was part of a narrow, old design. The Tartan is stiffer and heels significantly less, but at 35degrees of heel doesn't feel as happy.


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