Traditional Main vs In-mast Furling

[Pete7]

Originally Posted by Kenomac

so how do you explain the fact that we don't experience a rolling issue in anchorages or while underway in relatively calm seas without our main sail deployed? We never deploy the main to lessen roll.

You're sailing in a completely different sea for a starters, oh and the sea water density is different too.

Whilst waves are wind generated in the med and likely to come from one direction only into an anchorage, in the European NW the Atlantic swell coming from Brazil can be a completely different direction to any local wind making life quite uncomfortable as I have just explained.

Pete

[Kenomac]

Originally Posted by Pete7

You're sailing in a completely different sea for a starters, oh and the sea water density is different too.

Whilst waves are wind generated in the med and likely to come from one direction only into an anchorage, in the European NW the Atlantic swell coming from Brazil can be a completely different direction to any local wind making life quite uncomfortable as I have just explained.

Pete

You're saying the sea water density has changed near England since we left Ipswich six years ago? Has it also changed around Guernsey where I spent our first summer?

Has the swell also changed? Interesting....

The motion of our boat in anchorages hasn't changed.

[Dockhead]

Originally Posted by Jim Cate

Do remember, DH, that while your emphasis of greater polar moment and its effect on roll amplitude has merit, that with higher PM it takes a larger force to induce roll to a given deflection. I think that for roll induced by wind the roll will be reduced by higher PM, while roll induced by wave action it might well be increased, especially if there is frequency matching between the roll period and the exciting force.

It is a more complicated issue than first appearance suggests!

Jim

Yes, I think this is spot on, and in no way contradicts what I have written. My only quibble might be the bit about the larger force and the deflection -- you have to separate out righting moment from this. You are a physicist, right? Remember that force goes into acceleration, not motion as such. In the absence of righting moment (and damping), any force will get the boat over to any angle of deflection -- just at different rates of acceleration. Correct?


If you have Fundamentals of Yacht Design, I recommend you read the chapter on rolling -- it's very interesting. It's talks about all this, and with a lot of emphasis on resonance.

[Pete7]

Originally Posted by Kenomac

You're saying the sea water density has changed near England since we left Ipswich six years ago? Has it also changed around Guernsey where I spent our first summer?

Has the swell also changed? Interesting....

Yes to both.

The sea water you are currently floating in has a different density to the one you were used to in Ipswich. You should be floating higher in the Med. However, this doesn't take into account any increase in your wine cellar since arrival in the med.

The med has a short (sometimes viscous) waves normally from one direction unless there has been a recent wind shift. the exposed Atlantic coast is affected by waves generated thousands of miles away which are often have a different direction to the local wind and sit on top of the ocean swell.

Pete

[Dockhead]

Originally Posted by Kenomac

You keep writing the same stuff over and over again, but that doesn't make it more and more factual.

Our Oyster 53 has a slightly taller mast, keel the same depth and one ton more ballast than your "present boat," so how do you explain the fact that we don't experience a rolling issue in anchorages or while underway in relatively calm seas without our main sail deployed? We never deploy the main to lessen roll..
. .

I agree -- my writing it, and how I explained it, is not what makes what I wrote factual. It is the facts themselves and basic physics, which make I wrote in this thread, absolutely factual.


Concerning there differences between our experiences of rolling at anchor, we sail different boats in different waters, so there are various possible explanations:

1. Different sea states. I have a rolling problem maybe 1% of the time when I am anchored. I am describing quite isolated incidents, in weather which you will rarely if ever experience in the Med. Maybe you would experience the exact same thing, in the same anchorages as me and the same weather. Or maybe not.

2. Different hull form. As others have written above -- hydrodynamics play a bigger role than weight aloft, in roll behavior. You have a longer, less aggressive keel, and a skeg on your rudder, which are both good for hydrodynamic damping.

3. Whole different relationship of rig to boat. Your mast is 10 feet shorter than mine, your draft is a bit less, your boat is shorter and narrower than mine, but weighs 20% more than mine. Of course it will behave differently.


I'm happy for you, that you don't have this problem. Enjoy.

[tp12]

Originally Posted by UNCIVILIZED

Let's see, disadvantages of in mast furling:
- Loss of multiple sail shaping & tuning controls (over a dozen of them, easy).
- More weight aloft & windage from larger, heavier mast tube. As well as weight of sail being permanently hoisted.
- Main operates in more disturbed air due to larger spar section
- Less sail area for a given mast height
- Less efficient sail by a huge margin
- More sail induced drag due to poor shape via the sail's cut, in addition to the lack of controls to shape it.
- More heeling from poor sail shape, above, & more weight aloft.
- Poorer efficency from jibs due to inability to tune rig for conditions, & also to alter headstay tension. This includes decreased windware performance, especially in heavy air, when windward efficency is needed most.
- More heeling due to jibs being baggy from loose forestay, without a way to tension same. Again, most detrimental in heavy air.
- Sail jamming issues, along with "reefing" & furling learning curve.
- Less sail design options. Thus harder to create a main which perfectly matches the boat & your sailing style.
- Possible inability to tension leech, along with more tendency towards having either leech flutter or a cupped leech.

And there's more, but... you get the general idea.

EDIT: Note that there are literally dozens of other threads on this exact topic. It comes up monthly, or at a minimum, quarterly. Here's but one of many others about it. http://www.cruisersforum.com/forums/...st-163577.html

Amen.

I chartered a Bavaria 41 in Greece with furling everything and I couldn't get a decent shape out of the main. No matter what I did there was always some flapping in the top third of the leech. Leech line couldn't fix it.

I'd definitely go for a traditional main with some sort of zip up bag

[UNCIVILIZED]

Okay guys, here's a curious question. What percentage of catamarans get built with in mast furling? And I'm more than happy with simply an approximate number.
I ask as I'm trying to think up boats that you see such setups on, & am drawing a blank. Which then begs the question, why aren't these systems common on cats? Including charter boats. Or am I mistaken?

[Dockhead]

Originally Posted by tp12

Amen.

I chartered a Bavaria 41 in Greece with furling everything and I couldn't get a decent shape out of the main. No matter what I did there was always some flapping in the top third of the leech. Leech line couldn't fix it.

I'd definitely go for a traditional main with some sort of zip up bag

I once chartered a Norseman catamaran in the Windward Islands with a full batten main, and I couldn't get a decent shape out of the mainsail no matter what I did. It was a really nasty, baggy sail. Even the leech line couldn't get the sag out of the leech. And exactly the same thing with a Beneteau 423 I chartered in Turkey once from Sunsail.

I did not draw a conclusion from these experiences that all full batten mains are bad, and in fact my next boat will have one

[tp12]

Originally Posted by Dockhead

I once chartered a Norseman catamaran in the Windward Islands with a full batten main, and I couldn't get a decent shape out of the mainsail no matter what I did. It was a really nasty, baggy sail. Even the leech line couldn't get the sag out of the leech. And exactly the same thing with a Beneteau 423 I chartered in Turkey once from Sunsail.

I did not draw a conclusion from these experiences that all full batten mains are bad, and in fact my next boat will have one

I'm not blessed with your experience and I mean that genuinely, not sarcastically. I, of course, considered that the sail was stretched and lost its shape. But why should it? Is that just inferior materials or design?

My understanding is that the best performing main is not a roller furler, at all, but a good shape, laminate sail that flakes?

You're one of the people I respect on CF so I will give more weight/consideration to your view

[tp12]

Originally Posted by UNCIVILIZED

Okay guys, here's a curious question. What percentage of catamarans get built with in mast furling? And I'm more than happy with simply an approximate number.
I ask as I'm trying to think up boats that you see such setups on, & am drawing a blank. Which then begs the question, why aren't these systems common on cats? Including charter boats. Or am I mistaken?

My anecdotal experience would suggest that a very low percentage of cats have furling mains.

[Dockhead]

Originally Posted by UNCIVILIZED

Okay guys, here's a curious question. What percentage of catamarans get built with in mast furling? And I'm more than happy with simply an approximate number.
I ask as I'm trying to think up boats that you see such setups on, & am drawing a blank. Which then begs the question, why aren't these systems common on cats? Including charter boats. Or am I mistaken?

Great question. I've pondered it myself.

I think one answer is that almost all catamarans are used in latitudes where in-mast furling is not really useful. I have never seen a single catamaran in the North Sea -- not one. I've seen four or five in the English Channel in eight years, and two of those were upside down (seriously). And 99% of large cruising boats have in-mast furling up here.

In the Caribbean, in my experience, probably 50% or more of large cruising boats have full batten mains, and virtually all cats do, and cats are 50% of the fleet.

Also, cats -- for some reason that someone more knowledgeable can explain -- usually have small jibs and large roachy mainsails. They are mainsail-oriented rigs. In-mast furling would be no good for that.

Lastly, without ballast, they probably can't tolerate the weight aloft as well.

Those are my idle, uninformed speculations, anyway, FWIW.

[Kenomac]

Originally Posted by Pete7

Yes to both.

The sea water you are currently floating in has a different density to the one you were used to in Ipswich. You should be floating higher in the Med. However, this doesn't take into account any increase in your wine cellar since arrival in the med.

The med has a short (sometimes viscous) waves normally from one direction unless there has been a recent wind shift. the exposed Atlantic coast is affected by waves generated thousands of miles away which are often have a different direction to the local wind and sit on top of the ocean swell.

Pete

I'm guessing you missed my sarcasm in my follow up post, our boat behaves the same here in the Med as it did when we were in Ipswich, UK and Guernsey. No difference.

[Kenomac]

Originally Posted by Dockhead

I agree -- my writing it, and how I explained it, is not what makes what I wrote factual. It is the facts themselves and basic physics, which make I wrote in this thread, absolutely factual.


Concerning there differences between our experiences of rolling at anchor, we sail different boats in different waters, so there are various possible explanations:

1. Different sea states. I have a rolling problem maybe 1% of the time when I am anchored. I am describing quite isolated incidents, in weather which you will rarely if ever experience in the Med. Maybe you would experience the exact same thing, in the same anchorages as me and the same weather. Or maybe not.

2. Different hull form. As others have written above -- hydrodynamics play a bigger role than weight aloft, in roll behavior. You have a longer, less aggressive keel, and a skeg on your rudder, which are both good for hydrodynamic damping.

3. Whole different relationship of rig to boat. Your mast is 10 feet shorter than mine, your draft is a bit less, your boat is shorter and narrower than mine, but weighs 20% more than mine. Of course it will behave differently.


I'm happy for you, that you don't have this problem. Enjoy.

Our boat is the same length as yours (53'10"), the mast is the same height as yours (73ft) width is within an inch or two, keel in one inch less than yours, freeboard is less than yours, and our boat weighs 2000 pounds more than yours.

Check your boat specs.

[Dockhead]

Originally Posted by Kenomac

Our boat is the same length as yours (53'10"), the mast is the same height as yours (73ft) width is within an inch or two, keel in one inch less than yours, freeboard is less than yours, and our boat weighs 2000 pounds more than yours.

Check your boat specs.

According to the data sheet from your boat (not the type, but your specific boat), your mast is 20 meters high. Is that not correct? Mine is 23, about 50cm higher than subsequent M54's (mine was the prototype).

Other specs:

Oyster 53 M54

Hull length 16.00 16.54

LOA 16.40 16.72

LWL 13.75 14.02

Beam 4.65 4.88

Draft 2.21 2.35

Light ship displ. 22,250 20,060


One thing you're right about is the displacement -- my memory was wrong. The Oyster is 2.2 tonnes heavier, not 4.

The two boats are very similar, but not exactly alike. I was comparing them intensely 8 years ago when I finally bought my boat. There were a lot of things I preferred about the Oyster, including the fact that it was a bit smaller.

[Kenomac]

There's a couple of errors on your Oyster data. Mast height for our 53ft cutter rig is 23 meters or 73ft.