Traditional Main vs In-mast Furling

[Jim Cate]

Originally Posted by Dockhead

It's called "polar moment of inertia", and more of it makes rolling worse. Just like more weight in the bow or stern makes pitching worse. More polar moment of inertia means rolling or pitching is harder to initialize, but once started, keeps on going. LESS weight aloft is definitely a good thing.

DH, when we were dismasted years ago, the motion of the boat was horrific as we made our way onward. The amplitude of the motion was reduced, but the frequency and the acceleration involved were MUCH worse... literally had to hold on to something at all times to avoid being thrown around.

So, I'm not so sure that reduction of weight aloft is always good in terms of comfort. I suspect that the relationship of the roll frequency (which changes with weight aloft) to the exciting frequency (wave interval) is critical to the amplitude of rolling that develops. Old timers used to advocate hoisting heavy weights aloft at anchor to change this relationship and to increase comfort. Never have tried it myself, but it makes some sense to me.

Jim

[minaret]

Originally Posted by atlantical

of course its weaker, its the choice of a tube with a slot cut in it, or a tube without a slot cut in it. the one with the slot is more prone to twisting, very difficult to twist a tube without a slot cut in it.

Basic engineering principles.

Ummm....no.

[minaret]

Originally Posted by Lost Horizons

It is the opposite. Take a stick by its end and roll it with you arm. Now take the same length heavier stick and try rolling it. The difference will be apparent.

This fenomenon is called moment of inertia in physics.

This. I have made this argument many times on these threads in the past. On square riggers caught in the doldrums they used to hoist drums of water to the mastheads to decrease the roll. Weight aloft decreases roll.

[minaret]

Originally Posted by Jim Cate

DH, when we were dismasted years ago, the motion of the boat was horrific as we made our way onward. The amplitude of the motion was reduced, but the frequency and the acceleration involved were MUCH worse... literally had to hold on to something at all times to avoid being thrown around.

So, I'm not so sure that reduction of weight aloft is always good in terms of comfort. I suspect that the relationship of the roll frequency (which changes with weight aloft) to the exciting frequency (wave interval) is critical to the amplitude of rolling that develops. Old timers used to advocate hoisting heavy weights aloft at anchor to change this relationship and to increase comfort. Never have tried it myself, but it makes some sense to me.

Jim

Lol! Of course you went there first. Conversely, there are many accounts like yours from mariners who lost a rig and then found the vessel almost untenable.

[jtsailjt]

I don't think you have to worry about the effect on resale either way because based on the responses on this thread there are obviously folks with either preference. When we were looking to buy our present boat I eliminated any boat with in mast furling from consideration based on a jammed in mast furling main on a Able Apogee 50 I was helping to deliver for a friend. In retrospect I realize the jam was probably due to it being a new boat to all of us including the owner and we didn't know what we were doing with the furler. Nevertheless, I have to think that there are others out there who prefer slab reefing just as some prefer in mast furlers. We ended up with a boat that has a profurl behind the mast furler and, despite my dislike of in mast furlers, I figured I could easily remove this system and replace it with a hanked on sail and expected to do it soon after purchase. But, despite my prejudice against it, it's grown on me so now we're finishing our 4th season with this boat and I have grown to appreciate the advantages it offers and don't miss the supposed performance hit. On a cruising boat like ours I'm not sure that hit is all that large if you have a well made mainsail that's designed to be furled. The biggest advantage I see is the ability to always have just the amount of sail out that you want out for the conditions at that moment and you don't have to come up into the wind to do it. Our boat was built with the "tall rig" option so that partially makes up for the lack of roach in the furling main as far as performance goes although I realize this comes at the cost of higher CG and doesn't exactly equate to the advantage of having sail area at a lower height in the form of roach.

Much has been made in this thread about the disadvantages of windage and weight aloft but I think it's not as big an issue as some make it out to be. The weight aloft of the furling system amounts to an aluminum foil much like your jib has. Is that really a big deal? When the sail is unfurled that's the only weight difference between the two options. With the sail partially furled, on a in mast furling system you do have the weight of the furled part of the sail that is in addition to the aluminum furling tube, but in strong winds that led you to reef (furl) how much of a hit does a cruising boat take in performance by having half of the weight of its mainsail distributed along the length of it's mast? It's something, but I bet not enough for but very, very few of those who ever reads this post to be able to tell if they didn't already know. There is a different in weight aloft when the sail is entirely furled but as Jim Cate pointed out that might not be a negative. If you find yourself in a music store, or have access to one, play with a metronome and you'll see what I mean. The additional weight aloft will make the motion slower and less "twitchy" feeling.

Regarding windage, some furling masts are a bit more stout than a traditional mast but then I've seen some really rugged looking traditional masts too so I wouldn't take it for granted that a furling mast will always be bigger with more windage than a traditional one. Also, when the sail is fully lowered on a traditional rig, there is more windage along the boom than when an in mast system has the main furled inside the mast. So it seems to me, overall windage isn't much of a negative for in mast furling systems.

Jams: Lots of discussion and even a bit of fear mongering about jams but as has been pointed out, they are rare and the longer you have the system the rarer they seem to get. Also, they almost always happen when trying to unfurl, not while furling the sail. So the worst that's likely to happen is that until you become familiar with your system you might not be able to get out as much sail area as you would like so you'll sail slower until you get around to clearing your jam. Not exactly dangerous in most scenarios. On the other hand, occasionally a traditional sail refuses to come down when you really need it to and that's bad news.

But eventually, for us, when our present system wears out, rather than spending all the $$$ for a whole new rig with in mast furling, we'll just remove our furling system and get a hanked on main and I know I'll be happy with that as well. We'll be sure to have a well thought out and nearly bulletproof reefing system set up and a nearly frictionless track or ball bearing batt cars, we'll have 3 reef points and we'll diligently reef early and we'll have well arranged lazy jacks and a stack pack type sail cover.

It comes down to YOUR personal preference and I wouldn't worry even a little bit about how it might affect resale because both options have advantages over the other and those who prefer them over the other. Good luck with making YOUR choice.

[daletournier]

Originally Posted by minaret

This. I have made this argument many times on these threads in the past. On square riggers caught in the doldrums they used to hoist drums of water to the mastheads to decrease the roll. Weight aloft decreases roll.

Wow, never heard of that, interesting.

[Phil Mavis]

Originally Posted by Dockhead

My experience is the same. My opinion is that in-mast furling is a really good thing to have in heavy weather, and the heavier the weather, the gladder you are to have it.

Not just because reefing it is safer and easier, but maybe more significantly -- an in-mast furling main has a flatter shape when reefed down. It gets flatter and flatter as you reef it. Once you start reefing, all performance advantages of normal battened mainsails disappear.


Because you don't have to head up to reef, you can change the sail area even in horrendous sea conditions. A significant safety advantage. You can reduce sail almost instantly, and also increase it almost instantly -- so it's easier to keep the boat moving. Serious offshore sailors know how dangerous it is right AFTER the storm, when the wind has dropped but the sea is still up -- and how easy it is to broach if you can't keep way on. If you are using a storm trysail, it's a whole production to get it down, get your boom re-rigged, and get your mainsail back into action. With in-mast furling, the storm trysail is built-in, and you can deploy mainsail area in an instant when you need it, without leaving the cockpit. It's a really good thing in heavy weather.

Thank you for this very insightful advice! Never thought of it this way. Perhaps the high windage would furl the main tighter too so light wind sailing might pose more of a threat of jamming than the leech being under tension.

I've also hear the vang either being tight pulling the boom down or adjusted so it's level when furling. Different orientations of the boom will adjust how the sail furls and perhaps jams. My broker says it's like learning a dance and following the same steps. If you start free styling...at least for me...things get messed up. That's why I think a furling mast would work for me. I'm anal. I admit it. I don't care.

However, how I got into sailing, other than lessons provided by my dad as a kid, is racing and volunteering on other captain's boats. We bought a Catalina 30 cruiser and love her. We raced her (just little club races although we did compete for a bottle of rum on New Years Day. Recorded a 55 kt on First Sight in the marina. We finished although well overpowered.

When I cruise, I fiddle. I like to learn/know what's going on. Be engaged. How many more 1/10ths of a knot can I get? You can play with sail shape a lot more with traditional main. Love your safety and immediately for deploying/furling response. Still like other alternatives (boom furling or traditional mains). But your argument is really thought provoking.

Phil

[Jim Cate]

Not just because reefing it is safer and easier, but maybe more significantly -- an in-mast furling main has a flatter shape when reefed down. It gets flatter and flatter as you reef it. Once you start reefing, all performance advantages of normal battened mainsails disappear.

I meant to comment on this before but lost the plot!

DH, I'll stipulate the ease of reefing and the possible advantage of infinite variation in sail area. But I'm having some trouble with your claim of better sail shape when reefed. My slab reefed main also gets flatter as it is reefed. By the time I'm down to the third reef (and it is damn small) it is quite flat, but still has the remains of the roach to present a good plan shape. Also still has a batten to help control the leech. I think this is a better shape than the one presented by a deeply reefed in mast sail, and so does my sailmaker.
Further, the fatter cross section of the roll up mast surely spoils the flow over the reefed sail, does it not?

You've also commented on the extra drag generated by a reefed tall rig compared to a shorter rig. This is true, but I question what percentage of total drag for the boat is represented by the extra mast height. I suspect that it is pretty small potatoes in the big picture, but don't have the data to support my suspicions. If I'm right the penalty for the tall rig might not be so onerous! If one really sailed where there were ALWAYS strong winds, the rationale for the shorter rig might be valid. But even in your area there are light air days (in between gales), and then the extra sail area would be welcome.

Enough! Without the input from a NA and perhaps some wind tunnel tests, we'll just have to ride with our gut impressions. If proper data exist, I'd love to see them.

Jim

[Dockhead]

Originally Posted by Jim Cate

I meant to comment on this before but lost the plot!

DH, I'll stipulate the ease of reefing and the possible advantage of infinite variation in sail area. But I'm having some trouble with your claim of better sail shape when reefed. My slab reefed main also gets flatter as it is reefed. By the time I'm down to the third reef (and it is damn small) it is quite flat, but still has the remains of the roach to present a good plan shape. Also still has a batten to help control the leech. I think this is a better shape than the one presented by a deeply reefed in mast sail, and so does my sailmaker.
Further, the fatter cross section of the roll up mast surely spoils the flow over the reefed sail, does it not?

You've also commented on the extra drag generated by a reefed tall rig compared to a shorter rig. This is true, but I question what percentage of total drag for the boat is represented by the extra mast height. I suspect that it is pretty small potatoes in the big picture, but don't have the data to support my suspicions. If I'm right the penalty for the tall rig might not be so onerous! If one really sailed where there were ALWAYS strong winds, the rationale for the shorter rig might be valid. But even in your area there are light air days (in between gales), and then the extra sail area would be welcome.

Enough! Without the input from a NA and perhaps some wind tunnel tests, we'll just have to ride with our gut impressions. If proper data exist, I'd love to see them.

Jim

Input from a NA would be really interesting. What I know is just based on sailing different kinds of boat in different conditions, so is far from scientific.

But windage high up is really bad -- I think this should be fairly obvious if you think about it. First of all, the wind is stronger up there. Second, it creates heeling moment -- the drag is applied over a longer lever. This drag might be counteracted by lift from the sail, but it might not be.

A taller rig needs more ballast. That makes more wetted surface and more hydrodynamic drag.

All of these things are fine in light wind where you can use all the sail area. But once you start reefing, all these things become burdens which slow you down. That's on top of the lost efficiency of reefed sails, dramatic in the case of headsails.

That's why the size of the rig needs to suit the type of sailing you do.

It also shows an important advantage of a normal batten main over in-mast furling main -- the mast is lighter and thinner, so for a given height of the rig, there is less drag and less need for ballast.

[Dockhead]

Originally Posted by jtsailjt

. . .

Much has been made in this thread about the disadvantages of windage and weight aloft but I think it's not as big an issue as some make it out to be. The weight aloft of the furling system amounts to an aluminum foil much like your jib has. Is that really a big deal?

Well, you made the point below that some normal masts are fatter than others, so the difference may not be that great -- that's a good point.

But in-mast furling masts are truly massive, and the difference is a lot more than the foil. They are larger to accommodate the chamber into which the foil goes, and they are massively built to keep the whole thing rigid -- if the mast bends, the foil bends, and you have all kinds of problems.



seldenfurlingmast.pdf

Like so many things with sailing, there are tradeoffs, and of course there are some advantages to having a really rigid mast too.

Originally Posted by jtsailjt

Regarding windage, some furling masts are a bit more stout than a traditional mast but then I've seen some really rugged looking traditional masts too so I wouldn't take it for granted that a furling mast will always be bigger with more windage than a traditional one. Also, when the sail is fully lowered on a traditional rig, there is more windage along the boom than when an in mast system has the main furled inside the mast. So it seems to me, overall windage isn't much of a negative for in mast furling systems.

Yes, but remember that windage along the boom is far less harmful than windage up high. It doesn't create heeling moment. Also, you don't care about it as much when the sail is all the way down. You really, really care about windage when you are trying to go long distances upwind -- fighting the good fight between lift and drag.

Originally Posted by jtsailjt

It comes down to YOUR personal preference and I wouldn't worry even a little bit about how it might affect resale because both options have advantages over the other and those who prefer them over the other. Good luck with making YOUR choice.

Indeed!

[Dockhead]

Originally Posted by minaret

This. I have made this argument many times on these threads in the past. On square riggers caught in the doldrums they used to hoist drums of water to the mastheads to decrease the roll. Weight aloft decreases roll.

Weight aloft definitely does not reduce roll in all cases. It might in some cases.

What I said was overly simplistic, and this is too, but this is more wrong than what I wrote. Let's drill into it.

There are two different components of rolling -- angular acceleration, and amplitude. So you can't just say "reduce roll". Reduce what component of it?

Less polar moment of inertia means roll is more easily induced, but more easily stopped -- so you have higher angular acceleration. More polar moment of inertia means roll is less easily induced, but less easily stopped -- the inertia keeps the roll going longer. Less angular acceleration but more amplitude.

Another completely separate effect is that once the mast is not vertical, the mass of the mast will be pulling the masthead down creating a completely separate and independent force increasing the angle of roll. This effect increases the amplitude of rolling in all cases. But can be offset by more ballast.

The third effect is RESONANCE -- how the period of oscillation of the rig matches with that of the waves. Really nasty rolling happens when you get resonance between these two so that they reinforce each other.

So it's true that sailboats without masts are very uncomfortable -- they have a nasty twitchy roll motion. The amplitude of rolling is small but the angular acceleration is very high -- seasick city. Motorboats have hull forms designed to reduce the inception of rolling. A sailboat with no chine, especially one with a fin keel, depends on its rig.

Sailboats with heavy and/or tall masts roll with less angular acceleration but greater amplitude. This might be more comfortable. Or might not be depending on how far the roll goes in a given sea state.

A barrel of water hoisted into the rigging of a square-rigger might be useful for killing resonance in a particular sea state, or might be needed to reduce the angular acceleration of roll in a particular sea state, but it will increase the amplitude of the roll. So probably not useful in all circumstances.


If you sail a boat with a tall in-mast furling mast, you will feel for yourself the greater roll amplitude, which can be really awful. My boat really suffers from this, especially at anchor, but other in-mast furling boats I've sailed are just the same.

[Kenomac]

Originally Posted by Dockhead

If you sail a boat with a tall in-mast furling mast, you will feel for yourself the greater roll amplitude, which can be really awful. My boat really suffers from this, especially at anchor, but other in-mast furling boats I've sailed are just the same.

Not necessarily. Our boat never experienced any more roll than other Oysters with non-furling main sails or other boats with non-furling mains. Many times less roll. Excessively high freeboard seems to have more to do with increased roll on some boats. Why bother worrying about a few pounds inside the mast, when the entire deck is 12-24 inches higher up above the waterline and you have that rolling back and forth.

Oysters have very low freeboard.

https://m.youtube.com/watch?v=Xm7xEd_hQRw

[Dockhead]

Originally Posted by Kenomac

Not necessarily. Our boat never experienced any more roll than other Oysters with non-furling main sails or other boats with non-furling mains. Many times less roll. Excessively high freeboard seems to have more to do with increased roll on some models. Why bother worrying about a few pounds inside the mast, when the entire deck is 12-24 inches higher up above the waterline and you have that rolling back and forth.

You've actually sailed on an Oyster without a furling main? I've only ever SEEN one Oyster without a furling main, and have certainly never sailed on one.

The deck has a lot less influence on rolling because it is further from the roll center.

Think of a metronome -- move the weight out to the end of the arm, and the metronome has a slower oscillation, but the arm moves further. Move the weight inward, and the metronome goes faster, but the arm doesn't go as far. That is exactly what happens on our boats with more or less polar moment of inertia.

My boat behaves poorly at anchor -- just like other in-mast furling boats I've sailed on including Oysters. I believe Ken has a flopper-stopper? It's on my list for this winter as well. Previous boats of mine with regular masts did not need flopper stoppers at all.

Unlike weight aloft, a flopper stopper reduces both acceleration AND amplitude of rolling. I plan to deploy mine off the end of my 9 meter long spinnaker pole - should be highly effective. I hope.

[Kenomac]

Yes, on the Britican Oyster 56 in Sardinia. Spent time on their carbon fiber rig, no in mast furling. I doesn't make any difference regarding the amount of roll. Silly argument, increased freeboard makes the biggest difference.

It takes the Britican couple an hour to put their sail away and cover it up, it takes me 20 seconds to furl ours.

[Kenomac]

Another important point to make for the benfit of the OP, is that the Oyster 56 WITH the carbon fiber non-furling mast sold for $100,000 below market because it didn't have a furling mast. So apparently.... purchasing a new non-furling mast boat is a quick way to devalue it substantially in the marketplace.