Advantages of a taller rig/30% larger sail area?

[poiu]

Originally Posted by Dockhead

The only thing I would quibble with in this post is this.

More inertia does not necessarily make it harder to get into a resonant state. Talking about yachts, the opposite is more often the case.

Resonance happens when the natural roll period matches the wave period. Adding inertia increases the roll period. The normal range of wave periods is longer than the normal range range of roll periods of yachts. The overlap is at the lower end of wave periods and the upper end of yacht roll periods.

Small ships can be very badly, even disastrously affected by resonant rolling -- see the video posted above.


What is very true in this post is that larger yachts lie better at anchor in general than smaller ones. Like Poiu, I often lie in places where smaller boats can't or wouldn't. Normally there is no problem, even in somewhat boisterous conditions. My boat is fairly light for her size though, 20 metric tonnes light ship, so she gets tossed around more than Poiu's big heavyweight. But if resonance happens -- all bets are off.

More inertia does help, and here what I am talking about particularly is polar moment of inertia. This is the main reason why sailing yachts with the same inertia (displacement) as motor yachts roll much less and why dismasted yachts roll more. When I use the word more in this context, I mean in a sense of more unpleasantly.

And to put my point in another way, I think more inertia in and of itself does actually mean less rolling for another reason and that is the big swell needed to start off the rolling in a heavy boat is much rarer to encounter. How often have you seen an anchored supertanker rocking from gunwale to gunwale?

I'm sure a mathematical analysis could be done. If any maths boffin is here then pipe up.

[atmartin]

Originally Posted by poiu

More inertia does help, and here what I am talking about particularly is polar moment of inertia. This is the main reason why sailing yachts with the same inertia (displacement) as motor yachts roll much less and why dismasted yachts roll more. When I use the word more in this context, I mean in a sense of more unpleasantly.

And to put my point in another way, I think more inertia in and of itself does actually mean less rolling for another reason and that is the big swell needed to start off the rolling in a heavy boat is much rarer to encounter. How often have you seen an anchored supertanker rocking from gunwale to gunwale?

I'm sure a mathematical analysis could be done. If any maths boffin is here then pipe up.

Increasing the mass moment of inertia should increase resistance to rolling. Your example of sail vs power boat of same displacement is probably true as most sailboats will have more weight further away from the axis of rotation. Although, that discounts the roll resistance that come from hull shape and buoyancy. Many powerboats are beamier than traditional sailboats and have harder chines, giving them more roll resistance due to buoyancy, rather than mass moment of inertia alone. Hollow chine, wineglass shape little sailboats roll quite easily at anchor.

We need some formulas at this point because while mass moment of inertia surely increases roll resistance, I question whether any small boat is going to have enough inertia to resist the energy of even moderate waves at sea. Sure, tankers don't roll in smallish waves at anchor, but Dockhead's tank test shows that even moderate waves can induce serious rolling if the right frequency is hit.

[Dockhead]

Originally Posted by poiu

More inertia does help, and here what I am talking about particularly is polar moment of inertia. This is the main reason why sailing yachts with the same inertia (displacement) as motor yachts roll much less and why dismasted yachts roll more. When I use the word more in this context, I mean in a sense of more unpleasantly.

And to put my point in another way, I think more inertia in and of itself does actually mean less rolling for another reason and that is the big swell needed to start off the rolling in a heavy boat is much rarer to encounter. How often have you seen an anchored supertanker rocking from gunwale to gunwale?

I'm sure a mathematical analysis could be done. If any maths boffin is here then pipe up.

The big difference between motor yachts and sailing yachts is not inertia, but keels and underbody shape (and when under sail, sails.). As someone pointed out, and as it's written in Fundamentals of Yacht Design, damping is the more important part of the equation.

As to supertankers -- they also roll -- but since their beams may be 40 or 50 meters, it takes a different kind of wave to do it. This is geometry -- and the same thing applies on a much smaller scale to bigger vs. smaller sailboats.

Certainly more inertia may inhibit the onset of rolling, and might prevent rolling in really tiny ripples carrying little energy. The more damping you have, the better this will work. But beyond a certain point, the boat is going to roll no matter what. And then, the only thing inertia does is change the period. With a longer period, you have less acceleration, and that's why a slower roll might be more comfortable in some cases even if the amplitude is greater.

Take a metronome, and move the weight in and out along the arm. With the weight far out, it's not much harder to get the metronome running. The spring pushes the arm over like the waves push our boats over. With the weight out, the metronome runs slower, but the arm goes over way further. It's exactly the same principle.

[Snowpetrel]

Originally Posted by TheThunderbird

"And the extra roll moment of inertia may reduce slightly the capsize risk in severe weather."

Not in my Physics

http://www.nytimes.com/1983/05/29/sp...-big-wave.html

This is old research, well documented by many sources since, that the roll moment of inertia helps resist the impact and rollover potential of a single rogue wave. It can be a double edged sword on boats with less ultimate stability like powerboats where the rolling inertia can capsize them eg parametric rolling.

Its a complex subject with lots of real world complexities that arent easily modeles in a testong tank. But I haven't seen any new research that shows the opposite for a ballasted yacht. And real world experaince seems to back this up, ie when boats loose their mast they seem more prone to capsize.

[Snowpetrel]

Originally Posted by Dockhead

Just want to point out a couple of facts:

1. APPARENT wind is ahead of the beam more than 50% of the time.

True, but I have never really had an issue making miles with the wind just forward of the beam, biggest issue is slowing the boat down enough for comfort and to reduce pounding and possible damage. I'd say this is probably true up to about 60 or so degrees off the wind up to that point the extra windage and weight aloft doesn't seem to much of a killer, probably the bigger issue is the extra pitching moment making for a wetter deck. As the wind speed increases the real problem is often the waves as much as windage, and surface drift of the currents.

My boat's winter home is in the Solent, which has surely the highest concentration of racing yachts on the planet. You should see me blow by the racing boats with their big rigs, once they've got a roll in their headsails, when going upwind, if they don't manage to change sails. Despite my in-mast furling main (getting back to the original topic ) and bulky, draggy, telephone-pole-like furling mast.

This is probably as much due to the extra weight and size of your boat compared to the racing boats not the stumpy rig. It's interesting that all racing boats have gone to bigger rigs dispite the way it slows them upwind in a blow, it is overall much faster in most conditions. Eg even the sydney hobart, a more windward race than many is still consistantly won by boats with good light air performance rather than heavy weather windward performance. The 2006 race was a heavy windward one and some older IOR boats did very well, but the lighter big rigged boats hung on OK. Basically the gains in the light are worth more than the loss of speed in heavy windward overall. Your own case is different in that you bash against the SW winds back from the baltic regularly against a deadline, whereas most cruisers tend to work with the weather were possible, and motorsail to windward if fast progress needs to be made to reduce wear and tear on gear.

[Dockhead]

Originally Posted by Snowpetrel

True, but I have never really had an issue making miles with the wind just forward of the beam, biggest issue is slowing the boat down enough for comfort and to reduce pounding and possible damage. I'd say this is probably true up to about 60 or so degrees off the wind up to that point the extra windage and weight aloft doesn't seem to much of a killer, probably the bigger issue is the extra pitching moment making for a wetter deck. As the wind speed increases the real problem is often the waves as much as windage, and surface drift of the currents.



This is probably as much due to the extra weight and size of your boat compared to the racing boats not the stumpy rig. It's interesting that all racing boats have gone to bigger rigs dispite the way it slows them upwind in a blow, it is overall much faster in most conditions. Eg even the sydney hobart, a more windward race than many is still consistantly won by boats with good light air performance rather than heavy weather windward performance. The 2006 race was a heavy windward one and some older IOR boats did very well, but the lighter big rigged boats hung on OK. Basically the gains in the light are worth more than the loss of speed in heavy windward overall. Your own case is different in that you bash against the SW winds back from the baltic regularly against a deadline, whereas most cruisers tend to work with the weather were possible, and motorsail to windward if fast progress needs to be made to reduce wear and tear on gear.

Very interesting observation. And cogently argued.

But maybe it's not the rigs which are winning those races, but the hulls? A light boat with a lot of power -- a lot of righting moment -- needs less power, and so can tolerate more drag, right?

[Snowpetrel]

Yes you may be right, yacht design is a facinating field, and it seems to me that the trade offs are quite broad and also very subtle, ie narrow light boats can work well over a variety of conditions, as can wide heavy powerful boats. I always find the contrasts and compromises facinating. Really we should also chuck in Sa/wetted surface ratios and the dellenbugh angle or sa/righting moment to properly evaluate different designs.

[UNCIVILIZED]

To clarify something, light boats with lots of Rm aren't necessarily "powerful", especially upwind in a blow, & or with heavy seas. As they don't carry enough momentum to keep up their speed, nor enough speed to prevent lots of leeway, when punching uphill through such conditions. It varies by design of course, but you can't make broad sweeping statements about it.

There are times that even when the light boats with high Rm's could go to weather in such conditions, you have to slow them down regardless, as if you don't they'll self destruct. Where in such conditions, due to less acceleration & deceleration that's staved off by their momentum, heavier boats can keep pushing harder, longer. Even if they aren't necessarily stronger structurally. Though if they are, then they can continue pushing to windward that much longer, in conditons that would just rip the lighter boats into expensive flotsam.

Imagine putting water ballast, & a stouter rig into say a Santa Cruz 70'. She'd have the available horsepower (& some of the mass) required to go to weather in some pretty stiff conditions, both on paper, & in the real world. But if you did it for long in one, she would soon start to come apart.
If memory serves, this is what happened to some of the faster, custom boats in the '98 Sydney-Hobart, which would normally have been line honors & overall race contenders.

[Dockhead]

Originally Posted by UNCIVILIZED

To clarify something, light boats with lots of Rm aren't necessarily "powerful", especially upwind in a blow, & or with heavy seas. As they don't carry enough momentum to keep up their speed, nor enough speed to prevent lots of leeway, when punching uphill through such conditions. It varies by design of course, but you can't make broad sweeping statements about it.

There are times that even when the light boats with high Rm's could go to weather in such conditions, you have to slow them down regardless, as if you don't they'll self destruct. Where in such conditions, due to less acceleration & deceleration that's staved off by their momentum, heavier boats can keep pushing harder, longer. Even if they aren't necessarily stronger structurally. Though if they are, then they can continue pushing to windward that much longer, in conditons that would just rip the lighter boats into expensive flotsam.

Imagine putting water ballast, & a stouter rig into say a Santa Cruz 70'. She'd have the available horsepower (& some of the mass) required to go to weather in some pretty stiff conditions, both on paper, & in the real world. But if you did it for long in one, she would soon start to come apart.
If memory serves, this is what happened to some of the faster, custom boats in the '98 Sydney-Hobart, which would normally have been line honors & overall race contenders.

OK.

That kind of brings us back to where we started from. But I think we all agree that all this is very complex.

[jtsailjt]

So I think your idea of building a narrow boat is a good one, but question the short rig and light weight part. Why not keep the narrow hull but with a bit more emphasis on ruggedness with a little more weight and a taller rig for horsepower in light air along with a more comfortable ride in heavy seas and at anchor? There's something really attractive to me about a narrow boat that has enough ballast to stand up and really go in high winds, and enough "oomph" to keep going through the tops of the waves instead of smashing down on top of them. I'd want a moderately long cruising fin keel in order to have adequate ballast to keep that narrow hull upright without having a 10' draft that a shorter keel would require. But then I've read about the Sundeer and Deerfoot boats that were narrow and had a very low D/L and had good reputations as fast passagemakers, though their appearance could certainly be improved. Maybe there's something to your idea of the long length making a very low D/L OK from a comfort perspective. I'm anxious to hear what your NA says about all this so I hope you'll post his recommendations and reasons for them on here so we can all learn from him.

[UNCIVILIZED]

There's a good explanation of the Dashew's boat designs, & the reasoning behind it in their book Offshore Cruising Encyclopedia which you can download free at SetSail FPB » Free Books & while you're there, do the same with their other excellent works.

[Paul J. Nolan]

Sail area is like money, sex, and horsepower. In general, more is better.

Paul

[hellosailor]

Tom-
"I expect everything from 0 to 70kts, "
Have you spoken with a sailmaker yet? I ask because many of us sail with what fits on the boat and fits in the budget, which is a much smaller and less flexible sail inventory than ideal.
If you go with the tall rig and 30% more sail area, your sails will be more expensive. And to cover that wind range without abusing sails, you'll need more sails and of better [more expensive] construction.
So, possibly the tall rig is going to be somewhat less than optimal, unless you make a substantial addition to the sail budget. Possibly staying with the short rig and investing in the sail inventory would pay off more in the long run.
Just something to consider.

[Suijin]

Personally if I were set on a Malo 40 I would buy the one in the best shape I could find and take whatever rig it had on it. Being selective about the rig, while understandable, could well make you pass on better found boats and in the long run be something you wished you had not done.

Of course of you find two in similar condition with different rigs, it's not an issue, but that's a pretty rare event in the market for older boats.

[SimonFirth]

This has been a very interesting read.

If I might say so the answer to the question depends upon who you are, where you intend to sail and to what use you intend to put your boat.

Like Stormpetrel, I come from Tasmania. After 30 years racing offshore I bought a 41 foot motor sailer and discovered the piece of mind of a short rig and an adequate diesel. My headsail is used at least one day a week and is 45 years old. My 40 year old mainsail succumbed to thumbs shoved through it while putting away and was replaced with a 10 yo little used rather powerful sail for the grand sum of $500. I have been caught in 60 knot changes and all I do is roll up the headsail and start the diesel. 96hp fixes most things.

But this approach only works in coastal cruising. Long distance stuff requires long legs and under rigged boats don't cut it. Similarly the lower the latitude numbers the less pressure you have and the more power you need. While I have a great deal of fun running rings around ancient Sydney Hobart winners while dragging a 28" 3 bladed prop in light winds, that only works if you don't need to go anywhere.

So consider the uses. Daysailing and overnighting, go for the short rig. If you intend crossing oceans, go for the big one and learn how to tame it. quickly. And don't forget to consider how you feel about the alternatives. You don't go to sea to be frightened ... at least I don't! Egos buy trouble at sea.