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Old 09-08-2015, 09:07 AM   #1
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Question Stabilizing sail

Pardon the sailor in me, but why don't I see the use of stabilizing sails in use?

I see the small mast & boom on many designs, would that help in beam seas
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Old 09-08-2015, 09:14 AM   #2
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I don't know why you don't see more of them in use. They do work. Not as well as other forms of passive or active stabilization. But designed and deployed properly they do definetly help with roll.

Maybe people feel they don't work well enough to justify the cost? Or they think they are to much hassle to setup?
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Old 09-08-2015, 09:20 AM   #3
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We looked at adding a sail to Hobo. With our current boom and mast we could only have about a 110 sq' sail and our displacement is 44K lbs. That and having to beefed up the standing rigging we didn't see the added benefit/effort.
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Old 09-08-2015, 09:23 AM   #4
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Maybe people feel they don't work well enough to justify the cost? Or they think they are to much hassle to setup?
I'd say yes and yes.

What has always been much more remarkable to me is the large number of cruising sailboats I see without a sail up, rolling and yawing in conditions perfect for sailing, or at least a reefed main.
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Old 09-08-2015, 10:17 AM   #5
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Originally Posted by caltexflanc View Post
is the large number of cruising sailboats I see without a sail up, rolling and yawing in conditions perfect for sailing, or at least a reefed main.
A sail should be up, not sure why.
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Old 09-08-2015, 10:44 AM   #6
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I often think the same thing, they don't even take the sail covers off!
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I'd say yes and yes.

What has always been much more remarkable to me is the large number of cruising sailboats I see without a sail up, rolling and yawing in conditions perfect for sailing, or at least a reefed main.
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Old 09-08-2015, 11:12 AM   #7
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Quote:
Originally Posted by Jimbo2015 View Post
Pardon the sailor in me, but why don't I see the use of stabilizing sails in use?

I see the small mast & boom on many designs, would that help in beam seas
FWIW: Almost all of George Buehler's Diesel Ducks utilize some sort of sail stabilization and or paravanes.
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Old 09-08-2015, 11:30 AM   #8
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Just comparing stabilizing effects on my own boat while underway in a beam sea, my bilge keels reduce the rolling by an estimated 10%. Raising my sails reduces the rolling by a further 70-80%. The only time they aren't extremely effective is when there is no wind.

The time and effort needed to raise a small set of sails is minimal. It takes me less than 5 minutes, singlehanded, in most conditions. With a self tacking jib, they are almost "set & forget" unless I want to wring the last 0.1 knot out of them.

A limiting factor may be than many trawlers (but not all) do not have a keel designed for sails. Without ballast down low, sail area may have to be limited to the point where the effect is negligible. At least 30 square feet per ton of displacement is needed to be effective. Some of the Taiwanese trawlers have about half this, and this may have added to the myth that steadying sails don't help much.
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Old 09-08-2015, 11:39 AM   #9
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On my last boat the sail hardly reduced roll at all until the wind got above 10 kts or so. It really helped at anchor though, to prevent 'hunting'.
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Old 09-08-2015, 12:02 PM   #10
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We need at least 10 knots from the beam to be effective and adds about a half-knot if moving below hull speed with both sails hoisted. Most of the time, however, winds are from astern or forward where I operate.



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Old 09-08-2015, 12:57 PM   #11
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We have a steady sail but does very little for stability, but does reduce the sway hunting at anchor. I have seen a few long range coastal ocean trawler with forward deck sail like Marks for added range. Krogan use to and diesel duch still does. For our 40 ton boat fish para vanes are the best bang for the buck for stability.
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Old 09-08-2015, 01:06 PM   #12
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Most are so small , and weak they nhardly matter.

If serious long range cruising is being planned the Motor Sailor has come a long way from the 50/50 of the 1950s.
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Old 09-08-2015, 01:47 PM   #13
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Quote:
A limiting factor may be than many trawlers (but not all) do not have a keel designed for sails. Without ballast down low, sail area may have to be limited to the point where the effect is negligible. At least 30 square feet per ton of displacement is needed to be effective. Some of the Taiwanese trawlers have about half this, and this may have added to the myth that steadying sails don't help much
Great point, makes sense! Thanks!
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Old 09-08-2015, 02:50 PM   #14
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Originally Posted by AusCan View Post
At least 30 square feet per ton of displacement is needed to be effective.
.
Where did you locate that 30' requirement?



Fond this article kinda interesting.

"For a couple of decades I owned an older Willard Horizon motorsailer.
The Willard had a full keel displacement hull with gently rounded
chines, a high bow and a rounded stern. The design was similar to that
of small sail working boats of a century ago with all that that
implies. Power was supplied by a Perkins 4-107 driving an 18" x 14"
prop. It was easily driven below hull speeds and had good seakeeping
qualities but tended to roll in beam seas.

The boat carried 260 sq. ft. of sail on a low aspect rig, a large
foresail and a smaller main. This is only about half the sail that a
cruising sailboat of similar specifications would carry and the Willard
could be considered to be sailing under perpetually reefed conditions.

On a calm day and with a clean hull it required 22.6 hp. to drive
PUFFIN at its 7 kt. hull speed. This estimate was confirmed by careful
fuel consumption measurements kept over several years. The best speed I
had ever gotten under sail alone in a beam wind was 5 kts. It took
approximately 8.2 hp. to move the boat at this speed under power.
Sailboat designers estimate that sails can produce about 1 hp. for each
27 sq. ft. of area under good conditions. The 260 sq. ft. of sail on
the boat should generate about 9.6 hp. of propulsive effect. The 1.4
hp. difference between the 9.6 hp. generated and the 8.2 hp. required
to move the boat at a 5 kt. speed is undoubtedly due to the drag of the
large non-feathering prop. In essence, the prop drag costs 15% of the
generated sail power.

To make only 3 kts. in a get home sailing mode, the boat will
theoretically require approximately 1.8 hp. Allowing for prop drag the
sails will have to generate about 2 hp. Under good sailing conditions
this would require 54 sq. ft. of sail, about that of a small sailing
dinghy or Sunfish. Obviously this is for ideal conditions. To be on
the safe side, a minimal get home rig for the Willard would require at
least 100 sq. ft. of sail. And, since get home conditions are likely to
be in horrible weather, the mast and rigging should be strong and the
sail made in storm sail weight. A low aspect ratio 12' x 10' standing
lugsail would suffice.

Scaling this data up for a 45' LWL, 45,000 lb. displacement boat, 3 kt.
get home speed, allowing for prop drag, would require 2.75 directly
applied hp. under ideal conditions. This could be generated by about 75
sq. ft. of sail area. Using a safety factor of 2, the get home rig
should carry 150 sq. ft., about that of a small daysailer. This might
require a 20' mast and a 15' boom. As in the previous case, the rig
should be suitable for storm conditions. Low aspect ratio rigs, perhaps
a gaff, spritsail or lugsail would be best for carrying the maximum
amount of sail on an unballasted boat. This type of sail is more
efficient in beam and following winds anyway. Even a square sail would
do but these require more rigging and knowledge than most of us want to
burden ourselves with.

I would like to point out that either of these minimal get home rigs
will have very poor sailing performance by modern standards. They would
parallel those of ancient Greek and Egyptian vessels. Pointing ability
would be almost non existent. The boat could make progress only in beam
or following winds. That's exactly the way the ancient ships sailed.
They stayed at anchor or rowed until the wind was favorable. Still,
with patience, a boat could cross oceans with this type of rig.

Getting back to the main topic. Steadying sails are not for propulsion
and are effective in stopping roll in beam winds. I have found a reefed
mainsail minimizes roll when motoring in choppy conditions. For the
Willard that meant about 50 ft. of sail area. The sail is sheeted in
tight amidships and offers no propulsion power. The boat takes up a
slight angle of heel and and the roll is attenuated. It is far more
effective, of course, to actually sail using the full sail area. In
that case the roll disappears almost entirely. We did most of our
cruising along the Atlantic coast in a motorsailing mode, using both
power and sail whenever the wind was suitable. Fuel consumption dropped to low levels and the sails stabilized the boat.

Again scaling up to bigger boat size, a 75 to 100 sq. ft. sail would be
effective as a steadying sail. But, if you are going to rig a sail
anyway, why not go whole hog and make it a get home sail.

Finally, under the windy conditions in which get home and steadying
sails are used, there is a lot of stress on the mast and stays. The
rigging should be sized primarily for the stiffness of the boat not for
the sail area. While a 150 sq. ft. sail area daysailer may get by with
1/8" wire rope for mast stays, a trawler using the same sail might need
to upgrade the stays to 1/4". Most of the force on the sail is
translated to downward pressure on the mast and upward pull on the
windward stay. Typically trawlers are not constructed to resist deck
compression forces and the structure under the mast may have to be
reinforced or a compression post installed to transfer load to the
keel. Using sails as roll dampers is even harder on the rig than steady
sailing and the chainplates, the places where the mast side stays are
attached, must be firmly fixed to the hull structure and not just the
cabin sides. The ultimate disclaimer, of course, is to have your get
home or steadying rig designed by a good naval architect."


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Old 09-08-2015, 04:21 PM   #15
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Interesting article Jimbo.

The 30ft2/ton figure was from my own experiences.

A 105 ft2 jib alone does very little to reduce rolling on my 6.5 ton boat. (16 ft2/ton)
Under a reefed mainsail alone (23ft2/ton), although it stabilises rolling under strong winds, it is still a lot of motion with winds under 15-20 knots. Under full 200 ft2 gaff rigged mainsail (31ft2/ton) it becomes very comfortable. When I add the jib, it is a solid a rock.

Obviously, wind speed & direction comes into the equation as well. Smaller sail area becomes more effective when winds are blowing hard in the same direction as the swell.
My suggestion of 30ft2/ton was to cover most conditions including lighter winds.

I still get caught when I wait for a storm to pass, then head out the day after with little or no wind, but still rough mixed up seas. That's when I wish I had paravanes.
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Old 09-08-2015, 04:37 PM   #16
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It's always been my understanding that a true steadying sail is cut flat. Not that you can't make one that is cut for lift.

I wonder if one cut flat makes it any more effective as a pure steadying sail?
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Old 09-08-2015, 06:05 PM   #17
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What about wakes? In the rivers where we normally boat, it is difficult to avoid large semi-displacement or planing vessels and their large wakes.
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Old 09-08-2015, 06:22 PM   #18
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A steady sail will do little or nothing about wakes. Unless perhaps the wind is blowing strong and the boat is already pinned over very hard to one side.
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Old 09-08-2015, 06:59 PM   #19
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In Voyaging Under Power, Beebe's experience with a steadying sail had very little effect on reducing roll. Don't remember the percentage, but he said it wasn't worth the trouble IIRC.
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Old 09-08-2015, 09:02 PM   #20
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Quote:
Originally Posted by Capt.Bill11 View Post
It's always been my understanding that a true steadying sail is cut flat. Not that you can't make one that is cut for lift.

I wonder if one cut flat makes it any more effective as a pure steadying sail?
Doubt it, but a flat sail would be easier/cheaper to make.

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