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Old 05-06-2011, 04:45 AM   #1
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Steadying Sail vs. Get Home Sail

Steadying Sail vs. Get Home Sail
<hr size="1" />.Lifted , from another board, food for thought

..just found this thoughtful anaylsis on another forum...thought it could be appropriate to some of these discussions...brian



Unlike most of the scholastic arguments on the TWL, I have some
practical data on this one.

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.

Riding sails are useful for high bowed or forward pilothouse trawlers
that sheer back and forth at anchor. These are small sails mounted at
the stern of the boat that serve as feathers on an arrow, keeping the
bow pointed toward the wind. A small 20 or 30 sq. ft. sail will usually
suffice. Recent research at MIT shows that a small riding sail will
substantially reduce anchor loads by minimizing sheering.

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.

Larry Z

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Old 05-06-2011, 07:21 AM   #2
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RE: Steadying Sail vs. Get Home Sail

Thanks Fred.
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Old 05-06-2011, 07:24 AM   #3
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RE: Steadying Sail vs. Get Home Sail

I feel pretty much the same as Old Stone...I doubt my mast/boom will handle the loading of a sail.
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Old 05-06-2011, 08:23 AM   #4
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RE: Steadying Sail vs. Get Home Sail

We have a stead sail 17 ft by 14 ft or 196 square ft that we did try to sail with.* Long Newbie story.* The 58 ft did come with a forward mast, our was removed, but I know where the mast step and stays were.* I found very little effect when under way, in fact more of a negative than a positive, so I would use it only for anchoring to reduce the swing.
*
There is a 58 ft RW, Dorothy June, that larger mast and sails where added to increase the range and maybe a get home.* Just last week I talk to a rigger who was re rigging a sail boat behind us about increasing the stays of the mast in preparation of fish stabilizers and we did talk about adding sails.* The concern is the 58 was not built to hold full sails, and does not have the ballast.* The Dorothy June used the fish stabilizer with full sails up, so if bigger sails where going to be added, fish stabilizers would be required at a cost of about $30,000.00.*
*
So I will not be adding sails but instead use the 30,000 to improve the get home methods already in place on the Eagle as it does have a get home using the Gen set to power the prop, and/or the forward thrust of our bow thruster.* However, the gen set motor needs to be twice the HP.* ***
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Old 05-06-2011, 10:15 AM   #5
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RE: Steadying Sail vs. Get Home Sail

this might qualify as a "get home" rig:

*
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Old 05-06-2011, 01:45 PM   #6
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Steadying Sail vs. Get Home Sail

Hey guys,

Right now there's a video on big ships using parasails at sea as a fuel saving device.

Mark,

I suspect you could sail very slowly a little to left or right but no other heading.


-- Edited by nomadwilly on Friday 6th of May 2011 01:48:32 PM
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Old 05-06-2011, 06:10 PM   #7
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RE: Steadying Sail vs. Get Home Sail

Quote:
nomadwilly wrote:
Hey guys,

Right now there's a video on big ships using parasails at sea as a fuel saving device.

Mark,

I suspect you could sail very slowly a little to left or right but no other heading.



-- Edited by nomadwilly on Friday 6th of May 2011 01:48:32 PM
*Back in the '80's or '90's an offshore oil platform was moved down the BC coast and beyond while assisted by a sail rig. Apparently it gave them huge savings on fuel. Unfortunately, as far as I can tell no info or especially photos exist online.
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Old 05-07-2011, 01:06 AM   #8
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RE: Steadying Sail vs. Get Home Sail

Guys,
Presently I am looking at a 28" parachute as an emergency propulsion unit for dire emergency if I am well off the coast and away from home with drastic engine failure.
It looks like you can sail with the breeze any where from the aft 30 to 40 deg either side.
In these situations one would not be too fussy which way one would go.
The parachute pulls the boat and does not push it.
www.sailinginbrunei.com
These guys have been using it a while .
Once the new engine is in and I get a chance I will set it up and see if I can get any movement.
*
Benn
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Old 05-07-2011, 09:04 AM   #9
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RE: Steadying Sail vs. Get Home Sail

Did you notice that in last week's Economist there is an article about how some superyachts are becoming "green"?* Included is a picture of a large yacht being pulled by a sail held several hundred feet away from the vessel.* Somehow I feel the motivation is guilt rather than economy considering the financial resources of the owners.
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Old 05-07-2011, 12:01 PM   #10
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RE: Steadying Sail vs. Get Home Sail

"green"?

Yes 2, 85W solar panels and your dual GE turbine toy is indeed green at 250GPH cruise!
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Old 09-08-2013, 07:01 AM   #11
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Reviving an old thread.

I don't even know how to phrase these question but I will try: how are these get home sails attached on the mast, how are they operated, with furlers, how to reef and so on....
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Old 09-08-2013, 07:08 AM   #12
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Befoe you gt too serious...most are probably "get to land from the open sea" sails..not reall get "home" sails.

I doubt most trawlers could sail well enough in any specific direction...but making landfall from an engine failure would be possible.

There are hundreds of possibilities depending on the size of the size of the rig and whether you just want it to assist in mild conditions and/or make it steady in up to storm conditions. Your particular desires would determine the size, engineering and options the rig would be/have.
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Old 09-08-2013, 09:22 AM   #13
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Ignore this one. I started to comment, and then realized that my comment was out of line. Sorry.
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Old 09-08-2013, 10:06 AM   #14
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Quote:
Originally Posted by jwnall View Post
*I doubt most trawlers could sail well enough in any specific direction...but making landfall from an engine failure would be possible.

*Um, I suppose that anything is possible, if the wind and currents cooperate. The relatively small amount of sail area, plus the lack of a keel (at least on my trawler anyway) makes it pretty iffy, though. Just mulling the question over, running a forestay from the top of the mast down to a bow cleat and rigging up a makeshift jib might help.
.

Not really out of line...I can see where some people might think that...but it's true of why sailboats have engines...sailing to a specific destination while all but in a few cases is possible/probable...an engine puts it into the realm of realistic cruising....at least one with some sort of schedule With a meager sail and the right direction even a trawler without a keel can sail downing/broad reach possibly against a decent current also.

As I posted...you can rig a thousand ways...with a difter sail or cruising spinnaker...you don't even need a forestay...especially without a keel as the chances of going to windward are slim.
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Old 09-08-2013, 10:40 AM   #15
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A steadying sail does not have the area to move the boat. Usually the are at the back of the boat to be sort of a weather vane when at anchor and to dampen the roll when under way. Some leave the sail up all most of the time and tied down straight in line with the boat. So once its up there is no messing changing it. The Eagle has one mainly for at anchor too reduce the swing.

True story.

When we bought the Eagle we where green wantabe newbies. We found the sail so we decided to go sailing. We tried for several frustrating hours. Finely a Seattle police boat came out to inquire what the heck we where trying to do. We told them, trying to learn how to sail. Anyway with grins they explain to us what the small area sail was for.
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Old 09-08-2013, 11:00 AM   #16
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Arhhh matey! I've got visions of a junk rig or Viking sail billowing in my mind

Something small enough to not topple a modestly back stayed trawler "mast" yet big enough to run down wind after losing the main engine, or to give an extra boost when winds are strong enough from astern. Might be a viable option with the long wind funnelling channels on BC's north coast.
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Old 09-08-2013, 11:15 AM   #17
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Several trawler offer sails as an option which I thought would be come popular by now or a modified trawler motor sailor. Nordhavn is the only one I know of. Krogan did and of couse the Duck. I looked at adding sails to the Eagle but 20+ grand buys a lot of fuel. If added it would be to increase the range and get home to cross an ocean.
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Old 09-08-2013, 02:12 PM   #18
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Very informative, nice write up. I have been curious about stabilizing options, a steadying sail was a consideration. I don't believe my Willard has the structural reinforcement to mount a functioning mast, as it sits on the cabin roof. I am resigned to a "decorative" mast so I can use the boom for pulling my shrimp pots and to hang my rain cover over the cockpit. My current mast is wood, irregularly shaped, and made out of four pieces "boxed" together, which required sanding the "box" to a sail mast shape for about 18" to attach the radar mount.
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Old 09-08-2013, 02:58 PM   #19
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Most trawlers don't have a tall enough mast to set up a decent sailing rig.
Retro-fitting is doable but expensive. Benn's Tidapah should be a beaut when it's finished.

As a very rough calculation, the equivalent horsepower of sails, IF set up properly, produce about 0.05 horsepower per square foot of sail in a 20knot breeze.

The mast on my 30ft motorsailer is the size of what the average 24 foot sailboat would have. With 205 square foot gaff rigged main sail and a 95 square foot jib sail, it is easily singlehanded, but is like sailing with a permanent reef in the sail. I do have another reef point but have yet to use it. (It may be needed in 40+kts of wind)

With a self tacking club footed jib, the sails do their own thing, with very little sail trimming required. Kokanee sails at about 5 knots with a 20knot breeze when heading downwind or with the wind on the beam.
It will only just very slowly work its way into the wind without engine power assistance, but it is do-able with 20kts+ of wind, if required.

The biggest plus of the sails is definitely for roll reduction. I have the sails raised whenever there is a 10+ knot wind unless heading directly into the wind just to smooth out any rolling action. A bit of fuel savings and extra speed is a bonus.

The only time I have ever needed them to "get home" (due to a failed starter motor), there wasn't a breath of wind.
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Old 09-08-2013, 03:07 PM   #20
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George Buehler's article on "backup sailing rigs" for trawlers;

Sails
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