Minimum Wind Speed

[Don Guillette]

I was trawling other sites searching for an interesting topic and found the above. The question was "what is the minimum wind speed needed to sail a boat". That's too general a question -- for example, what point of sail and what size boat. So let's assume it's a Catalina 30 or a Hunter 30 or a Benny 30 and the point of sail is closehauled.

I've never heard this question before even though I've spent many morning hours drifting around Long Beach, Ca harbor waiting for the wind to pipe up. It probably should have occurred to me to figure out how much wind would be needed to get the boat moving.

I'll bet Stu J has never had this problem in San Fran but Joe from San Diego probably has!!

I'll bet RichH knows the corect wind speed and my guess is that about 3 knots would be needed to start to move the above 3 boats. I just made that up as I have no idea but I have to start somewhere, so what do you listers think?

 

[Stu Jackson]

I'll bet Stu J has never had this problem in San Fran but Joe from San Diego probably has!!

Don, in the summer, you're right. But in the winter, we have light or non-existent winds. As many of you may recall, we sail with an 85% jib and a single reef in our "April to September" mainsail setup.

During the winter months, however, I drop our 85% jib and replace it with our "working" jib, a 110%, and fully raise the main.

That said, no wind creates the basic question that Don asked.

Our trick? Our slip on Alameda Island offers two different ways out to The Bay. The 'standard" route is west out the Estuary. There is a little known other way that I call "The Back Door" which requires VHF calling and the opening of four drawbridges: Park Street, Fruitvale, High Street, and Bay Farm Island.

Interestingly enough, high water is required to motor out this way, and, it is almost exactly the same amount of time to go this back way to get to "sailable" water than the Estuary route.

High water thus means that the South bay is ebbing. Once clear of the limited dredged 8 foot deep channel between Alameda and Bay Farm Island, the water drops to 20 feet deep at the green daymark for the Bay Farm Island ferry terminal channel.

Even with no wind, the resulting ebb can be moving north at anywhere from 1 to 5 knots.

That water movement starts the boat moving and the sails can fill enough to get us moving.

Answer: zero knot wind!!!

Those of us who sail on tidal bodies of water can make great use of currents. Those of you on lakes, not so much. In that case, I think 3 knots would be required, almost regardless of boat size.

 

[Ted]

Don, are you referring to true or apparent wind speed? I will have real wind driven boat speed and control when there is 3 knots of true wind on a beat. Similar size boat to the ones you referenced. (C&C 29-2)

 

[Bill Roosa]

on my hunter 40.5 with "standard mainsail and 115% jib" it takes 4.5 knots of 'indicated" wind speed to move the boat. If we deploy the .75 oz spinnaker and main it drops to 2 knots. Does not seem to matter what POS we use BTW.
I say indicated as at that boat speed true and apparent are pretty much the same and as Stu noted the current is the dominant factor.

 

[RichH]

Hint: there's nothing you can do to increase the TRUE WIND. ;-)

 

[topcat0399]

Is apparent wind even possible with out a true wind?

 

[Don Guillette]

Ted; True wind -- I want to know the speed of the wind to get these boats moving.

 

[Bill Roosa]

I'd disagree Rich. I find praying to work satisfactorily. I have more issues with decreasing the true with though

On a related topic;
if you measure boat speed as a % of true wind speed what is the fastest you have ever sailed?
I managed 1 knot boat speed over ground (no current) in 2 knots of true wind or 50%

 

[Stu Jackson]

Is apparent wind even possible with out a true wind?

WADR, please read my first post.

The answer is YES, but only with current. Think about it...

 

[shemandr]

For the Hunter 356, I used to consider 7 its. true sailable. Not that you couldn't sail in less but 7 kts. felt like sailing.

 

[soldier1964]

just putting

I have sailed my Helms 25 in as little as a 3kt wind. You won't break any speed records or anything like that, but it is relaxing none the less. Everything moves at a much slower pace.

 

[dlandersson]

Re: just putting

I tend to agree - at 2-3 knots I can get moving and at 5+ I can move right along.

 

[RichH]

Is apparent wind even possible with out a true wind?

almost YES !!!! and even with NO current! ... see following post ;-)

 

[RichH]

I'd disagree Rich. I find praying to work satisfactorily. I have more issues with decreasing the true with though

On a related topic;
if you measure boat speed as a % of true wind speed what is the fastest you have ever sailed?
I managed 1 knot boat speed over ground (no current) in 2 knots of true wind or 50%

It is extremely rare for the wind to be absolute ZERO velocity. Usually even with totally flat water there will be 'wind'. The process is to get the boat moving (and in any direction), which then builds apparent wind, which builds speed, which in turn builds apparent wind, up to a maximum of the energy available .. and then once the apparent wind is 'built up' to the maximum for the present condition ... then sail in the intended direction (except for dead downwind).
Sailplanes are a prime example of this effect of forward motion generating apparent wind; and in 'zero' wind, once initiated into forward motion (by towplane) can 'sail' at extraordinary glide slopes (30:1 or greater) ... as long as they 'keep moving'. ;-)

In lightweight boats or boats that are 'very easily driven', one can 'aid' the 'starting process' by artificially healing the boat and then 'by flapping' the mainsail in & out, etc. 'to get started'; once 'started' with forward boat motion the apparent wind will increase due to the forward motion of the boat ... and increase up to the limit of the max. energy provided, etc. ... the sailor then reshaping the sails (amount of draft) as needed to keep the changing velocity of air flow 'attached'. Thats how the top Wednesday Night Beer Can racers (the 'masters' of sail shaping) 'practice/practice/practice' for sailing in near ZERO wind conditions. No matter how 'light' the wind above ZERO, you 'can' create apparent wind. Of course, the camber/draft of sails in such conditions are initially set nearly 'dead flat as a sheet of plywood' in 'draft' until moving and as the boat progresses to max. forward speed is the camber/draft adjusted to be maximized with the maximum forward speed and the energy transfer happening on the sails.

The answer to the 'related topic' ... as an example: there have been novel (quite scientific) trials of making a boat go faster dead downwind than the true wind speed by using a passive 'rotating fan with blades' connected to a propeller for propulsion (no energy input other than the wind) ... which depends on the 'pumpkin seed effect' ... squeezing a slippery seed between thumb and finger and creating massive speed on the seed as its 'shoots' at almost 90 degrees to the pressure applied (trigonometry - dividing by the SINE of the angle of intercept ... AWA ... to the blades of the fan). In such trials even in near zero wind speeds, the boat is first given forward motion to get the 'fan' and boat started, which converts fan speed to boat speed and which increases apparent wind, etc. etc. etc. Very 'novel' and produces downwind speed that are 'faster' than true wind speed. Some discussions on the pumpkin seed effect w/r sailing DDW, etc. faster than the true wind speed: http://www.ybw.com/forums/archive/index.php/t-251615.html


Epilogue: I really didnt want to get into this discussion for some time as its better for folks to 'discover' the elemental truth on their own. This topic really boils down to 'the precise sail trim and sail shape' (and perhaps a few 'hints' of how to get to this level) ... and thats what this forum is all about !!!!!
For starters, get Don's 'guides' and work your way up from there as if youre not in near-perfect trim to begin with, you simply wont 'move' very well. A boat that is 'moving' is what creates the 'apparent wind'. In super-light winds, either you MAKE your own apparent wind!!!!! .... or you turn on the engine.

 

[Calif. Ted]

3 knots is about my tolerance level, both my 270 with a 155 and my 320 with a 110 would/will make between 1 and 1.5 kts. close hauled to slightly abaft the beam (true). You can keep the boat moving thru the water at lesser airs but you are going backwards against the .5 to 1.5 kt downcoast current. Sometimes you can go so slow that the knotmeter stops turning and you only know you are moving because you are still passing plastic bags and stuff floating on the surface and a slight ripple off the hull.
The assy. will want to start to collapse below 3.5 when carried deep DW, but you can carry it on the beam and above down to 2.5 even to the point of using it like a drifter.
I'm not superstitious but I've been caught "scratchin' a backstay for a bit of breeze".
BTW the 320 has a 110 instead of the 135 standard for these boats because it came out of San Francisco.

 

[Don Guillette]

RichH: When I discovered this topic I knew that you would have the answer!! Thank you for waiting with your reply because many times when you, Stu J, Scott, Alan, Joe from San Diego and a few others (including myself) hit the topic early it just dies as the newbies don't try to "discover" and think thru the explanation. If they think the subject through on their own they'll better remember and learn something new about sail trim.

 

[RichH]

Thanks Don.
A related question that applies to ultra-light wind sailing and to further the discussion: .... BIG jib or SMALL jib? ... and why? ;-)

 

[Bill Roosa]

I would concur Rich.
when the true wind speed is less than the boat speed I find pointing to be pretty difficult. If I start on a broad reach and build up speed then slowly turn the boat into the wind while adjusting sail trim to keep her going i have found that you really can make your own wind. At least enough to cool off the crew.

 

[Gudenuph]

Is apparent wind even possible with out a true wind?

Yes. For an 'apparent wind' all you need is boat speed/wind and since the wind vectors are added, not multiplied, any one of them can be zero.

Geohan

 

[Stu Jackson]

almost YES !!!! and even with NO current! ... see following post ;-)

Don was right in his OP! I don't know how to sail with no wind with NO current. Rich explains how and why it can be done. Darned SF winds and currents! :dance: