Overpowered

[southchinasea]

Probably a silly question. I read a lot about yachts being overpowered under certain conditions. Sailing to weather even I can work out when I run out of
helm or the rial is in the water etc. I need to do something. What about running downwind.....What are the signs I am 'overpowered'. Please don't say a broach.
Thanks

 

[ccscott49]

When the flesh on your face is dragged backwards by the G force!

 

[southchinasea]

Ha ha!

 

[billskip]

Cant beat that reply cc .. cant type for laughing....somtimes I find the seagulls cant keep up though..

 

[tonyleigh]

Depends on so many factors. Simplest "guide" is when you feel "apprehension" in any particular scenario. Eg: I usually singlehand and my rig is very comfortable running goosewinged with main by the lee and genoa boomed. If I feel conditions will make struggling to drop the pole even in the shelter of a gybed main a twee problematical I start to take reducing action. With a crew I would delay action no doubt a little longer. Obviously, reaching one has more latitude but the basic "guide" applies and I implement a series of sail reductions etc to keep one step ahead (hopefully!!!) of being caught out. Of course there is no point in carrying more sail than achieves best speed but I am sure others will cover this in a much more scientific answer than I could. Much more difficult to identify "flashing warning lights" although an earlier boat used to signal quite clearly through the rudder that things were getting slippery. With a 3/4 rig I guess I would act earlier as it is (?) less easy to get that comfy balance that masthead rig allows and being precipitated into a broach far more likely. It's actually a very interesting question - thanks.

 

[Twister_Ken]

Depends to a large extent on the boat's underwater shape. The old leadmine types (like mine) will just dig a bigger hole in the water if you pump in too much power. Conversely, lighter boats with flatter runs and broad aft sections will pop up onto a plane, speed will jump, sometimes into double figures, and if more or less downwind, this actually reduces the apparent wind strength.

On a real displacement boat, the size of the quarter wave is not a bad indicator. Once it's humping up to rail level that's about as much speed as you're going to get out of her. Of course, whether you actually want to go this fast is another question. Comfort, comfort of mind, and longevity of sails and rigging also come into the equation. So does the ease with which you can reduce sail further if the wind increases.

 

[Mirelle]

Much more difficult downhill than up. I am regularly caught out by this one. When the boom drags in the water I have definitely overcooked it! I would suggest when the helm starts to get squirrelly on the back of a wave. This is just when steering downhill becomes fun, so the temptation to carry on is very great.

 

[jamesjermain]

When there is a bit of a sea running, it can be great run to surf at nine or ten knots down the face of a wave, but the lightness in the helm and the sudden stop at the bottom of the wave should be telling you that you are approaching the limit of control. Carry on by all means with a strong crew and good helm but otherwize take in a tuck and pull in a roll.

A much more telling line of thought, though is this. What would happen if you broached, and how will you reef the main? Remember that many reefing systems, including in-mast, are diffiult or impossible to use while running and require a short, but sharp, moment or two with the wind forward of the beam.

You may be running at six knots with a gentle apparent wind of 12 knots. But when and if you round up (by force in a broach, by choice to reef the main), you will find that the real wind speed is 18 knots. To this will be added three to four knots of boat speed and suddenly you move from a gentle Force 4 to a raging 5 to 6.

Reduce sail downwind therefore, in such a way that, if you have to come on the wind in a hurry, you will still be in control.


JJ

 

[claymore]

Comfort

Ken refers to comfort and this has to be key - once your boat has reached hull speed it isn't going to go any faster and so the surplus loads created are going to have to be absorbed by the rig and the crew - uncomfortable.

 

[Miker]

Hull speed?

How does one calculate hull speed?

 

[Stemar]

Re: Hull speed?

Multiply the square root of the waterline length by a constant that varies a bit according to the shape of your hull, but is typically 1.34.

For example, a 25ft w/l boat will have a hull speed of 5x1.34 = 6.7 knots

 

[billskip]

Re: Hull speed?

wots a ..constant that varies a bit.?????

 

[Stemar]

Re: wots a ..constant that varies a bit.?????

It's a constant for a given shape of hull - alternatively it might be the opposite of a variable that never changes. You choose!

 

[boatone]

Re: Hull speed?

a variable constant.....?

TonyR
boatone@boatsontheweb.com

 

[BarryD]

Note: Variables won\'t constants arn\'t. NM

<BG>

 

[billskip]

Re: Note: Variables won\'t constants arn\'t. NM

Are thy used any where else?? variable constants that is..or is it constant variables...???

 

[BarryD]

See also..

Dynamic Stability
Military Intelligence
Civil Engineer

I could go on but I think that is enough <G>

 

[billskip]

Nice flag

You forgot abouy the political lot...

 

[BarryD]

Good point, well made. NM

NM

 

[Miker]

Re: Hull speed?

Must be quite a variable constant as my boat, LWL 7.35 metres, touched 10 kts on a broad reach, admittedly with, I suspect, a tad generous log calibration setting.