The dangers of surfing

[themount2]

I've read much about fast downwind sailing but never really had the dangers of exceeding hull speed explained although I think I have gathered it leads to veering off course and possible broaching.
Scuttling back from Yarmouth to Gosport yesterday running/broad reaching with full genoa I realised that while the conditions were not THAT bad, they were of the type that causes this problem that I do not yet understand, if you see what I mean.
What actually happens? Is it the rudder is too small to have sufficient effect at higher speeds and gets overpowered by the speed thereby leading to loss of helm control OR is it the higher forces against the rudder at the higher speeds cause excessive direction changes above those normally expected for the rudder size OR is it something else?
Cheers
Brian

<hr width=100% size=1>

 

[Twister_Ken]

Broaching in those conditions is usually caused by heel, which levers the rudder partially out of the water, leading to loss of effective steering area. The result is that the now asymmetric underwater shape of the boat then takes over and steers you to windward, which overpowers the sails, flattening the boat even further, and causing the rounding-up to continue to the point where the sails are too close to the wind, at which point the boat staggers back upright, shakes herself, and says "oops".

The heel, in the first place, is usually caused by rolling induced by a big quartering sea. One extra aspect is that the rolling changes the dynamics of airflow over the sails, increasing the apparent windspeed as she rolls up to windward, decreasing it as she rolls to leeward. This can make the roll self-sustaining and self-amplyfying. You can mitigate this to a degree by not steering the boat in a straight line, but by steering her to stay under the rig - as she rolls to leeward you steer to leeward, and vice versa. Great fun.

Of course, the sensible thing to do is to drop the main and sail under genny alone which also reduces the dangers involved in any involuntary ybe.

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>

 

[snowleopard]

the other risk with surfing, especially in a lightweight boat, is of overtaking the wave in front as you charge downhill. this causes the bow to dig in and the boat to decelerate rapidly. in extreme cases it can cause a pitchpole.

multis rarely broach because of directional stability but the dig-in has happened to me a few times. once it brought green water right back over the wheelhouse which was a bit scary. we were doing 16knots and reduced to 5 in a couple of seconds!

when running you tend not to notice an increase in wind strength so you keep the rag up longer than you would if pounding into it. in our case it had gone up from 25 to 35 knots and all we noticed was that we were going a bit faster. moral: reef early.

<hr width=100% size=1>

 

[Mirelle]

Just to add a little more - rudder effect is rapidly diminished, to zero in fact, if the crest of the sea overtaking you starts to break under the boat - because the water is travelling at the same speed, or even faster than, the boat.

When this happens you no longer have steering at all. You can feel this starting to happen when the helm goes light and feels "dead" on the crest of each wave.

There is also a possibility that the rudder may be operating in aerated water, which reduces its effectiveness, but certainly as Ken says the changes in the position of the CB as the waves pass under the boat are the most important thing.

The current "Classic Boat" in an article on Beken reproduces the 1995 picture of a Class One offshore racer heading rapidly for the bottom of the Solent having just dug her bows into the back of a wave.

<hr width=100% size=1>

 

[Oldhand]

My last yacht surfed very easily and I never found it dangerous. She had a very powerful rudder, moderate displacement and very easily driven hull. All that was required was helmsman concentration to obtain speeds up to 17.4kts without any drama.

<hr width=100% size=1>

 

[tcm]

In the same sea as the orig poster, up the solent, we goosewinged up at towars 10 knots thru sea, 12.6 sog. the tirck is to neuralize/centre steering before each wave, so that a kick can be made thru the crest. In flat water, goosewinging, the doginess come partly from lack of steerage (running 17 knots relative to 30 knots wind, and with tide losing more steerage) but mainly as each sail needs to spill wind (boat @10 knots, wind at 25+) then if more than 5ish degrees off dead run, one sail spils the lot, other sail drives and broaches. But ones at near nintey degrees, steerage returns and it all starts again.

<hr width=100% size=1>

 

[Miles]

Not really so dangerous thiugh it can be scary. We did it on exactly this route last year The wind was touching gale force and more as it funneled through the gap between Beaulieu and Gurnard. With genoa only we tocuhed 14.4 knot and broached when a particularly nasty gust hit us. You can see the pictures at www.veramara.com and click on F8, be there. Sure there was violent and noisy flogging of the genoa for a while as we rounded into the wind but the angle in the pictures between backstay and horizon is not that great. I'd be more worried about having too much sail up and less so about suddenly finding ourselves surfing.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Miles on 09/06/2003 22:15 (server time).</FONT></P>

 

[Maxidom]

Some very good and informed comment - I too was returning from Yarmouth in the same conditions that day. Maximum windpeed 35kts and fun. I agree with all that has been said but for me the most important thing is keeping the boat under the rig and tarcking straight and as level as possible, then working the waves to induce faster surfing. Fun
DO'M

<hr width=100% size=1>

 

[Roberto]

What about this?

http://utenti.lycos.it/Timonieri/HTMLobj-189/aniGif.gif

<hr width=100% size=1>

 

[jamesjermain]

Caution

Lots of wize words here from skippers/helms with experience and probably strong crews. But before you go out and try surfing at 17 knots in your Westerly Centaur, I would like to emphasise a couple of points only hinted at here.

1) Surfing at speed requires concentration and experienced helming because when things go wrong the consequences can be serious. Its quite true that surfing at speed is quite safe as long as the boat is held on course and steered to the waves and wind shifts. But you are on a knife edge and a rogue wave, moment's loss of concentration, other traffic or fixed obstructions (land!) can force a change of course.

2) When running fast in a rising wind you should always be aware of the true wind speed. Remember: apparent wind speed 10 knots, boat speed 8 knots = true wind 18 knots. Also, if you suddenly have to turn head to wind, true wind 18 knots plus new boat speed 5 knots = apparent wind 23 knots - over twice the original apparent. Most cruising skippers like to carry no more sail down wind than they would be comfortable with on a close reach

3) When you eventually decide you have to reef, you will almost certainly have to come on to a close reach at least. Few boats can reef the main on a run, although you can usually roll the genny to reduce area as you round up.

4) Practice and enjoy

<hr width=100% size=1>JJ

 

[Stingo]

Re: What about this?

(courtesy of Roberto)

<hr width=100% size=1><A target="_blank" HREF=http://www.stingo.co.uk>http://www.stingo.co.uk</A> <font color=blue>- still showing at a computer near you</font color=blue>

 

[jimi]

Re: Caution

Also ... apart from any danger to the rig the real main danger of a broach is when it happens in large seas ... when the dangers of a boat almost flat in the water beam on to a large breaking wave with no steerage way is obvious.

<hr width=100% size=1>

 

[nicho]

Re: Caution

Your second point came home to me when, as a relative newbie to sailing I was recently running from Cowes towards Gilkicker in front of an F6 with only the (full) genoa up. With a largish commercial vessel coming up the channel I decided to turn 90 degrees towards Osborne Bay, and proceeded to winch the genny in. Suddenly we were hit by the full force of the wind just forward of the beam, and the result was (to us at least!!) unexpected and rather alarming. The boat heeled and took off at a rate of knots, the wind strength taking me completely by surprise. I realised that I had the ST60 wind display set on "apparant", and running downwind, I did not appreciate how much wind had got up!!

I will in future ensure I get rid of some sail before making such a manoeuvre again. God there's so much to learn!!

<hr width=100% size=1>

 

[snowleopard]

there\'s so much to learn!

too right, i leaned to sail in 1958 and i've still got a lot to learn.

but it's fun to learn as long as you set about it sensibly. it's the 'captain calamitys' who don't know enough to be afraid who are the biggest dangers to themselves.

<hr width=100% size=1>

 

[wpsalm]

Re: there\'s so much to learn!

its modern boats in general with their light weight flimsy construction fin keels and spad rudders course there dangerous but guess thats part of the fun..

<hr width=100% size=1>

 

[Close hauled]

Re: there\'s so much to learn!

OK - this has got nothing to do with cruising yachts but all to do with surfing! I (mis)spent my boyhood surfing in Cornwall. It gave me valuable lessons. Later I raced a Dart 18 cat out of Pentewan in S Cornwall. In the right breeze you get a decent surf on the beach. We could get over 20 knots and with the cat surfing could jump the wave in front and catch the next one. Getting on to the beach was not in an RYA approved style - nice fast reach, weight back and straight up the sand. Extra points were gained if you stepped off on DRY sand.

I get a kick out of getting a yacht to surf but you are on the edge of the envelope and need to keep sharp.

<hr width=100% size=1>

 

[vyv_cox]

Great fun but not great for the racing!

Running cats straight up the beach is fine for a well-used cat but not for one that is expected to give of its best in racing. Sand can take the gelcoat off in a couple of beachings. My last few cats, Hobie 16, Dart 18, Prindle 18-2, never touched the ground without some sort of fender beneath them.

I fully agree about the surfing experience. Stood me in very good stead when cat racing and I almost always reckoned to gain a few places on the downwind legs if there were waves. There's a limit, though, and using these techniques racing off Stonehaven led to some very spectacular pitchpoles.

<hr width=100% size=1>

 

[Close hauled]

Re: Great fun but not great for the racing!

True enough but when there was big surf there was no other option - trying to get them onto a trolley usually ended up in tears and broken boats.

Mind you my Dart was ancient but very quick - my problem was I usually went quick the wrong way!

<hr width=100% size=1>