Calculating aprox sailing speed for planning

[pcatterall]

I was looking for some rule of thumb guide so that if one knows the expected wind speed and direction it is possible to get a fair idea of what sailing speed to plan/aim for.
I know there are very many variables to take into account but many of the basic ones could be factored in.
I have found an interesting site where there is a usefull diagram but most of the craft featured were high performance jobs. Just wondered if there was something for plodders?

 

[Deleted member 36384]

I plan on 5kts for passages. The yacht is a Rival 41C. It appears to work out okay for most wind speeds from F3 upwards. Of course on the day its down to the wind and current.

 

[Spyro]

I plan on 5kts for passages. The yacht is a Rival 41C. It appears to work out okay for most wind speeds from F3 upwards. Of course on the day its down to the wind and current.

I do the same, if I get there quicker it's a bonus.

 

[skip50]

On a Sigma 362 I find 5.5 knots pretty close for planning purposes.

 

[pcatterall]

Yes, thanks guys. For ball park planning with my last yacht I was using 4 to 5 knots but I had thought that closer to the departure time and with a more certain forcast I could refine this a little.

 

[LittleSister]

A friend I used to sail with used to base his planning on an average speed of 4 knots. As his boat was on the heavy side and not particularly generously canvassed, it would take something like a force 4 to reach that speed. His rule was that if it was forecast 6 or more we didn't go out. And did I mention the boat wasn't particularly close winded? Hence we did an awful lot of motoring!

 

[doug748]

I plan on 5kts for passages. The yacht is a Rival 41C. It appears to work out okay for most wind speeds from F3 upwards. Of course on the day its down to the wind and current.

How refreshing.

I have read in the past of people who claim 7 kts and God knows what, in fact I think, for the average monohull, you would be near the mark.

Whenever I hammer along all day, with the speed never seeming to drop below 6 and 7kts plus, the average always turns out to be 5 ish.

One way to cheat the 5kt sticking point is to put the engine on as soon as the speed drops below 6kts. However most might prefer to sail in comfort at 4kts, rather than motor sail at 6+.

 

[westernman]

I usually plan on 4kts. Usually make 5kts in the end with the usual mixture of no wind, head winds and good sailing conditions. I hate putting the motor on - particularly at night - so will happily drift through the windless patches and cream along with the 400% genoa (not sure what the proper name for it is but it has more sail area than my 4 bedroomed house has floor area!) in the light stuff.

For tomorrow I am planning on less than 2kts. It is a head wind all the way for 45 miles so I am counting on 24 hours and have warned the catering department that it will be 36 hours.

And that is when there is wind. And the starter motor is broken - so no engine in the windless bits.

 

[Monique]

I plan for 5 Kts. Anything over this is a bonus.

Deep keel, tall rig with newish sails.

Beats the average most times and it pleases everyone

 

[puddock]

Storm 33, plan at 4.5 knots in lighter winds (and if motoring expected) and 5 knots in F4 + ...

 

[boguing]

'Tis down to setting parameters.

You're not racing, so you need to look at the weather and see what the probable window for semi-favourable wind is.

Once you've done that you know if the trip is in any way time critical from the weather point of view.

Then factor in how long you'd like it to take. Arrival time in the dark isn't comfortable, so speed up or slow down.

Height/rate of tide when you get there.

For example, you are leaving a drying mooring in Rye to sail to a locked and tide restricted harbour at Dinard. Tide gives you a number of windows. Forecasts another one. Lights are fine so no worries about entry.

As you work through it you'll come up with an 'engine on' least sailing speed. By hunch rather than calculation.

If I'm in Greece and we don't need shops, then it might be as low as half a Knot. Cross Channel to Alderney's tidal gates via tss zones it might be 5 Kts.

 

[Red Admiral]

Eric Hiscock

I believe it was Eric Hiscock who wrote that "every boat sails at an average speed through the water of 4 knots except to windward when the average speed drops to 2 knots". Granted, he had heavy boats not modern lightweight flyers, but I suspect his figures are closer to the truth than most yachties would like to admit. In my heavy tub I have seen over 9 knots on the gps but I was going (sideways) through Kyle Rhea at the time!

 

[jbweston]

Like many of the others above, I plan on 5 knots and everyone is pleased when that turns out to be beaten. I reckon I could use 6 knots but then there wouldn't be the same psychological bonus.

That's a Malo 37 sailed as a cruiser - ie for comfort (and time to enjoy the scenery and conversation) not speed. If the wind's on the quarter we go a lot faster, and except when the wind is very light, sailing is faster than motoring.

With average speed, a lot depends on how long and how varied the conditions you are averaging. Is it two hours on one point of sailing, or calm water motoring, or average over all weather on say a 24 hour passage.

Some modern boats seem to provide polar diagrams showing boat speed for various wind speeds and angles and sail configurations. I've got one but never use it.

 

[rob2]

I guess everyone's summed it up now. From experience you should be able to estimate your speed against the forecast wind but once out there it's more important to have a handle on any tidal gates or areas you don't want to be when the tide turns, so plotting your actual progress is more important. One instructor said to me he never heads a page in the log as "...on passage to..." but "...on passage toward..." as one often ends up in an alternate haven.

Rob.

 

[vyv_cox]

We log religiously every hour, no matter what or where. During the winter I put all the data into a spreadsheet and calculate all sorts of info, that mostly has no further use!

Times in the figures below are start to stop, before leaving port or anchorage, include slow going in anchorages on arrival, going to fuel berths, waiting for anything (e.g. locks on Canal du Midi, 2005), closing down and writing up the final log entry for the day. From 2004 to 2009, sailing six months of the year from Holland to the Aegean, we averaged 3.9, 3.5, 3.9, 4.4, 3.5 and 4.1 knots. Sadler 34, sailed as much as possible, motoring when sailing speed drops below about 3 knots.

 

[ChrisE]

I was looking for some rule of thumb guide so that if one knows the expected wind speed and direction it is possible to get a fair idea of what sailing speed to plan/aim for.
I know there are very many variables to take into account but many of the basic ones could be factored in.
I have found an interesting site where there is a usefull diagram but most of the craft featured were high performance jobs. Just wondered if there was something for plodders?

I think the answer must depend upon the type of sailor you are. By nature I get bored very quickly so it's engine on as soon as boat speed drops below 4 knots. Also I don't much like slow tacking to windward especially if going cross channel. So I plan on 6 knots and usually do better but then I'm probably using the engine more than most.