Passage Planning for a 20 foot sailing boat

Lucky Duck

Lucky Duck

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I'm looking at two passages, one just over 40 miles and a longer journey which may need to be split up into similar distances - both more likely than not, given the prevailing winds, with the wind on the nose for the entire trip.

Its been a while since I had any experience of sailing this type of boat but I was working on a passage planning speed in the region of three or four knots (ignoring tide which if fair would be four or five knots I suppose)

Does this seem right or am I being overly cautious or optimistic?

Boat is typical 1970s design with masthead rig, fin keel and an outboard rather than a lightweight flyer.
 
Little Grebe said:
I'm looking at two passages, one just over 40 miles and a longer journey which may need to be split up into similar distances - both more likely than not, given the prevailing winds, with the wind on the nose for the entire trip.

Its been a while since I had any experience of sailing this type of boat but I was working on a passage planning speed in the region of three or four knots (ignoring tide which if fair would be four or five knots I suppose)

Does this seem right or am I being overly cautious or optimistic?

Boat is typical 1970s design with masthead rig, fin keel and an outboard rather than a lightweight flyer.
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Tell us where your going & I'm sure the experts will advise.;)
 
I would be expecting a speed through the water of about 4.5kn when close hauled, giving a VMG of no more than 2.5, so around 4 with a favourable tide. This might give you a ten-hour passage, but very much less if you can get a slant on the wind, or very much more if it gets bumpy.
 
My experience of passage planning with small boats is that its a waste of time until about 12 hours before departure when you have a better chance of an accurate forecast.

I tend to choose my destinations to suit the forecast .

Beating to windward in a 20 foot boat for 10 o 12 hours isn't my idea of fun.
If you look ahead a few days you may often find you can get a good slant on the wind in both directions .
 
I would agree with Graham, you really do need a good slant on the wind or you will not do 3kts. If you go with the prevailing wind and a fair tide you will probably have a lumpy, wind over tide, sea which will bring the boat up short.

If you could, it would be nice to wait for a beam wind and a strong tide. Otherwise 40 miles will make a very long day.
 
I don't think you'll average four knots in a regular 20 footer unless you have near perfect conditions. A small boat is more affected by sea state, harder to hold on a good course, and has a lower maximum speed than a larger boat (all things being otherwise equal). Also factor in a that a 40 mile trip in a twenty footer is far more tiring than the same thing in, say, a 30 footer.

I'm with the others who say wait for a more benign forecast. If you can't, allow much more time for the trip, both underway and resting.

Of course none of the above applies to an Anderson 22!;)
 
My Rowan is 22 feet and weighs 2 tons. Long keel too, but I can usually average about 4 knots. On a reach I can get over 6 knots. Done several 100 mile channel crossings and they usually average about 20 hours, so 5 knots or so. Everything's possible except last year with strong Easterlies it was just not possible to gain any ground, so Plan B was better! BTW, I do have a larger genoa than the boat's sail plan, which helps.
 
They are right , 40 miles in a 20 footer is 12 hours of graft.
Our first boat was a 22' 1980's Newbridge Venturer, & we use to plan on 12-16 miles a day depending on tide
 
My planning would be along the lines of 'how far can we get before the tide turns against us?'
If it can be split into 6 hour spells with favourable tide, that is a lot easier.
Or if you can get out of the tide in the bay for 6 hours or so.
Main thing is to know how the wind is going to change, being on the right side of the shift makes a huge difference, if it's a beat.
But you need to consider tide too.

I would want the bottom clean as well!
 
You might get 4 knots as an average speed through the water. Fine if your destination is not a beat.

If you have to beat, you will do well to get 2.5 knots VMG (less if bad leeway).

All things being equal, I would look to be off your departure port 1 - 1 1/2 hours before the tide turned in my favour and to be in about the same after it turns against you.

Whether your 40 miles is one leg therefore depends on tide lift and wind angle. 2 knots average lift for 6 hours plus 4 knots of boat speed gets you 36 miles. A couple of hours against the last / first of the foul tide and you're done in 8 hours.
If you're beating, it's almost certainly two legs. Even with 2 knots of tide lift you will do well to get 28 miles in one tide. Against the foul tide, you will make almost nothing.

Remember that if you split the journey, you don't need to go into a harbour for the foul tide. You could simply anchor somewhere sheltered for 4-5 hours to avoid the worst of the tide and then carry on again.
 
I'm sure I've missed something here, but how can such micro tide advice be given without knowing where the journey is to take place, or at least a few dets about the local tidal patterns :confused:
 
dom said:
I'm sure I've missed something here, but how can such micro tide advice be given without knowing where the journey is to take place, or at least a few dets about the local tidal patterns :confused:
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We are assuming (reading between the lines a bit!) a trip along the coast. Mostly that involves tides turning every 6 and a bit hours with a bit of local variation.
Obviously need to check the almanac, pilot and/or tide stream atlas to make it work.
 
dylanwinter said:
40 miles is a tough day in a 20 footer under almost any conditions

hope you have a tiller pilot, an outboard with a bit of poke and some ear defenders

D
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Did 56 miles in under 11 hours in a 19'er in fog, motoring with a 5hp outboard (sails up), but with the advantage of a double tide - out of the Thames with the ebb and down Channel with the flow. No tiller pilot, ear defenders - not necessary, GPS or pokey o/b just good compass, chart and eyes - buoy hopping!
 
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