Question for Hitech navigators.

Re: Question for any navigator with commonsense

I’m not a Solent local so have never done this passage but it looks like following the compass course will give you an advantage of about 4NM over following the rhumb line over the course of 12 hours (using a 12NM set E and W for the flood and the ebb respectively – although isn’t the tide stronger on the French side?).

If you follow the rhumb line you’ll make a good bit towards Cherbourg on the ebb with it’s strong W set but you’ll more than lose it by having to punch the tide on the flood.

For a mobo the important thing is whether they can get over in the 6 hours of a single tide. If they can then I’d have thought they would always leave on HW and follow the rhumb line. The saving will depend on their actual SOG but could amount to 8-10NM for a boat taking the full 6 hours to cross compared to a worse case departure on LW.
 
Re: do they have bears in the CI?

I think it was meant to read beer.So you will be fine /forums/images/graemlins/grin.gif
 
Re: Question for any navigator with commonsense

[ QUOTE ]
OK... if you end up off track, then yes you could, but then you wouldn't be following the GPS rhumb line

[/ QUOTE ]If the current's strong enough and the boat's slow enough then, even following the rumb line, you can get to the point where you are pointing straight into the flow - but moving backwards!

This is the point at which you just can't follow the rumb line anymore! /forums/images/graemlins/smile.gif
 
Its going to take about 14 to 16 hours including motoring out and sailing inside the harbour entrance.Set your calcs off West Princessaand plot the rumbline course. List then add up all the westabouts and all the eastabouts to calc an aiming point between the harbour entrances.

If you have GPS keep an eye on the crosstrack error and plot that against what you calcd would be the crosstrack error each hour. Get three hours into it before you do any course corrections and hold the aiming point between the entrances. When you get a few miles off see which way the tide's going and the winds and decide which one you want. Don't try and stay on the rhumb line you'll normally add lots of extra miles heading against the tide one way and then heading against it the other.

with a five knot passage you'll probably add at least 11 miles to the passage. Don't do it. Use the sea don't fight it.
 
Well, I certainly agree with that statement. It's been an interesting post on a gloomy wet day (with thoughts for the West Mersea Lifeboat crew who were called by the Maroons at about 3.30pm this afternoon). You are also right that if the cross track error is kept at 0, that it doesn't matter when you start or finish. It would be a considerable challenge to stay on the Rhumb Line though monitoring all that XTE all the time. I think I would rather do it properly. The Channel East book gives the advantages as i. the vessel holds its track throughout (don't see much advantage there on this particular passage), EP's are more readily obtained and give greater visual comfort on the chart (umm - pre GPS comment that I think - not sure a 'comforting EP' is the real object). Disadvantages are stated as i. Chartwork increased (not if you are using the GPS of course), ii. Sailing time is increased and the slower the speed of the craft, the greater will this increase, iii. Unless the wind is near to or abaft the beam, a sailing vessel may not be able to lay all the sundry courses demanded by this system.
 
You must log in or register to reply here.

Share this page

Top