GPS backup and waypoints

My first GPS for was the very basic Geko 101 below. Since getting Little Grace I obtained the Garmin Map 76cx and the Geko was demoted to backup.

Garmin Geko 101

Garmin Map 76cx

 



However, I did not get round to entering the waypoints we amassed during one (2010) and a half (2012) seasons of sailing. This has left the daunting task of manually entering 92 waypoints into the Geko. Apart from being time consuming there is the concern that one wrong digit could get us up close and personal with the hard stuff. As we will now have an infant on board for one of the two of us to look after a backup GPS to verify where we are in relation to the same waypoints marked on the paper charts and pilotage in the real world is a welcome tick in the box of measures taken for getting us all home safely.

 

Enter the Etrex 10, it is relatively cheap but basic unit. Maps can't be loaded but that is where I started with the Geko and many boats have basic units to use alongside paper charts as their only GPS, so no problem there. The Etrex 10 does have the advantage that way points, routes and tracks can be uploaded from the computer.

 

I contacted Garmin help to check the Etrex 10's compatibility with Mapsource, the computer program I use to plot waypoints and plan routes to upload to the Garmin 76. I was told that the Etrex 10 was not compatible with Mapsource but I could upload routes and waypoints from Mapsource to the 76, download them into Garmin's free basic map program, Basecamp, then upload them to the Etrex 10. Apparently this process could be reversed but that is of no interest to me.

 

 

I tried it and it worked but if a waypoint occurred in more than one route it was listed the corresponding number of times in the waypoints list. I contacted Garmin again and was told I could get round the problem with another Garmin program, Homeport. For €29 this would interface with both the 76 and the Etrex. I was about to pay the €s when it occurred to me to check that the Etrex 10 is not compatible with Mapsource myself. It turns out that waypoints and routes can be upload to it from Mapsource without any problems. I will have to check a few waypoints to ensure they are where they should be but the coordinates are correct.  

 

Some readers used to sailing in more open waters may be thinking that 92 waypoints is excessive but with so many islands and rocks there's is always plenty of navigation to do.

 

The appropriate paper chart is always open on the chart table or in its plastic cover in the cockpit, along with the pilotage plans for the tricky bits.

The GPS is used to verify our position and course to the next waypoint by checking it against the chart and the real world. The waypoints are placed where boat routes change course or significant navigation points. In addition to being numbered I have added the description of what buoyage to look for in the real world. For example, 061 PB = WP 61 Port Buoy.  

 

  

A  typical part of one of the electronic charts. Click and then zoom to see the detail.

Shorter forestay

When we removed the mast at the end of the season in 2010 I stupidly released the forestay under tension and it finished up in a tangled mess but a least no one was injured.

I replaced the forestay last year but noticed that the mast rake was too great when compared to boats Little Grace moored along side. There was also more weather helm than I remembered from the 2010 season.

I contacted the supplier of the forestay (North Sails Turku - very helpful) and we agreed that they would reduce the forestay by the minimum possible, which was 5cm. Last year the bottle screw was closed right down (see photo below) and it has a combined thread of 8 cm, so if the replacement forestay proved to be too small I would be able to compensate by extending the bottle screw and I won’t be caught out with an unusable forestay at the beginning of the year.

Of course, I should put the mast up and do some proper measurements but that is simply not possible at the moment and I don’t want to waste time I haven’t got at the beginning of the season sorting it out.

I asked those smarter than me on the Alacrity/Vivacity forum; how much will a reduction of 5 cm of forestay change the angle of the mast (which is 7m from deck to masthead)?

This was the helpful reply I received from one of the forum members after I gave the additional measurement of 1.9 m from the bottom of the forestay to the bottom of the mast (the J measurement).

 "By a crude process of working the angles backwards I estimate a change in length of 0.0546 m would result in an angle change of 0.7º."

That got me thinking. After using grid lines in Photoshop to check the horizontal on the coach roof in the photograph below I used a Breton Plotter (I couldn’t find the protractor) to calculate that the mast rake is between 2 and 2.5 degrees.

The circumference of a 7 meter (the height of the mast) radius is 43.982297150257104 divided by 360 = .122 (12.2 cm). x 2 degrees (to be conservative) = .244 (24.4 cm - 9 ¾ inches) rake at the masthead. The ideal is on an Alacrity is about 15cm (6 inches), apparently.

Using the calculation of – 0.7 º should mean (if I have got this right) .122 ÷ 10 x 7 = 0.085 (8.5 cm - 3 1/4 inches) leaving a mast rake of just under 7 inches?

A 8 cm reduction in forestay length would be 1 º and 12 cm (4 ¾ inches) at the masthead leaving a rake of 12.4 cm (5.5 inches). I can safely reduce the diffrence down to 4 cm by extending the bottle screw, i.e. .5º = 6 cm (2 ¼ ish inches) at the masthead. So if the current rake is 2.5 º I am covered, I hope. So I sent of the old forestay as the measure for a new one of 8 cm shorter. They have both arrived back, leaving me with the option of going back to the one we used last year if my calculations are all wrong.

 

On inspecting the turnbuckle for the forestay that came with the boat I found that the threads had seen better days. In addition it had been wearing the bow fitting as the clevis pin is 6mm and I measured the hole in the bow fitting to be 8.5 - 9 mm. Concerns about the threads on the original turnbuckle now that I may have to extend it to accommodate the new forestay and an article that discussed the issue of the wrong sized clevis pins damaging bow fittings in Practical Boat Owner prompted me to buy a Selden 5/16 turnbuckle. The clevis pins are 8 mm and the overall quality is better.

New crew member and the to-do list

I have not added anything to this blog for a long time but not because of lack of interest or things to write about. In fact for the last six months, nearly, I have been preoccupied with raising the new crew member, Marc, and keeping up with my work, mostly from home, while Tuulia has been working hard at our clinic.

Despite this preoccupation I have had time to turn ideas over in my head and occasionally remind myself of the to-do list, which I hope to complete before Little Grace goes in the water, and the need to complete the blog items related to Little Grace's refurbishment.

The to-do list

• Shorten forestay
• Improve the Windex so it does not get stuck
• Connect the GPS to the VHF/DSC (Radio)
• Mount the GPS on a board that folds back so it can run off the battery, be permanently connected to the VHF/DSC and allow fee access through the companionway without having to duck under it.
• Connect the existing metal gas pipe to the gas bottle in the new gas bottle locker and the cooker. This is so the gas bottle does not have to stand in the cockpit to be connected to the cooker by a standard 1m flexible hose - not done - here's why
• Separate the starboard cockpit locker from the bilge with independent drainage through skin fitting. I have contemplated this one a lot and I keep coming back to the fact that I can't achieve it and maintain convenient stowage for the boat hooks and paddles. It looks like I am going to have to find a compromise I am prepared to live with.
• Replace the plastic cap at the end of one of the spreaders (it pinged off when the mast was removed) - done.
• Add a new cleat for jib downhaul and cleat guards to prevent unwanted cleating for it and the pole downhaul.
• Create food storage area under companionway - not done because the water bottles were not relocated.
• Relocate water storage to above keels - not done, there is no better position than the one they have.
• Invert bow light so it is suspended under the pulpit.
• Strengthen aft locker catches - Proved to be unnecessary.
• Replace washers for mast bolts - done.
• Either manually input 92 waypoints into the backup GPS or replace it with one that can be uploaded from the computer.

There is plenty of time!