Sails, Rigging, and Diesel

On the way to Bob's boat to tell him about the area of the staysail I realized that I had made a dumb mistake in making the simple calculation. The area of the stysail is 142, not the 312 square feet that I reported yesterday. According to Bob's equation the area of the staysail for Pachuca should be 125 square feet, which seemed too high to me. It then seemed sensible to investigate the relationship between sail area and wind speed.

I used the wind load calculator at http://www.sailingusa.info/cal_wind_load.htm and got the following basic numbers, where the sail area is in square feet and the loadings are in pounds:

Sail Area, 30 Kt, 45 Kt, 60Kt
142, 550, 1239, 2203
100, 388, 872, 1551
80, 310, 698, 1241

It appears that the load on a sail is proportional to the square of the wind speed. What this means is that if you double the wind speed you quadruple the loading on the sail, as is shown in the case of my staysail where the loading in 30 knots of wind is 550 lb and at 60 kt wind is 2203 lb. But for any given wind speed the loading of the sail is directly proportional to the sail area. (For example, if you halve the sail area you halve the loading.)

I didn't worry about the absolute numbers themselves but rather the relationships between the numbers.

I found that my staysail of 142 square feet was extremely comfortable at 30 knots and was at the edge of overpowering the boat at 45 knots. At 60 knots the sail would have been untenable. It looks like a 100 sq ft sail will take me to about 50 knots. In a "survival" storm it looks like the 80 sq ft sail would be the way to go.

Yes, it would be nice to have a roller furler staysail but I don't have one. (I'll probably install one back at Fremantle.)

I've issued two requests over the Club Cruceros net for a second hand storm jib of 100 sq ft with no response. However, I have had a response from a sail maker who can make me one. I replied that if he can supply a new sail by the end of this month to please send me a quotation.

Still on sails, I rearranged my lines to accommodate the two lines that should enable me to reef the mainsail from the cockpit. I am waiting for a calm day so that I can raise the mainsail and tie the two lines on the respective luff reefing rings and then see how the system works.

We got a sobering warning about rigging from the VHF 22 Club Cruceros net this morning. A boat that departed from La Paz for the South Pacific lost an aft shroud and then a forward shroud. Then one of the chain plates broke off. This boat had recently been on the hard stand here in La Paz and the rigging had looked OK. But looks can be deceiving. The recommendation was to not go over the horizon with rigging that is more than 10 years old. After my experiences I don't think that I'd go over the horizon with rigging more than 5 years old.

I spoke with Colin the mechanic this morning. He had not received a call that the head is ready. To avoid my pestering him with phone calls I asked him to send me an email as soon as he has the heads so that we can arrange the installation. He thought that the email was a good idea, but I'll probably still phone him at 8.30 AM every day.

Yesterday afternoon I did my third "pack horse" trip to CCC for supplies. I'm getting pretty good at estimating how much I can carry. This time I had the heavy stuff in my back pack and the lighter things in two green shopping bags that I brought from Australia. I arrived at The Dock cafe and had two cold Coronas with lemon (Even pack horses must be watered.), but I didn't have a meal because I came back with a beautiful sirloin steak, potatoes, broccoli, and onions to cook on the boat. I have found beef to be one of the bargains of Mexico. I brought back a nice piece of sirloin that barely fit in the large frying pan that cost the equivalent of $3 USD.