MacGregorSailors.com

Judy B wrote:

Dimitri-2000X-Tampa wrote:
Hi Judy, congrats on your new project!

Your standing rigging calculations do make me think about MacGregors, primarily the fact that the forestay on the 26X is thinner (1/8) than the side shrouds at (5/32). Now I don't know anyone who has had a failure (without a valid reason) and I know some people have beefed up the forestay just out of caution but my question has to do with putting heavier sails on the 26x than what it was originally designed for. As we know, the stock sails are very light (4oz I think) so if you put heavier sails on (ie 6+ oz), by definition, the weight aloft increases. So does that change the geometry of the rig, the righting moment and the safety factor of the original standing rigging?

Dimitri

No,
No, and
No.

Let me explain using real numbers, numbers from my own project. You'll have to ask Roger if you want the numbers for a 26X

1.No. The geometry of the rig doesn't change when you add weight aloft. The weight aloft changes.

2. No, adding weight aloft does not increase the loads on the rig. It reduces stability and makes the boat more tender
Adding weight aloft "neutralizes" ballast.
The boat gets more "tender" and heels further for a given wind speed or sail area. You have to reef sooner.
The boat will capsize more easily.
But the forces on the rig remain the same.

3. No, Going from 4 oz to 6 oz adds only about 1.75 pounds of weight aloft. The maximum righting moment is 4060 ft-pounds. (and that occurs at about 40 degrees of heel. That extra weight aloft "uses up" a little of the righting moment only in the sense that the boat will be more tender by less than (by way less than 1%). It doesn't change the maximum righting moment, which is the sole determinant of how much of a load the wind can place on the sails before the boat tips over.because of #1 and #2

QED

That's overly simplified, but for practical purposes its accurate.

However, if you add gear and people to the boat that generally DOES increase the righting moment.... so if you add a couple of six packs of beer as ballast to the boat, that will increase the righting moment. If you add so much beer that you exceed the designed capacity of the boat one the following things will happen: you'll lose the rig or you'll fall overboard or you'll get arrested for DUI and get taken to jail -- thereby getting the weight of the boat back within the designed capacity so all is right within MacGregor-Land again .

None of that would have anything with physics, but I'm sure somebody will blame the boat's engineering

Seriously, boats are engineered to handle the forces at maximum allowed capacity. Then a safety factor is thrown in on top of that to allow for less than perfect maintenance. MacGregors don't lose masts because the wires are too small. The wires on the Macs are fine!!!! Macs lose masts due to metal fatigue and corrosion. The wire strengths are more than adequate . There may or may not be other problems but wire size ain't one of 'em!

For decades I have been trying to convince people that bigger forestays or shrouds are rarely needed on a properly engineered boat. Wires fail due to bad installation practices or lack of maintenance or physical depreciation. In fact there are numerous drawbacks to increasing the wire diameters having to do with the elasitic modulus of the steel and the force.

Fair winds,
Judy