Thursday, January 28, 2016

Opinions Versus Knowledge

Getting to this point in my design and build has taken a lot of time just doing research.  Finding out what other people have done, what works, what doesn't, what is worth trying at least, what should be abandoned as an idea entirely - it all takes so much time to sort through and filter.

Knowledge based on fact and experience is one thing and an opinion is something else entirely.  Both are valuable though.  A statement of fact from a credible source can be almost taken to the bank.  An opinion from whomever warrants further investigation.

In the end, you have to do your due diligence and make your own choices.

Here is something I'm working on now:

My main mast in it's present form (as a fantasy in my head) extends 26 feet above the tabernacle and will carry a sail of about 450 square feet.  Most of what I have read out there on the Internet says that to size your mast you must first know the righting moment of your vessel.  Sail area is disregarded.  In essence what the size of the mast is based on is strength required to withstand a heeling force of around 30 degrees for said vessel - plus a safety factor.  Say 3 for a heavy displacement cruiser or 1.5 for a racer.

A narrower, lighter boat will heel easier than a beamy, heavy boat so the scantlings for the mast will be much smaller.

Attending to the problem in this manner, where sail area is not a consideration -  only righting moment - ensures a mast that won't buckle or break regardless of what is thrown at it by Mother Nature.  Hurricane, gale, Williwaw - doesn't matter.  The boat gets knocked down but the mast don't break.

So, this is a great way to approach the problem for a conventional boat.  Meaning one that will heel.

What if the boat won't heel (easily) and is more like a fixed and rigid object?  Our boat has a crazy big righting moment.  I would not want to even think about the righting moment at 30 degrees for a boat that is 10'8" wide for its full length of 34 feet, and may weigh fully loaded 6 or 7 tons.

Bottom line is I don't really want the boat to go over that far any more than I would want to experience a 30 degree heel on the Spirit of Vancouver Island.


So what I'm mulling over at this point is would it be better to break or bend a mast in our sailing barge than to capsize it?

Opinions welcome :-)

Anyway, she's still going together...having so much fun!


3 comments:

  1. The big consideration is your motor and fuel. If your mast breaks, and you cut away the remainder, can you motor to safety? This depends of course on where you are going to be sailing. From what I know of where you intend to sail, turning your ship into a motor boat would be safer then trying to recover from a capsize. With this thinking in mind, look at your motor size and fuel stores.

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  2. IMHO: a mast that breaks first. The achilles heel of barge sailers is not being self righting. If you're way out in the boonies and you go over than very bad news. Id rather limp home or to a port than not limp at all. In my eyes a prudent sailor plans for all he can envision and it's fairly easy to envision a stray williwaw. At 10 wide you are getting a awesome righting moment though. Not as much as a trilocat though: spreading it out to 20' beam. Depends on what level of risk you are comfortable with. I play it far less safe when it is just me and not me and my wife. Really coming together..... looks beautiful.

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  3. If you haven't seen it already, VanLoan presents a formula for mast sizing that lets you tweak all the variables. It agrees well with that in PJR, but (as I recall) much friendlier.

    One consideration is whether you'll be sailing unreefed in knock-down conditions, which have to be wild indeed to knock a barge over (wind plus wave).

    Since (wide) barges sail at low angles of heel, you've got a lot of safety margin (warning/time to round up) before the tipping point.

    I'm guessing you'll find AUTARKIA to stand up well, yet still have plenty of shock absorbency.

    And if in doubt, consider running stays for special conditions?

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