Mailport January 15, 2003 Issue

Mailport: 01/15/03

Looser Lifeline Debate
Ralph Alter's letter in favor of keeping lifelines looser rather than tighter (Mailport, November 1, 2002) offered a challenge: "Let the arguments begin!" That challenge has been answered by quite a few people. We'll lead with the first respondent, Eric Baicy from Seattle. His original letter was five pages long, and full of diagrams and sine language. We'll put the whole thing in Online Mailport, along with other letters we don't have room for here.

Ralph's analysis is essentially correct, but there is one assumption he made that is somewhat unrealistic. The force he describes for 1" of sag when 200 lbs. is applied is about 4,800lbs. The mistake is assuming that tension is caused by the 200 lbs. The correct way to re-word his solution is: If I tension my lifelines to 4,800 lbs. and then stand on them, they will only move 1" (assuming 48" to the center of the span).

The effective weight of the cable by itself is very small. It doesn't take much tension to make them run straight in between the stanchions, maybe 20-30 lbs.

The effect of pre-loading this small amount of tension won't be noticed in comparison to the application of 200 lbs., and the sag produced in both cases (tensioned and untensioned) should be very close to each other.

As a rule of thumb, if you find yourself tightening your lifelines often, then you are probably putting too much tension on them.

-Eric Baicy
Seattle, WA

I am not a mechanical engineer or boat designer but Mr.Alter's calculations for lifeline tension produced by 200 lbs. of force applied against a tight lifeline are correct. I got 4801.04 lbs. of force as my answer. I agree with his conclusion as well. It would appear that if lifelines have a little slack in them the loads are dramatically reduced.

Similar techniques for multiplying force are used frequently on sailboats: the Y-shaped backstay tensioners and the technique of "horsing" a halyard to name two.

-Don Karon
Via e-mail

Ralph Alter's engineering observations are essentially correct. The matter is resolved if one thinks of it in terms of trigonometry. However, substitute force, load, or speed and direction for length of line. Navigators are familiar with the technique when determining a course to steer after considering speed, current, set, and leeway. This is also why we "sweat" halyards to obtain a bit more luff tension. Further, this effect explains why upper shrouds have spreaders. The brace angle is larger, which reduces the total shroud tension for a given lateral support. However, the use of spreaders imparts lateral compression loads on the mast. That is why it is so important to balance shroud tensions. Otherwise, unbalanced loads will bend the mast sideways and the overtensioned side could be overloaded when on that tack. These are why I have wanted to name our humble little Precision 23 "Vector Sum." However, so far, my wife won't let me.

My lifelines are set to be loose with a bit of visual sag, or deflection.

Keep up the good work. If I spent more time reading financial publications instead of your fine magazine, I might be sailing a larger boat!

-Blake W. Fulton
Via e-mail

What Ralph is missing is the fact that lifelines are also intended to keep you inside the plane of the deck of the boat. Slacking by 6" is kind of like putting up a fence 6" past the edge of a cliff.

If you read the US Sailing Rule 49.2, it states that if lifelines are required, they shall be taut.

-Mark Rode
Winthrop Harbor, IL


Fuel Filters
Your article on fuel filters [November 15, 2002] was very interestingand informative. It was nice to see a comparison of the various filters. The Baja filters have the reputation of being extremely effective but expensive. The test results in the article indicate that the West Marine unit is as good or better at cleaning fuel than the Baja filter, and sells at a much lower price.

An important feature which was not covered in the article is the rate that fuel flows through the filter. From a practical sense, a filter that cleans very well but allows a very slow rate of fuel may not be preferable to one does not clean quite as well but that has a good flow rate. Without that information it is difficult to select the filter best suited for actual use.

-Hap Pudewa
Long Beach, CA

No water =No HUMbugs is absolutely true. Getting rid of any water in the fuel tank is essential, for diesel fuel or gasoline.

There is very little chance that the loudmouth at the fuel dock will put any water in with your fuel. Virtually every fuel dispensing pump has a final filter that will shut down the flow if any water tries to get by. I can't vouch for the fuel dock in Tonga or the other exotic ports, but I'm sure that none of them wants a bad reputation. Incidentally, the pick-up in most fuel dispenser's tanks is six or more inches off the bottom of the tank. The tanks are frequently tested for water, and if any is found, it is removed long before it gets close to the pick-up pipe. These tanks are never shaken.

By far the largest contributing factor to water getting into the fuel tank is the O-ring seal at the fill cap. I have long been pushing this point wherever I can. The O-rings crack with age (some very young) and water can seep by. The gap around the fill cap acts like a funnel and keeps water against the O-ring until it can get through. Each time it rains, each time you wash the deck, each time a sea comes aboard, and even each time there is heavy dew, some water is trying to get past that O-ring. I stress this point when I conduct engine seminars. Our gas dock loudmouths are constantly reminded to check the O-ring whenever they have a fill cap in their hands, the same advice that I give to boat owners.

As you state, you don't know how much stuff is in the tank until you shake it up. You have room between the pick-up tube and the bottom of the tank to allow a half-inch or more of water to accumulate before it can cause a problem, unless the motion of the boat creates a wave at the water/fuel boundary to get to the pick-up. Many times I am told, "I was just sold a batch of bad fuel." That's probably never the case. A slow accumulation followed by a shake-up is the real reason. No matter how good your filter, it won't stop this.

Getting water (and the associated bugs) out from under the fuel is relatively easy. You simply get a pump suction to the very lowest point in the tank and pump a bit. If the tank is absolutely flat-bottomed, heel the boat to make a lowest point. A halyard pulled to one side is an easy way to do it. The water will go promptly to the lowest point. The longer you maintain the heel, the more of the slower-moving sludge will get to your pump.

Pumping out all the fuel and putting in new will not necessarily get rid of water and other contaminants unless the bottom of the tank is also dried.

Fuel additives are another of my pet peeves. If you read the labels on the additive containers, each is the best. There is virtually no way to perform meaningful testing since each fuel formulator has already put additives in the fuel they sell, depending upon the climate of a given area. No fuel manufacturer wants to get negative press, so they all make the fuel to work and to last. Taking a bottle of something off the auto store's shelf and dumping it into your fuel has little chance of making an improvement. As your article states, many additives are mostly alcohol, probably priced higher per ounce than some very good Scotch. If you add too much alcohol-based additive, the result could be that the diesel fuel gets so volatile that the engine will not run once it gets hot.

-Gordon Torresen
Torresen Marine, Muskegon, MI

Also With This Article
Click here to view "Where Credit is Due."

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