PI PILOTPI PILOTPI PILOTPI PILOT’’’’S GUIDES GUIDES GUIDES GUIDE

PART 2 PART 2 PART 2 PART 2 ---- ANCHORING ANCHORING ANCHORING ANCHORING

Survival on the Beach

Getting the most out of Danforth

anchors and anchor line setups

Why some anchors hold and others fail

Why anchor lines that are stretched tight pull

less than loose ones when the wind blows

The math behind it all (if you want to know why)

The time you spend picking your beach may be the most important part of your vacation.

Give yourself enough time to find the RIGHT beach.

Don't be in a hurry

Survival on the beach ……………………….. 21 Why anchors hold, and why some fail …… 22 Anchoring by the numbers ………………… 24 Things that can lead to trouble. …………... 26 Where you set your anchors matters …… 26 The anchor line loop you CAN untie …….. 28 The Math part (if you want to know WHY) 29

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Survival on the Beach - Avoiding Anchor Failures We've all been through it.

We're anchored on a beach somewhere in Paradise, and every blast of wind seems to hit a little harder than the one before. The boat is moving around, and making noises we don't like. The windward anchor

lines are stretched like banjo strings, and the lee-side lines are slack and in the water. Everyone's adrenaline level is up and climbing.

We all have had the same thoughts:

Will the anchors hold?

Are the lines strong enough?

How far can these lines stretch before they break? What can we do to get through this in one piece?

We'll answer that last question first, and then consider the others. Right now, your anchor setup is

whatever it is, so let's focus on getting through this in one piece.

� Bilge Blower ON. � Check the back deck and swim platform, and secure anything that can blow or get washed

overboard. This is not the time for a towline to get fouled in a prop.

� Start the engines and put them in forward gear. Put helm hard over AWAY FROM THE WIND (wind from the left - turn the wheel hard right).

� Use the throttles to control the situation. Unless the wind changes direction, leave the helm hard over.

� Send your extra crew topside, and secure anything that can blow overboard. If it can, it will. I've seen lounge chairs take off like helicopters.

One of the good things about this technique is that any of your crew can take a turn at the helm when

it's 3AM and the storm has been blasting you for hours. All they have to do is watch the downwind anchor lines, increase the power when the lines start to dip toward the water, and back off when the

lines start to get tight. The job requires constant attention, and it's more tiring than you might expect. You'll welcome the chance to take a break.

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Anchor setups that HOLD - (And why some anchors fail) The Danforth-style anchors on the PI will hold a tremendous load when they are properly set in a good

location. As long as the anchor has enough sand BELOW it to dig in deeper as the load increases, these

anchors almost never pull out. An anchor placed in loose, dry sand is one exception.

Wet sand is stronger than dry sand. Ask anyone who ever built a sand castle. An anchor in damp and undisturbed sand will hold more than twice the load of one in dry sand, or sand that is not well

settled. When you have a choice, go for the damp sand.

Anchor failures are almost always the result of one of the following:

� Setting the anchor in sand that is too shallow.

� Setting the anchor in loose, dry sand (sand "flows" around anchor). � Setting the anchor too far up the beach (increases leverage when lines stretch).

� Failing to adequately pre-stretch the anchor lines before the storm hits.

Don't be in a hurry - find a good beach. Send a scouting party out in a speedboat (hopefully with a VHF radio) when you're still 10-15 miles from where you think you're going. This will give them at least an hour to locate and evaluate beaching sites, and look around for

something better if it turns out they need to. Have them take a Horse Shoe stake and a small

hammer (there's a hammer in the main tool box or prop tool (red) box below decks). Use the stake to probe the sand and make sure it isn't hiding a slab of rock a foot below the surface.

TIP: Send a handheld VHF radio along on the scouting party. If you find a beach that "will do", but

want a better one, leave a crew with the handheld and their "beverage of choice" on the "so-so" beach to hold it against raiding parties while the speedboat keeps on looking.

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Setting up your anchorage involves lots of trade-offs and compromises. At the end of the day,

we take the best we can get. The decisions you make along the way will determine the outcome when the storm hits.

Your most important decision is a commitment to monitor the weather broadcasts on the

VHF radio. Stay on top of the forecast and pay attention to the observed wind at various locations

around the region. If you know the wind is coming, there's a LOT you can do to improve your chances of riding out the storm in good shape.

Places to avoid:

� Anywhere you can see across several miles of open water when you're standing on your beach. The waves get higher the farther they travel.

� Downstream from Anasazi Canyon (buoy 52) - any beach that has a straight view

onto the main channel will take tour boat wakes. Count on it.

Getting a Danforth to HOLD Dig a hole, but you needn't bury the anchor. Just dig the RIGHT KIND of hole.

We'll use the power of the houseboat to pull the anchor into the sand. It will bury itself:

NEVER use a sledgehammer! You'll just damage (or break) the anchor.

TIP: If you find "your" beach occupied, and have to settle for the one around the corner, cruise by your neighbor's boat and ask how long they will be staying. Moving the PI is a lot of work, but if you're going

to be there for several days, having prime beachfront property can make everything else go better. Don't

get caught napping. Stay in touch with your neighbor, and be ready to move as soon as your new site is vacant. Some smart somebody is always out there looking for a better beach.

Believe it or Not…

To help set the anchor as solidly as possible,

you can sort of bounce up and down (no kidding) on the crown or the stock as the

anchor slides the last couple of inches into its

hold while the houseboat is pulling hard on it. Two anchor tenders are nice - each of them can

take one end of the stock and work it down.

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By the Numbers: Typical anchor setup

Our goal is to pre-stretch (preload) the lines as much as we can. Another way of saying this is we want the lines as tight as we can get them. The importance of this will become apparent in a couple of pages

when we look at what happens when we get hit broadside by a 50 MPH blast of wind.

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Why less sag in the inside lines? Check out the math diagrams at the end of this.

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Things that can lead to trouble.

Don't worry about the anchor lines (or anything else) breaking. We've never had a failure of the equipment unless it had been damaged. We had one anchor break after it had been beaten

to death (cracked the Crown) by sledgehammers. The weakest link is the shackle that connects the line

to the anchor stem. That shackle is rated at 12,000 lb., with a 2-to-1 safety margin to the ultimate failure load.

NEVER pound on a sand anchor with a sledgehammer. You don't need to, and you may start a

crack that can give way when you or someone else desperately needs the anchor to stay in one piece.

At the end of the day, it's the strength of the sand (and how hard your setup pulls on it) that matters.

Our anchor lines will stretch almost 30% before breaking. This is mostly a very good thing. All

that stretch equates to a tremendous amount of shock-absorbing power. But, this same stretch can work against us. It can dramatically increase our anchor loads when the wind hits. It's how

the line stretches (and how much line we have out there to get stretched) that can make a big difference

in how well our day (or night) ends up. So…

How far up the beach did you set your anchors? The trade-off: During the early season when the Lake is rising, we all have a natural tendency to set

our anchors well up the beach, so we won't have to move them when the Lake rises, the boat moves

forward, and we need to re-tighten our lines. What we trade for this convenience is longer anchor lines, which can lead to trouble.

It's all about leverage and line stretch (and a little geometry).

For simplicity, we will look at what happens when a 50 MPH gust hits the boat straight on the side. In round numbers, this results in a 5000 Lb. side force pushing against our AFT anchor cleat. If you're into

math, check out the last few pages of this paper.

Once the boat starts to swing under the wind loads, It's ALL about leverage. The leverage increases as

the boat swings (the anchor line lever arm gets shorter). This in turn pulls harder on the line, which stretches it more, which increases the leverage… Things rapidly get out of limits past about 20o of swing.

Even in the best sand, don't expect the anchors to hold onto more than about 10,000 Lb. of load.

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Takeaway for this illustration: The more anchor line you start with, the more swing you end

up with. The more the boat swings, the harder it pulls on the anchor line. If you think you are in for a bad blow, and your anchors are set far up the beach, seriously consider moving

them closer to the water (shorten the lines) before the storm hits. Doing so will greatly reduce the ultimate stress on your anchor system, and perhaps your adrenaline level as well. It's a lot of work,

but it might well be worth it.

Your lines will loosen up during the storm. Count on it. The anchors will move a little (hopefully not a lot) when hit with storm loads that are much higher than the pull you used to set them in the first

place. If they are well-set in good sand, the movement will be minimal, and small movements are OK as long as the anchor is digging deeper, not pulling up and out. Keep an eye on them.

Any time of year, when the wind blows or the wakes and waves come by, the boat moves. The boat will move forward and loosen the lines with each motion of the boat as the bow grinds its

way farther into the beach. The anchors are pulling the bow forward with almost two tons of force when your lines are tight. The sand will move out of the way, and the lines will get loose.

When the water is rising, your lines begin to loosen the moment you finish tightening them. In May and June, the

Lake can rise a foot or more in a day, and the boat will move forward at whatever rate the beach slopes. You'll go to bed with

the lines tight, and find them sagging in the water the next morning. The same goes for having them tight when you leave for

a day trip and finding them loose when you get back.

Cut your losses. Pick the beach with the steeper slope

when you have a choice. Not only will the boat move less due to rising water, but there's also more sand to push out of the way

when the storm hits.

Tip: When you set anchors up the beach (anywhere but at the water's edge), put your loop as far toward the houseboat as you can. The line between the loop and the anchor is doubled, so that

portion of your line will only stretch half as much as the rest of the setup.

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How tight (pre-stretched) are your anchor lines?

There is no trade-off on this one. Loose lines are a disaster in progress. Your safety margin when the storm hits is mostly the stretch you already have in your lines. Whatever stretch you have

stored in your lines will be subtracted from the total amount the boat will swing when the wind hits.

Be sure you CAN quickly re-set your anchors and re-tension your lines. Learn to tie an

anchor loop that WILL come loose when you need it to: The "Anchor 8" knot. We all tie a loop in our anchor lines so we can adjust them when we need to, and get a better (2-1)

purchase when hauling on the line.

Lots of new Crew tie a "Trucker's Hitch" or "Slip Knot" to make the loop. Do NOT use this knot.

With a little practice, you will learn to tie this loop into your anchor line in under three seconds, with your eyes closed. Be SURE that anyone you send out to tend anchors knows and uses this knot. The time will

come when you need to re-rig your anchor setup in a hurry. A frozen knot is the last thing you need

right then.

The Trucker's Hitch

(These are all the SAME knot, laid differently)

Many frustrated people have spent HOURS, sometimes using screwdrivers, ice

picks, and other tools trying to get this knot to break loose. The line can be easily damaged in the process, and you can't re-rig the anchor until you get

the knot out of the line.

NEVER USE THIS KNOT IN AN

ANCHOR LINE. Under load, especially

when wet, it will jam so tightly that it can be

almost impossible to untie.

Use the "Anchor 8"

Easy to learn, quick to tie,

Can be easily untied, even after extreme stress.

The knot you CAN untie - always. This knot tends for form an "arch" when under stress. Hold the knot in

both hands, and "break its back". If it's stubborn, soak it for 30-60 seconds. It will come loose.

Take about this much line - Form a big loop and a small loop. Drop the big loop over the top of the line that leads to the boat. Reach around and under, and bring the big loop back over the top and down through the small loop. Viola!

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The Math Part…

How hard does the wind push on the houseboat?

The general formula for wind force is:

where Cd is the houseboat's drag coefficient (about 1.17 for a flat-sided box), P is the

density of the medium (air in this case , which is 1.293 kg/m^3),

A is the frontal surface area, and v is the velocity of the wind.

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We'll do this in metric units, just because it's (a lot) easier, and then convert back to lb. of force at the end.

We'll ignore the canopy shade top and the back deck overhang because they wouldn't

change the results a lot, and things will be bad enough without them.

SO:

A is 807 ft^2 = 74.97 m^2 (hull, house, skirt & flybridge)

v is 50 MPH = 22.35 m/s (wind speed)

P is 1.293 kg/m^3 (mass density of air)

Cd is 1.17 (drag coefficient for a flat plate sticking up out of the water)

Fw = ½Pv2ACd = ½(1.293kg/m3)(22.35m/s)2(74.97m2)1.17

= 28,321 N

= 6,361 Lb. f

acting on an approximate center of drag @ 37 ft. from the bow yields a total moment about the pivot of 241,700 lb./ft torque at the point of contact with the sand / 50 ft. lever arm to

aft anchor line cleat = 4,834 lb. side load at the cleat.

Close enough to 5000 lb. to use it in our examples. (or we could make the wind blow at 51.2

MPH…)

Why the shorter anchor line (the inside one) should sag less: No math, a picture is worth a thousand equations…

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How hard do the engines pull on the lines while we are anchoring?

Note: With the helm hard over, your dives are almost directly in-line with the anchor lines. That means you have about 3600 lb. of thrust to fight the strain on those lines when the wind is howling. Also note that engine power alone is NOT enough to hold the boat on the

beach with a 50 MPH wind on the side.

Between the engines and the anchors, you can take over 70 MPH on the side and survive.

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Takeaway for this:

If you leave the houseboat for a day trip with the lines tight, and a Monsoon Thunderstorm blows up while you're away, the boat can ride out a 50 MPH blast on its own, so long as

you've set the anchors in good, strong sand (and rising water hasn't loosened you up).

Remember: The longer you stay away when the lake is rising fast, the less your chances

that everything will be the way you left it when you get back. Keep an eye on the weather!