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Old 20-11-2012, 08:30   #1
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Purpose Of The Marked Waterline

I know "what" the waterline is and I know how to determine the waterline.

On my boat the waterline doesn't coincide with the "marked" waterline.

Since I have an internal engine, I wonder if it's(maybe), the engine was an option that raised the makes the waterline lower on the boat than the marked waterline(which is now about 6" higher).

Anyway . . . my interest is what's the actual purpose for the waterline?

Is it for handicapping or exactly what?

Odd that I can find almost everything on the internet about marked and marking waterlines . . . I just can't find anything as to any purpose, let alone the "real" purpose of the waterline.
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Old 20-11-2012, 08:46   #2
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Re: purpose of the marked waterline

Either A: the line was put on in the wrong place or B: the line indicates the max depth you can squat the hull with a load on board but six inches would be a hell of a lot of stuff.
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Old 20-11-2012, 08:48   #3
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Re: purpose of the marked waterline

A waterline mark is sometimes used for handicapping on measured boats and for some one-designs fleets. If you show up for a race above your waterline, you can be protested for a Rule #2 infraction.
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Old 20-11-2012, 08:54   #4
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Re: purpose of the marked waterline

it's a nice place to know where painting anti-fouling paint should stop. That is probably the case here. The anti-fouling paint is above the water line because of "splash growth".

That is my vote. But is subject to the type of paint the waterline is.

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Old 20-11-2012, 08:57   #5
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Re: purpose of the marked waterline

How is the waterline marked?

If it is a painted strip around the hull, the strip was made while the boat was out of the water and is a guess of how much "stuff" your're going to put on your boat. Cruisiers find that they need to raise the waterline before leaving their home port.

In most cases it's not a waterline but reather how far up the side of the hull you apply anti'fouling paint.
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Old 20-11-2012, 09:33   #6
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Re: purpose of the marked waterline

It is a boat. Which is to say that the boat sits in the water displacing water in volume which has he same weight at the boat. Put more things in the boat and the boat sits lower.

Contrasting colors on the water line would show you how loaded you are. You might have an unloaded waterline and a fully loaded waterline. If you are a cruising boat ready for a passage you might be well beyond the designed waterline.

Also. the waterline mark tells you about trim. It will show how evenly the weight is distributed in the boat. Does it list or is it down at the bow? Move some stores around.

Lastly it is common to paint bottom paint above the actual waterline so as to keep ugly growth from taking hold.

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Old 20-11-2012, 10:19   #7
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Re: purpose of the marked waterline

The line has been remarked(I left the "sludge" on & remeasured the "sludge" line).

In general, then line runs within an inch or so of "true"(?), but the bow is way off . . . like it was adjusted or something.
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Old 20-11-2012, 10:25   #8
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Re: purpose of the marked waterline

Quote:
Originally Posted by SURV69 View Post
The line has been remarked(I left the "sludge" on & remeasured the "sludge" line).

In general, then line runs within an inch or so of "true"(?), but the bow is way off . . . like it was adjusted or something.
Unfortunately, you didn't give enough information in your reply.

Is the sludge within the new waterline? Is the paint anti-fouling or normal?

You say the bow water line has been adjusted, how? Deeper or more shallow?

Up or down isn't helpful. This depends on your view. Deeper or more shallow are better terms. (higher water line actually implies deeper, but that could be paint or water....which is deeper?)

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Old 20-11-2012, 10:25   #9
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Re: purpose of the marked waterline

I always figure it was so anyone driving by your boat could quickly tell whether your boat was sinking!
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Old 20-11-2012, 10:39   #10
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Re: purpose of the marked waterline

Emv1024 is exactly right. Read his post again
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Old 20-11-2012, 11:58   #11
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Re: Purpose Of The Marked Waterline

So you know where to stop the "bottom paint". ALL boats sit at different depths depending on load. Go to any harbor and look at the big boys. You'll see marks like "winter MAX draft" and a scale running up the side that shows how deep it is at any given time...
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Old 20-11-2012, 12:10   #12
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Re: Purpose Of The Marked Waterline

Defining a new waterline based on the sludge line is tricky. If you don't get it right it will look terrible. I used a cheap laser tool that projects a line. I set it up at dusk on a stepladder next to the boat aligning it with tape marks bow and stern. By adjusting the height you can put a little shear on it which raises the line a little at the bow and stern if that's what it takes to cover the sludge line. Mark the line with pieces of tape or pencil. DO NOT USE A SHARPIE. Sharpie bleeds through LPU paint instantly.
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Old 20-11-2012, 12:11   #13
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Re: Purpose Of The Marked Waterline

Keep in mind that knowing your design water line is an important safety consideration too. Many cruising boats are way overloaded (mine included) and move up their bottom paint line to compensate, but technically this is not the best of ideas.

Commercial vessels are marked with "plimsoll lines", but these are not required on recreational vessels (however, they would not be a bad idea).
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Old 20-11-2012, 12:12   #14
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Re: Purpose Of The Marked Waterline

The waterline as marked on the hull by the builder should be the waterline which the designer struck and used for his calculations. All those numbers that buyers of used sailboats are so fond of looking up on the internet are based on this line. What often happens in real life is that the builder builds the boat too heavy so when the buyer starts adding stuff the boat sinks below this line so he raises it a few inches making all those numbers just fantasy, sometimes this happens a few times over the years as owners get seduced to add more and more amp eating gismos and more batteries to feed them.

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Old 20-11-2012, 12:37   #15
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Re: Purpose Of The Marked Waterline

A cautionary tale that actually occurred... A successful family of Alaskan crabbers had a yard in Seattle build 3 crabboats for them to use in the Bering Sea in a forthcoming crab season. There was the usual rush to get the vessels finished and launched to drive them north for the upcoming crab season. To meet the schedule, the yard required the paint crew to come in on a Sunday to finish off the painting chore.
The painting foreman checked the plans and chalked up the hulls to apply the bottom paint, boot stripe and plimsol lines and the crew went to work. Evidently, the paint foreman either misread or miscalculated the design drawings and painted the boot stripe higher than the design called for attempting to allow for the load of crab and pots.
The vessels left for Dutch Harbor, loaded their pots there and proceeded to the fishing grounds. It was common practice to load pots until the water hit just below the boot stripe line. I know because I used to fish those waters. One of the worst storms to hit the area in years blew in and all three vessels sank with a loss of all but a couple of crew on one of the boats.
It took several years of inquiries, investigation and countless months of heartache for the remaining family members before the cause of this terrible accident was finally figured out.
Although pleasure craft, sail or power may be cavalier about adjusting boot stripes to 'look good' underway fully laden for cruising, IMO you should be cautious about doing so. Phil
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