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Old 03-08-2012, 19:51   #1
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How do i mark the waterline on a new boat

Hi there everyone,

I am starting to get ready to paint the hull of my 28' steel yacht problem that i have is how do i get a reasonably accurate waterline on her.

She is still an aquatic virgin and never seen the water and at 40 + years old shes itching to get there, so I'm interested in ways to get my waterline right prior to going in to the water (give or take a little).

I have heard of a few ways that might work and will details them for you so that you guys can give me your welcomed advice. If by chance other forumites think that all these ways work then that would be good as i could do all three and cross reference them to see if they all come up in the same or similar lines

So here are the ways that i have read about

1. "The easier sounding way", according to the design she is meant to have a draft of 4' 9" so i just measure up from the lowest point of the hull and then transfer this line all around the boat.

2. "The dodgy sounding way" Transfer the interior floor level to the outside of the hull as i have read that the interior floor should be set at the waterline?

3. "The more accurate old school method i found"
Calculate the volume of the hull by lenght x width x height into cubic feet, then calculate as shown below using my boats total weight.

Then use this old school boat builders saying that i scrounged of the net
8 pints, 8 pounds, the world around.....

8 pints = 8 pounds, 8 pints in a gallon = 8 pounds in a gallon, 8 gallons in 1 cubic foot and 8 pounds in one gallon

So supposedly 8 gallons x 8 pounds each = 64 pounds in one cubic foot

One cubic foot of seawater = 64 pounds

So take the hulls cubic feet x 64 the divide that number by the number of inches in the height of your hull.

This should give the answer as to how much weight will sink your vessel 1 inch into the water

Then take that weight and divde into my vessles weight and i am meant to have my water line

*** Do this sounds like it will work to the more experienced person out there? If so, how do i do the measurements length width height.

Straight line from point to point? Or follow the curvature of the hull? And then also from what point, e.g from top of hull down round the hull under the keel back to the top of the hull?

Any help would be appreciated, like all of us I'm on a budget and where it would be great just to wait until i get back to a boat yard, float my boat, mark the line in water, then re-lift out finish painting etc i would like to avoid that extra cost if possible.

So please accept my thanks in advance and hopefully i will get some knowledgeable replies.

Matthew
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Old 03-08-2012, 20:33   #2
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Re: How do i mark the waterline on a new boat

Go with number one, it is easy and quick. If it wrong just repaint it next time it is out of the water
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Old 03-08-2012, 21:37   #3
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Re: How do i mark the waterline on a new boat

I'd try all 3 and average them! Seriously, I would be inclined to prepare your boat as you would with all the provisioning, fuel, food, gear that you plan on cruising with, splash her and measure where your water line falls. While it may cost you an 'in and out', you will be assured it is correct.
I mention this because of a tragic error in waterline painting that occurred on 3 three new crabbers headed for the Bering Sea many years ago. All three identical vessels were built in the same yard in Seattle. The painter came in on a weekend to complete the job on all three boats and used method #1. All three sailed for Dutch Harbor the next week, picked up their crab traps at the dock and were loaded down to the waterline painted in the Seattle boat yard.
They left together for the crabbing grounds, hit some really heavy weather and because the waterline was painted too high on the hull, they were all over loaded carrying water as ballast in their empty crab tanks and were swamped. I believe all three vessels sank with considerable loss of life, many from the same family. A tragic story but a valuable lesson learned at high cost. Capt Phil
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Old 03-08-2012, 21:49   #4
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Re: How do i mark the waterline on a new boat

I can't tell you how to figure out where to put the waterline but I can tell you an easy way to make it straight. Borrow or rent a contractors rotating laser, set it up on a tripod at the right height and use the laser line to mark the waterline on the hull. A buddy of mine did this and it worked great.
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Old 03-08-2012, 21:55   #5
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Re: How do i mark the waterline on a new boat

Fore and aft trim will be your biggest problem as weight forward and aft quickly changes the waterline there vs elsewhere. I've heard of a megayacht sailboat where the stern had to be loaded with lead ingots because it ended up much more bow heavy (or stern light) then the designer anticipated.
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Old 03-08-2012, 23:22   #6
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Re: How do i mark the waterline on a new boat

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Originally Posted by HopCar View Post
I can't tell you how to figure out where to put the waterline but I can tell you an easy way to make it straight. Borrow or rent a contractors rotating laser, set it up on a tripod at the right height and use the laser line to mark the waterline on the hull. A buddy of mine did this and it worked great.

This only works if the boat has been leveled both fore and aft as well as athwartships. I usually use a digital level on the interior floorboards to determine level, as the molds are usually leveled in the factory so they can build the floors and counters level. Most yards don't block level and some will become annoyed with you if you make them do it.
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Old 04-08-2012, 01:54   #7
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Re: How do i mark the waterline on a new boat

Use your first method, and then add say four inches for luck. Boats often float below designed waterline.
If the boat is set up level, the easiest way is to solder a bit of copper pipe into the bottom of a can and join say 30 ft of clear plastic tube to it. Support the can at waterline level and fill it with water. Bleed the bubbles out of the hose and then move the hose around the boat, marking the water level in the tube onto the hull. This will give you an accurate line around the hull, assuming the hull is level in both planes before you start.

Regards,
Richard.
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Old 04-08-2012, 01:59   #8
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Re: How do i mark the waterline on a new boat

If the boat is level in both planes, solder a tube into the bottom of a can and attach a long length of clear plastic pipe to it.
Support the can at the waterline and put enough water in so that the water level is where you want to put your waterline marks.
With all the bubbles out of the tube, the level of water in the tube will stay at the level of water in the can, and you can mark an accurate waterline from that, by just moving the end of the tube around the hull.
Regards,
Richard.
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Old 04-08-2012, 04:53   #9
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Re: How do i mark the waterline on a new boat

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Originally Posted by boden36 View Post
If the boat is level in both planes, solder a tube into the bottom of a can and attach a long length of clear plastic pipe to it.
Support the can at the waterline and put enough water in so that the water level is where you want to put your waterline marks.
With all the bubbles out of the tube, the level of water in the tube will stay at the level of water in the can, and you can mark an accurate waterline from that, by just moving the end of the tube around the hull.
Regards,
Richard.
Don't bother with the soldering bit ,just use a funnel at ea. end
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Old 04-08-2012, 05:34   #10
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Re: How do i mark the waterline on a new boat

Splash it, then go around with a chinagraph pencil and mark it. I did a previous boat by launching it in a river with a deep tea colour, stained the hull nicely and gave is quite a fair line as a starting point.

The reason I say splash it is because you didn't build this boat did you, so it might vary slightly from the plans etc. Whilst the draft might be 4'9" that could be at the stern of the keel and the front part of the keel higher. Also there is little chance of the yard levelling her exactly, so the water in the clear tube idea doesn't work. Tried that one.

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Old 04-08-2012, 06:33   #11
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Re: How do i mark the waterline on a new boat

I've seen a boat splashed and left in the slings (loose) while the yard poured a bunch of sawdust around it, then hauled it out again. Worked pretty well. Don't know how much they charged, if anything (they did a bunch of work on this boat).
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Old 04-08-2012, 07:41   #12
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Re: How do i mark the waterline on a new boat

Quote:
Originally Posted by HopCar View Post
I can't tell you how to figure out where to put the waterline but I can tell you an easy way to make it straight. Borrow or rent a contractors rotating laser, set it up on a tripod at the right height and use the laser line to mark the waterline on the hull. A buddy of mine did this and it worked great.
Only if the boat is perfectly level. A difficult item in a boatyard.

Edit: I see Minaret beat me to it...
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Old 04-08-2012, 08:15   #13
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You can set the laser at any angle you want. The suggestion was that it will show you a "straight" line on the hull. It doesn't have to be level to the earth.

The water hose level idea is the one that requires the boat to be level.


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Old 04-08-2012, 09:14   #14
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Re: How do i mark the waterline on a new boat

Gene is correct, the laser just allows you to draw a long straight line. I think my friend made a mark at the water line at the stern and another at the bow and used the laser to connect the dots.
I like the saw dust trick. I'll remember that.
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Old 04-08-2012, 10:26   #15
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Re: How do i mark the waterline on a new boat

The idea of leveling the waterline to coincide with the floorboards is problematic IMO. Floor boards can be set at any height to accommodate short medium and tall folks depending on how much interior space they want to use/lose.
Load and splash is best in my opinion... see previous post. Capt Phil
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