Setting the waterline mark with a laser level

[coopec43]

Originally Posted by Pauls

The OP mentions that he has limited side clearance. For an option which will work with limited clearance, is very inexpensive and easy to use I'd recommend the water filled tube approach. Some important points with this:
1. I've seen many posts that say to just fill a tube with water and walk it around. This does not give an accurate result. Moving the tube will either straighten or bend it, and these deformations change the internal volume of the tube and thus the water level in it. The solution is to attach the tube to a container filled with water. The volume of water in the container is large enough that small changes in the internal volume of the tube have no significant effect. You can attach a fitting to the bottom of the container, or run the tube in from the top, using the siphon effect.
2. Put some food coloring in the water. It makes the level very visible.
3. Obviously, this approach will create a level water line. You will need to level the boat.

This approach is simple, cheap, and quick to do. As long as the boat is leveled it will produce a quality result.

I think the water filled tube is the best approach too.



Since the waterline on my yacht is 32ft I found it was a two man job. (It was certainly a two man job when I checked the height of the waterline from one side to the other by taking the tube under the yacht)


I was aware the volume of the tube would alter if I stretched the tube so I made sure the tube was considerably more than the waterline length (45ft)

[chrisr]

i've just noticed the OP's comment that this is a new build

In such as case, how do you know what waterline line the boat will float on ? unless you are talking a mass produced plastic fantastic (beneteau / catalina / etc), its very rare for a new boat to float on the designed waterline, due to variances in the build weights etc.

i'd splash the boat first, mark the waterline (perhaps after adjusting the trim), then pull it out again and paint it

cheers,

[alaskasail]

I'm doing the same thing on a boat I've owned for 30 years. I've removed most of the cruising gear I won't be using so the boat trims out differently. Now we are out of the water. I'm just using the scum line which, thankfully is the same on each side of the boat, but still quite different than the manufacturers line.

[slug]

Water level...clear tube and it’s Bubble is the easiest

A laser is rather difficult to use when your field of view is cluttered

When striking you water line and laying out your bootop remember to sheer the line

A water line rises in the ends..this cosmetically preventS the boat from looking bow down, stern down ..when loaded

Google sheered waterline for explanation and formulas

[MicHughV]

...way back.....I built my first boat and went thru' this dilemma.

...first job was to ensure the hull was level. I used a filled water tube for this purpose and placed one end each side about amidships and measured to the shear line. I did this in several places along the hull.

...my hull had to be moved incrementally, not that difficult, ease the jack stands on one side raise them on the other side.

...a bigger issue was ensuring the boat was level fore and aft, this I got close, but not close enuff and had to re-do the waterline at my first haul out. A royal pain in the rear end.

..nonetheless, I used a water level....about 50' long x 1/2" clear tube and filled it almost to the top. It laid straight on the ground alongside the hull and I did not experience any problems.

..what was difficult, was striking the water line around the stern as the waterline here disappears under the curvature of the hull. The hose ends up at an angle to horizontal making for a difficult determination.

...in addition, my boat had a boot stripe. Around the stern area, this stripe has to become quite wide in order to " appear" uniform with the rest of the boot stripe.

...after I had ticked off the hull with the water level, I used some masking tape to connect the dots. This was definitely a 2 man job.

...I don't think using a laser or any other type of level is any easier as the same problems will have to be dealt with around the stern, etc.

..all in all, everything came out relatively good :-)

[GrowleyMonster]

Originally Posted by HankOnthewater

Most home builders, I would think, paint their waterline at least twice: the first time is as per the estimated guess/ as per drawing, and a few months, or year later to do that again, then taking into account deviations from the original plan, the various stuff loaded on board etc.

As others have said above, a boat on the hard is seldom perfectly level, therefore laser level or water-in-hose trick doesn't work.... except maybe when the laser level can be put at the same sloping angle as the boat.... maybe that is possible.

There was a boat builder in Fremantle, so the now popular story goes, who got the waterline of his (plywood) professional fishing boats always spot-on, without moving gear or ballast. His secret was to splash the boat the evening/night before final painting, mark the waterline with the boat in the water, take it out again, and then paint it (in daylight). The new owners were suitably impressed about the accuracy of the waterlines and contributed that to his skills as boatbuilder.

That is EXACTLY how to do it if you want to get it right in one shot. Give it a float test. Load her up with water, fuel, provisions, sails, and a few sandbags in the cockpit. Pots, pans, tools, spares, the works. Level the boat if there is any list at all. Pick a slick calm morning, slip into the water with a grease pencil and mark the actual waterline about every foot. Haul it back out and apply your boot topping and bottom paint. Done.


Else, level the boat side/side, and establish a reference. A laser is fine for marking the line but you need to check it with a water/hose level. Paint, then splash the boat and see how far off you were. Correct it next haulout.



When you arrive at your perfect paint line, I suggest that you carefully measure at every convenient reference point such as chain plates, portholes, bulkheads, etc and write them down for future reference.



If you used someone else's plans, find other builders and see if you can measure the deck/waterline distance all around, and go by that. If there is a list, you can just average the measurements with their twins on the other side.

[CaptJimFrei]

or use a brick mason's chalk line.

[oscarkramer]

I did this very thing for my Morgan 38 a few years back. With a sharp tool, you only need to mark three spots on each side while the boat is in the water: near the bow, amidship and as close to the aft end as you can reach accurately (Mine had a healthy overhang so a bit difficult). Then with the boat out of the water, I set the laser on a tripod about 15-20 feet away from amidship. I rotated the laser about its "vertical" axis (i.e., sweeping left and right), observing where the laser beam falls relative to the marks. After a few adjustments to the height and rotational plane of the laser( i.e., vertical axis), the beam hit all three marks. The only way the beam can hit all three marks is if the laser beam is sweeping along the water plane. You can then easily mark out the full waterline accurately. My results were perfect, even in the stern overhang where the hull meets the water at a smaller angle. The beam was a bit spread in the vertical direction in this area. Just mark the middle of the beam (assuming you put the reference mark in the middle of the beam spread as well!). I highly recommend this technique. Good luck.

[GRIT]

I just did this last year, on our new build. Using a laser level, cheap at the hardware store. One of those with cross hair lasers. There's no need to go to the neighbour's yard, you only have to be an inch or so to the side of the widest part of the the beam. We lined the laser up just ahead of the bow and an inch wider than the boat, pointed aft. Don't worry about getting it all in one shot. Mark what you have, then go to the stern, point the laser fwd, and line it up with what you just marked, and continue the line aft.

Once it's marked, tape and paint.
I'm sure everyone knows the boat has to be level in both directions...

Our boat is a 50 foot cat. So we had to ensure the hulls were marked identically.

Easy peasy.

I didn't read the entire thread, so if this has already been mentioned.... I "plus one" the suggestion.


Cheers.
Paul.

[sailorman14]

Originally Posted by Dsanduril

You can use a water level, but there are a ton of laser levels around that will do the trick. You should be able to pick up a "cross line laser level" for < $100. The really cheap ones start about $50, but the more you spend the further they will go, and also the more visible they will be outdoors (green is recommended over red for outdoor use).

Bosch makes many of the units sold in big box stores. Or Dewalt, or.... You'll also need a tripod on which to place/adjust the level.

You can also rent them from construction tool places (usually the larger/more sophisticated units).

Not a good idea to use a water level because you cannot guarantee the boat is perfectly level.
Much better to use a rotating laser. Mark the bow the middle and the stern. Then adjust the laser to touch all three points.

[oscarkramer]

Originally Posted by GRIT

I'm sure everyone knows the boat has to be level in both directions...

The orientation of the boat doesn't matter if you make the reference marks first while the boat is in the water. You can do this from a dinghy. The laser mount is adjusted until it swings on the virtual water plane given the boats orientation on land. It doesn't have to be parallel to the real water plane.

[Group9]

Originally Posted by Dsanduril

You can use a water level, but there are a ton of laser levels around that will do the trick. You should be able to pick up a "cross line laser level" for < $100. The really cheap ones start about $50, but the more you spend the further they will go, and also the more visible they will be outdoors (green is recommended over red for outdoor use).

Bosch makes many of the units sold in big box stores. Or Dewalt, or.... You'll also need a tripod on which to place/adjust the level.

You can also rent them from construction tool places (usually the larger/more sophisticated units).

Our ABC Rental place here in town rents them out. They have become our go-to place for expensive things we know we will only need once!