striking the waterline

[starbacca]

Does anyone have a foolproof method for striking a new waterline that does not rely on laser levels and transits? I have used a waterlevel in the past with mixed results. Would love to hear other approaches.

[TimH]

You could find an identical boat with the waterline already marked and take measurements off of it.

[djyachting]

For a small boat, level a wide straightedge - probably 1.5 to 2 x the half beam of the boat - at the bow waterline. The length depends on how fine the ends are, particularly the stern.

Attach the end of your - high quality and not too stretchy - masking tape to the waterline point at the stern and unroll the masking tape to the bow so that it is taut and the bottom edge is resting on the straight edge and the sticky side is clear of the hull.

Slowly, maintaining tension, walk the tape in to the bow. Ideally have someone touch it to the hull every now and again for security.

You won't get a completely straight line as the forces of gravity make the tape sag, but the gentle curve is virtually unnoticable on a realtively beamy boat.

If you are really clever you can remove the sag by strategic lifting of the tape as you approach 'midships.

But, unless you use a laser, which is my preference, the only really accurate way is with two straightedges and two tight wires which are sighted by one person while a pencil mark is made on the hull by another.

When you have established the line, use a tenon saw held horizontally to permanently scribe the line and make a good clean edge which you can cut to with a brush.

DJ

[mobjack68]

We used the plastic aquarium tubing/water trick on a 42' boat some years ago. There was a waterline painted on but is was quite wavy. We decided to use the existing waterline points at the point of the bow and the corners of the transom. We taped one end of the tubing securely to the bow with about 6 inches extending above the w/l. Filled the tubing with windshield washer solution (the blue stuff) until the meniscus touched the top of the w/l....If you hold the free end of the tubing against the boat and above the waterline, the liquid will show level at both ends of the tubing (it will seek its own level so long as the extra tubing is below the w/l ) We moved the tubing along the hull and marked the level of the liquid as we moved from front to back . We just used pencil marks about 8" apart and then taped to the pencil marks. Worked out well for us, the boat owner was tickled and the old timer that showed us how it worked was quite proud. One thing to remember...the boat has to be level to begin with...

[eastern270]

I'm hoping to be finished with my build in a couple weeks. I was going to float my boat and somehow mark off the actual waterline as it sat in the water. My boat is only 17' and easily transported.

[Jay Greer]

Although I have never tried it, I once heard of setting up a parallel plank near the hull and then a strong light behind it. This is supposed to cast an accurate shadow on the hull.
Not expensive to rent, my favorite method is using a transit to mark the water line. I have one, a simple farmer's Starrett, that was donated to me by a friend who worked for the trash dept. in Los Angeles. People toss away the darndest things!
Jay

[switters]

Dynamite Payson had a method for small boats (under 20'?) in one of his books, I'll see if I can find it tonight. It involved getting the boat level on the floor and making something like a finger gauge and rolling the block along the floor while marking the sides. Obviously not going to work a yacht but I think it is reasonable for 17'.

[Captain Intrepid]

I suppose you could rig up your own laser level using a camera tripod, a spirit level and a laser pointer. Us the spirit level to level off the mount of the tripod, attach the laser point, and then just swing it a few inches at a time down the hull so you can mark points on the waterline. The tricky bit would be getting the laser pointer level on the tripod.

[DuncanvdH]

For a small boat, level a wide straightedge - probably 1.5 to 2 x the half beam of the boat - at the bow waterline. The length depends on how fine the ends are, particularly the stern.

Attach the end of your - high quality and not too stretchy - masking tape to the waterline point at the stern and unroll the masking tape to the bow so that it is taut and the bottom edge is resting on the straight edge and the sticky side is clear of the hull.

Slowly, maintaining tension, walk the tape in to the bow. Ideally have someone touch it to the hull every now and again for security.


DJ

I used this method with great succes. I used 3M blue fine line tape of 3 mm width. Very easy!

Duncan

[Ian McColgin]

The water level is the best and most cost-effective way. It does require that you level the boat both fore and aft and athwartships first - easily done if you either find a spot on which to rest your bubble levels or create a spot by laying a plank across the gunnels.

On a properly leveled boat, the water level gives a perfect reference, though you will naturally (by eye but also see the WB magazine article on this - cite anyone?) flare the bow and stern a tad. Do you need detailed instruction in the water level?

G'luck

[Andrew Craig-Bennett]

For a small boat, level a wide straightedge - probably 1.5 to 2 x the half beam of the boat - at the bow waterline. The length depends on how fine the ends are, particularly the stern.

Attach the end of your - high quality and not too stretchy - masking tape to the waterline point at the stern and unroll the masking tape to the bow so that it is taut and the bottom edge is resting on the straight edge and the sticky side is clear of the hull.

Slowly, maintaining tension, walk the tape in to the bow. Ideally have someone touch it to the hull every now and again for security.

You won't get a completely straight line as the forces of gravity make the tape sag, but the gentle curve is virtually unnoticable on a realtively beamy boat.

If you are really clever you can remove the sag by strategic lifting of the tape as you approach 'midships.

But, unless you use a laser, which is my preference, the only really accurate way is with two straightedges and two tight wires which are sighted by one person while a pencil mark is made on the hull by another.

When you have established the line, use a tenon saw held horizontally to permanently scribe the line and make a good clean edge which you can cut to with a brush.

DJ

result using this method:

http://i535.photobucket.com/albums/ee352/acraigbennett/mirelle2.jpg?t=1240418752

[eastern270]

I'm a little confused. Alot of the reply posts above are telling you to level the boat. What are you leveling to if you don't have an existing waterline and have no idea of how the boat is going to float ? For example. The boat I'm building obviously has never been in water. I would think the only real way to establish a waterline would be to float the boat. Please help me understand what it is everyone saying to level to.

[DuncanvdH]

It does require that you level the boat both fore and aft and athwartships first
G'luck
I found this impossible. With the tape-method you can adjust the orientation of the straightedge to the orientation of the boat.
Put water level on boat, record position of bubble. Put water level on straightedge, adjust straightedge accordingly.

Duncan

[Canoeyawl]

The boat should have a designed waterline.
If you float the boat and find it is not at the designed waterline you will want to know why...and correct it.

edit to add: you can rent a laser "builders level" for about 20 bucks a day. This is the easest way, but the boat must be "on it's lines".
A transit is way too complex for this job.

[Ian McColgin]

Every boat has a slightly different way to get at leveling. I have used a variety of methods depending on whether I was leveling a light open boat or a 20 ton schooner.

The athwartships level is easiest. Just a matter of tweeking the jackstands or whatever, no heavy lifting. Hardest case - stuff in the way of a straight gunnel to gunnel run - pile stuff on the gunnels till you have a clear shot. Then a flat plank or a string with a hanging bubble in the middle. But do this after you have her leveled fore and aft!

Fore and aft leveling takes a little in the way of assumption but the plans should give you a good notion of stem and stern reference points. A little boat might be easiest done upside down.

Hard way: On a larger boat, you just drop equal reference bobs, move them out as the blocking will be in the way, and level that line. The moving out is likely to be close enough that your 3' normal carpenter's level should do the job in setting up stakes for the parallel line. Again the string and stringbubble (any hardware store and dirt cheap) are the ticket for the long run stem to stern.

Easy way: Your water level - assuming that your clear tube is long enough. Just jack the boat around till the stem mark and stern mark match the water level at each end of the tube and block her thus.

G'luck

[kendall]

I agree with Eastern, the most accurate way would be to float the boat and mark the lines. When I repainted my little sprite, (10ft) I just put it in the swimming pool, rigged it and marked the lines, works great for small boats. (how small depends on pool size!)

In my opinion, (grain of salt here, I have yet to build one, but studied many plans, and done quite a few boat repaints, and rebuilds) as far as leveling goes, there are always several points on a hull that are -supposed- to be level, so the trick is to use those points as your level reference.

Using the string and bob method, I've leveled side to side by attaching a temporary bowsprit with two bobs on it, one 6 inches or more ahead of the other, then sighting the lines to the center of the keel/stem, gives three points to align so it will be level side to side. cam be done at the stern by snapping a line on the transom and aligning the same way. Front to back you need to know what is 'supposed' to be level and use that as your reference.

ken.

[Steveh]

Once you've worked out the best method of striking the waterline I would consider what Ian suggested by flaring the line at the bow and stern, eg lifting the waterline at the ends. Higher at the bow than the stern.

Any designer worth his salt would factor this in the plans.

When I wooded Ngatira I discovered 7 waterline scribes!!! She's 105 years old. So I've picked the last known WL and adjusted for the conversion back to gaff. There will be bets placed as to if I got it right.

[mmd]

Or, you can keep meticulous records of the weights and centres-of-gravity of all materials and equipment used in constructing the 70,000-lb, 65-ft boat so you can calculate the weight & CG of the completed vessel - or it's projected weight upon completion. Then you can, using tried-and-true naval architectural principles combined with the linesplan, calculate the draft and trim of the boat and mark it on the linesplan. Then, you transfer the marked waterline on the linesplan to the real boat, compensating for the out-of-plumb and -level position of the boat and adjusting for the non-level and un-even floor of the building shed using a variety of tools and techniques as mentioned above. From this you can confidently (?) paint on the primer, bottom paint, boot-top, and topsides paint. Come the day to put your artistry in the water, you can be easily recognized in the gathered crowd by your profuse sweating, nervous tics, and constant mumbling.

Ask me how I know this...

[S B]

You don't have to level, any part of the boat , to scribe a water line. Regardless of whether you used plans or not,by now you should have a fair idea of how the boat will settle in the water, fore and aft. Mark this stem and stern. It is easier if you level the boat,side to side. Lay a plank athwarts midship, lay spirit level on it and adjust props until level. At the stern, erect a straight edge, twice as long as the boat is wide, level, with it's top edge in line with mark. Do the same at stem. Start by tying string 1' from boat, at stern, take a couple of turns arround the straight edge, so the line leaves on top, stretch to stem straight edge and adjust to meet,but not touch the hull, secure line. Record point on hull. Readjust lines to get further points. Every two feet is good. With a thin wide straight edge" door skin" connect at least three points at a time. Two will not be fair. Putting the boat in water to record water line, is easier said than done. to be accurate you have to leave it there with sandbags to replace the passengers untill an algae ring developes and then you only get the displacement water line not the paint line.

[CJ]

starbacca:

I can't speak for this method being "foolproof", but it worked very well for me with my 18' skiff. I did it as others have suggested as follows (I think I saw this method detailed in Greg Rossel's "Building Small Boats" a while back):

Launched the boat on a calm day with ballast to simulate any uninstalled parts and future outboard motor. My "ballast" used an 8' level set athwartship across the gunwales and shifted her weight until level.

http://i255.photobucket.com/albums/hh147/cjg0601/44.jpg?t=1240552301

Using tape strips I applied prior to launch (see pic), I carefully cut the tape at the actual waterline with a utility knife and removed the lower portion of the tape that fell below the water.

Back home, I measured my marks to verify that they were, in fact, the same on both sides - and they were - within 1/8".

Then, using a tecnique suggested already, I set the boat level again in my driveway using scraps and shims, then set two boards with perfectly straight edges perpendicular to the centerline of the boat, perfeclty level and at the same height as my marks (fore & aft).

http://i255.photobucket.com/albums/hh147/cjg0601/71.jpg?t=1240552407

Using a taught line, I marked the point where the line touched the hull as I moved one end toward the boat and the other away until I marked the whole length about every 2 feet. Take a batten and connect the dots ensuring that the line crosses the other marks along the hull that were made in the water. A bit verbose, but maybe these pictures will be worth another 1,000 words.

http://i255.photobucket.com/albums/hh147/cjg0601/102.jpg?t=1240552499

[Gary E]

That's the idea... IT LOOKS GOOD ON THE TRAILER....
and that's the ONLY THING THAT COUNTS
cuz when you put anything or anyone or even your dog in the boat
the water line is going to be wrong so make it look good on the trailer...

[2MeterTroll]

splash mark with sharpy pull it and add three to six inches. Never seen a plan that got the waterline right yet. by the time you get the boat built all the load calc the person that designed the boat did is out of date because the gear and materials have changed since the boat was drawn.