Thread: Marking the waterline

Darren, I guess my question is 'why?'.

This isn't a reflection on you. I've watched this discussed on yankee forums where it has assumed the status of religious imperitive ... and I can't for the life of me work out why.

To me, you paint your hull a particular colour and leave it at that.

But that doesn't answer your question and to be honest, it doesn't matter 'why' you wish to do so, only that you 'do'.

So, how do you do so?

My first question would be: "how accurate do you want it?"

If you're concerned about the 'waterline' being absolutely accurate, you really have no choice but to wait until she's finished and you can sit in her in the water because your weight and the kayak's weight will work to give different answers for different people.

However, if you sort of resemble an average human (in weight) and you reckon you've managed to build the boat as per the plans, I reckon you can work off the waterline shown on the plans (assuming a half decent designer). Once you've marked one waterline point on the boat as per the plans, it shouldn't be hard to mark the rest of it using a water level. The theory is that water in a tube will assume a level relative to gravity - using a piece of clear plastic pipe with water in it, it's not hard to fiddle around so that the water level lines up with a known point on the hull ... and mark the other points on the hull where that have the same water level. Join up those points and you have a line that reflects every point at that level.

Laser levels are very cheap now and they'll do the same job. They might even be accurate but a well used water level will be every bit as good.

Personally though, I'd just paint the hull the same colour all over and ignore the waterline as irrelevant.

Richard

Even on a cargo vessel, I expect that only the theoretical waterline can be established from the plans. In my very imperfect understanding, certifying agencies may require actual in-the-water testing, and possibly re-verification as the ship ages or undergoes repairs or modifications.

Note: I'm not a naval architect, nor do I play one on the tube, but I have stayed at Holiday Inn Express.

Joe

Yes - the plans are the thing.

The problem is with stitch and glue type constructions the displacement and balance of the canoe or Kayak is never worked out.

However with traditional builds and stitch and glue there is a datum waterline on the plan.

A simple way to mark a waterline is to set up the boat the way it shows on the plans on a level floor. A kayak or canoe might need to be raised on blocks.

Then work out where the waterline is at the bow and the stern - get them level an equal distance from the floor. Make sure the boat is sideways level too.

Before you mark there are two things to realise.

Usually the paint of a waterline goes above the waterline. For a canoe or kayak this might be 12mm.

Second - you are never really sure just how the boat will float with different gear and different people or if the designer got the line exactly right. So it looks REALLY bad if the waterline is high at the back and low at the front when the boat is being used. So generally the front is made a bit higher than the back - so I would add another half inch there.

Skilful artisans sometimes make the waterline a bit curved - so they will use the half inch high point in the middle of the boat - add half an inch at the bow and add a quarter inch at the stern.

Bigger boats - bigger distances - or use a boot topping - bottom paint ends then a narrow band of contrasting colour is above that.

You can join the series of dots using a masking tape - pull out a metre and a half at a time and sight along it while moving your hand closer to the surface.

Or if you have a couple of friends you can join with a batten. The batten needs to be stiff vertically and flexible laterally. That way you can hold it vertical (at all times) against the line of marks on the hull (it is flexible enough sideways to follown the boat shape and draw long straight lines.

And everything is easy compared to clinker/lapstrake boats!!! But it is not too hard if you remember the angle that you look at the line when doing the job is different from how it will look in the water - most people will be looking DOWN toward the waterline.

People sometimes use more sophisticated methods such as laser levels or dumpy levels too. Great if you have one in the shed!

Best wishes
Michael Storer

Michael

OK, I have never done a full-size boat, so this might not work. You've been warned. When I mark the waterline on a model, I rest it on blocks so that it is level. I then attach a pencil to a piece of timber. Run the end of the timber on the floor, and you will get a consistent waterline. On a larger boat I suspect you would need to arrange quite a large base so that you could maintain it square to the floor. Then just mask along the pencil line.

Peter

Hi,

Thanks for the replies Here's my responses:

Peter - that's how I do it on model boats too. But seemed a bit "iffy" to try to get a pencil on a level lined up on a level bit of string. And my floor isn't completely flat so can't run it along there.

Richard - Why? I ask myself that when trying to picture it But the bottom panels were my first ever scarph joints, and not too neat, and there is the row of stitching holes along the side join. Hull to deck join has a cover strip. So I figured I'd paint the hull bottom and up the sides to the waterline, with a chevron feature at front and rear. So it probably doesn't matter exactly where the line is, as long as it's straight.

Mik - Yes, my concern is having it up at the bow or stern. But I think it will float pretty level lengthwise so may go with the water tube or laser level method once I've got the boat level.

Will post pictures of the results, be they good or bad

Thanks,
Darren

I run into this issue often in restoration work. Waterlines are often removed with planking, sanded away by a helpful owner or just not reliable for one reason or another.

Small boats are dramatically affected by trim. Gear, equipment, supplies and crew will substantially alter the LWL. A decision has to be made as to a "static" line or a "dynamic" line. Again, on small craft (say under 4 meters) the LWL will move a lot with different loads, so static is usually the only option.

You can make a guess the keel is parallel to the LWL or you can splash the boat, which is what I usually do. I'll install all the things that would normally be there except the crew, as if it was waiting at the dock for the owner to return from a beer run. This would include anchors, oars, dock lines, PFD's, radio(s), etc.

I'll wax both sides of the bow about where I think the LWL will be, again the same at the stern. Then splash the boat in a calm area. Let the waves settle down a bit, then using a spray can of regular old primer, I'll put a dot at the bow and stern. If a transom stern, then a dot on each corner of the transom. The water will not let the primer stick. The wax will not let the primer stick very well to the boat, but it does leave a visible reference.

Trailer the boat home and block it level to the primer marks (both longitudinally and athwartship). This is the static LWL. The slickest way to get a dead bang straight as a preacher's wife line, is a laser level. It also makes easy work when you can just tape along a laser line. If no laser, then a water level works as does a bubble level on a stand worked around the LWL perimeter.

The primer usually wipes off easily, because of the wax, but mineral spirits will also remove it without damaging a pretty paint or varnish job. I typically "scratch" a line into the finish, so it can be found at a later date also.

Darren

I would think that if you wanted the water line to look right you really have to put it in the water. Have you thought of wrapping it in a sheet of clear plastic and making marks through the plastic with carbon paper? If you can get a mate to help you do this while you are sitting in it you will get the water line to match your weight and seating position.

Peter

One of the things to realise is that the waterline that is painted is not normally the actual waterline. Usually is it marked a bit up as you want it clearly visible when the boat is afloat - otherwise it doesn't make much of an aesthetic impact.

The tweaks suggested above reduce the risk of an estimated waterline being a little bit out.

Best wishes
Michael

Originally Posted by PAR

The primer usually wipes off easily, because of the wax, but mineral spirits will also remove it without damaging a pretty paint or varnish job. I typically "scratch" a line into the finish, so it can be found at a later date also.

When doing a boat restoration it can be like finding gold when someone has done this!

Another way that will make a later maintainer or restorer weep with joy (in a positive way) is a series of shallow holes - very shallow, more like dimples - drilled into the hull at even intervals.

By very shallow - maybe a 4mm drill bit and go in 1 or 2 millimetres at the deepest point maybe 600 mm apart or bigger on large boats Sometimes fibreglass boats have them moulded into the surface. Not really visible unless you are looking for them

They get filled with paint or epoxy later on but the change in colour is often enough to allow the waterline to be picked up again.

I have found those "bits of gold" but unfortunately not very often and wondered if I should trust it when I did. I've marked a lot of LWL's over the years and now have been using a laser for several.

I have a set of formulas, designed by Starling Burgess, which describe how big a boot stripe should be, how much sweep is should have, the location of the sheering and the differences between the bottom and the top of the boot stripe. I've used it on a few occasions, but mostly just use the eyeball method. Again on small craft, adding sweep to a boot is silly, though I do if the beam is dramatic (fat boats). This is to offset the optical illusion when the boot transitions from the widest portion of the beam to the stem (and stern in double enders).

Another area is the turn of the bilge at the bow, especially on power boats. This area can transition from nearly horizontal to nearly vertical in just a few feet. This causes another optical illusion, which makes the boot strip appear as if it gets skinny, then fattens again. The laser level will catch this, but sometimes you have to cheat what the laser is telling you so it'll look right.

On a skinny hull like a catamaran, canoe or kayak, I'd use a straight boot without any sheer in the stripe.

Hi,

Thanks for all the tips. Stored away for when I make something bigger.

After much levelling, string lines, masking tape and lasers today, marking out waterlines that matched the plans, where it should be, and where it looks right, I finally decided to do without the waterline.

So went full loop on Daddle's question of "why?" to get to "why bother?" if it's in the water and will be at different levels depending on whether it's loaded with gear or not.

At present looking to paint the sides with a couple of diagonal bare wood stripes for styling and a bare wood deck. I have British Racing Green but may go for white. Another decision for tomorrow when I'm trying to rid the workshop of every last speck of dust.

Darren

You'll be amazed at how imperfections just disappear. Redback is pretty rough when you do a 'show boat' inspection, but no-one ever notices enough to make comment, not even my father who's never shy about such things (not with his son anyway - the strange thing is, it's always meant kindly. Bloody fathers ). There are problems I haven't noticed (at least not in the last three years) until sitting on a looooooooooonnnnnnnnng tack the other weekend and quite frankly, at that point, I was looking for something to notice

Richard

Wise decision.
With little boats like Kayaks, trim variations makes it more sense to change colours at the sheer line.
cheers
AJ

Originally Posted by PAR

I have found those "bits of gold" but unfortunately not very often and wondered if I should trust it when I did. I've marked a lot of LWL's over the years and now have been using a laser for several.

I have a set of formulas, designed by Starling Burgess, which describe how big a boot stripe should be, how much sweep is should have, the location of the sheering and the differences between the bottom and the top of the boot stripe. I've used it on a few occasions, but mostly just use the eyeball method. Again on small craft, adding sweep to a boot is silly, though I do if the beam is dramatic (fat boats). This is to offset the optical illusion when the boot transitions from the widest portion of the beam to the stem (and stern in double enders).

Another area is the turn of the bilge at the bow, especially on power boats. This area can transition from nearly horizontal to nearly vertical in just a few feet. This causes another optical illusion, which makes the boot strip appear as if it gets skinny, then fattens again. The laser level will catch this, but sometimes you have to cheat what the laser is telling you so it'll look right.

On a skinny hull like a catamaran, canoe or kayak, I'd use a straight boot without any sheer in the stripe.

I saw Par's reference to the Starling Burgess waterline formulas. Any chance of getting a link to them??