How to Mark a Waterline.

With the boat chocked ashore and the old antifouling removed ready for the waterline to be marked up against the boot-top, the question now gets asked, how is best to mark up a straight line.

With the boat chocked ashore and the old antifouling removed ready for the waterline to be marked up against the boot-top, the question now gets asked, how is it best to mark up a straight line.

Hand repair or restore any blemishes or damage to the Hull, Keel and bow then applying two coats of antifouling up to the old water line should be fairly straight forward.

Overtime after many applications of Marine gloss the manufacturers waterline may have disappeared under the paint on the hull. Trying to keep the existing boot top line parallel to the existing water can prove tricky, what you need to do is measure upwards vertically from the line in several places and then join the marks, (tip: measuring equal distances on the hull itself will give you a curved line as you will make no allowance for the horizontal component of the measurement.

Traditionally a very taut length of string would have been used to to mark the boot top, however this method has its issues, obtaining a very tight tension on the string is the first that you may encounter, the second being the string may stretch and sag. In today's technology driven world, a good tool would be a tripod mounted laser line spirit level, these project a level line accross the surface and may be raised or lowered by the centre post on the tripod.

Making sure the spirit level is perfectly level then the Laser needs to be aimed at the original waterline, raise the spirit level slightly then proceed to mark the first point with masking tape. Move to the next line along the Hull, (tip: revert to equal distances creates a very nice curved line). Continue until the entire side has points masked off, now you may join these points up and masking tape an entire line accross the Hull. It's also important to aim the laser at right angles to the waterline so that you follow the curve of the hull.

There are specialist tapes that allow for curved surface like hulls, but it is alway worthwhile double checking and resighting the line to make 100% sure it flows prefectly and parralell on the Hull.

Finally apply your two coats of antifouling to complete the project.

Below we have included 4 ways to mark a waterline.

1 - Water level, providing your boat is chocked up perfectly level both fore, aft and athwartships, you can use  a length of clear pipe filled with water. Fill the pipe with water and tape the clear tube to the Hull at a single point, Use this as a reference point and mark the pipe at the level of the new waterline, at this point a second pair of hands is required as you walk around your boat to prepare the pipe for levelling and marking the otherside.lift and lower the pip accordingly to level the water off then makr both sides of the Hull, move onto the next mark and apply the same method.

2 - String, beams, and a spirit level.
This kind of method is capable of coping with a boat not being 100% level but errors can occure if the vessel is leaning and just foward of the bow, we do advise if your boat is leaning this can be dangerous, try and make as level as possible.

3 - String, Beams and a Spirit Level
The biggest issue with the above method is that it can require exceptionally long beams to allow the string to be in contact with the hull at the bow and stern. an alternative method is this, setup a string at the waterline level parallel to the boat but this time use a spirit level to transfer the level of the line to the hull, without deflecting it ensure the spiriit level bulb remains level and mark where the level contacts the hull.

4 - Laser level
Most laser levels spread a beam horizontally, if the boat is level fore and aft set the laser lever with a new waterline and mark the beam spread at equal points then join the marks up to create a perfect parallel line. (tip: although the laser level is perfect on white hulls, blue, red, black hulls the beam spread could be difficult to read)


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