GIS Waterline?

[DALukens]

Hello All:

Getting ready to epoxy the bottom of my GIS, then paint etc. I was wondering -- does anyone have any easy way to determine (or does anyone know) the waterline for the GIS? I will be using anti-fouling paint on the bottom and may also paint a boot stripe.

Thank you!

Dana Lukens

[jmk89]

I don't know the answer, but this thread (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=70863&highlight=waterline) has some useful info (altho' directed to kayaks)

As for anti-fouling,I would have though it was only useful if your boat is going to be kept moored in the water. If it is kept on dry land, I can't seewhat you would gain except weight...

[Daddles]

Don't you fill the pool with paint, drop the boat in, then carefully lift it out and let it drip dry? :rolleyes:

Richard

[Boatmik]

I have a reply mostly written but I need to finish it ... will be up thisevening.

MIK

[Boatmik]

Hi Dana,

Just to make sure that you are doing the right thing as antifouling a dinghy is not common,.

Antifouling type paint is only needed for boats that are going to be in the water for longer periods without drying out on land. It is very rare to antifoul (it is a toxic paint) a dinghy to prevent marine growth as they don't really spend enough time in the water for the problem to occur.

However, you may have an unusual situation, so this is just a note to check that you have not received the wrong advice from someone.

JMK's link is perfect as it explains almost the problem from every angle. but the real detail is difficult to extract.
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The easiest way to mark a water line is to put the boat on some level and flat surface then set it up so the bow is higher than the stern by a particular amount.

Read this next bit carefully...

To get the Goat perfectly level the bottom of the bow would normally be 22mm (don't use this number yet!!!!) higher than the bottom of the stern. However the problem is that the boat will float at many different angles depending on how much weight it has aboard.

Because of the way the Goat is designed, as it is loaded up, the bow will sink faster than the stern, providing people sit near the mid seat as they are supposed to in sailing mode or are on the three seats in rowing mode.

So the general practice with boats is to move the waterline up a bit at the bow as well as moving it higher than the actual design waterline.

I would suggest that you set the GIS up with the bow only 10mm higher than the stern. This makes sure the waterline will usually be 12mm higher at the bow when the boat is afloat. For a 20 to 30 footer I would probably set it up so that the line was 25mm higher at the bow.

Now, how high do you make the waterline? Where is the starting point? I would choose the corner of the bow or a bit higher.

The easy way is just to cut a block of wood that will sit flat on the floor that is the right height compared to where you want to start. Then you place it beside the hull and it will show you where to mark.

Do not draw a continuous line or you will pick up any undulations in the floor!!!! Make marks about 300 to 400 mm apart and you can fair them later.

The masking tape you need to use is the blue paper tape ... the creme coloured one is crap - it will fall to pieces while you look at it or when you take it off the boat it will fall to pieces. Also paint goes under it very easily.

To fair the line you can put the boat upside down (this is the Goat, for something bigger it might be necessary to do this the right way up) - do one of two things.

1/ Get a nice wide but thin fairing batten at least half the length of the boat (preferably longer - if you do have to move it along ... move it about half the length of the batten each time so there is an overlap with the part of the line you have already drawn).

Invite a few friends (tell them it is boring but necessary and give them beers AFTER doing the job) over to hold it in place while you check it is ok by walking around and looking from different angles until is is right. Then draw a line

Sometimes you can get masking tape to hold down the batten if you are by yourself and the batten is not too stiff.

"Right" is the same principle as marking out the hull panels (but without using nails!!!). If the original marks are wrong then ignore the ones that are wrong but get the line as close as you can to hte majority of marks while making sure the line looks sweet to the eye.

Then follow the masking tape method (you can use the masking tape method directly on the marked points without marking the line too).

2/ The other way of marking the line is to use masking tape.

The problem that everyone with masking tape is the same as driving a car. If you look close in front of the car you will wobble everywhere, but if you look further ahead the car will follow the road in a smooth way.

So the trick is to attach the end of the tape at one end then walk about two metres down the boat so there is two metres of tape stretched out. Now move the roll toward the surface in a slow but smooth action while watching the marks on the hull. It is OK if it misses some of them because the point is the tape has to be smooth. Only do about a metre and a half of the taping then press down what you have done so far.

then pull out another two metres of tape by walking further down the boat and repeat watching the tape rather than the marks. if there is a bump in the transition from where you stopped the first run carefully lift up about 300 mm of the tape that is stuck down then continue ... using your eyes to check the smoothness and keeping a slight eye on the marks at the same time. Push down the tape to the surface except for the last 300mm

When you have done a metre and a half pull out another couple of metres .... which should just about finish the boat. Any bumps between the last 2metres and the current one and pull about a foot of tape up and start again. And you should just about be finished.
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YOu can also do this as a two person process with a lackey who follow along and can pat down the tape as you move along or help pull it off the surface in a controlled way if there is a bump. Just keep a metre and a half ahead of him all the time and control where the tape goes down. If the lackey tries to place the tape it will be all bumpy ... the guy in the lead who is looking along the tape is the one who will get it down smooth.

With boats getting curves smooth is the biggest secret. I've seen 11ft boats that were out an inch and a half on one side but no-one noticed including me because the curves were just so smooth and nicely done.

Masking tape costs nothing so don't be afraid to use it.

But JMK's link covers almost everything = arguments/counterarguments, other methods etc.

Best wishes
Michael

[DALukens]

Mik:

Thanks for the tips on marking the waterline. Because I intend primarily to leave my GIS moored near my lake house, I was advised to use anti-fouling paint. I too was skeptical, but several people gave me this advice.

Here is a pic of the GIS (current progress) and the lake. (Calm in this picture but it can get very windy and rough.)

Thanks again, Mik.

Dana Lukens

[Boatmik]

you might (actually probably will) need some weight strapped in under the mid seat to make it sit happily.

Michael