finding the waterline on trailer

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sailingbud
Bottom Paint Application Technician
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finding the waterline on trailer

Post by sailingbud »

Greetings, My boat is on a trailer and the hull is down to bare fiberglass below what looks like a waterline (the bootstripe is gone). I would like to find the real waterline so as I build up fresh fiberglass and eventually paint it, I'll have something like a bootstripe where it is supposed to be.
My idea is to first level the boat. Placing a level across the cabin benches and another level across the cockpit benches. Almost all of this boat is gutted. The only interior parts are the bulkheads and benches less folding table. The designed waterline is reported at 21ft. When I measure the bare glass bow to stern it is 24ft. My guess is that the grinder took off a bit above the original line. Using the clear hose trick I could find a level mark front and back that is 21 ft long and that should be where the boat floats. Is this reasonable?
Quetzalsailor
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Re: finding the waterline on trailer

Post by Quetzalsailor »

My first thought is that you shouldn't put the trailer in the water and thus don't need a waterline.

Perhaps more useful: Find a matching boat and take some measurements. Or float it. There's no reason that the seats would be level fore and aft. The painted waterline is usually higher than the actual floating line. And it's usually higher at the bow than at the stern as a matter of custom and taste. Examine the boat carefully, the intended paint line is sometimes incised into the mould so it may show in places where the grinding was less enthusiastic.
sailingbud
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Re: finding the waterline on trailer

Post by sailingbud »

Thanks for the thoughts. Your right. I just need to keep the trailer out of the water.
I'm pretty sure there isn't a sistership for over 1000 miles. If I were trying to level or find the water line on my daysailer it would be easy to splash her and make some marks. My boat is not able to launch without a lift so I'm wanting to finish everything so just one launch for as long as this bottom job lasts anyway. Unfortunatly, I wasn't in the picture when the lower hull was ground down.
Zach
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Re: finding the waterline on trailer

Post by Zach »

You can strike your boot top now, but don't paint the bottom paint until a day or two before she goes over. Bottom paint oxidizes and isn't much good after it has...


See if anyone, anywhere has a line plan of the boat. That would be the easiest...


Find a picture of the finished boat, and print it out.

Measure out the picture's waterline. Enlarge it until the waterline reads correct and proper on a 1/4, 1/2 or 1 inch per foot measure. It should be 21 feet, but boats are notorious for being labeled wrong, so measure the deck line on your boat and then use that to compare notes, not what it is supposed to be.

Then measure up the stem's waterline, plumb... (extend the waterline, lay a square on it.) Same for the transom. A caliper, vernier scale, or steel rule and a very careful eye will give you a funny looking decimal, or fraction. If you get a whacky fraction, figure it to the smallest you can eyeball. Then take that 15/32nds or what have you, Divide 1 by the bottom number, multiply by the top number now you have the decimal equivalent.

Then you can either use an engineers scale/architects scale (staples and drawing stores sell them) or do some math to take that inch and change, and multiply it by your scaling factor of 1/4, 1/2, or 1 inch. What you get is how many feet down from the bow and stern you need to go. Multiply by 12, to get that into inches. Your leftover fraction or decimal place should look less weird, except it is in tenths of a foot. Now you multiply the decimal, by 12, and get inches and parts of inches.

The parts of inches, gets converted back to a fraction so you can read it on your tape measure. Now you can cross multiply, put the decimal over 10 on one side, and x over 12 on the other... and get something that still isn't on your tape measure and is in 10ths or whatever. Look up a decimal equivalency chart, drill chart and get a fraction that is close.

If the boat is sitting out of level fore and aft by a whole lot... If you are working alone you need to extend the waterline on your drawing, and grab a protractor or angle finder and drop a plumb line from the transom and stem. If you don't have one you can measure the three sides of the triangle you have drawn. Measure out where your plumb line hits the waterline, go cut a plywood gauge block that you can slide a tape measure down on the straight side. Put a line across from the straight side to the angled side with a square and that will be your mark to mark the hull. If you measure down the diagonal of the stem, there is often nothing to hook your tape on, nor can you see the top and bottom of it at the same time. By yourself, a gauge block is easier to get perfect. Also know that the length measured laying the tape on the stem, and plumb to the waterline like she'll measure floating.

If the boat is level perfectly, and you have a helper you can measure down to the top of a level to mark the hull.
1961 Pearson Triton
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Hirilondë
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Re: finding the waterline on trailer

Post by Hirilondë »

Zach wrote:You can strike your boot top now, but don't paint the bottom paint until a day or two before she goes over. Bottom paint oxidizes and isn't much good after it has...
That depends on the paint. Micron Extra, an ablative, works just fine the next year so long as there is enough still on the boat.
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
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Gresham’s Law of information: Bad information drives out good. No matter how long ago a correction for a particular error may have appeared in print or online, it never seems to catch up with the ever-widening distribution of the error.
Zach
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Re: finding the waterline on trailer

Post by Zach »

Cool! I didn't know that about Micron Extra. That may sway my future paint choices...

Thanks,

Zach
1961 Pearson Triton
http://pylasteki.blogspot.com/
1942 Coast Guard Cutter - Rebuild
http://83footernoel.blogspot.com/
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Rachel
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Re: finding the waterline on trailer

Post by Rachel »

While you're being swayed, just note that it's not peculiar to Micron Extra. A number of other bottom paints are similar in their ability to be left out of the water without being spoiled.
Hirilondë
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Re: finding the waterline on trailer

Post by Hirilondë »

If you go with an ablative it is good to have a tracer coat on first. Paint the bottom some color that contrasts with your choice of color. Then paint 2 coats of the color you want. Now any year you think the paint is building up do not paint that year. Or just hit the high wear spots (leading edge of keel and rudder and the waterline). You will always have that tracer coat to show that almost everything has worn off. You will find also that most ablative paints can be painted over most hard paints. You will also find that no hard paints, or anything for that matter, should be painted over any ablative paint. The logic is rather obvious. The prep work needed each season before painting is a selling point for ablatives as well.
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
Gresham’s Law of information: Bad information drives out good. No matter how long ago a correction for a particular error may have appeared in print or online, it never seems to catch up with the ever-widening distribution of the error.
seasailor55
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Re: finding the waterline on trailer

Post by seasailor55 »

This may sound pretty basic, but I'm trying to mark a waterline on a hull (Pearson Ensign). There are plenty of drawings out there for the boat, so I have no problem finding waterline locations at the bow and at the stern, from a profile view. It gets tricky when you get up under that overhanging stern, since a painted waterline flattens out and widens considerably as it wraps around under the stern. Is there a simple way to get the waterline straight (curved?) all the way around the boat without doing a projection onto the hull (at night, with a laser level, etc.)? I've read the posts and it sounds do-able, but how do you measure and mark along both sides from bow to stern and ensure they're the same? Did I miss something? The boat is sitting on a trailer and can be leveled.
Paulus
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Re: finding the waterline on trailer

Post by Paulus »

Get one of these and trace the marking lines at dusk... create two lines at the vertical distance you desire and they will project on the boat on "eyesight" basis, adjusting the actual width as you described.

Image

Home Despot sells them relatively reasonable - I have one that projects a red line
CharlieJ
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Re: finding the waterline on trailer

Post by CharlieJ »

Better yet- find some one who installs drop ceilings and borrow one.
Hirilondë
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Re: finding the waterline on trailer

Post by Hirilondë »

I still use my manual optical David White vintage 80s transit. By the way, why are people still looking to find the waterline of a trailer? ;-)
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
Gresham’s Law of information: Bad information drives out good. No matter how long ago a correction for a particular error may have appeared in print or online, it never seems to catch up with the ever-widening distribution of the error.
seasailor55
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Re: finding the waterline on trailer

Post by seasailor55 »

Dunno, Hirilonde,

I guess so someone can holler "OOPS - you're past the trailer waterline!" when you back that $30,000 truck too far down the ramp. Maybe we'd be better off putting waterlines on our tow vehicles :-)
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