CD36 waterline question

[Troy Scott]

Folks,

I've been measuring the lines that are etched or molded into the gelcoat to indicate the elevations of the waterline and boot. I'm guessing that these were done at the factory, and are probably part of the mold. I've also measured carefully to determine how these marks relate to the design waterline. The brochure says my boat has a 5' draft. My best measurements reveal that the mark which I'm assuming is the original top of the bottom paint, is actually 63" above the bottom of the keel. If my assumptions are correct, this would mean that the plan was to have three inches of bottom paint showing when the boat was floating on her lines. Does this seem right to you? Three inches seems like a lot to me. The hull is all sanded and ready for new barrier coat and bottom paint, but there are sufficient remnants of the old barrier coat to indicate where the level had been. Also, I measured and recorded the positions of the bottom paint and boot stripe when the boat came into my life, even though these positions differ somewhat from the etched in lines. I believe that the barrier coat and bottom paint had been raised, but only about half an inch, just moved up into part of the space that is usually left between the bottom paint and the boot stripe.

Is three inches of bottom paint visible above the waterline correct or common? I know that the boat is probably a little heavier, and will likely float a little lower than the designed waterline, and that this would reduce the three inches somewhat. Does anybody know how much additional displacement would accompany a one inch change in draft near the design waterline? I'm wondering if I should stay with the apparently planned three inches, of if I should plan to change it one way or the other.

[Matt Cawthorne]

3 inches would be right. Now add full water, fuel, 4 anchors, lots of chain, a 50 lb tool box, provisions, spare sails (at least storm sails), pots, pans, spare parts, a dinghy, outboard, larger batteries, extra lines, spare rigging materials, refrigeration, etc, etc. and you will wish that you set it at 64 inches. My recommendation is to barrier coat with something smooth up under the boot stripe. If you ever need to raise the waterline it is then reasonably easy.

[Neil Gordon]

3 inches would be right. Now add full water, fuel, 4 anchors, lots of chain, a 50 lb tool box, provisions, spare sails (at least storm sails), pots, pans, spare parts, a dinghy, outboard, larger batteries, extra lines, spare rigging materials, refrigeration, etc, etc. and you will wish that you set it at 64 inches. My recommendation is to barrier coat with something smooth up under the boot stripe. If you ever need to raise the waterline it is then reasonably easy.

How much of that is designed in, I wonder? Water, fuel, one anchor and the like would seem to make sense. What about the crew... Are the "sleeps __" and their gear designed in?

[mahalocd36]

We just raised the waterline on Mahalo. We can measure what the new one is for you for a datapoint.

[Troy Scott]

Melissa,
That would be great! A height above the keel bottom would be ideal, but I can interpolate if you just measure from the bottom of the rubrail to the top of the bottom paint at a specific point: maybe even with the aft end of the house (companionway).

Folks,
When the crane lifted my boat, without the mast but pretty much loaded with all the usual stuff, he reported 18,000 pounds. The design displacement, WITH the mast, is 16,100. I know she's a little heavy.

[M. R. Bober]

Melissa,
That would be great! A height above the keel bottom would be ideal, but I can interpolate if you just measure from the bottom of the rubrail to the top of the bottom paint at a specific point: maybe even with the aft end of the house (companionway).

Folks,
When the crane lifted my boat, without the mast but pretty much loaded with all the usual stuff, he reported 18,000 pounds. The design displacement, WITH the mast, is 16,100. I know she's a little heavy.

I can't find the source, but if I recall correctly it takes 813 pounds to force a CD330 down the first inch below her designed water line. If that is correct, I suspect that it would require about 1,000 pounds to force a CD36 down that first inch.

Also the scales on the travel lifts that we have ridden are not that accurate (5%, 10%...) plus gelcoated fiberglass will absorb water.

If anyone has a link for the displacement info, I would appreciate it.

Mitchell Bober
Sunny Lancaster (where displaced folks are "come heres"), VA

[John Danicic]

Troy:

There are three CD36s out of the water at our marina.

As part of my still ongoing cradle project, I was going to measure each next time I am up. While I am doing it, I could measure the water lines of each if you like. I know I measured one compared to mine from the rail down and was surprised that my water line was much higher. His boat and my boat both sit in the water on their lines. His was a 1979 round the world cruiser. Mine is a 1984 and always in fresh water. She is pretty much out of the factory when it comes to the bottom which, hasn't been painted since the mid 90's and maybe only once before that.

Let me know where you want the measurements taken. I will headed up next on May 12th. Wet snow in the forecast for tomorrow. So it goes in the Spring of 2011.

[John Danicic]

In the ratios section of the 1983 CD 36 owners manual, it states that it takes 900 lbs to displace an inch. (Approximate)

Page 54

It also states "Movement to trim 1 inch = 1400 foot pounds"

Not sure what that means.

[Matt Cawthorne]

About 8 years ago the travel lift operator indicated that my boat was over 18,000 lb as well. At that time the holding tank and the water tanks would have been empty, but it would have had full fuel. Roughly 100 gallons of water would = about 700 lb. I have raised my waterline 3 inches. Since then I have bought more tools, added a Corean sink in the head, added spares, another 65 lb anchor, another 100 feet of chain, SSB, new wiring, etc. The boat still appears to be trimmed slightly aft as the bottom of the boot stripe there comes out of the water with barnacles whereas the boot stripe at the front is about 1/2 inch out of the water. I helped that a few years ago by moving my batteries from the lazerette forward to the starboard berth and removing about (guestimate) 300 lb of lead.

[John Vigor]

"Movement to trim 1 inch = 1400 foot pounds"

Not sure what that means.

John, I believe you measure fore or aft from the center of buoyancy.

For example, if you place a 100-pound weight 14 feet aft of the CB, the stern will trim (sink) by 1 inch. And if you place a 200-pound weight 7 feet forward of the CB, the bow will trim by1 inch.

John V.

[Russell]

"Movement to trim 1 inch = 1400 foot pounds"

Not sure what that means.

John, I believe you measure fore or aft from the center of buoyancy.

For example, if you place a 100-pound weight 14 feet aft of the CB, the stern will trim (sink) by 1 inch. And if you place a 200-pound weight 7 feet forward of the CB, the bow will trim by1 inch.

John V.

Are you sure it isnt refering to port/starboard trim? I am shy of 200lbs and I am pretty sure standing on my bow doesnt sink the boat an entire inch, much less 2 (that would be 13 feet). However standing on all the way outboard on either side at the widest point certainly does (200lbs at 6 feet from center).

[Troy Scott]

John Danicic,

It would be very helpful to have more real-world information. If you get a chance, it would be good to know how other CD36s have dealt with the waterline issue over the years. I think a good place to measure is about even with the aft end of the house, in line with the companionway/main bulkhead. I'd like to know these bits of information:

A. Bottom of the rub rail down to the top of the bottom paint.

B. Bottom of the rubrail down to the actual waterline. (Usually there is some color change and/or other indicators that suggest how the boat was actually floating.)

C. How much difference (if any) there is between port and starboard.

Right now I think I would settle on one additional inch of bottom paint, which would put the paint 64 inches above the bottom of the keel on this boat that was designed to have a 60 inch draft. With the additional information from you and Cathy, I can refine my plan and put to rest any lingering doubts!

WRT the list that I hear about so often, I'm thinking that relocating one battery ought to take care of that if it proves to be an issue.

[Russell]

Keep in mind Troy, there are 3 distinct CD36 models. Measurements from each may differ a lot.

From 1979 to 82
late 82 to mid 85
then an odd year, 85 was transitional, the cockpit changed but interior didnt
late 85 to end of Cape Dory

People from various model years have found lead stuffed in odd places to change trim, water tank location changed when the interior layout changed in 82, though the layout change in late 85 I think kept the tank layout.

All these things will affect fore and aft trim for the waterline. I would hate for you to go through all this trouble then to splash the boat and find the aft end with the bootstripe 1" below the water and the forward end 1" above.

[Troy Scott]

Russell,

Thanks for your concern. I do know about the various changes as the CD36 evolved. I have some old brochures, but there are gaps in my collection. Did the design displacement ever change? Even if it did, I doubt that Cape Dory would have deliberately made a change that would have affected the fore-and-aft trim significantly.

My plan is to stay parallel to and possibly at the molded-in waterline marks on my hull. If I make any change at all it will be to go higher. The results of this present research will help me decide how much, if any, to raise the waterline. If I find later that she floats with a list, trims low at the stern, or whatever, I would deal with that by moving something internal, probably a battery. I dislike the idea of adding trim ballast, but I would as a last resort.

In the refit I've removed some old and heavy items but I've added a few relatively heavy things, so we may float about the same.....

[Len]

There are three distinct issues here. 1. Where is the actual water line of "my" boat when it's in the water (loaded to my needs). and 2. How much higher should I apply bottom paint.

3. The design "line" is really irreleavnt, unless designiing or comparing (theoretica)l hulls. You already know where your boat floats. Why change this unless you plan changing weight or you are unhappy with the appearance of your hem line. We know that everyones boat weights different, not only because of add ons (masts, people, etc) but also because of amount of fiberglass, water absorbtion, etc. etc. All of your measurements are well and good but the real measurement is where was your hem line when the boat's afloat

Lets say you plan a long voyage and add three thousand lbs of groceries, fuel,friends etc. and your boat sinks appx 3 inches.I suppose you would want to have bottom paint at least to the waterline. The rest of the time (non long voyage) you bottom will show 3 inches of green,( white , red) bottom paint. So where should you out that line( up zero, up 1 1/2 up 3 etc.) Do you want to look good at the mooring? would you prefer protection of more bottom paint?

I turned green with envy when I read that John D had not had to paint hbis bottom since the mid 90's. Makes you want to move to fresh water !