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Old 07-08-2016, 17:30   #16
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Max Draft?

SteveinMd

A Depth sounder is sonar, so just like looking at sonar, it will reflect different in hard rock than weeds. I have a draft of 5 feet, loaded up for cruising some more. I went into Midway Marina on the Tenn-Tom reading 4 feet due to the weed growth, so sometimes you know there are differences. I was going slow and never went aground. Once tied up at the dock and paying for my night 's stay, I commented on it to the marina owner. He said they had seven feet and it had been a banner year for weeds.

When I go into an area of limited depth, I use both my depth and sonar screen to see what is happening, and they are different depending on bottom conditions.


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Old 08-08-2016, 00:52   #17
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Re: Max Draft???

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Originally Posted by landsend View Post
Inches will matter when entering channels or marinas for fueling etc, at least in the Florida keys and shallow depth areas.
In the sense that if your draft is a few inches greater than the depth, why, you run aground, then yes, inches matter.

But the point is that very seldom will you know the depth of water ahead of you to that degree of accuracy, so knowing your draft to inch accuracy does you little good.

And once again, the only way to really know your own draft is to measure it. And you can do that to whatever degree of precision you wish.

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Old 08-08-2016, 05:08   #18
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Re: Max Draft?

My experience is that the draft the manufacture quotes is draft with boat empty. Unfortunately my 1.8m draft is now 2m, I found the original waterline last year when scrapping anti foul off.
Last week my draft was 1.6m or the mud was extremely soft coming up the boat lagoon channel in phuket and I was a plough.

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Old 08-08-2016, 05:25   #19
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Re: Max Draft?

Don't forget about swell and waves. You may very well be in 7 feet of charted flat water but in two foot swell you may only have 6 feet under the keel at times... Or whatever.


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Old 08-08-2016, 05:41   #20
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Re: Max Draft?

Loading her down will increase draft of course, but it seems it reduces performance at least as much, so if you can, keep it light.
My IP which is not a performance boat, but when I got her she really did much better than I expected, My Avatar photo was taken by a friend in a Lagoon 380, we were both reaching in the bay, now I won't say we were racing but two boats going the same track you know?
Anyway I was pulling away from them slowly and eventually got significantly ahead, and I was under the understanding that in a 15 kt wind on a broad reach, the Lagoon should have run away from me?
That was when the boat was light, it had zip for equipment, not even a windlass, and three smallish Walmart batteries, and the Lagoon was a live aboard, and I assume significantly loaded down.
Now that my boat is loaded also with gear, a generator, windlass, bigger bank, etc. She has slowed down, it takes more wind to get her going. I went from a 110% Genoa to a 135% and a folding prop to get the performance back.

But she sailed "better" when she was lighter
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Old 08-08-2016, 05:48   #21
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Re: Max Draft?

You needn't worry about it much, though measuring it can't hurt. Either in the water or out.

Realistically, your draft will increase by 1" per 1,100lbs (+/-) added. And you can get an exact figure from the manufacturer, or perhaps the owner's association.

The latter being a good idea to be in contact with regardless. As most such groups coordinate many social activities, as well as knowledge sharing. Including forums, & a lot more.
Here's one, but there are others https://www.catalina36.org/

Enjoy the boat!
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Old 08-08-2016, 10:41   #22
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Re: Max Draft?

Thank you all, you have greatly helped us understand the draft.

Uncivilized, that puts it into perspective for sure. Thank you I will check out their site now.
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Old 08-08-2016, 23:07   #23
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Re: Max Draft?

OP, I generally agree, that you should call the manufacturers specs your draft for your purposes and not worry about it. But I strongly disagree that inches don't matter for boaters in general. I live a mile from the Rideau Canal which is strictly depth controlled by Parks Canada to 60"

My sailboat, depending on load draws between 56" and 58". I definitely care about a couple inches difference in draft or water level.
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Old 09-08-2016, 00:39   #24
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Re: Max Draft?

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Originally Posted by Ungvar View Post
OP, I generally agree, that you should call the manufacturers specs your draft for your purposes and not worry about it. But I strongly disagree that inches don't matter for boaters in general. I live a mile from the Rideau Canal which is strictly depth controlled by Parks Canada to 60"

My sailboat, depending on load draws between 56" and 58". I definitely care about a couple inches difference in draft or water level.
Many cruisers sail where there are things called "Tides". The water level goes up and down regularly. There are tables that purport to calculate how much change from charted depth may have occurred. They are a general guide, but NOt accurate to inches. In some areas, atmospheric pressure changes water depth significantly. in others, on or off shore winds do the same. The result is that the poor cruiser really can't possibly know what the depth is within inches at any given time.

So, I'll stick to my statement that for most cruising sailors, inches don't really matter!

Jim
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Old 09-08-2016, 05:45   #25
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Re: Max Draft?

I am familiar with this phenomenon known as "tides". If you chose to ignore the existence of thousands of "cruisers" who live in depth controlled areas on canals in Europe, Great Britain, the Mississippi, the ICW the Great Lakes then I guess you're right, that inches don't matter, from a narrow minded, self interested perspective.
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Old 09-08-2016, 05:46   #26
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Re: Max Draft?

Even boat speed changes draft. As you push up a large bow wave most boats ride a bit lower in the water. Temperature and salinity also have some effect too. Silting is a factor as is depth sounder condition and bottom type. With all these variables you will never know exactly what your draft is or even exactly how deep the water is in front of you. You just can't play it that close.
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Old 09-08-2016, 06:42   #27
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Re: Max Draft?

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Even boat speed changes draft. As you push up a large bow wave most boats ride a bit lower in the water. Temperature and salinity also have some effect too. Silting is a factor as is depth sounder condition and bottom type. With all these variables you will never know exactly what your draft is or even exactly how deep the water is in front of you. You just can't play it that close.
Yes, boat speed does influence draft, in fact in 1992 the QE 2 ran aground because the crew failed to accurately determine their draft at speed in shallow water. In the attached article, the Oasis of the Seas used her squat to pass under a bridge. https://en.wikipedia.org/wiki/Squat_effect

So if 30 cm (12 inches) matters to the Oasis of The Seas, how does 3 or 4 inches not matter to a boat with a draft of 5'10"? I would do the great loop via the Trent Severn canal with a draft of 5'10', but if I had a draft of 6'1" I would add a week or so to my journey and take the Welland Canal.

If I am in depth controlled waters of 5' and I draw 4'10' I idle, so as not to cause squat, because I can pass safely with 4'10", but motoring at 7 knots, my draft increases, not only by an increase in total draft, but also a change in trim, that will make the draft of the trailing edge of my full keel increase disproportionately to my total increase in draft.

The pro's don't calculate their loads based on Tons Per Foot Immersion or Tons Per Meter Immersion, they calculate their loads for Tons per Centimeter Immersion or Tons Per Inch Immersion. Knock a couple of inches draft off the global maritime cargo fleet and you have influenced the world economy by billions of dollars. If the Captain tells you to load a ship to 28', but you decide to load to 28'2" or 27'10" you are going to have some explaining to do.

Sloppy draft calculations seem to be incongruous with a community that would spend hundreds of dollars extra on carbon fibre winch handles to save grams of weight. I guess those carbon fibre winch handles and Kevlar sails really are just about status and have nothing to do with weight?
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Old 09-08-2016, 14:33   #28
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Re: Max Draft?

Quote:
Originally Posted by Ungvar View Post
I am familiar with this phenomenon known as "tides". If you chose to ignore the existence of thousands of "cruisers" who live in depth controlled areas on canals in Europe, Great Britain, the Mississippi, the ICW the Great Lakes then I guess you're right, that inches don't matter, from a narrow minded, self interested perspective.
From my narrow minded, self interested perspective, I wonder if the depths in all those wonderful "controlled" areas are in fact "controlled" to a matter of inches? From my distant past when I lived on the banks of Lake Michigan, I seem to recall the overall lake levels vacillating by feet, and by wind direction, and by seiche on a shorter time scale.

And I believe that the depths in the canals in France sometimes drop enough that much traffic is stopped.

And I keep hearing here on CF that the ICW is silting up in places and that you can't trust the charted depths.

This is "control"?

Frankly, I don't think that knowledge of one's draft to an accuracy of a couple of inches does matter to most cruisers. You may be an exception, but you ain't most cruisers.

And that continues to be my narrow minded, self interested opinion.

Jim
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Old 10-08-2016, 04:10   #29
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Re: Max Draft?

Now, before you pull out your cruising rule book and start telling us what cruising is and what cruising isn't, I would wager there are a heap more cruising boats operating on the inland waters of North America and Western Europe than there are living on the hook in the South Pacific. So now who ain't the typical cruiser?

You will recall from your youth that the water level at the banks of Lake Michigan isn't relevant to whether you can successfully transit a canal. What matters is the depth in a very specific point and that point is the cill of the lock, one inch too deep and you can't cross the cill.

There may be variation in the canal authorities ability to control the depth over a cill, depending on geography. However, the depth at the cill of a lock will be known, yes, to within inches.

When that water depth is known, if you know your draft accurately, to within inches, you can make a decision whether you want to enter that canal or water way or not.
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Old 10-08-2016, 04:25   #30
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Re: Max Draft?

Oh dear....

Thinking that you can safely navigate anywhere ( lock sills included ) to a depth tolerance measured in inches is akin to giving position reports to the third decimal of a minute of arc......
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