Draft question
- Thread starter Yellowjeepman
- Start date
I see a line of stick on tattoos showing up in the forum store, the "reduced manoeuvrability" one being added after sufficient hydration.Yah, I don't do tattoos.
Sailcalc lists the Oday 34 as 1156 lbs/inch immersion. https://web.archive.org/web/20140328112219/http://www.image-ination.com/sailcalc.html
As others have posted if the offset is set correctly it will make no difference though.
As others have posted if the offset is set correctly it will make no difference though.
Google sail calculator. O'day 34/35 are listed as 1156lb/inch. Or 1 inch more draft for each 1156 lbs over your design weight.
Cannot disagree with that.... and even if they knew what it meant... would they care?
Not under command eh? Not married huh?
Not under command...
I should just wear that on my t-shirt:dance:
... or maybe when out carousing I could wear a t-shirt with...
Restricted
Maneuverability
\
Kermit if you wore one of my T shirts it would have holes in it
but i do like rgranger's idea ..but it would be really cool if it was a haliagrham
....so the numbers that are posted in sailboat data that show "max draft", what do you guess that is based on?
Perhaps we could provide a simpler, useful, albeit not precise answer to Yellowjeepman's newbie question...
1. As mentioned above, it is most important to determine whether your depth reading is adjusted to read from the keel bottom or from the water line. That is easily measured and determined at the dock.
2. Comparing those measurements will give your minimum floating working draft.
3. Adding fuel and people is not likely to change that draft by more than an inch or two on that boat.
4. The sea bottom is never a smooth, gradient surface. Variations and small sunken obstacles are everywhere. Give yourself an extra six inches to a foot and go slowly in shallows and you should be okay.
1. As mentioned above, it is most important to determine whether your depth reading is adjusted to read from the keel bottom or from the water line. That is easily measured and determined at the dock.
2. Comparing those measurements will give your minimum floating working draft.
3. Adding fuel and people is not likely to change that draft by more than an inch or two on that boat.
4. The sea bottom is never a smooth, gradient surface. Variations and small sunken obstacles are everywhere. Give yourself an extra six inches to a foot and go slowly in shallows and you should be okay.
All vessels drafts are calculated on dry weight. The more weight you add the farther down your boat will sit.If you have a depth gauge check to see where the transducer is mounted, if on the bottom of the boat you need to program the unit for the added depth your keel is, if mounted on the keel you need do nothing. At your dock take a reading before adding anything to the boat, then again when fully loaded with crew, this will give you the added depth your boat has settled down.I have a Macgregor 2-24 and with 20 gallons of fuel,20 gallons of water plus a 20 gallon holding tank she only sits 4 inches lower in the water then when dry. Hopes this helps.
Not sure how this got from draft to lighting rules but going back to draft; get a 25-50' or so cloth or plastic tape measure (they come on a reel and it is convenient to get one calibrated in tenths of feet rather than inches) and tie/tape a 1' long piece of 1/4" re-bar to the bottom. Make sure the top of the re-bar is on the 1' measurement on the tape. Drop it over the side adjacent to the position of your depth transducer. Calibrate your depth gage to the taped reading. This can also be useful to get your loaded draft. Just ease the boat into shallow water until you GENTLY ground and measure the bottom.
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I've done this in my slip when the water is blown out of the creek and I'm on the bottom. However, just as the Annapolis Parade of Lights started, my 4'9" boat was aground- at 6.5 feet on the meter. Bottom compostion makes a difference, too.
As a hydrographic surveyor I tend to over analyze the sonar depth issue so forgive me if I do. The main issue for us is to understand how close are we to running aground at any one location. I have heard some people want to know their keel clearance and some want raw water depth adjusted for transducer draft so they can calculate an estimated clearance where they are, based on tide, wind etc. You also have to remember what datum your chart is using. If its mllw then chances are you will have more water than the chart would indicate. However safety dictates that we not get into that grey area. I have found along the north coast of the Gulf of Mexico that I usually have more water than the chart indicates (high tide or normal tide, south winds, compared to chart datum). Myself I only calculate my transducer draft as a check to actual soundings taken. When taking a manual sounding you have to consider the density of the bottom also. If you use a hammer on hard sand your probably ok if you measure the offset to the hammer head and tie you tape to compensate for handle length etc. (remember we want a true depth). Some places in south Louisiana are so soft you cant feel the sounding lead hit the bottom, it just slowing sinks into the slush. I refer to the bottom as "chocolate pudding). A 12lb lead with a 6 inch bottom generally will stop at a density of what a 200 kHz sonar will penetrate. However that gets iffy depending on other things that have nothing to do with keeping our keels out of the mud. I digress, on my boat I pick a nice calm day and take a manual sounding on a hard flat bottom and with my boat level (no heel) I record a sonar depth. the difference is your transducer draft or the difference between the raw depth and the sonar depth with whatever transducer draft is set in it. (I reset mine to zero draft before the test). Also don't forget the effects of shoaling from rivers and streams. All bets are off down here after a hurricane and no mater what the chart says you have under you, a submerged log on the bottom will probable not be on the chart. I use a draft on my Catalina 27 of 4.0 ft and I get nervous in 8 feet of water. logs, pilings, wrecks, shoals, etc. I prefer raw water depth so all I need is my chart and a tide table. The rest is my margin of safety for how shallow do I want to run. My two cents. And by the way I have run aground in some "chocolate pudding" and according to my sonar the water was 3 feet deep. it was so soft I sailed along in it for over a mile before I finally ran out of water and had to retreat. So much for that short cut. LOL
Re: Draft
I am fairly certain that the specified draft of your vessel is dry weight.
As for the calculations for predicting how much draft you will lose when loaded, I cannot help. They are probably a bit complicated since hull shapes vary greatly.
What I do may or may not be recommended. I am hoping that I am using common sense. I just keep an eye on where my boot stripe is in relation to the water on the hull. Compare it to when you are fully loaded to when you are not fully loaded. This is usually only a few inches. In other words, consider your draft a few inches deeper or not. Of course, you should consult an expert if you think you are carrying more weight than the boat was designed for or the water on the hull gets up to the boot stripe.
I am fairly certain that the specified draft of your vessel is dry weight.
As for the calculations for predicting how much draft you will lose when loaded, I cannot help. They are probably a bit complicated since hull shapes vary greatly.
What I do may or may not be recommended. I am hoping that I am using common sense. I just keep an eye on where my boot stripe is in relation to the water on the hull. Compare it to when you are fully loaded to when you are not fully loaded. This is usually only a few inches. In other words, consider your draft a few inches deeper or not. Of course, you should consult an expert if you think you are carrying more weight than the boat was designed for or the water on the hull gets up to the boot stripe.