Newbie question on draft

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GilliganChris
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Newbie question on draft

Post by GilliganChris »

Hi all,. My wife and I are the proud new owners of a 1976 F30 Flybridge. It's our first boat and we are looking forward to learning a lot.

I apologize if this has been asked, but I couldn't find a definitive answer using the forum search. I have learned a lot from you all, in reading through the forum for the last couple of weeks, though.

I've read that my boat's draft is around 2' 6". I'm not sure if that includes the shafts and props or just the bottom of the hull.

I'll be using the navionics app on my iPad to help navigate our fairly shallow lake, and would rather not run aground. What is the realistic minimum depth I should stick with?

Thanks in advance, Chris.
1976 Trojan F30 Flybridge <- First boat EVER.
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prowlersfish
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Re: Newbie question on draft

Post by prowlersfish »

That's should include running gear . But remember as you load the boat it gets lower . When you put it in gear it gets even lower ,the more throttle the lower it goes .
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Svend
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Re: Newbie question on draft

Post by Svend »

Do you have a good depth gauge device? I use mine all the time and consider it essential gear, especially on my lake. I have the sensor at the bottom of my hull, and my props stick down 1 foot. So if the depth says 3 feet, I know I have 2 feet to the props. (there is probably a way to create an offset in my depth gauge, but have not read the manual for that item yet... )
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Cmount
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Re: Newbie question on draft

Post by Cmount »

Just be careful. Chart depths are not really that accurate to navigate by in the low numbers. If you need 2.5 feet and you are looking at going places marked 3...just not enough room...and if you get in to places where you are close, all it will take is a rock, or a bottle or a sunken log to ding a prop and ruin a day....stay in the deeper water as much as you can.

And for sure GET A DEPTH finder! Best money you will spend as a new boat owner.

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GilliganChris
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Re: Newbie question on draft

Post by GilliganChris »

Thanks all, for the great feedback.

Unfortunately, as the boat sat unloved over the years, the electronics seems to have been scavenged. There are still mounting brackets where the VHF radios and depth finder used to be.

I'm already planning on having a new depth/fish finder installed when the marina pulls the boat out for the winter, in a couple of weeks. In the mean time, I intend to stay in 6+ feet of water whenever I can.

Good point about the boat needing more water when on plane, etc. I only foresee being in shallower water if I'm docking at the municipal dock across the lake, to go for lunch in town. I'm told the water is around 3.5 to 4 feet deep there.

Looking forward to getting to know the boat a bit more in the next couple of weeks, before she's shrink-wrapped for the long Ontario winter.
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captainmaniac
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Re: Newbie question on draft

Post by captainmaniac »

A few notes... unless you set the 'offset' function on a depth sounder, you are getting depth from the sounder's transponder - not depth of the water. So if it reads 4' you may actually have 6' if the sounder is mounted 2' below water line.

In general, try not to operate the boat in < 6' of water if you can avoid it. In shallow water your prop(s) is (are) likely to stir up sand and sediment off the bottom. You don't want to suck that in to your engine cooling intakes to mess up the intakes, hoses, and filters. This is more important when reversing, when going into forward gear after backing up, or spinning by splitting the engines. In my experience, water over 6'-8' is normally deep enough that I don't stir much stuff up. Then again, bottom density where I am may be different than where you are.

If you have to operate in lower water levels, keep in mind what might happen with sand and sediment being stirred up, and try to use the prop(s) accordingly. If you dock bow in, can you push the boat back out of its slip, and only engage engines in forward when its clear? Any way you can dock without hitting reverse (approaching dock very slowly)? If you are stern in, can you leave dock without putting anything in reverse? How can you use the minimum of reverse to get the boat into the slip?

Also remember depth sounders are not perfect - depends on density of the bottom as to what they will read. A really soft bottom (loose sediment) with more solid bottom below, it may only tell you about the solid bottom while your keel / prop / rudder are dragging through the loose sediment. 20' of depth with 16' tall dense weeds, it may read 4'. Also consider wave action -- if you are in 4' of water and someone screams by (maybe even in deeper water) and throws a 2' wake, your depth may drop a lot, quickly! If you are in a tidal area, need to factor that in as well. Also in some places (like Muskoka lakes, Trent-Severn waterway, and Rideau Canal in Ontario) water depths are controlled by a federal ministry - at any given point may be a few feet higher or lower than any chart info portrays to ensure water levels are appropriately regulated.
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Re: Newbie question on draft

Post by rickalan35 »

Hi Chris,

Welcome aboard.

Where roughly in Ontario? I'm on the Rideau Lakes in Eastern Ontario and as a result of this drought plagued summer, we are out of water at my marina. My boat is now waiting in-line to be pulled.

My former tricabin used to draw 2 feet 10 inches and a couple of times I strayed into four feet of water (at which point I became very nervous). I never touched bottom though in the sixteen years I owned her.

My current Trojan has a deeper draft which means I have to be even more careful.... unlike the captain of the Costa Concordia was off the coast of Italy in 2012. I always considered the grounding of the Costa Concordia to be a lesson to us all about being cavalier and/or careless about how much water we have to spare under the bottom of our rudders. (That captain was apparently busy having dinner with a cute passenger at the time of the accident.)

Rule of thumb, I would always try to keep three feet between me and the bottom unless the circumstances demanded it.

By the way, the depth finder that you eventually purchase won't indicate the actual depth of the water from the water's surface to the bottom, but rather it will indicate the depth under the transducer itself which is usually mounted inside the boat at a low point in the bilge. Some members here on the Forum may weigh in on whether I'm correct but that's how I've always viewed it.

Cheers

Rick
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captainmaniac
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Re: Newbie question on draft

Post by captainmaniac »

Yanking the Costa Concordia lesson .... not really much point in passing it along as most won't care or get it.
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Big D
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Re: Newbie question on draft

Post by Big D »

rickalan35 wrote:....By the way, the depth finder.....won't indicate the actual depth of the water from the water's surface to the bottom, but rather it will indicate the depth under the transducer itself.....
As mentioned earlier, most units have an offset that can be set to compensate for this. Some folks like offsetting to indicate depth from the surface to the bottom, while others prefer to offset so that the reading shows how much water they have below the lowest point of their boat such as keel, props, or rudders. If you're going with the reading below the running gear, there's not much to think about in terms of how much room you have. If you're going with the true depth offset, always keep in mind the safe reading that you should not go less than. This reading needs to be your draft and a safety margin based on above and below water conditions such as wake, boulders, weight, weeds, etc.
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lawyerdave71
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Re: Newbie question on draft

Post by lawyerdave71 »

Depth Finder?

What happened to the the old tie a rope to a brick and throw it overboard?? Oh yes, one has to remember to hang on to the rope!
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GilliganChris
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Re: Newbie question on draft

Post by GilliganChris »

Big D wrote:
rickalan35 wrote:....By the way, the depth finder.....won't indicate the actual depth of the water from the water's surface to the bottom, but rather it will indicate the depth under the transducer itself.....
As mentioned earlier, most units have an offset that can be set to compensate for this. Some folks like offsetting to indicate depth from the surface to the bottom, while others prefer to offset so that the reading shows how much water they have below the lowest point of their boat such as keel, props, or rudders. If you're going with the reading below the running gear, there's not much to think about in terms of how much room you have. If you're going with the true depth offset, always keep in mind the safe reading that you should not go less than. This reading needs to be your draft and a safety margin based on above and below water conditions such as wake, boulders, weight, weeds, etc.
Very good points. I like the idea of setting the offset to represent depth to the lowest point of the running gear (with a bit of margin). That will reduce the need for mental math when looking at the readings.
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GilliganChris
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Re: Newbie question on draft

Post by GilliganChris »

lawyerdave71 wrote:Depth Finder?

What happened to the the old tie a rope to a brick and throw it overboard?? Oh yes, one has to remember to hang on to the rope!
Oh I like that. You just gave me my next weekend's project.
1976 Trojan F30 Flybridge <- First boat EVER.
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