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Old 05-03-2016, 09:18 PM   #1
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What is boat length measured?

In searching for a new boat I'll see "boat length" or "nominal length." Since most boats that interest me have a bow pulpit or over hanging anchor at bow & swim platform at stern, are these figured into advertised length of a boat? I like to see LWL (length at water line).
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Old 05-03-2016, 09:45 PM   #2
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There are at least 4 different ways to quantify boat length:
1) Documented length -- I don't know the formula, but I believe it excludes swim steps and bow pulpits.
2) Length overall (LOA) -- this is what most marinas (at least on west coast of US, Canada and mexico) base their slip fees on, and is often used by owners to describe the size of their boat;
3) Length at water line (LWL) -- probably most useful, but least used,
and
4) manufacturer's "designation" (like a 550, implying 55 feet) -- practices are wildly inconsistent between manufacturers with many "stretching" (even beyond LOA), but a few, inexplicably, understating.

For an apples to apples comparison, I would suggest documented length or LWL
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Old 05-03-2016, 09:48 PM   #3
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Quote:
Originally Posted by MYTraveler View Post
There are at least 4 different ways to quantify boat length:
1) Documented length -- I don't know the formula, but I believe it excludes swim steps and bow pulpits.
2) Length overall -- this is what most marinas (at least on west coast of US, Canada and mexico) base their slip fees on;
3) Length at water line -- probably most useful, but least used,
and
4) manufacturers "designation" -- practices are wildly inconsistent between manufacturers with many "stretching" but a few, inexplicably, understating.
I have heard your definition of 1) described as Length on Deck (LOD).
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Old 05-03-2016, 10:09 PM   #4
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Documented length (Register length in Canada) is measured from the inner part of the stem to the foremost edge of the rudder stock. I'm a Transport Canada Appointed Tonnage Measurer.
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Old 05-03-2016, 10:19 PM   #5
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Originally Posted by boatpoker View Post
Documented length (Register length in Canada) is measured from the inner part of the stem to the foremost edge of the rudder stock. I'm a Transport Canada Appointed Tonnage Measurer.
Unless they have changed since the '70s, if you had a sternpost they
measured to it.

Still valid?

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Old 05-03-2016, 10:27 PM   #6
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I have heard your definition of 1) described as Length on Deck (LOD).
And centre line length.
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Old 05-03-2016, 10:29 PM   #7
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When referring to smaller (runabout size etc.) boats there was a
difference between Canadian or American measurements.
Canadian used the centerline length, American measured from
the bowstem to the transom around the gun'ell.

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Old 05-03-2016, 10:37 PM   #8
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Quote:
Originally Posted by Ted;
American measured from
the bowstem to the transom around the gun'ell.
Ah yes, the old take the long way from A to B and use a rubber tape.

If I'm not mistaken Bayliner started that one.
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Old 05-03-2016, 10:42 PM   #9
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I don't know who started it, but it was in use in a book of
plans by Mechanics Illustrated from mid 1950s.

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Old 05-03-2016, 10:43 PM   #10
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So many different methods.
You would have to think that C.L.(centreline) from the actual bow to stern of the hull - disregarding bow spit, duck board , pulpit and pushpit etc. would be the only true indication of the vessels length.
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Old 05-03-2016, 10:47 PM   #11
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I don't know who started it, but it was in use in a book of plans by Mechanics Illustrated from mid 1950s.
That leaves me hangin' on by a thread then. Bayliner started production in 1957.
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Old 05-03-2016, 10:49 PM   #12
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My Mainship 37 is 41' 4" if I measure from the aftmost bumper molding on the swimstep to the forwardmost edge of the forward-angled bow pulpit rail. If I'm checking into a marina that charges by the foot I'm a 37. If I'm boasting, I'm a 41 or 42.
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Old 05-03-2016, 10:58 PM   #13
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It's all a question of why you want to measure the boat. If it's to fit in a slip then you need to include pulpit and swim step. If you want to show off to friends that's a good number too, rounded up of course! If you want an idea of the speed then waterline length is the most interesting. In fact, the LOD or CL is the least interesting in some ways. It gives you an idea of how big the boat is from a livability perspective, but to be of any use you really need to include beam and cabin height (and double decking if any).
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Old 05-04-2016, 12:31 AM   #14
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I just wish there was not only some consistency from builder to builder, but that builders would also share how they denominate their boats. I have seen boats listed as a "34" or "52" but when looking at the measurements, LOD, LOA, LWL, whatever, not a single one of them will be 52! With Krogen, they clearly list their models by LOD and make it plain that is what they have done. I wish more builders did the same.
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Old 05-04-2016, 01:09 AM   #15
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The state of WA limits the use of their mooring buoys to boats 45' in length. My boat is a DeFever 46' but the length at the waterline is 43 and change, so how the boat is measured is important. I emailed the parks and rec dept for an answer and they stated that they go by whatever length is on the registration, so I am SOL for using state mooring buoys.
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Old 05-04-2016, 02:02 AM   #16
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Quote:
Originally Posted by Ted View Post
Unless they have changed since the '70s, if you had a sternpost they
measured to it.

Still valid?

Ted
I received my training in 1999. Don't know about the seventies.
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Old 05-04-2016, 02:04 AM   #17
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Quote:
Originally Posted by drb1025 View Post
The state of WA limits the use of their mooring buoys to boats 45' in length. My boat is a DeFever 46' but the length at the waterline is 43 and change, so how the boat is measured is important. I emailed the parks and rec dept for an answer and they stated that they go by whatever length is on the registration, so I am SOL for using state mooring buoys.
Get it documented, it'll come up a few feet shorter.
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Old 05-04-2016, 02:05 AM   #18
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Quote:
Originally Posted by THD View Post
I just wish there was not only some consistency from builder to builder, but that builders would also share how they denominate their boats. I have seen boats listed as a "34" or "52" but when looking at the measurements, LOD, LOA, LWL, whatever, not a single one of them will be 52! With Krogen, they clearly list their models by LOD and make it plain that is what they have done. I wish more builders did the same.
These are the same builders that started calling planing and semi-planing boats ...."trawlers"
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Old 05-04-2016, 08:05 AM   #19
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These are the same builders that started calling planing and semi-planing boats ...."trawlers"
They were probably ex audio peddlers from the 70s as well. No 2 audio equipment manufacturers of components used the same standard for their specs. It was a jungle out there.
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Old 05-04-2016, 08:14 AM   #20
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Our Krogen 42 is documented at 43'. We're 46' overall from the tip of the bow pulpit to the edge of the swim platform. The swim platforms 3' as is the bow pulpit.
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