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Old 03-09-2016, 08:50 PM   #1
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How do I properly read these specs?

Been reading some boat specs on boattraders.com, got quite confused.

Dry Weight: So I guess this means hull, engine, machineries, structure, but no fuel, water nor people?

Displacement: What does that mean? Full displacement? Hull displacement? Is there any convention people follow or do everyone just put whatever they want there?

Draft: Is this the max draft? I guess it has to be, right?

One critical piece of information seems to be missing from almost all online post is the certified capacity. I was told most boat has a plate with that info on it, but looks like no one bother to include it when they post on line? Is there any general guide like for a 50000lbs dry weight boat, roughly how much can it carry?
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Old 03-09-2016, 08:55 PM   #2
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Not much consistency in the boat world...especially older boats say pre 2000.

Capacity plates are only mandated on boats 20 feet and less but I believe a few larger boats might have them...probably no boats over 30 feet, yet some do give limits for upper decks/flybridges.

Boat carrying capacity is all over the map for any given length due to great variations in design...so no...not even a rule of thumb is applicable for larger (say over 30 feet with cabins) boats.
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Old 03-09-2016, 09:09 PM   #3
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Quote:
Originally Posted by chicagoq;
Dry Weight: Is derived from actually weighing the empty vessel as though it was needed for shipping purposes. Now, I don't know at what size that becomes impractical.

Displacement: Is the weight of water displaced when the vessel is set, again empty, into the water. It is the weight of the boat as mathematically calculated by the designers.

Draft:Is this the max draft? I guess it has to be, right? Right.
What I would like to see in listings, along with the specs, is ER headroom from a usual standing, squatting, kneeling position.
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Old 03-09-2016, 09:14 PM   #4
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I'm sure weight-displacement/people-deployment has lots to do with a boat's stability and performance. Put 12 people (over a ton of weight) on the flying bridge or one side of the boat could have unwelcome consequences.
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Old 03-09-2016, 09:16 PM   #5
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Originally Posted by markpierce View Post
I'm sure weight-displacement/people-deployment has lots to do with a boat's stability and performance. Put 12 people (over a ton of weight) on the flying bridge or one side of the boat could have unwelcome consequences.
He's talking specs, Mark, not special effects.
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Old 03-09-2016, 09:18 PM   #6
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Originally Posted by Hawgwash View Post
He's talking specs, Mark, not special effects.
Theoretical or practical?
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Old 03-09-2016, 09:23 PM   #7
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Rather than a single person aboard, how well would a dozen of "in the wrong place" people do in this situation?



I'd have serious concerns.
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Old 03-09-2016, 10:28 PM   #8
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OK, Thanks! If there's no general guidance I can follow, could someone tell me for a boat like Hatteras 53 MotorYacht(or similar boat), how much weight can it carry? Including water, fuel, everything on top of dry weight? Not looking for anything precise, just a rough number.
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Old 03-09-2016, 10:40 PM   #9
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Chicago-can't give you precise #'s on the 53 Hatt, but can give you some comparison. Our boat is 58', full displacement, weight loaded is around 52 tons or so. Per design specs, it takes just over 10,000 lbs to lower the boat 1" in the water. Now, that assumes even weight distribution and is not a measure of stability. As has been noted in previous posts, where the weight is can, and often is, more important than the weight itself. But in general, overloading our boat has not only never been an issue, we have never even thought about it. When it comes to people on the boat, our measuring stick is simply comfort-how many can be comfortably accommodated for what we are doing, i.e. a short 1 or 2 hour cruise? or a daylong excursion? or an overnight? In order, we have had up 20 on the boat, in the second instance we have had 10-12 and overnight 4 (except for my daughter's birthday we had 6).
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Old 03-09-2016, 11:04 PM   #10
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Just to be clear - displacement is the same as weight. As Archimedes pointed out, a floating vessel displaces a weight of water equal to its own weight. I see "half load" quoted a number of times. I'm not sure if that means tanks half full? On my boat the combined weight of full tanks of fuel and water total over 13,500 lb.
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Old 03-10-2016, 01:20 AM   #11
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One of Tollycraft's gurus... who goes 1970's and 80's decades deep inside the Tolly company as lead purchasing agent runs this site... has a pretty good stat referral block; model's pictures listed by year on page top.

Tolly Classified - Model Selection
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Old 03-10-2016, 08:43 AM   #12
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Chicago-can't give you precise #'s on the 53 Hatt, but can give you some comparison. Our boat is 58', full displacement, weight loaded is around 52 tons or so. Per design specs, it takes just over 10,000 lbs to lower the boat 1" in the water. Now, that assumes even weight distribution and is not a measure of stability. As has been noted in previous posts, where the weight is can, and often is, more important than the weight itself. But in general, overloading our boat has not only never been an issue, we have never even thought about it. When it comes to people on the boat, our measuring stick is simply comfort-how many can be comfortably accommodated for what we are doing, i.e. a short 1 or 2 hour cruise? or a daylong excursion? or an overnight? In order, we have had up 20 on the boat, in the second instance we have had 10-12 and overnight 4 (except for my daughter's birthday we had 6).
10,000lbs is just one inch? Woo, that's much bigger than I had in mind. Thanks!
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Old 03-10-2016, 08:57 AM   #13
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Wait, I am still confused, how wide is your beam? Even if I count your boat as a square box:
58' x beam x 1/12 x 7.48(CuFt to Gallon) x 8.34(water weight per gallon) = 10000lbs
If my formula is correct, the beam needs to be at least 33'?

Is my formula wrong?
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Old 03-10-2016, 09:25 AM   #14
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Greetings,
It's my understanding that the weight of the boat is NOT the displacement. Displacement has to do with cargo carrying capacity or some such.

Our vessel "weighs" aprox. 25 tons (according to travel lift #'s). Gross displacement is registered as 41.43t. Net displacement is registered as 31.07t.
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Old 03-10-2016, 09:35 AM   #15
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Quote:
Originally Posted by chicagoq View Post
OK, Thanks! If there's no general guidance I can follow, could someone tell me for a boat like Hatteras 53 MotorYacht(or similar boat), how much weight can it carry? Including water, fuel, everything on top of dry weight? Not looking for anything precise, just a rough number.

There is the question of how many people can a fully fueled, watered boat hold? In that calculation you need to figure that everybody on that boat will be on the upper deck and run to one side when the New Years Eve fireworks start. That scenario should cut the number of people you deem safe on your boat, in half.
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Old 03-10-2016, 09:38 AM   #16
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Originally Posted by RT Firefly View Post
Greetings,
It's my understanding that the weight of the boat is NOT the displacement. Displacement has to do with cargo carrying capacity or some such.

Our vessel "weighs" aprox. 25 tons (according to travel lift #'s). Gross displacement is registered as 41.43t. Net displacement is registered as 31.07t.
https://en.wikipedia.org/wiki/Displacement_(ship)

Displacement or displacement tonnage is the weight of water that a ship displaces when it is floating, which in turn is the weight of a ship (and its contents). It is usually applied to naval vessels rather than commercial ones, and is measured when the ship's fuel tanks are full and all stores are aboard.[1][2]
Displacement should not be confused with other measurements of volume or capacity typically used for commercial vessels such as net tonnage, gross tonnage, or deadweight tonnage.
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Old 03-10-2016, 09:53 AM   #17
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Originally Posted by Larry M View Post
https://en.wikipedia.org/wiki/Displacement_(ship)

Displacement or displacement tonnage is the weight of water that a ship displaces when it is floating, which in turn is the weight of a ship (and its contents). It is usually applied to naval vessels rather than commercial ones, and is measured when the ship's fuel tanks are full and all stores are aboard.[1][2]
Displacement should not be confused with other measurements of volume or capacity typically used for commercial vessels such as net tonnage, gross tonnage, or deadweight tonnage.
Thus my post #2 basically saying that the recreational boating community has been fed the trash boat companies call brochures and have created "word monsters" for so many nautical terms...oh...say...like trawler?
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Old 03-10-2016, 10:09 AM   #18
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Quote:
Originally Posted by chicagoq View Post
Wait, I am still confused, how wide is your beam? Even if I count your boat as a square box:
58' x beam x 1/12 x 7.48(CuFt to Gallon) x 8.34(water weight per gallon) = 10000lbs
If my formula is correct, the beam needs to be at least 33'?

Is my formula wrong?
Your formula is correct and does bring into question the statement that 10,000lb only lowers the boat 1".
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Old 03-10-2016, 10:15 AM   #19
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For reference...


Our 34' tri cabin Tolly weighs 17K lbs. as she comes out the factory door. See stats link for Tollycraft on post 11. With filled 200 gal fuel tanks, 77 gal water, and all sorts of extra "stuff" I calc she weighs 20K + lbs.
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Old 03-10-2016, 01:12 PM   #20
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The "design" displacement of a Krogen 42 is 39,500 lbs at "half load". Our cruising weight, with stores, full water and fuel is just over 45,000 lbs. It also takes 2000 lb/inch immersion. We have raised the water line.
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