# How exactly does a boat float? **URL:** \ **Category:** Factual Questions\ **Created:** [June 21, 2003, 12:30am UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317 "2003-06-21T00:30:22Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 7:08am UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/61 "2003-06-24T07:08:57Z")
I guess sometimes ignorance is wilful, and can’t be fought. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [June 24, 2003, 11:20am UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/62 "2003-06-24T11:20:19Z")
Indeed. :rolleyes: ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [June 24, 2003, 11:36am UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/63 "2003-06-24T11:36:22Z")
> [@](#): > > \*Originally posted by Omar \* > \*\*Well, according to this cite, you are pretty much wrong. > > [http://www.getsmarter.org/mstv/L3\_a.cfm](http://www.getsmarter.org/mstv/L3_a.cfm) > > In order for an object to float, it has to be lighter than an equal bulk or volume of water. So the amount of water does matter. \*\* Omar, that was your original post and what you are saying now is not the same thing you said there. It is silly to play these games and much more elegant to just admit you made a mistake. \>\> In order for an object to float, it has to be lighter than an equal bulk or volume of water. True. that is what we are saying. The point is that the equal volume of water does not need to even exist. \>\> So the amount of water does matter. You are confusing things. You were talking about the amount of water **displaced** and now you are talking about the water not displaced. You are mixing them both and got yourself confused. Give it up. **tastycorn** was correct all along. **yoyodyne** was also wrong and did not have the elegance to admit it. ---
**Author:** ![Hobie\_the\_One](https://avatars.discourse-cdn.com/v4/letter/h/e99b99/32.png) [@Hobie\_the\_One](https://boards.straightdope.com/u/Hobie_the_One)\ **Post date:** [June 24, 2003, 2:20pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/64 "2003-06-24T14:20:56Z")
**Omar** Not sure why everybody is jumping on you for this one. The amount of water needed is directly proportional to the difference in the volume of the container and the volume displaced by the ship. In other words, the bigger the difference, the more water you’re gonna need. In this you are absolutely correct. What the important part is, and what you do seem to have grasped, is that you don’t need to have the amount of water that needs to be displaced (which is a constant btw) in the pool originally. That’s what **yoyodyne** was saying and it aint so. Oh, you said that too but you haven’t said it in a couple of posts so you seem to understand now. To float the bugger, you just need a really well designed container and a little bit of water. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 2:36pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/65 "2003-06-24T14:36:05Z")
> [@](#): > > \*Originally posted by Hobie the One \* > **The amount of water needed is directly proportional to the difference in the volume of the container and the volume displaced by the ship.** Directly proportional? More precisely, it’s directly proportional with a proportionality constant of unity. The more sensible way of stating that is to use the word “equal”. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [June 24, 2003, 2:45pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/66 "2003-06-24T14:45:29Z")
Demo, read it again, he is not saying what you think he is saying. This thread seems to be full of misunderstandings. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [June 24, 2003, 2:50pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/67 "2003-06-24T14:50:43Z")
Ór maybe I misunderstood what you were saying. Never mind. ---
**Author:** ![Hobie\_the\_One](https://avatars.discourse-cdn.com/v4/letter/h/e99b99/32.png) [@Hobie\_the\_One](https://boards.straightdope.com/u/Hobie_the_One)\ **Post date:** [June 24, 2003, 3:15pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/68 "2003-06-24T15:15:21Z")
**Demo** , not necessarily equal is it? For example, float a canoe in your swimming pool and you can have far more water than necessary but the minimum amount will not fill all of the available space. See what I mean? It actually depends on the container. **Sailor** amen to the misunderstandings. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 3:29pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/69 "2003-06-24T15:29:22Z")
> [@](#): > > \*Originally posted by Hobie the One \* > **Demo, not necessarily equal is it? For example, float a canoe in your swimming pool and you can have far more water than necessary but the minimum amount will not fill all of the available space. See what I mean? It actually depends on the container.** Let’s look at what you said. > [@](#): > > \*Originally posted by Hobie the One \* > **The amount of water needed is directly proportional to the difference in the volume of the container and the volume displaced by the ship.** Can you think of an example where the amount of water is say, twice the difference between the volume of the container and the volume displaced by the ship? Or an example where the amount of water is half the difference between the volume of the container and the volume displaced by the ship? ---
**Author:** ![Hobie\_the\_One](https://avatars.discourse-cdn.com/v4/letter/h/e99b99/32.png) [@Hobie\_the\_One](https://boards.straightdope.com/u/Hobie_the_One)\ **Post date:** [June 24, 2003, 3:49pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/70 "2003-06-24T15:49:28Z")
Demo, if the amount of water is twice the difference, the excess will spill out of the pool and no longer be a part of the system. You _can_ however have less water if you are talking about a larger container. For instance, can you float a canoe in a half full swimming pool? Of course you can. Is the amount of water less than the difference between the volume of the **container** and the volume displaced by the canoe? You betcha. The size of the container makes the amount of water relevant but not necessarily constant. Can you still go sailing when the water level of a lake is down? Yes, you can. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [June 24, 2003, 3:57pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/71 "2003-06-24T15:57:08Z")
Up to the line of flotation. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 3:59pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/72 "2003-06-24T15:59:12Z")
You obviously don’t know what the term “directly proportional” means, and you shouldn’t have used it in the first place. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 4:02pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/73 "2003-06-24T16:02:59Z")
**sailor** ’s qualification “up to the line of flotation” is the thing that allows proportionality, and also requires equality. ---
**Author:** ![PeeWee](https://avatars.discourse-cdn.com/v4/letter/p/c0e974/32.png) [@PeeWee](https://boards.straightdope.com/u/PeeWee)\ **Post date:** [June 24, 2003, 4:08pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/74 "2003-06-24T16:08:06Z")
But I don’t understand…if steel is more dense than water, how does it float? ---
**Author:** ![PeeWee](https://avatars.discourse-cdn.com/v4/letter/p/c0e974/32.png) [@PeeWee](https://boards.straightdope.com/u/PeeWee)\ **Post date:** [June 24, 2003, 4:12pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/75 "2003-06-24T16:12:05Z")
😃 Ha, ha, ha…sorry, I couldn’t resist! This is the funniest thread I’ve read in a long time. I’m a naval architect, so I could just see people’s faces getting red with each new post! :mad: I think it’s time to start a new thread titled, “Semantics, why it matters and how it affects your life.” Robby and Omar can moderate. 😉 ---
**Author:** ![dylan\_73](https://avatars.discourse-cdn.com/v4/letter/d/ecccb3/32.png) [@dylan\_73](https://boards.straightdope.com/u/dylan_73)\ **Post date:** [June 24, 2003, 4:15pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/76 "2003-06-24T16:15:02Z")
> [@](#): > > \*Originally posted by Desmostylus \* > **Let’s look at what you said.Can you think of an example where the amount of water is say, twice the difference between the volume of the container and the volume displaced by the ship?** Now _I’m_ confused…if my little boat displaces 2 litres of water and the volume of the container is 3 litres…the difference is 1 litre. Twice the difference is 2 litres and is enough to float the boat. In fact, the difference so obviously won’t be equal when you consider a ship floating on the ocean that I don’t understand what the argument is at all! ---
**Author:** ![Hobie\_the\_One](https://avatars.discourse-cdn.com/v4/letter/h/e99b99/32.png) [@Hobie\_the\_One](https://boards.straightdope.com/u/Hobie_the_One)\ **Post date:** [June 24, 2003, 4:16pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/77 "2003-06-24T16:16:15Z")
Absolutely and that is what I was saying. There was no need to get snarky. You notice that nowhere in my previous post did I mention “up to the line of flotation.” Perhaps my wording was ill-advised and I’ll amend it accordingly. My mistake was posting at work and not reading what I had written fully. The reason I posted initially was that Omar was getting unnecessarily stomped for saying something that was factual. The amount of water does depend on the volume and shape of the container. Thanks PeeWee. I think we needed that. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 24, 2003, 4:21pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/78 "2003-06-24T16:21:07Z")
Take it easy, **dylan\_73**. **Hobie the One** made a silly claim and I was dragging it out. The amount of water that you can float the thing in is equal to the difference between the volume of the container and the volume displaced by the ship, plus any arbitrary (non-negative) constant. ---
**Author:** ![Hobie\_the\_One](https://avatars.discourse-cdn.com/v4/letter/h/e99b99/32.png) [@Hobie\_the\_One](https://boards.straightdope.com/u/Hobie_the_One)\ **Post date:** [June 24, 2003, 4:32pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/79 "2003-06-24T16:32:43Z")
> [@](#): > > Originally posted by _Desmostylus_ > Hobie the One made a silly claim and I was dragging it out. Mea culpa. I misspoke. > [@](#): > > Originally posted by _Desmostylus_ > The amount of water that you can float the thing in is equal to the difference between the volume of the container and the volume displaced by the ship, plus any arbitrary (non-negative) constant. Very elegantly put. ---
**Author:** ![tastycorn](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@tastycorn](https://boards.straightdope.com/u/tastycorn)\ **Post date:** [June 24, 2003, 4:43pm UTC](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317/80 "2003-06-24T16:43:23Z")
Good one PeeWee 🙂 Hey, I have a couple questions about Hull Speed and Hydrofoils. Within the realm of your expertise? If so, I’ll start a new thread. [Previous page](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317.md?page=3) [Next page](https://boards.straightdope.com/t/how-exactly-does-a-boat-float/183317.md?page=5)