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Ballast Question.. It's a different type of Q

 
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Breezer
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PostPosted: Jan 23, 2003 12:07 pm    Post subject: Ballast Question.. It's a different type of Q Reply with quote

Picture your boat sitting in the water. There is a water line on the outside of your boat. Picture the imaginary plane that where this water line cuts through your boat. Probably somewhere at the floor level of your boat.

Now to the question. If you were to add a hypothetical amount of weight "x" to your boat, would you gain more wake height by adding it below that imaginary plane or above that imaginary plane of water. It seems like to me that you would get your boat to sit lower in the water by adding it above that imaginary plane of water. What do you think.
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bluefish86
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PostPosted: Jan 23, 2003 12:18 pm    Post subject: Reply with quote

It shouldn't matter how high/low the ballast is, the weight and downward force is still the same. What does matter thought is the front/back and left/right placement.
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Breezer
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PostPosted: Jan 23, 2003 12:37 pm    Post subject: Reply with quote

Bluefish86, I'm not so sure it is that black and white.
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PostPosted: Jan 23, 2003 12:48 pm    Post subject: Reply with quote

How would having higher ballast push the boat down more? It makes no sense why height would change anything Confused Question
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PostPosted: Jan 23, 2003 1:28 pm    Post subject: Reply with quote

Breezer.
That is an interesting way of thinking! Unfortunately, you are not the first
to think about like it that. Try doing a search in google for Isaac Newton.
Perhaps you could enhance your search by also including the word "gravity".

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PostPosted: Jan 23, 2003 2:11 pm    Post subject: Reply with quote

It wouldnt make a diff when your boat is just sitting. In a turn having it up higher would definetly make the boat lean more to one side. During acceleration you would also get a more of a tilt to the back (with the weight up higher) till you got to a constant speed
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PostPosted: Jan 23, 2003 3:01 pm    Post subject: Reply with quote

there is more to it that it seems.

I work for a work boat company.

Our fast support vessels have planing hulls and the captains say they notice a big difference when they store 10,000 lbs of water below deck vs. 10,000 lbs of material above deck.

they prefer the above deck load out, they say they keep more of their speed like that.

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PostPosted: Jan 23, 2003 6:41 pm    Post subject: Reply with quote

It would make a difference due to gravity. The farther you get from the center of the earth the less pull. So in theory it would be heavier the lower you get it. I doubt if it would be actually possible to measure this little amount though.

What about something to help break the surface tension of the water. This would alow the boat to set deeper in the watter without having to add weight! Something to think about!

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bluefish86
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PostPosted: Jan 23, 2003 6:47 pm    Post subject: Reply with quote

What would work better is if something broke the surface tansion behind the boat. That way the wake would rise higher, but you wouldn't have to use the extra gas to keep the boat planning.
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PostPosted: Jan 23, 2003 7:09 pm    Post subject: Reply with quote

not to mention the higher the balast the more its going to steer the boat you want to keep the weight as close to the center of gravity as possible. that's also what the captians are talking about
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Alan Whitaker
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PostPosted: Jan 23, 2003 7:12 pm    Post subject: Reply with quote

Do we really have a lot of options of how high we place weight?
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PostPosted: Jan 24, 2003 7:34 am    Post subject: Reply with quote

I'll tell ya what. Tie a dozen cinder blocks to the top of your tower and let me know how it all works out.
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PostPosted: Jan 24, 2003 7:36 am    Post subject: Reply with quote

Seeing as how i have an engineering degree i would say this. Th height doesn't matter. It will effect the way the boat handles though very much. The higher the weight placement the more wobbly the boat will react. Also it will cause major lean in th turns. Force has nothing to do with height at theses distances, and also the weight is not in motion.


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PostPosted: Jan 24, 2003 7:46 am    Post subject: Reply with quote

blufish- the surface tension is already broken behind the boat. Besides surface tension is really not enough to make a difference with a 4-5000 lb. boat.
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PostPosted: Jan 24, 2003 3:32 pm    Post subject: Reply with quote

wes, Onthe contrary
The surface tension and bouyancy are what keep the boat afloat. Never thought I would be using that #$%^ in a normal conversation.


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PostPosted: Jan 24, 2003 5:04 pm    Post subject: Reply with quote

how does surface tension keep the boat afloat?
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bluefish86
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PostPosted: Jan 24, 2003 7:24 pm    Post subject: Reply with quote

My boat only weighs 2100 lb, and I was only expanding on what mullet man said... I have no idea if it's true or not.
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PostPosted: Jan 24, 2003 7:49 pm    Post subject: Reply with quote

I'm just bored out of my mind and felt like messin with people.
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PostPosted: Jan 25, 2003 11:07 am    Post subject: Reply with quote

Suface tension keeps the boat afloat by exerting a force back on the boat equal to the force (for the most part) that the boat is putting on the water. The displacemnet is the amount of water the boat pushes out of the way so it can sit low in the water(how deep the hull sits) The more weight you put in the more the water is displaced (easy enough). If you evere reach the equal point the boat will go down. The surface tesion and the displacement are related somehow I just don't recal the formula. I think its M*A (mass *surface area) with a couple of other formulas to figure out for the water itself, I can look it up if you guys are interested in that.

Think of it like trying to push you finger through a plastic bag the bag is pushing back on you with a force that is equal to the force that you finger is pushing on the bag until you finger overcomes the force and busts through.


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PostPosted: Jan 25, 2003 4:37 pm    Post subject: Reply with quote

To get an idea of what surface tension is like, think of a blob of glue that has just dried enough that there's a thin skin on top, but is still almost all liquid. Surface tension on water is like that skin on the glue, but a lot less strong. If you sit something small of a certain weight on the glue, it might break through, but if you sit something else with the same weight but bigger on the glue, it would stay on the surface.
You can use surface tension to "float" a pin on top of a glass of water if you set it down carefully enough sideways, even though it is dense enough that if you just dropped it in, it would sink.
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PostPosted: Jan 25, 2003 4:57 pm    Post subject: Reply with quote

yeah it would make a difference, cant you tell by where you place your sacs in the boat?
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PostPosted: Jan 25, 2003 6:18 pm    Post subject: Reply with quote

Ever take a Physics class? It doesn't matter at what height the ballast is for the wake size, just for the handling of the boat. Think about moment of interia for boat handling.
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PostPosted: Jan 25, 2003 6:56 pm    Post subject: Reply with quote

dude yall are all talking about buoyancy. the surface tension of water is broken and is no longer a factor the second your boat touches the water.

also it does not matter where you put your sacs (higher or lower) as to how much they weigh. therefore it would not make any difference if you put the sacs on the seats of the boats than it would if they were under the floor. they still weigh the same. if the sacs were placed higher it would however raise the center of gravity of the boat making it handle different while turning. much like how suv's lean a lot more than cars when turning.
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PostPosted: Jan 26, 2003 12:25 am    Post subject: Reply with quote

Wes is correct. Bouyancy is the issue, not surface tension as I stated.

Why hasn't a boat company actually designed a hull that will create a bigger wake. Who cares about performance. It could be a wakeboard specific boat. All of the current wakeboard boats are based off of planing hull design characterstics which help the boat to plane better, hence creating a smaller wake. What if you made a boat hull designed to plane poorly! Pushing more water down causing a bigger wake.

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PostPosted: Jan 26, 2003 1:35 am    Post subject: Reply with quote

Mullet Man, bigger but not neccicarly better. i mean why not just put a cube of wood in the watter.
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PostPosted: Jan 26, 2003 3:49 am    Post subject: Reply with quote

I think they should be able to design a hull that would make a bigger and better wake. I know that performance would suffer, but who cares. Make something for riding only. Would be interesting.
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PostPosted: Jan 26, 2003 1:07 pm    Post subject: Reply with quote

i agree with you mullet. i think maybe malibu has started thinking of this with their wedge. i wonder what a reverse stepped hull would do. on the off shore racing boats they step the hulls to make them plain better. if they turned those steps around i think it would push more water out form under the boat making a bigger wake.
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PostPosted: Jan 26, 2003 2:23 pm    Post subject: Reply with quote

mullet, the new tige looks like it would do that, the convex hull is suposed to suck the hull down into the water
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PostPosted: Jan 27, 2003 1:07 am    Post subject: Reply with quote

Even though I have had problems with Tige as a company, I must admit that you are right. I think it is very minor though. I have worked with shaping surfboards for years. Shapers found long ago that a lot of rocker on the back half of the board greated a downward pull. What works even better is an actual round hump on the bottom of the board. A company made a product once that looked like a bowl that you glued onto the bottom of the surfboard. It actually worked very well. Maybe a larger bowl shaped object to put on the bottom of a boat. You can test this theory. Fill up your sink wiht a couple inches of water. Leave the water on. Take a spoon and while holding it place the bottom of it on the water surface right next to the stream of water coming out of the faucet. You will notice that as the water passes under the spoon it creates a great deal of down force.
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PostPosted: Jan 27, 2003 8:13 pm    Post subject: Reply with quote

If i weigh 100 pounds and put a 5 lb. weight in my pocket, i will still weigh the same if i hold that same 5 lb weight over my head instead.
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PostPosted: Jan 28, 2003 6:09 am    Post subject: Reply with quote

I think you guys misunderstood my question.

If you are submerged in water and hold 5 lbs. above your head or put the 5 lbs. in your pocket, which one makes you sink more?

The "invisible plane of water" is not an airplane. It is a geometric term. I know that if you put water on top of the engine compartment or on top of the tower you would not have a difference in the displacement of water.
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PostPosted: Jan 28, 2003 6:38 am    Post subject: Reply with quote

If you are submerged in water and hold 5 lbs. above your head or put the 5 lbs. in your pocket, which one makes you sink more?

This analogy doesn't really apply to the situation, but here's the answer...

Putting the weight above your head will make you sink more because if you put the object under water it will be displacing water, adding buoyancy to the you/object system. With the object over your head you will sink until you displace 5 more lbs of water. With the object in your pocket it will depend on how much water it displaces. If it displaces 5 lbs nothing will change, if it displaces more than 5 lbs you will float up, and if it displaces less than 5 lbs you will sink until the amount of water displaced by you and the object is equal to your weight + the objects. The reason you will always sink more with the object over your head is because no matter how dense it is, it will still displace some water, unless it has 0 volume which isn't possible. Think of a pontoon from a large pontoon boat, if you hold it above your head, you will most definitely sink until the pontoon is in the water. However, it you could fit it in your pocket, you'd float at pocket level.

The reason this doesn't apply to a boat situation is because whether the object is below the water line or not, it's volume does not displace water. Now, if we are talking about attaching the object to the outside of the boat underwater it would be applicable.

Here's what happens with a boat:

My boat weighs 2000 lbs, it will sink in the water until it displaces 2000 lbs of water. I get on the boat with my 150 lbs, the boat will sink more until it displaces 2150 lbs. Now, it doesn't matter where I am in the boat because the hull is rigid. Let's say instead of putting me in the boat, we strap me to the bottom. Now, my body is displacing water and since I ordinary float, I'm displaces more that 150 lbs of water, we'll say 160 lbs. Since I'm connected to the boat, it now only needs to displace 1990 lbs and will float higher in the water then before since I'm adding floatation to it by being strapped to the bottom. The waterline has nothing to do with it, it is all related to water displacement.

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Last edited by OttoNP on Feb 27, 2011 2:39 pm; edited 1 time in total
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PostPosted: Jan 28, 2003 8:55 am    Post subject: Reply with quote

you guys are way to smart to spend your time on this website. Im not saying that my fellow peeps are dumb (belive me there not., I am), but you should be finding a cure for cylmidia or somthing, like finding out how to make a bigger wake with less weight. Oh wait......

I usually put the dead bodies in the boat so I have a bigger wake.

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PostPosted: Jan 28, 2003 3:20 pm    Post subject: Reply with quote

Good explanation, OttoNP. I'm glad someone paid attention in school. Anyway, anyone thinking of ballasting their boats with ton of lead might like to consider your post and how much water lead displaces for its weight. If ever a lead-ballasted boat were to capsize *god forbid* it would likely sink like a rock, creating a dangerous situation. A fat sac-equipped boat would, on the other hand, behave pretty much the same as an empty boat.
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PostPosted: Jan 29, 2003 1:20 am    Post subject: Reply with quote

Another thing to consider: According to Coast Guard Regulations, adding lead can be included in the total carying capacity of your boat, while adding water does not affect the total carrying capacity of your boat. I have heard that a few boats have been checked for that at some of the poplular wakeboarding lakes in SoCal.
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