Decking a boat

[werkellys]

I have a aluminum 15' boat it looks like it used to be decked, if I redeck it can I put some kind of foam to help stabalize or offset the weight of the wooden decking it would be approx 1 1/2 inch or so would that be enough to help and do I leave the drain galleys open or let the water go on top? I appreciate any and all help as always

 

[109jb]

Re: Decking a boat

Anything you put inside the boat, including foam, is just weight. The boat floats because of the water it displaces, or pushes aside. If the boat weighs 500 pounds it has to push 500 pounds of water aside. If a boat weighs 500 pounds and has 20 pounds of foam inside, then it has to push 520 pounds of water aside. Foam only hellps if the boat sinks.

 

[werkellys]

Re: Decking a boat

109jb
thank you do you know how to get the weight rating on my boat I can not read the plate it is so faded

 

[Fisherball]

Re: Decking a boat

Get your HIN (hull ID number) from the back of the transom, usually on the starboard side (right). Run a search on this or the Boat Topics forum & some one will direct you from there.

 

[Yacht Dr.]

Re: Decking a boat

Anything you put inside the boat, including foam, is just weight. The boat floats because of the water it displaces, or pushes aside. If the boat weighs 500 pounds it has to push 500 pounds of water aside. If a boat weighs 500 pounds and has 20 pounds of foam inside, then it has to push 520 pounds of water aside. Foam only hellps if the boat sinks.

Wrong..

YD.

PS. look up displacements before your post m8..

 

[werkellys]

Re: Decking a boat

YD

What is the truth then? I read some guy put pool noodles under his deck will that help? I'm really trying to learn. Is there a resource other than this forum that you know of? Is the new pressure treated wood harmful to aluminum?

 

[ondarvr]

Re: Decking a boat

Wrong..

YD.

PS. look up displacements before your post m8..

IS there another option?


Engineering
? Engine displacement, the total volume of air/fuel mixture an engine can draw in during one complete engine cycle
? Displacement (fluid), an object immersed in a fluid pushes the fluid out of the way
? Positive displacement, a pump or flow meter which processes a definite fluid volume per revolution
? Displacement has several meanings related to ships and boats
o Displacement hull, where the moving hull's weight is supported by buoyancy alone and it must displace water from its path rather than planing on the water's surface
o Displacement speed, a rule of thumb for non planing watercraft to estimate their theoretical maximum speed
o Displacement (ship), several related measurements of a ship's weight

 

[Woodonglass]

Re: Decking a boat

This might give you some helpful info

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Aero_p020.shtml

I'm just sayin...

 

[109jb]

Re: Decking a boat

Wrong..

YD.

PS. look up displacements before your post m8..

NOT WRONG. YOU LOOK IT UP.

500 pounds has to displace 500 pounds of water. 600 pounds has to displace 600 pounds of water. If it doesn't it sinks.

 

[ezmobee]

Re: Decking a boat

Wrong..

YD.

PS. look up displacements before your post m8..

You're way wrong on this one dude......and even if your weren't, there is no need to be rude to another member when disagreeing.

 

[Yacht Dr.]

Re: Decking a boat

You're way wrong on this one dude......and even if your weren't, there is no need to be rude to another member when disagreeing.

Im not trying to be rude.. just explaining what foam will or will not do.

I am right on this one ( no need to call me Dude then tell me not to be rude in one sentence .. kinda rude )..

I can build a 500 lb flat bottom boat and it will take WAY more then 500 lbs in water ( 63 gallons of freash water to displacement) to sink it.

"I have a aluminum 15' boat it looks like it used to be decked, if I redeck it can I put some kind of foam to help stabalize or offset the weight of the wooden decking it would be approx 1 1/2 inch or so would that be enough to help and do I leave the drain galleys open or let the water go on top? I appreciate any and all help as always "

The boat does not know if there is foam.. so It wont work unless your counting on balist from the foam ( nobody wants to say that ? ).

" Anything you put inside the boat, including foam, is just weight. The boat floats because of the water it displaces, or pushes aside. If the boat weighs 500 pounds it has to push 500 pounds of water aside. If a boat weighs 500 pounds and has 20 pounds of foam inside, then it has to push 520 pounds of water aside. Foam only hellps if the boat sinks. "

I really dont understand this.. and kinda missleading.. Of Coarse the Wieght of the boat and all components measure some weight.. and the hull volume of displacement is NOT the same from boat to boat ( I dont care if the hull is 500 Lbs .. its the Displacement ( not the entire boat weight ).

Did not mean to be Rude..

But I know I am on many points...

YD.




All I was saying i

 

[ezmobee]

Re: Decking a boat

Just for clarity, are you saying that adding foam to a hull increases its buoyancy (when not swamped)?

 

[109jb]

Re: Decking a boat

Im not trying to be rude.. just explaining what foam will or will not do.

I am right on this one ( no need to call me Dude then tell me not to be rude in one sentence .. kinda rude )..

I can build a 500 lb flat bottom boat and it will take WAY more then 500 lbs in water ( 63 gallons of freash water to displacement) to sink it.

"I have a aluminum 15' boat it looks like it used to be decked, if I redeck it can I put some kind of foam to help stabalize or offset the weight of the wooden decking it would be approx 1 1/2 inch or so would that be enough to help and do I leave the drain galleys open or let the water go on top? I appreciate any and all help as always "

The boat does not know if there is foam.. so It wont work unless your counting on balist from the foam ( nobody wants to say that ? ).

" Anything you put inside the boat, including foam, is just weight. The boat floats because of the water it displaces, or pushes aside. If the boat weighs 500 pounds it has to push 500 pounds of water aside. If a boat weighs 500 pounds and has 20 pounds of foam inside, then it has to push 520 pounds of water aside. Foam only hellps if the boat sinks. "

I really dont understand this.. and kinda missleading.. Of Coarse the Wieght of the boat and all components measure some weight.. and the hull volume of displacement is NOT the same from boat to boat ( I dont care if the hull is 500 Lbs .. its the Displacement ( not the entire boat weight ).

Did not mean to be Rude..

But I know I am on many points...

YD.




All I was saying i

I never said a 500 pound boat would sink with 500 pounds of water in it. I said a 500 pound boat displaces 500 pounds of water when it is floating. That is fact pure and simple. Now put 50 pounds of foam INSIDE that same boat. The hull now has to displace 50 pounds MORE water. Again, fact pure and simple. The foam inside the boat doesn't make the boat sit higher in the water. The shape of the boat doesn't matter either. A 500 pound cube has to displace 500 pounds of water if it is to stay afloat. Likewise a 500 pound boat has to displace 500 pounds of water to stay afloat.

As for my original post lets disect it sentence by sentence:

"Anything you put inside the boat, including foam, is just weight."
So are you saying if I put foam inside a boat that it will float higher, or is it additional weight that the hull has to carry? I say it is just additional weight.

The boat floats because of the water it displaces, or pushes aside.
Well that's how it works. The hull displaces the same weight in water as what the hull has to support. This includes the hull weight, motor weight, people weight, anything else in the boat.

If the boat weighs 500 pounds it has to push 500 pounds of water aside.
Again, this is just the way it works.


If a boat weighs 500 pounds and has 20 pounds of foam inside, then it has to push 520 pounds of water aside.
500 pound boat and 20 pounds additional inside. If it is to stay on top of the water it has to displace 520 pounds of water.

Foam only hellps if the boat sinks.
If the foam is inside the boat it surely doesn't help the boat float unless the boat is swamped.

Sentence by sentence it makes perfect sense. I don't believe my original post was misleading at all. If you don't understand a post how about saying you don't understand it instead of just claiming it is wrong.

 

[JAFO1]

Re: Decking a boat

YD

What is the truth then? I read some guy put pool noodles under his deck will that help? I'm really trying to learn. Is there a resource other than this forum that you know of? Is the new pressure treated wood harmful to aluminum?

I'm going to leave the 'displacement issue' alone.
My understanding of flotation foam is, that it will provide flotation if your boat is inundated with water, but it doesn't make it float or more buoyant.

Here is a picture relating the importance of flotation foam. I took it from a thread here on iboats.

And, don't use treated plywood on aluminum. Aluminum will react negatively to treated plywood.

http://forums.iboats.com/attachment.php?attachmentid=62899&d=1281014915

 

[adamjr]

Re: Decking a boat

When it comes to displacement of water it is not necessarily a 1:1 ratio. 231 cubic inches displaces 1 gallon of water which is equal to 8 pounds if we are discussing fresh water.

If you really wanted to test the theory you would need to put the vessel being judged into a pool of a known volume. For simplicity's sake it (the pool) should need to be a known depth, width, and length and rectangular or cylindrical without a taper. To determine the volume multiply depth times width times length in inches and divide by 231. This will be the gallon volume. Then lower the vessel into the water and remeasure the height of the water and re-calculate the volume. Subtract the original measurement from the new measurement and this will be the volume displaced by the vessel in gallons. Multiply by a factor of 8 and you will have the weight the vessel displaces. You can weigh the vessel on a commmercial scale to see what the actual weight ratio of the displacement is.

Regardless of the answer no vessel should be without floatation foam. It might save your life. Saving teh vessel should be an afterthought.

 

[109jb]

Re: Decking a boat

When it comes to displacement of water it is not necessarily a 1:1 ratio. 231 cubic inches displaces 1 gallon of water which is equal to 8 pounds if we are discussing fresh water....

It is a 1:1 ratio by weight. To float 1 pound boat or anything else in any kind of liquid you have to displace 1 pound of that liquid whether it be fresh water, salt water, milk, juicy juice or whatever. The volume of the liquid displaced might be different due to its density, but 1 pound of liquid will still have to be displaced for every pound of weight. Nobody said anything about the volume of water displaced, only the weight that needed to be displaced.

This is only for things that float. If it doesn't float then this doesn't apply. For example, as pointed out a gallon of water is about 8 pounds but 1 gallon of water is not displaced if you pitch an 8 pound lead ball in the water. Put that 8 pound lead ball on something so that it will float and it will displace a gallon of water plus whatever extra is needed to float what the lead ball is sitting on.

 

[ondarvr]

Re: Decking a boat

I think YD may have misunderstood the meaning of what you said and that's why he responded that way.

 

[emoney]

Re: Decking a boat

And, of course, there's a difference between buoyancy and flotation. All of
it has to involve both volume and density. I can see why both sides would
argue their side and why the OP asked if there's a 'formula' to factor in how
much should foam to use (etc. etc.). The overriding factor is probably the
density. I would imagine that a lot of foam doesn't add a lot of weight. So,
when you factor in the "flotation" of the foam, shouldn't it, in fact, add to the
"flotation" of the "buoyant" boat?

Take my "floating dock" into consideration. The only flotation is the foam
that's on the underside of it. Where that it wasn't there the dock would
not be bouyant at all, it would sink to the bottom of the channel. In a nutshell, what the OP is asking (at least I think)is how does the foam affect the boat, in the manner that it affects my dock?

 

[imported_rick]

Re: Decking a boat

How's this take on it?

If the boat is not swamped the foam is just extra weight, as 109jb said, whatever the weight a cubic foot of foam is, it will definitely be less than the weight of the water it displaces when submerged. A cubic foot of water is somewhere around 63 pounds, the foam may only be 2-3 pounds so you'd have around 60 pounds subtracted from the weight of the bought when swamped.

If you filled the boat completely with water and if the boat was 500 lbs then I guess you would need about 8+ cubic feet of foam to resemble the picture in the link provided by JAFO1, no?

The OP asked if the foam would offset the weight of the wooden deck, I say yes, if he was to put the foam under the boat, in the water, otherwise no. Besides, wood has a lower specific gravity than water so it would sorta cancel itself out as a factor in aiding to sink the boat anyway.

Or, I could be wrong.

 

[JAFO1]

Re: Decking a boat

And, of course, there's a difference between buoyancy and flotation. All of
it has to involve both volume and density. I can see why both sides would
argue their side and why the OP asked if there's a 'formula' to factor in how
much should foam to use (etc. etc.). The overriding factor is probably the
density. I would imagine that a lot of foam doesn't add a lot of weight. So,
when you factor in the "flotation" of the foam, shouldn't it, in fact, add to the
"flotation" of the "buoyant" boat?

Take my "floating dock" into consideration. The only flotation is the foam
that's on the underside of it. Where that it wasn't there the dock would
not be bouyant at all, it would sink to the bottom of the channel. In a nutshell, what the OP is asking (at least I think)is how does the foam affect the boat, in the manner that it affects my dock?

I think your dock and a boat hull are two different principals in action. Or maybe not. In a boat, the only thing foam does, is keep the boat from sinking if it is inundated, or swamped. All polyurethane foam does is hold air bubbles. Your dock is floating on the same air bubbles, encased it whatever medium, PE, Styrofoam, etc.