Flotation

[wideopen23]

I was just reading another thread about a boat sinking. Sorry to hear this, I hope they find it.
In this thread someone mentioned something about using inertubes as flotation. I just happen to be in the middle of looking for something to use. Has anyone else used these for this purpose and how many do you use?
Thanks for the info.
JC

[Kindsvater Flat]

A couple of inner tubes and just air them up after you put them in the bow. I have 2.

[texas-19]

I bought a small tractor tire,stuck it in as far as possible,and filled it as full as could get it.Been in their 2 years with no problem.I also bought a small plastic utility box that floats and put my wallet,gps,keys etc in it,just in case.

[dmontzsta]

Its good that it was brought up. I need to do this and think everyone should do it as well...to make their boat easier to retreive.

[Morg]

I have also told the guy's that I run with to have a rope ready. I am planning on having a 100' rope with a float on one end & a hook on the other. If it turns ugly even with floatation it can still go down. But it should give you time to hook the rope to the bow eye.
I have pulled a jet up from the bottom & had it floating with the pump missing, The driveline let go, broke the intake & ejected the pump out the back. luckily the 19' boat sunk in 19' of water. We hooked onto it & got it up on plane. Then across the lake to next to the trailer. Winched the boat back onto the trailer. Amazingly enough after all that the reverse cable never let go. the newly rebuilt pump was not lost.

[HammerDown]

Will one or two innertubes under the bow really keep a BBC and related boat items bobbing at the surface... Me don't think so.

[Jeanyus]

I saw a diver retrieve a boat by inflating 1 innertube in the bow, it was a
V-6, but had a heavy sterndrive.

[texas-19]

Will one or two innertubes under the bow really keep a BBC and related boat items bobbing at the surface... Me don't think so.
I don't know from experience and hope i don't find out but i been told by someone that seen it happen that the innertube does work.Guess it depends how much air you get in it and how heavy the boat is.I KNOW what i am going to do.

[steelcomp]

My Bahner came with (or maybe someone put in) about a dozen plastic balloons, about 8" in dia. that were up under the bow of the boat. My Southwind Tunnel had the same thing.

[Beautiful Noise]

I have 10 Pillow size Air Bags under my Deck,It has saved my Boat twice from going down.It just bobb's around till you get a line on the front,Then just tow slow till it gets on plane then just tow it around till you get all the water out and put it back on the Trailer. :smile:

[Not Twice]

I am currently redoing my sub-floor and have removed all of the foam and do not want to put it back in. Does anyone know were you can buy any of these pillows or airbags? My concern is the durability of the bags over time, bouncing and rubbing against the hull.

[dmontzsta]

I have also told the guy's that I run with to have a rope ready. I am planning on having a 100' rope with a float on one end & a hook on the other. If it turns ugly even with floatation it can still go down. But it should give you time to hook the rope to the bow eye.
I have pulled a jet up from the bottom & had it floating with the pump missing, The driveline let go, broke the intake & ejected the pump out the back. luckily the 19' boat sunk in 19' of water. We hooked onto it & got it up on plane. Then across the lake to next to the trailer. Winched the boat back onto the trailer. Amazingly enough after all that the reverse cable never let go. the newly rebuilt pump was not lost.
That is a damn good idea too, going to have to use that one. :D

[CrdStang]

You can always fill in under the floor with ping pong balls. Assuming you can find them cheap.
They won't absorb water and rot out the stringers like foam, and they're not messy either.

[BLEWBAYOU1]

My Eliminator Bubble deck Has two large plastic bags full of peanut sized foam.With that and being the bow area is somewhat airtight with the deck and bulkhead glassed together I think it would be able to keep the bow above water,at least long enough for recovery.
Brian :cool:

[LUVNLIFE]

Mine has foam blown in the sponsons. But I think an innertube is in order also.

[1978 Rogers]

Was putting flotation a standard thing to do? I have a 1978 Rogers Bonn. My bow is closed off with a carpeted piece of plywood. I've never taken it out, so I have no idea whats up in the bow.
Any help?

[HammerDown]

You can always fill in under the floor with ping pong balls.
Uh, are you serious?

[Mr.&Mrs.Budlight]

Flotation is not done by any manufactures I know of. The main purpose For some kind of floatation device is put into the bow, is where the rubrail is mounted on the boat, all the air pocketed in the bow will escape thur the mounting holes for the rubrail. The inner tube traps the air so it can't leak out. Budlight

[BLEWBAYOU1]

Flotation is not done by any manufactures I know of. The main purpose For some kind of floatation device is put into the bow, is where the rubrail is mounted on the boat, all the air pocketed in the bow will escape thur the mounting holes for the rubrail. The inner tube traps the air so it can't leak out. Budlight
My Eliminator has the peanut foamed plastic bags in the bow from the factory.I'm the second owner And I know the original. :cool:
Brian

[moneysucker]

All of my south wind drag tunnels had the plastic balloons, my tahiti had a fuel tank in the bow which would have helped it sink. My Crusader DT had some brain surgeon fill popcorn tubs with expanding float foam and shoved them through a hole that he cut with a hole saw in the bulkhead.
Anyone who boats where the water is deep flotation is a good idea. If you aren't going fast enough to have the boat grenade the rope and floaty would work. Though, at Martinez I have watched the cops tell a boat that was towinf a sinking hydro to stop and sank it at the end of the fuel dock. as the tow boat tried in a panic to bring it up again the tow rope broke. When a friend of mine tried to hook to the bow eye to get it up the cops told him, "If you touch that boat you will be arrested."

[HammerDown]

I had a really LARGE air bag 8'x4', however with all the bulkheads in my 21 Daytona I couldn't use it sold to a member here.
Innertubes won't work either.
Maybe a bunch of lets say 1'x1' air bags. But where to get them?

[moneysucker]

I have dial up. It took me that long to watch that video. That thing went down very fast. It was good to hear the engine on the rescue boat. I haven't heard that since it was warm. I hope he gets it back with out too much expense and repair costs. Definately good of the board members to volunteer their services.

[BLEWBAYOU1]

Uh, are you serious?
Funny thing is I heard the same thing. I guess they have a high boyancy rateing. :eek:
Brian

[CrazyHippy]

Some of the bass boat guys are sealing the top and bottoms of their Jackplates, and then filling them w/ ping pong balls. supposed to pick the back of the boat up 3-4" off plane. That is only 1 cubic foot, and it's not all submerged.
If i'm not mistaken the USCG requires manufacturers to put flotation in newer boats. My brain keeps saying 1984 and newer, but i've stabbed it w/ q-tips a few times :boxed:
BJH :rollside:

[moneysucker]

Funny thing is I heard the same thing. I guess they have a high boyancy rateing. :eek:
Brian
Don't you guys watch myth busters? They raised a sunken ship by injecting the insides with ping pong balls.

[texas-19]

I had a really LARGE air bag 8'x4', however with all the bulkheads in my 21 Daytona I couldn't use it sold to a member here.
Innertubes won't work either.
Maybe a bunch of lets say 1'x1' air bags. But where to get them?
You say innertubes won't work.Have you seen a boat go down with one?Not trying to be a smart a#@ just want to learn from your experience.
When you mentioned 1' x 1' air bags something came to mind.We get Arizona green tea in 1 gallon jugs made from tough plastic with the screw on lids.You could fill in the voids with them or something close to it.
Also my last jet boat was a mariah and it had about a dozen of those plastic pillows under the deck.Not sure if they were put in by the manuf but i could see they had been in their for a long time.

[21rayson]

here's what i took out of my 21 rayson they were in there since the boat was built in 1975. http://www.***boat.com/forums/attachment.php?attachmentid=8876&stc=1

[Kim Hanson]

Its called " Expandable Foam In a Can "....unseen and it stick to everything , my v-drive will have that in alot of place's this year and an inner tube in the bow..........( . )( . )............. :smile: My V-Drive was pointing skyward also , it just plain sucks. :idea:

[77charger]

why is that when i sank my old boat at havasu 12 years ago the guy who was pulling my boat out was ordered to let the boat sink cop had to go to a call the boat helping out reved up and towed me out again and kept going.
A I have watched the cops tell a boat that was towinf a sinking hydro to stop and sank it at the end of the fuel dock. as the tow boat tried in a panic to bring it up again the tow rope broke. When a friend of mine tried to hook to the bow eye to get it up the cops told him, "If you touch that boat you will be arrested."

[wideopen23]

Dial up is a bitch isnt Moneysucker. I have it to. Anyways, thanks for all the comments guys. I have seen some people say the inner tubes wont work and some that do. I cant seem to find anything else that sounds as good as that. I guess this is better than nothing.

[LVjetboy]

Inner tubes, ping pong balls, blow foam, tea bags, whatever. All sounds good until you sink and find out (after the fact) that bouancy wasn't enough? We had this discussion a long time ago on RJB. There is a way to know how much is enough...
Or we could just guess. What do you think, maybe 100 ping pong balls? How about 1000? :confused: :) How big the tube? How many tubes?
jer

[Jake W2]

Is this a dumb question?WHY IN THE HELL would the boat cops tell you to let it sink?It would seem more of a hazard to let it sit in the lake then to pull it out?
Jake

[LVjetboy]

Who knows? And does a "boat cop" know what's best in all circumstances? I'm thinking no. In fact I know no. But he is the "law" after all...with the power to influence your life better or worse. No small thing.
jer

[steelcomp]

Is this a dumb question?WHY IN THE HELL would the boat cops tell you to let it sink?It would seem more of a hazard to let it sit in the lake then to pull it out?
Jake
I'm thinkin that by the time I was done getting my (or my friend's) boat out of the water and safely on a trailer, that cop would have more to worry about than a sinking boat. And I'd definately get arrested, but not for helping out. :devil:

[77charger]

as for the cops forcing it to sink at that time i was wondering how much kickback they get :D .Although i never found out the answer that is why i ask might have to ask boatcop about that

[MudPumper]

To know if your boat will float or sink you need to figure out how much water your boat will displace when it is submerged in water. That is the hard part, measuring the boat to see how much water it displaces. I don't know how this can be done without sinking the boat in a giant tank where you could measure.
Archimedes Principle States: Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. It is simple math to figure out if it will float or sink as long as you know the displacement.
1 cubic ft of freshwater weighs approximately 62.4 lbs. Salt water is approximately 64lbs. For example an object that weighs 100lbs on land and displaces 1 cubic ft will weigh 37.6lbs in fresh water.
Figure out how much the boat displaces and you can figure out how big of an innertube, how many milk jugs, ping pong balls etc......... you will need.

[moneysucker]

as for the cops forcing it to sink at that time i was wondering how much kickback they get :D .Although i never found out the answer that is why i ask might have to ask boatcop about that
I am thinking that the cops want to stop a potentially dangerous situation. Recovery of a boat can go bad and sink the rescue boat also. There are many scenerios that can happen to increase the hazzards and the cops know nothing of your experience in boating or recovery and they know that the launch area no wake zone law will be broken once the boats get there. When Problem Child crashed at martinez, the cops came and told the people diving to hook a rope to it to stop or or face charges. The cops went about trying to find the boat by dragging anchors. The cops searched in vain until dark and they were going to call in the diver in the morning. The diver is the same guy that they kicked off the site the day before.
As far as ping pong ball flotation you need to watch The Myth busters on raising a sunken vessell. They have all the floatation info on there.

[lucky]

the ping pong ball on mb was insightfull - brought that tuna boat right up

[Mighty Thor]

So why not try a test? put a bunch of milk cartons ping pong balls etc in a net and see how much weight it takes to sink them? I would do it but it's been -13 here all week and the water is too stiff for me to get accurate results.

[MudPumper]

It's not just weight Thor, it's displacement. 2 objects both weighing 100 lbs but displace a different amount of water will require different amounts of lift to make buoyant.

[mgar_red]

It would be interesting to hear the cops answer when asked why he wasn't doing anything to help? And also to recite verbatim the law being broken? I'm sure the media would have a field day exposing how a Good Samaritan was within feet of finishing helping someone and was told by Johnny Law to ditch all his efforts.

[MudPumper]

I would imagine, and this is just speculation, that the cop instructed the people to cease because of an unsafe condition. The grounds for arrest would be for disobeying a lawful order of a peace officer, or something along those lines.

[Brooski]

I would imagine, and this is just speculation, that the cop instructed the people to cease because of an unsafe condition. The grounds for arrest would be for disobeying a lawful order of a peace officer, or something along those lines.
Dang Mike, you are full of insightful information tonight. Been reading up on engineering while you arent working cuz of the rain? :cool:

[LVjetboy]

"That is the hard part, measuring the boat to see how much water it displaces. I don't know how this can be done without sinking the boat in a giant tank where you could measure."
I'd say calculating displacement nearly impossible, certainly not practical. But there's another way to estimate the lifting force...and the ballpark answer's a lot better than having no clue.
jer

[BobS]

"That is the hard part, measuring the boat to see how much water it displaces. I don't know how this can be done without sinking the boat in a giant tank where you could measure."
I'd say calculating displacement nearly impossible, certainly not practical. But there's another way to estimate the lifting force...and the ballpark answer's a lot better than having no clue.
jer
I'm confused, don't you just have to know the weight of the boat (or whatever you are trying to raise) and displace an equivalent amount of water? If so, I take my ride to a truck scale and it weighs 6400 lbs. I need to displace 100 cubic ft. of water at 64 lbs per cu. ft. Therefore, I would need a weightless air bag 5'x5'x4' (plus an r.c.h.) to raise it from the bottom.

[Mighty Thor]

It's not just weight Thor, it's displacement. 2 objects both weighing 100 lbs but displace a different amount of water will require different amounts of lift to make buoyant.
Actually it is just weight, ifn you got a hunert pound boat and it takes two hunert pounds to sink your milk cartons you are pretty much guaranteed to float your boat with your milk cartons. But I know what your sayin which is that a hunert pounds don't necessarily weigh a hunert pounds when it is in da water. Still, it would be handy to know how much weight it takes to sink your flotation of choice. At least you got half the equation then.

[Mighty Thor]

Here's my thought, take your barbell weight to the lake or nearest 50 gallon drum of water. hook it to a hardware scale etc. weigh it above water, weigh it below water, below water is weight that you will use as reference. Hook weight to flotation item and add weight or flotation til it just floats or just sinks. That should give you an idea of how much weight you can float per unit of floatation medium. plus any additional bouancy from your acutal h2o displacement is a safety margin. I guarantee that it will be better than an iron weight.
Course I could be all wet on this but not with the weather we been having.

[BobS]

Actually it is just weight, ifn you got a hunert pound boat and it takes two hunert pounds to sink your milk cartons you are pretty much guaranteed to float your boat with your milk cartons. But I know what your sayin which is that a hunert pounds don't necessarily weigh a hunert pounds when it is in da water. Still, it would be handy to know how much weight it takes to sink your flotation of choice. At least you got half the equation then.
Okay, I'm getting it. In my example, because my submerged boat already displaces some water, I don't need quite as much flotation to raise it.

[fkeys]

I actually took a tape measure after my hull and roughly "blueprinted" it. Forgot the volume I came up with, but using Archimedes Principle (with some assumptions) to calculate I would need about 25 cubic feet of that 2-part flotation foam to keep mine from going to the bottom again. Don't know how ping-pong balls, tea jugs, etc would compare but I'd bet they'd be pretty close.
Guessing the weight of your boat submerged is the key. If a recall correctly :idea: it was about 50% of the dry weight, but don't quote me on that figure. That discussion was from the RJB forum, long time ago.

[cruser]

There is another wrinkle that no one has mentioned. Using enough air filled media to prevent your boat from sinking will likley not provide enough "lift" to raise it from the bottom of a lake. As the ballons/inner tubes/ping pong balls/whatever sink to greater depths, they contract due to water pressure, displacing less water and loosing lifting power. One of the dangers divers run into when recovering sunken objects at depth using air bags is that as the object raises, the bag get bigger, displacing more water, increasing the bags ability to lift, causing the object to rise faster, etc. If not closley monitored, the object (boat) can get out of control and you may damage it more or loose it again. Hopefully you are not in the way when that happens. That is why salvage operations are so dangerous.
As part of my dive training, I had to raise an object from 35' of water. It was surprizing how much that object accelerated when not carefully monitored.

[texas-19]

Cruser,
Do you think an innertube will keep a jet boats nose out of the water ?I agree that a small one would not help much but i have a tractor tire under my deck that is as full as possible.

[spectras only]

I think new boats 18' and under require positive flotation.Very few boats were built like that in the past except Cruisers and Boston whalers. Their boats floated level filled with water including passengers. I think the 18' spectra had positive flotation too, but were manufactured for short time only before Southwind built them. Malcolm on the board has an 18footer ,I'll ask him to test his boat for us on the board :rollside: :D

[Mighty Thor]

Interesting historical note, I once saw a picture of a Hammond circa mid 70s that was floating just beneath the surface of the water with 4 seated passengers. Marketing claim was that you couldn't sink. :eek:

[spectras only]

Found the picture .Hope Brent doesn't mind ;) =http://www3.telus.net/spectrasonly/playitsafe.gif

[Jake W2]

WOW it's to bad they don't all do that.Cool add
Jake

[HammerDown]

Yea, that would work...so how can we do it?

[Aluminum Squirt]

One thing to consider when attempting to float your boat in case of a catastrophic failure is your water conditions. I understand we boat in a very different environment, but if you are dealing with moving water, think very carefully before you make it unsinkable. If it was slightly negatively buyont, at least in our shallow rivers, you may be looking for your boat for awhile, as its going to be skipping along the bottom until it gets hung up on something. Of course if its unsinkable, you could send it un-powered over something like Shanghai Bend which could also have its draw backs. I'm a rookie when it comes to white water, maybe Baldy can share some stories, but I don't think I've seen any floation material/equipment in any white water boats, at least those of the race variety. Something to think about even if you are on a relatively tame river, by our standards anyway, such as the Colorado-Aluminum Squirt

[LVjetboy]

"I'm confused, don't you just have to know the weight of the boat (or whatever you are trying to raise) and displace an equivalent amount of water?"
That would give you over twice the lifting force needed. Doesn't account for the weight of the water displaced by the boat and engine. Why? Because the boat weighs more on the truck scales than when it's under water. Volume displacement and all.
"Okay, I'm getting it. In my example, because my submerged boat already displaces some water, I don't need quite as much flotation to raise it."
Yes. I just read your last post. Overkill not always a bad thing. As long as you know it's overkill and can make the compromise to accomodate extra floatation volume.
jer

[LVjetboy]

"That discussion was from the RJB forum, long time ago. If a recall correctly, it was about 50% of the dry weight, but don't quote me on that figure."
That's about right. Although that number's conservative for a "weightless" float. Conservative means it doesn't account for traped air and so on. If it did, then your sink time if any would be significantly less. More time to attach a rope.
jer

[LVjetboy]

"...but I don't think I've seen any floation material/equipment in any white water boats, at least those of the race variety."
To me that make sense. If you sink there's a question of movement and successful recover effort than your typical lake boat. Unless that lake boat sinks at 400 feet?
jer

[Mighty Thor]

"...but I don't think I've seen any floation material/equipment in any white water boats, at least those of the race variety."
To me that make sense. If you sink there's a question of movement and successful recover effort than your typical lake boat. Unless that lake boat sinks at 400 feet?
jer
I guess the question is also what kind of recovery are you gonna want to try. Looks like recovering the spectra in the pictures above would be fairly easy and so movement might not be much of an issue. Recovering something that is floating 3 inches off the bottom of the lake or river might be a heck of a lot more challenging. Looks to me like the best plan would beto choose, don't let it go under all the way and salvage immediately or let it go to the bottom and then recover via marker and line.

[Mighty Thor]

Interesting historical note, I once saw a picture of a Hammond circa mid 70s that was floating just beneath the surface of the water with 4 seated passengers. Marketing claim was that you couldn't sink. :eek:
http://www.classicglastron.com/78hammond-and-11.JPG

[LVjetboy]

"That is the hard part, measuring the boat to see how much water it displaces. I don't know how this can be done without sinking the boat in a giant tank where you could measure."
Here's an alternative to sinking your boat in a giant tank... :rolleyes:
Lifting force equals the weight of water displaced by the boat and floatation device minus the boat weight. Since we don’t know the boats physical volume, calculating displaced water weight can only be done indirectly using material densities. For example, you can estimate the volume of water displaced by the engine if you know engine weight and the densities of steel and aluminum. The answer won’t account for the many different materials used in an engine or trapped air, but at least it’s ballpark instead a total wag. Here's numbers for my boat...
Estimated weights:
Engine + Tanks: 800 lbs
Pump + Plate + Linkage: 200 lbs
Hull + Fuel + Battery + Rig: 1050 lbs
Total Boat weight: 2050 lbs
Densities:
Steel: 490 lbs/cuft
Aluminum: 170 lbs/cuft
Hull + Rigging: 80 lbs/cuft (est.)
Water: 63 lbs/cuft
Assuming 30% aluminum and 70% steel, the engine’s density is (0.30 x 170) + (0.70 x 490) = 394 lbs/cuft. Except for the shaft and some cases impeller, most pumps, ride plates, etc are aluminum so I used aluminum density for the pump. Hull and rigging density hard to know. Depends on resin density, how much air trapped in the glass mat, copper wiring, plastic trim and insulation, on and on. Most likely more than water density, but less than pure resin. So I estimated with 80 lbs/cuft.
Volume equals weight divided by density, so:
Engine = 800/394 = 2 cuft
Pump = 200/170 = 1 cuft
Hull = 1050/80 = 13 cuft
These volumes represent what each component would displace if fully submerged without air pockets. So the total volume of water displaced by the boat = 2 + 1 + 13 = 16 cuft. And the weight of water displaced = 16 x 63 = 1008 lbs. Since the total boat weight is 2050 lbs, the underwater weight needing support by air is 2050 – 1008 = 1042 lbs. Or roughly 50% of the total boat weight. Finally, this gives an air volume of 1042/63 = 16.5 cuft of air. Remember, this's a conservative number not accounting for traped air, wood in the transom and stringers, glass mat in the resin, etc. But if you wanted to pad the result with a net positive lifting force of 100 lbs, you’d add about 1.5 cuft for a total of 18 cuft of air.
A tube inflated to a 1.4 ft cross sectional diameter would need to be 5 ft in overall diameter to give 18 cuft of air.
That’s a good sized tube…won’t fit in my bow.
http://members.cox.net/lvjetboy/FloatTube.jpg
Where,
Tube overall diameter, Do = 5.12 ft
Tube cross sectional diameter, Ds = 1.4 ft
Giving a tube volume of, V = 18 cuft
Or about 18,000 ping pong balls! Maybe a bit expensive? And rattle around? Rubber tubes are cheap, easy to inflate and remove later. But I’d be concerned about the tube putting pressure on the deck to hull joint or causing stress cracks. Seems like it would be hard know how much pressure was too much if there’s a clearance issue.
Bottom line: If you're going to add floatation, some idea of how much needed is a good thing without actually sinking your boat. And yes, that CAN be estimated.
(Edited from my original post on RJB.)
jer

[HammerDown]

"That is the hard part, measuring the boat to see how much water it displaces. I don't know how this can be done without sinking the boat in a giant tank where you could measure."
Here's an alternative to sinking your boat in a giant tank... :rolleyes:
Lifting force equals the weight of water displaced by the boat and floatation device minus the boat weight. Since we don’t know the boats physical volume, calculating displaced water weight can only be done indirectly using material densities. For example, you can estimate the volume of water displaced by the engine if you know engine weight and the densities of steel and aluminum. The answer won’t account for the many different materials used in an engine or trapped air, but at least it’s ballpark instead a total wag. Here's numbers for my boat...
Estimated weights:
Engine + Tanks: 800 lbs
Pump + Plate + Linkage: 200 lbs
Hull + Fuel + Battery + Rig: 1050 lbs
Total Boat weight: 2050 lbs
Densities:
Steel: 490 lbs/cuft
Aluminum: 170 lbs/cuft
Hull + Rigging: 80 lbs/cuft (est.)
Water: 63 lbs/cuft
Assuming 30% aluminum and 70% steel, the engine’s density is (0.30 x 170) + (0.70 x 490) = 394 lbs/cuft. Except for the shaft and some cases impeller, most pumps, ride plates, etc are aluminum so I used aluminum density for the pump. Hull and rigging density hard to know. Depends on resin density, how much air trapped in the glass mat, copper wiring, plastic trim and insulation, on and on. Most likely more than water density, but less than pure resin. So I estimated with 80 lbs/cuft.
Volume equals weight divided by density, so:
Engine = 800/394 = 2 cuft
Pump = 200/170 = 1 cuft
Hull = 1050/80 = 13 cuft
These volumes represent what each component would displace if fully submerged without air pockets. So the total volume of water displaced by the boat = 2 + 1 + 13 = 16 cuft. And the weight of water displaced = 16 x 63 = 1008 lbs. Since the total boat weight is 2050 lbs, the underwater weight needing support by air is 2050 – 1008 = 1042 lbs. Or roughly 50% of the total boat weight. Finally, this gives an air volume of 1042/63 = 16.5 cuft of air. Remember, this's a conservative number not accounting for traped air, wood in the transom and stringers, glass mat in the resin, etc. But if you wanted to pad the result with a net positive lifting force of 100 lbs, you’d add about 1.5 cuft for a total of 18 cuft of air.
A tube inflated to a 1.4 ft cross sectional diameter would need to be 5 ft in overall diameter to give 18 cuft of air.
That’s a good sized tube…won’t fit in my bow.
http://members.cox.net/lvjetboy/FloatTube.jpg
Where,
Tube overall diameter, Do = 5.12 ft
Tube cross sectional diameter, Ds = 1.4 ft
Giving a tube volume of, V = 18 cuft
Or about 18,000 ping pong balls! Maybe a bit expensive? And rattle around? Rubber tubes are cheap, easy to inflate and remove later. But I’d be concerned about the tube putting pressure on the deck to hull joint or causing stress cracks. Seems like it would be hard know how much pressure was too much if there’s a clearance issue.
Bottom line: If you're going to add floatation, some idea of how much needed is a good thing without actually sinking your boat. And yes, that CAN be estimated.
(Edited from my original post on RJB.)
jer
And now we know why Jer makes the BIG :eek: ...money! :wink:

[bp]

just out of curiousity, how much pressure needs to be in that tube so it doesn't compress? if you use those smaller air bags, how much pressure do they contain so they don't compress too much? rather than an awkwardly sized innertube, perhaps just 18 ft3 of floatation in the spaces available?

[Brooski]

Since the discussion is about increasing flotation, here is my .02. If you decide to use expanding foam under the deck, be very very careful. I have seen 2 boats so far where someone has used expanding foam under the deck, then the foam expands too much and bows out the top of the deck, or splits the deck. Its amazing the pressure that stuff can build.

[Sundance]

This whole thread is getting way to complicated. Pulled all my seats out for a winter clean. Found behind the rear seat, that are positioned sideways, two 36"x1'x1' stryofoam blocks on each side. Talked to a buddy who is an exracer and he says that's what he used. My nose is sealed off and these on the sides they say will keep it afloat.
My only problem is I want to replace them but can't find anybody in my area who sells it.
What is the deal about the "foam in a can"? Where can you read up on it?
Keep it Up.
Sundance :chi:

[bottom feeder]

Sundance if it is the foam block you are looking for try a stucco supply house.

[TopCat]

my old Syndicate had the bow filled with foam and sealed it saved it from sinking in over 90ft of water but maybe 2liter soda bottles or clorox bottles mite work or maybe even a govt surplus balloon filled with foam mite be ideal hell big truck tubes filled with foam should do it any thing i'd use would be filled with foam incase from bouncing etc it rubbed a hole in the tube for example

[TopCat]

This whole thread is getting way to complicated. Pulled all my seats out for a winter clean. Found behind the rear seat, that are positioned sideways, two 36"x1'x1' stryofoam blocks on each side. Talked to a buddy who is an exracer and he says that's what he used. My nose is sealed off and these on the sides they say will keep it afloat.
My only problem is I want to replace them but can't find anybody in my area who sells it.
What is the deal about the "foam in a can"? Where can you read up on it?
Keep it Up.
Sundance :chi:
hot tub mfg will hav all the styrofoam u'll ever need :rollside:

[MANIC MECHANIC]

I'm not to much on math or physics but I have studied the subject and here's
what I learned and what I decided to do.
The "foam in the can" you can get at Lowe's or Home Depot is a heavy high
density foam that is suitable for stoping drafts in the house, but has no place in a boat.
The only proper foam to use is the "flotation" two part closed cell foam
available from most marine suppliers.
You mix it 50/50 and stir it for 45 secs and learn (by trial & error) how to direct it where you want it to fill while you pour it into place (if you try to direct it's position or expansion after you pour it into place you break up the bubbles in it and end up with a very heavy, thin glob of crap that has no flotation value).
As far as volume of flotation, on the last boat I rebuilt, I gave up on the math and just put flotation foam everywhere I could.
I filled the spaces under the floor, which allowed me to use much thinner flooring than I could have used otherwise (it's amazing how much foam will stiffen the boat).
While I had the boat flipped over I foamed the undersides of the deck... like
has been mentioned earlier, Be careful where you put it!...
Although the flotation was never tested, I do know that the boat was much more solid (or stronger) than it was before, and I'm sure that it would float
if flooded.
Just my .02 on the subject.
Tim

[TopCat]

I'm not to much on math or physics but I have studied the subject and here's
what I learned and what I decided to do.
The "foam in the can" you can get at Lowe's or Home Depot is a heavy high
density foam that is suitable for stoping drafts in the house, but has no place in a boat.
The only proper foam to use is the "flotation" two part closed cell foam
available from most marine suppliers.
You mix it 50/50 and stir it for 45 secs and learn (by trial & error) how to direct it where you want it to fill while you pour it into place (if you try to direct it's position or expansion after you pour it into place you break up the bubbles in it and end up with a very heavy, thin glob of crap that has no flotation value).
As far as volume of flotation, on the last boat I rebuilt, I gave up on the math and just put flotation foam everywhere I could.
I filled the spaces under the floor, which allowed me to use much thinner flooring than I could have used otherwise (it's amazing how much foam will stiffen the boat).
While I had the boat flipped over I foamed the undersides of the deck... like
has been mentioned earlier, Be careful where you put it!...
Although the flotation was never tested, I do know that the boat was much more solid (or stronger) than it was before, and I'm sure that it would float
if flooded.
Just my .02 on the subject.
TimEXACTLY

[LVjetboy]

"Although the flotation was never tested...I'm sure that it would float if flooded."
Why are you sure? ;)
Foam traps air and adds weight. Sure it works in the right amount as other things mentioned here. But unless you know how much expanded foam to float, you're just a guessin' and a hopin'
"This whole thread is getting way to complicated."
Are my posts too complicated? Sorry. :confused: Maybe I should post in some other so called "tech" forum.
We could just throw a tube and a couple of milk jugs up in there. Or maybe a couple hundred maybe a thousand ping pong balls? Or do whatever your cousin's friend said worked in his boat, but he never actually sank it. He swears he knows it works though. Or do what the dude who sunk his boat did, but then he doesn't have the same boat as you?
Then there's always the experimental approach. Spray foam here and there wherever you could, maybe throw in a styrofoam block or two...hope it's enough, then sink your boat and see. :D
Could get expensive though depending on how often you sank to figure that perfect floatation. Maybe throw in one more milk jug and next time you'd float? So-called "complicated" physics and calculations put rovers on Mars...that without 100 previous trial and errors. Trust me, those physics a h*ll of a lot more complicated than us figuring floatation! But those same physics can help us simple-minded jet boaters too. Not the, "What the heck, this should about do it" mentality. Don't you want to learn more?
jer

[DansBlown73Nordic]

I think Someone had a brain storm...Fill the front of the boat with empty soda bottles. I would think this is a great idea. They won't hold moisture.
I have two huge boxes of air bags I picked up. I tried to sell them on here 6-8 months ago but there was no interest.....?????
They are 3x5 feet...Air Pillows....Made for frieght shipments.
I will give a couple to someone if you pay the shipping. Id really like to get rid of some of them.

[DansBlown73Nordic]

Here is a picture of them. I have two sizes. Most are the smaller size. One of my fears is the boat floats just below the surface and another boat hits it.... :sqeyes:
http://www.***boat.com/image_center/data/500/76A2.jpg

[spectras only]

Looking at the picture ,you can tell the engineers at Cruisers Inc did the math before tried to sink this model http://www3.telus.net/spectrasonly/positve%20flotation.jpg

[Sundance]

Looks like silicon is being used for flotation. :chi:
Sundance

[cruser]

Another way to calculatethe displacement required to prevent your boat from sinking is to estimate the volume of the hull that is below the water line. Shouldn't be too difficult. If you found this volume, and created a closed air space of the same or slightly larger volume, using what ever method you might available, your boat would not sink as long as you don't substantially increase the weight of the boat later and the air space remains intact.

[LVjetboy]

"Another way to calculate the displacement required to prevent your boat from sinking is to estimate the volume of the hull that is below the water line. Shouldn't be too difficult."
Ok, if not too difficult then go for it. Have you calculated that number for your hull? I'm curious.
Don't forget, if your hull sinks, the displacement of your hull and engine below water is different than the total water displacement of your hull above water during normal operation. And keeping your sinking boat nose up is less bouancy force than keeping your boat floating during normal operation.
Did you read this posted earlier in this thread...
"I'm confused, don't you just have to know the weight of the boat (or whatever you are trying to raise) and displace an equivalent amount of water?"
To which I posted: ...That would give you over twice the lifting force needed. Doesn't account for the weight of the water displaced by the boat and engine. Why? Because the boat weighs more on the truck scales than when it's under water. Volume displacement and all...
Just estimating the volume of hull below the water line as you suggested and calculating the equilalent weight offset by a floatation device gives nearly twice the floatation needed. Overkill not always bad, but in certain limited space and weight applications like my jet? Not always good. If your jet weighs the same as mine and you have room for two truck tubes over 5 ' in diameter in the bow then go for it what the heck. You'll float your bow higher than any and no sweat hooking a rope to it.
jer

[RAIDER]

Well, alot of what has been discussed here is good information and for the most part, right on the mark. I studied Hydrodynamics and bouyanacy in college and have a liitle more info that might help.
Determining the amount of flotation you need depends on the total mass you need to float. The NMMA and BIA have guidelines for this.
First:
Basically, calculate the weight of the items that have a specific gravity higher than water. This will be the crew, engine, drive, hardware, gear, electronics, carpet and fiberglass/resin. Then calculate the weight of the items that have a specific gravity less than water, being polystyrene foam, wood, and the upholstery stuff. Granted, based on the size and shape of a wood bench seat, it is likely to go down.
Second:
Calculate the Bouyancy factor for each item:
B=submerged weight /deadweight in air
Third
Bouyancy required:
Weight of item x B (bouyancy factor)
Fourth:
Add up all of the required bouyancy results for the items with a Specific gravity higher than water and then subtract the sum of the required bouyancy for the items with a specific gravity less than water.
The result is the Pounds required to float your boat, like the adds shown on the forum.
An example from an old text book of mine is attached.
I hope this helps.. I don't mean to lecture or anything...
I suggest using a closed cell pour foam that has been developed for flotation, not any of the stuff you get at the lumber yard. That stuff is not closed cell and you will use a butt-load of it to get any kind of volume. Closed cell foam has been tested by our company for other reasons and has been found to be around 97% closed cell, Meaning, water cannot get trapped in it like a sponge. We had a corrosion problem on our steel and discovered that the foam in the floor mats were open cell and they held water on the steel and produced stage 4 corrosion. not good. same with wood, keep the moisture off the wood and it will not rot. There are alot of pros and cons about the use of floatation, I suggest if you use it, be sure it is 100% captured and the wood is completey sealed; either with WEST epoxy or a resin/MEK mixture. NEVER put wood in a boat without sealing it. I have been around the Wood Boat guys too, and they seem to have figured out to keep their wood boats from rotting away.
If you use anything that could "float" away if your boat snaps, rips or otherwise tears itself apart, you just lost your flotation.....
I damn near lost my Sleekcraft when the cooling water inlet hose split and I began pumping several thousand GPM's into the boat, thanks to the jet pump.
If it had not been for the foam under the bow and the foam under the floor, she would be sitting at the bottom of Possum Kingdom Lake right now (about 80 feet deep where it happened).
A source for foam:
US Composites - they have it in different densities - 2 lb, 4 lb and 8 lb. They also have glass, epoxy, resin and tools. even KEVLAR. check 'em out.
www.shopmaninc.com
regards,
PDV

[old rigger]

Flotation is not done by any manufactures I know of. The main purpose For some kind of floatation device is put into the bow, is where the rubrail is mounted on the boat, all the air pocketed in the bow will escape thur the mounting holes for the rubrail. The inner tube traps the air so it can't leak out. Budlight
This thread is too long to read and LVjetboys replys are giving me a headache again. lol
Me&Mrs Budlight are mistaken, all boat manufactures have to install floatation that meet coast gaurd standards. It's been that way since the early 70's. This only covers boats under 21 feet long.
The reason that little 18 spectra posted earlier in this thread is still floating is because it's running a belly tank, and the sides of the hull, (and the bow)where the tanks would normaly go, are full of pre formed foam blocks.
At Tahiti and Hawaiian we used the same style pre formed flotation to fit in front of the bulkhead. At Rogers, we used the long plastic tubes filled with tiny styrofoam balls. Had a big hopper filed with those messy things and a little iron seamer that would seal off each tube. At Advantage we used the little pillow sized inflated balls. A Warlock we didn't have any boats small enough to have to install floatation and at Howard (this was in the late 80s) the new owners of the biz didn't bother to install it.
Coast Gaurd requires only the very tip of the bow to remain afloat for a pre determined amount of time. I don't remember the amount of time or how they came to figure it out. This was for all inboards, meaning jets, I/Os and v-drives. Outboards had to float level, like that spectra 18 was floating, which was a mother focker to do and still offer some room in the boat for storage. It was a crap shoot. Most builders just stuffed the nose full of what ever their choice of floatation was and were done with it. You took your chances, the coast gaurd would buy one of your boats, with out you knowing it was being bought by them, and they would test it. Waste of a perfectly good boat. They'd drill the deck full of holes, pull the engine, replaced with matching weight, and sink it. The Tahiti, and the Hawaiian passed when I worked there, the Rogers passed with it's sacks of micro balls. I don't remember which shop it was at, (well I do remember, but I'm not going to say, lol) but one of them failed the test, and it only failed because it got out of the shop with no floatation installed. What a bitch when that happens. You have to notify ALL buyers that bought that model and retro fit each boat with the correct floatation, or prove that the boat has it. If the boat's out of state, the builder pays the charges to have the boat shipped both ways. Big bucks. It can kill a small company.

[Wet Dream]

why is that when i sank my old boat at havasu 12 years ago the guy who was pulling my boat out was ordered to let the boat sink cop had to go to a call the boat helping out reved up and towed me out again and kept going.
Punctuation helps!! :rolleyes: There is a bigger picture to this guys. Look at it from all angles. The cops pretty much have to tell you to let it go. You are towing a boat that doen't have enough flotation to keep it up on its own. Does the tow boat you're in have enough to float BOTH boats? Doubtful. The towboat is now at risk of being taken under itself from the weight and drag of the sinking boat. Whether the call of the cops is right or wrong, gotta look at it from the safety aspect.

[dmontzsta]

This thread is too long to read lol
This is true.
I need to add flotation to my boat. Can someone tell me what I should use? in short. :D thanks.