what is best way of adding floatation to a flatboat

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

i promise I don't exaggerate.... I can PROBABLY lift it with one finger on land.... I'm CERTAIN I can do that under water..... a buddy swamped his boat and I fished the battery out... keeping my nose above water I could only just barely reach it with one finger and was very surprised how much lighter it was under water... I'm not saying it was light but it was much lighter under water.

agree on the welding... might be asking for trouble in the form of cracks


Another benefit of the pour in foam is that it can be structural and allow you to use lighter weight floors and less bracing.

For traction I would etch prime and then paint with sand or rubber powder mixed in.

 

[mrdancer]

Re: what is best way of adding floatation to a flatboat

You need to do the two-part pourable closed-cell foam. The stuff is expensive, but only because it works. To reduce expense, fill the bilge with soda bottles (glue the caps on so they don't come loose over the decades). After you've filled the bilge with soda bottles, then add the foam to fill in all of the voids and hold the bottles in place.

This significantly reduces the amount of expensive foam you need, reduces waterlogging issues, holds bottles in place in case of significant hull breach, reduces issues with solvents (gasoline might eat the foam), and there is little penalty in weight.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

the plan is to put this on all flat surfaces when its finished: Restore 4-gal. Cape Cod Gray Deck and Concrete Resurfacer-46513 at The Home Depot

Have you considered riveting the aluminum deck down rather then welding it? I read your description of the pending deck work, and your planning to weld the new deck to the ribs & hull sides, correct?

Unless the welder is extremely familiar w/ welding the particular aluminum your boat's made of, welding can work harden the hull.

What's the plan to keep the new aluminum deck from being slippery..........

he is a professional welder by trade and builds boats for a living so im sure he knows what he is doing.

 

[jbcurt00]

Re: what is best way of adding floatation to a flatboat

Is Restore rated for application on metal? You're still planning to use aluminum plate for the deck, correct?

 

[metriccrescentwrench]

Re: what is best way of adding floatation to a flatboat

A couple things.

Have you considered using some screw-down access hatches. That would allow you to pour the foam and allow for expansion through the access holes if you pour a little too much. After the foam has cured you'd trim any excess, apply some sealant around the access holes and screw the covers in place.

As far as the amount of flotation required, as smoke alluded to it's going to be significantly less than the dry weight of the boat. It's a bit complicated to calculate, but is based on the specific gravity of each material used in the boat. Aluminum has a lower specific gravity than steel, therefore a pound of aluminum is going to weigh less than a pound of steel when it's under water. A pound of wood has an even lower specific gravity, and will be calculated as a negative weight when figuring flotation requirements. If anyone cares to get into all the nitty gritty details it's somewhere on the USCG website (sorry, I don't remember the link).

And finally, when doing flotation you also need to think about the fore-aft distribution of weight as the USCG requirement is that the boat float level when swamped. For example, a thousand pounds worth of floatation isn't going to do you any good if it's all in the bow.

 

[UncleWillie]

Re: what is best way of adding floatation to a flatboat

Let's do the math....

I just measured my battery in the garage. It is 10x8x7 inches and 45 lbs.
That means it will displace 560 cubic inches of water or ~20 lbs of water.

My Battery will weigh 45-20 = 25 lbs underwater. ~45% lighter.

It is all about displacement.

Concrete weights ~150 lbs per cubic ft. Water is ~60 lbs per cubic foot.
Concrete only weighs 90 lbs per cubic foot underwater.
More than one person has found out the hard way that their 4 ton mooring block only weighed 60% of what they thought it should after they sank it.

Aluminum is 167 lbs per Cubic foot or 107 lbs underwater. 64% of its dry weight.

A wooden canoe doesn't need any flotation foam!
Remember that even a 50,000 lb log floats!

 

[Home Cookin']

Re: what is best way of adding floatation to a flatboat

first I think you are overthinking the math for the floatation. Just stuff as much as you can wherever you can. Once a boat swamps, it rolls, and the motor sinks the stern, and a little bow is sticking up to hang on to. Floatation also helps displace water to the scuppers to drain, and helps keep a moored unoccupied boat filled with rain or leak water from sinking or sometimes flipping. But adding floatation is not welding on two 18' pontoons.

second if you pour/spray in foam you seal everthing in, such as hoses, wiring and gas tanks. For the first two, run them through chases (think wire in conduit) so they can be pulled and replaced. Go ahead and put strings through them now, too.

A great alternative to pool noodles are boogie boards--they come in flat panels! For sale cheap after the summer, cheap at yardsales, often in the trash.

 

[metriccrescentwrench]

Re: what is best way of adding floatation to a flatboat

Once a boat swamps, it rolls, and the motor sinks the stern, and a little bow is sticking up to hang on to.

Not if it complies with USCG requirements. That's why foam location is just as big a deal as the amount of foam. More at the rear to account for the weight of the engine, and some up high under the gunwales etc. to keep it from rolling.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

Let's do the math....

I just measured my battery in the garage. It is 10x8x7 inches and 45 lbs.
That means it will displace 560 cubic inches of water or ~20 lbs of water.

My Battery will weigh 45-20 = 25 lbs underwater. ~45% lighter.

It is all about displacement.

Concrete weights ~150 lbs per cubic ft. Water is ~60 lbs per cubic foot.
Concrete only weighs 90 lbs per cubic foot underwater.
More than one person has found out the hard way that their 4 ton mooring block only weighed 60% of what they thought it should after they sank it.

Aluminum is 167 lbs per Cubic foot or 107 lbs underwater. 64% of its dry weight.

A wooden canoe doesn't need any flotation foam!
Remember that even a 50,000 lb log floats!

I like to keep things in more simplistic terms to use for rule of thumb so based on your numbers above I can see that if you rounded things off to say they will lose 25-30% of their weight when under water (even though its more like 35-40%) then that is a safe estimate "rule of thumb" to always be sure you have around 10% more then the minimum needed floatation for the weight load.

 

[Home Cookin']

Re: what is best way of adding floatation to a flatboat

Not if it complies with USCG requirements. That's why foam location is just as big a deal as the amount of foam. More at the rear to account for the weight of the engine, and some up high under the gunwales etc. to keep it from rolling.

not in the real world. I have been in and around plenty of swamped boats made by good manufacturers. Whalers and sealed hulls do better, but when a boat with a bilge or a jon boat fills up, it's like sitting on a unicycle.

Floatation is a good thing but it is only marginal for safety. Too many people incorrectly think that a boat will floatation will keep them safe and dry. Tain't so.

 

[jigngrub]

Re: what is best way of adding floatation to a flatboat

, but when a boat with a bilge or a jon boat fills up, it's like sitting on a unicycle.

Floatation is a good thing but it is only marginal for safety. Too many people incorrectly think that a boat will floatation will keep them safe and dry. Tain't so.

I really like the way these 2 guys ride their unicycle!
Lund Boat Floatation Video - YouTube
Too bad they don't know they're in horrible, horrible danger eh?!

... I wonder when they're going to get unsafe and wet???

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

MOST boats are very unstable when swamped......there are exceptions.... I saw a video of one that was dropped from a crane on pavement and then they cut toe forward 5 or 10 feet off of the boat and then launched and ran it like 50 mph but it was definitely an exception

I'd bet dollars to doughnuts that the op's boat,even with foam filled floors and gunwales, when swamped would be at best VERY easily tipped. These super flotation boats aren't really relevant to the project at hand as they give up LOTS of space for the foam that his small boat can't spare.

 

[64osby]

Re: what is best way of adding floatation to a flatboat

Has a make / model ever been mentioned. How about a pic.

It might make the discussion much easier.

 

[smokeonthewater]

Re: what is best way of adding floatation to a flatboat

he says his current boat is an alweld 1548vv and his new one is the same model except 2' longer and 4" wider 1752vv?

Alweld Aluminum Boats - Jon Boats, Bass Boats, Bay Boats, Custom Boats

 

[UncleWillie]

Re: What is best way of adding flotation to a flatboat

Re: What is best way of adding flotation to a flatboat

The perception is a boat with flotation foam is going to float well out of the water. Not so!
Is is going to be floating just short of sinking. Swamped is a better description that floating.
It just isn't going to sink, as in, going to the bottom.

The OP's Boat already has flotation in the Bow and under the seat. It won't sink. Swamp? Yes!
If he adds a floor with flotation foam under it, the foam down low is going to want to surface and the odds of it flipping may be increased.

 

[limitout]

Re: what is best way of adding floatation to a flatboat

MOST boats are very unstable when swamped......there are exceptions.... I saw a video of one that was dropped from a crane on pavement and then they cut toe forward 5 or 10 feet off of the boat and then launched and ran it like 50 mph but it was definitely an exception

I'd bet dollars to doughnuts that the op's boat,even with foam filled floors and gunwales, when swamped would be at best VERY easily tipped. These super flotation boats aren't really relevant to the project at hand as they give up LOTS of space for the foam that his small boat can't spare.

yep, that's about the way I see it too I would think my boat would sit with about 6" of water in it and roll if you stood on the side.

and yes that's the boat - Alweld 1752vv

almost all the floatation is going to be in the floor only since the seat and bow floatation was removed to use for storage. I cant put much side floatation so for all intent it is going to be like a surfboard under water.

I am not sure how "stable" it would float until I try it out but I would think only people and wave action can influence its stability since there is nothing else to make it top heavy. not sure what that actually means until I test it but at this point I care more about "something" floating to hang onto then I am if I can sit comfortably inside the boat and wait for help.

The perception is a boat with flotation foam is going to float well out of the water. Not so!
Is is going to be floating just short of sinking. Swamped is a better description that floating.
It just isn't going to sink, as in, going to the bottom.

The OP's Boat already has flotation in the Bow and under the seat. It won't sink. Swamp? Yes!
If he adds a floor with flotation foam under it, the foam down low is going to want to surface and the odds of it flipping may be increased.

valid points but since I have removed the small amount of floatation the boat did have under the bow and seat to use them for storage, I want to be sure I replace that floatation value plus as much extra as I can fit. I feel there is no such thing as too much floatation and I want to have more then I need then need more then I have.

my personal thoughts on stable floatation of swamped boats is I think the weight staying above water and the hull width is where your level floating stability comes from. when swamped, a narrow boat will obviously roll over a lot easier then a wide boat

 

[metriccrescentwrench]

Re: what is best way of adding floatation to a flatboat

my personal thoughts on stable floatation of swamped boats is I think the weight staying above water and the hull width is where your level floating stability comes from. when swamped, a narrow boat will obviously roll over a lot easier then a wide boat

I actually just did some reading on this, including the Coast Guard regs .... a lot of flotation down low will contribute to the boat rolling when it's swamped. Some boat manufacturers don't put foam in the keel area so that if the boat swamps the lowest areas will fill with water and act as ballast to (hopefully) help keep it upright.

 

[Home Cookin']

Re: what is best way of adding floatation to a flatboat

well if you test it put a weight back there not the real motor.

 

[Lone Duck]

Re: what is best way of adding floatation to a flatboat

A couple things.

Have you considered using some screw-down access hatches. That would allow you to pour the foam and allow for expansion through the access holes if you pour a little too much. After the foam has cured you'd trim any excess, apply some sealant around the access holes and screw the covers in place.

As far as the amount of flotation required, as smoke alluded to it's going to be significantly less than the dry weight of the boat. It's a bit complicated to calculate, but is based on the specific gravity of each material used in the boat. Aluminum has a lower specific gravity than steel, therefore a pound of aluminum is going to weigh less than a pound of steel when it's under water. A pound of wood has an even lower specific gravity, and will be calculated as a negative weight when figuring flotation requirements. If anyone cares to get into all the nitty gritty details it's somewhere on the USCG website (sorry, I don't remember the link).

And finally, when doing flotation you also need to think about the fore-aft distribution of weight as the USCG requirement is that the boat float level when swamped. For example, a thousand pounds worth of floatation isn't going to do you any good if it's all in the bow.

I have often wondered why the flotation is put in the bottom of the boat. That will help it float but upside down. Why do they not put the foam under the gunnels? Boat will float right side up and foam will not get water logged before the emergency happens. Is it because there is not enough roam? If so, make the gunnels wider.

 

[Home Cookin']

Re: what is best way of adding floatation to a flatboat

I have often wondered why the flotation is put in the bottom of the boat. That will help it float but upside down. Why do they not put the foam under the gunnels? Boat will float right side up and foam will not get water logged before the emergency happens. Is it because there is not enough roam? If so, make the gunnels wider.

the point of flotation is not to keep you high and dry. it is to give you something to hang on to untill help comes, and something the rescuers can see and know where to start looking for bodies.

Some swamped boats can be bailed out (if everyone goes overboard first). Some stay upright for a while or in the right conditions and that is an added benefit, but not the primary purpose. Also if water can't fill the bilge, it can be more accessible for bailing or pumping, or draining out scuppers or a plug hole.

Flotation is a crucial safety feature but it isn't a magic carpet.