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craigman

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fellas,
Just got me a little 12' SeaNymph that i'm going to do a conversion on.
I see a lot of these little boats don't have squat for flotation foam incase you take on water. So my question is, what are you guys using for flotation foam?
Thanks for any info and/or tips!
Craig
 
Just be careful not to have them anywhere gasoline can get on them or they dissolve into goo.

Those 12' sea nymphs have two large foam blocks that fill the cavities under the middle and rear bench seats ~ 5 cubic feet in all which would support ~300lbs dead weight if the boat ever swamped. Figure the boat itself weighs 145lbs so it can reasonably support the weight of a battery, trolling motor and fishing gear in the event of an accident, but not much more.

If you're adding foam figure each cubic foot (12"x 12"x 12") of foam will support ~60lbs depending on the density of the foam but it must be attached to the boat/ strapped down so it doesn't separate in the event of a swamping. So if you add decking figure out the weight of the material you're adding and add a volume of foam capable of floating more than the additional weight.

Last thing - if possible mount the foam as close to the gunwales as your design will allow - this should help make the boat less likely to capsize in the event you do take on water as the uplifting force of the flotation will be above the center of gravity drawing the boat down & help to keep it upright like a fishing bobber with a weight beneath it.
 
onthewater102 said:
Just be careful not to have them anywhere gasoline can get on them or they dissolve into goo.

Those 12' sea nymphs have two large foam blocks that fill the cavities under the middle and rear bench seats ~ 5 cubic feet in all which would support ~300lbs dead weight if the boat ever swamped. Figure the boat itself weighs 145lbs so it can reasonably support the weight of a battery, trolling motor and fishing gear in the event of an accident, but not much more.

If you're adding foam figure each cubic foot (12"x 12"x 12") of foam will support ~60lbs depending on the density of the foam but it must be attached to the boat/ strapped down so it doesn't separate in the event of a swamping. So if you add decking figure out the weight of the material you're adding and add a volume of foam capable of floating more than the additional weight.

Last thing - if possible mount the foam as close to the gunwales as your design will allow - this should help make the boat less likely to capsize in the event you do take on water as the uplifting force of the flotation will be above the center of gravity drawing the boat down & help to keep it upright like a fishing bobber with a weight beneath it.


So is the foam only designed to float an empty boat or the boat at full capacity?

If I remove a bench (filled with foam) does that lower my total weight capacity?

Thanks
 
Doesn't take much foam for a person. Look at a life jacket, there isn't much foam in them, yet they support you in the water. Why? Man is mostly water, water in water floats, The foam supports the 11% that isn't water.

The goal of boat flotation is to support all gear in the boat, plus all occupants. You may have to cling to that boat for hours until help arrives. There should be a capacity plate on your boat, it will tell you how much weight it can support when fully submerged. If you are altering your boat, you must also alter your flotation accordingly. Things like poles, tackle boxes, boat motors, batteries are pretty much dead weight, pound for pound. You need flotation to support the dead weight pound per pound. Add in flotation for people and you should be good to go. If you are adding building materials, like a new deck. You better account for it in flotation capacity.

To be honest, one of the most dangerous boat modifications is adding a deck/flooring to a boat without a deck/floor. You must add flotation that equals/exceeds the added weight of the materials you installed. If you are replacing the deck/flooring you are swapping materials and not changing the weight of the boat. Extra flotation may not be needed. Adding stuff to exceed the capacity plate, make accommodation in flotation.
 
Thanks for the reply
If I remove no flotation, add a deck and take the weight of the deck off of my total capacity I should be good correct? My boat has 1300 lb capacity so i simply subtract the weight if the deck material from 1300lbs just like I would the motor, gas, passengers etc?
 
Givey1982 said:
So is the foam only designed to float an empty boat or the boat at full capacity?

The foam determines the capacity of the boat. The max capacity is supposed to be based on a submersion test according to the USCG boatbuilder's guide, but the red line guidance is only the max capacity a manufacturer can list - they can arbitrarily list a lower value too and you have no way of knowing.

Givey1982 said:
If I remove a bench (filled with foam) does that lower my total weight capacity?

Absolutely.

Givey1982 said:
Thanks for the reply
If I remove no flotation, add a deck and take the weight of the deck off of my total capacity I should be good correct? My boat has 1300 lb capacity so i simply subtract the weight if the deck material from 1300lbs just like I would the motor, gas, passengers etc?

You could do that - but I would suggest you include in your build additional foam that is more than sufficient to support the weight you've added so you don't have to worry about the integrity of the old foam (mice love to chew this stuff) or the honesty of the manufacturer etc.



Plenty of people will remove the foam from their boat all together, but they're gambling that nothing ever goes wrong which is a really naive/brainless approach to reality.

I struck a mostly submerged log floating in the middle of the lake on a windy day last time I was out that impacted my through-hull side imaging fishfinder sensor and **** near tore it off the bottom of the boat - and I was slowing down to enter a no-wake zone so I was doing no more than 12mph... It could just as easily have had a sharp branch protruding that could have punctured the bottom of my boat. You never know what is going to happen out there.
 
No.
In theory you could subtract the added weight from the capacity plate. However that is dangerous. Are you going to change the capacity plate? If not, when you sell the boat, the capacity plate will be incorrect and may cost the new owner his life.

There are lots of ways to add flotation. One of the simplest is expanding foam to fill voids within the flotation boxes. Another easy way is to fill any empty unused space with foam. Like the bow of the boat. Be sure to read up on the types of closed cell foam and its weight carrying capacity. Adding a 48 quart Coleman cooler as a live-well does two things, gives you a live-well and adds flotation value to the boat. Provided the cooler is secured so it can't separate from the boat in an accident. See my 16' Sylvan build thread for other ways to add flotation. Link in my signature.

A 4x8 sheet of plywood weighs roughly 25 pounds per 1/4" in thickness. If you are adding 1 sheet of 1/2" x 4' x 8' plywood, you added 50 pounds of weight, plus hardware (screws) and any new support structure (2x4, or aluminum angle). How much foam does that require?

I believe there is a sticky that will aid in foam calculations.
Here is a website that does a good job of breaking it down.
https://newboatbuilders.com/pages/flotdiag.html

Note the value for plywood. -0.81 This means plywood has a float value. In general wood floats, to a point. The seas, oceans and lakes are filled with old wooden boats that sank. How many trees do you fish under water? How many screw did you use to hold the plywood in place. What did you use to support the plywood so it supports your weight? All those add weight, and must be part of the calculation. Fortunately these are easy to figure out. Put them on a scale. Screws/nail/liquids are sold by the pound. 1pd box, 5 pd box, 1 gallon = weight, etc.

The other aspect of adding weight is how it will change the boat handling characteristics. If you are adding 180 pounds (deck and 1 trolling motor battery) to the bow, will your motor/prop configuration get you on plane? When anchored up, is the boat nose heavy and easier to swamp by waves? Foam won't correct either of those factors. The foam only comes into play when the boat becomes swamped. If the bow plows through the waves you are more likely to get swamped. If the boat sits nose heavy you are more likely to get swamped. See my 16' Sylvan build thread for weight distribution. I had to move my bow mounted trolling motor battery to the stern. Its a group 31 and about 80 pounds. Enough to make my bow low in the water on plane and sit bow heavy while anchored up. Moving it to the back brought everything back into perspective.

Adding a front deck is great, however there are real things that must be considered. Your life my depend on it. Be safe. Fortunately, it should be easy to account for added flotation needs, and weight distribution. It just takes work to figure it out.
 
perchjerker said:
Hanr

I agree with everything you are saying.

I see in your sig you have (or had) a pretty heavily modified 14ft Alumacraft

how did that boat work out for you?

thanks

That boat worked out great. I added a bunch of flotation plus a 48 quart Coleman cooler. That cooler alone added a bunch of flotation. I edited my original post during your post. Please see my 16' Sylvan build thread as well. I added more flotation to it as well. Plus I had to redistribute weight to maintain boat balance while under power and floating at sea.
 
Hanr3 said:
No.
In theory you could subtract the added weight from the capacity plate. However that is dangerous. Are you going to change the capacity plate? If not, when you sell the boat, the capacity plate will be incorrect and may cost the new owner his life.

There are lots of ways to add flotation. One of the simplest is expanding foam to fill voids within the flotation boxes. Another easy way is to fill any empty unused space with foam. Like the bow of the boat. Be sure to read up on the types of closed cell foam and its weight carrying capacity. Adding a 48 quart Coleman cooler as a live-well does two things, gives you a live-well and adds flotation value to the boat. Provided the cooler is secured so it can't separate from the boat in an accident. See my 16' Sylvan build thread for other ways to add flotation. Link in my signature.

A 4x8 sheet of plywood weighs roughly 25 pounds per 1/4" in thickness. If you are adding 1 sheet of 1/2" x 4' x 8' plywood, you added 50 pounds of weight, plus hardware (screws) and any new support structure (2x4, or aluminum angle). How much foam does that require?

I believe there is a sticky that will aid in foam calculations.
Here is a website that does a good job of breaking it down.
https://newboatbuilders.com/pages/flotdiag.html

Note the value for plywood. -0.81 This means plywood has a float value. In general wood floats, to a point. The seas, oceans and lakes are filled with old wooden boats that sank. How many trees do you fish under water? How many screw did you use to hold the plywood in place. What did you use to support the plywood so it supports your weight? All those add weight, and must be part of the calculation. Fortunately these are easy to figure out. Put them on a scale. Screws/nail/liquids are sold by the pound. 1pd box, 5 pd box, 1 gallon = weight, etc.

The other aspect of adding weight is how it will change the boat handling characteristics. If you are adding 180 pounds (deck and 1 trolling motor battery) to the bow, will your motor/prop configuration get you on plane? When anchored up, is the boat nose heavy and easier to swamp by waves? Foam won't correct either of those factors. The foam only comes into play when the boat becomes swamped. If the bow plows through the waves you are more likely to get swamped. If the boat sits nose heavy you are more likely to get swamped. See my 16' Sylvan build thread for weight distribution. I had to move my bow mounted trolling motor battery to the stern. Its a group 31 and about 80 pounds. Enough to make my bow low in the water on plane and sit bow heavy while anchored up. Moving it to the back brought everything back into perspective.

Adding a front deck is great, however there are real things that must be considered. Your life my depend on it. Be safe. Fortunately, it should be easy to account for added flotation needs, and weight distribution. It just takes work to figure it out.


Good sound advice. I am not adding much weight to the boat so it won't be that hard to add the little flotation needed.
Thanks
 
Wow, some good info fellas!
I do plan on adding a casting deck and using it for storage. Finding places to add foam will get tricky! LOL!!! Not much room on a little 12' boat!
I do like to error on the safe side of things. My local lake (Shasta Lake) can get pretty deep and have some ruff water at times. I would hate for it to ever sink! :shock:
Again, thanks for all the info!

Craig
 
There is always the DOW product "GREAT STUFF BIG GAP FILLING SPRAY FOAM" that you can buy at most hardware stores...if you're trying to fill little cavities beneath a deck but around your storage bins you can drill a small hole through the deck before you carpet or surface it & insert the spray hose & fill the pocket with polyurethane based foam which is a closed-cell foam.
 
I've thought about the Great Stuff and how it would work.
I've also thought about welding up some "boxes" on the back of the transom. I've seen it done on duck boats or river boat for super shallow waters. Thought about making those and filling them with foam. Could probably get 1 cubic foot out of each. (one on each side).
Hmm, decisions, decisions..
 
Even closed cell foam will eventually soak up water. If you can, leave a gap to the bottom so it has a chance to dry out.
 
yeah - biggest mistake in my 14' build was not allowing enough room for water to drain out under the foam - PITA to go back & fix later.
 

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