Boat flotation question

[Ed L.]

I finally determined that the foam under the floor was pretty saturated so it was time to pull it. My question is, based on Jon boats having flotation foam in side stern pods and under the bow deck and my boat has flotation foam in those locations as well (which has remained dry), is there another reason for all the foam they put in v bottom boats? Im thinking I will not replace unless there is a good reason. Your insights are appreciated.

 

[Huntindave McCann]

I finally determined that the foam under the floor was pretty saturated so it was time to pull it. My question is, based on Jon boats having flotation foam in side stern pods and under the bow deck and my boat has flotation foam in those locations as well (which has remained dry), is there another reason for all the foam they put in v bottom boats? Im thinking I will not replace unless there is a good reason. Your insights are appreciated.

The volume of foam placed by the manufacture, is based on CG requirements. Eliminating some or all of the foam is entirely up to you. The foam is there in the case of your boat swapping. The boat hull will still support you, preventing both the hull and you (providing you are holding on) from sinking to the bottom.
The volume used, has been calculated for this load. Is keeping you and your hull, from sinking to the bottom, a good reason to retain/replace the entire volume? Only you or maybe your loved one's can answer that.

If you are asking if it matters to us? I'll refrain from directly addressing that.

 

[William Reinicke]

Honestly, when I had a ribbed boat like that, I put a floor in and stacked that pink foam up to the top of the ribs. When I laid the aluminum floor, it gave it a nice support to prevent it from bowing or bending. I used aluminum sheets to keep weight down. It wasnt very thick stuff, so I had to find a way to support it, and stacked pink foam to a 1/4" taller than the ribs compressed down nicely once i riveted that aluminum sheet in.

If you decide not to replace, whats your plan for a floor in this boat?

 

[Steve Sanford]

The volume of foam placed by the manufacture, is based on CG requirements. Eliminating some or all of the foam is entirely up to you. The foam is there in the case of your boat swapping. The boat hull will still support you, preventing both the hull and you (providing you are holding on) from sinking to the bottom.
The volume used, has been calculated for this load. Is keeping you and your hull, from sinking to the bottom, a good reason to retain/replace the entire volume? Only you or maybe your loved one's can answer that.

If you are asking if it matters to us? I'll refrain from directly addressing that.

Dave~

Years ago there was a link here to the Coast Guard flotation regulations. In addition to keeping a designed weight (boat + motor+ people + gear) afloat, I believe it also required that the vessel float level when swamped. I am thinking that explains the lateral flotation "chambers" in some designs. Obviously, decked vessels have more options to place the flotation higher up.

The most important thing (to me) that I have learned in recent years: There's only one A in FLOTATION.....

All the best,

SJS

 

[Eric Patterson]

On top of the advice of Dave and Steve I'll add in spite of flotation in the bottom allowed by USCG, the last time I looked, personally, I think it's a really bad a idea unless your boat never sees rough seas. When the center of buoyancy is lower than the center of gravity the hull can flip in rough water or if the load is highly imbalanced. Also a bunch of water on the bottom will slosh around, by waves, and can quickly lead to an imbalanced situation. Instead of standing in a swamped boat you could be clinging to the hull. Swamped boat, rough waves, physics wins, you lose. Three point flotation or flotation around the perimeter is best.

Then there's the whole issue of waterlogged foam adding weight and no flotation.

 

[Ed L.]

On top of the advice of Dave and Steve I'll add in spite of flotation in the bottom allowed by USCG, the last time I looked, personally, I think it's a really bad a idea unless your boat never sees rough seas. When the center of buoyancy is lower than the center of gravity the hull can flip in rough water or if the load is highly imbalanced. Also a bunch of water on the bottom will slosh around, by waves, and can quickly lead to an imbalanced situation. Instead of standing in a swamped boat you could be clinging to the hull. Swamped boat, rough waves, physics wins, you lose. Three point flotation or flotation around the perimeter is best.

Then there's the whole issue of waterlogged foam adding weight and no flotation.

All points well taken. I grew up basically in a boat this size. 16', 72" beam but with 3 seats with foam in them. It was maybe 3" shallower and had a 25hp 2 stroke. There were days we should have stayed home. Wind and 3 foot rollers, ice forming on the gunnels and loosing free board quickly. That said my dad was a good pilot and only a couple of times I became a little frightened crossing the channel in the dark on the Mississippi River. Today is a different time and remembering very few times those hunts yielding many more ducks and geese than many blue bird days. I dont put myself out there today. My hunts are slough and potholes. Not the half hour to hour boat rides on 18 degree days. Today I can put the boat in and be in my deer stand in less than 10 minutes. Where I live the river runs east to west and if the winds are much over 15 miles an hour out of the west, as a solo hunter I watch the river from my sliding glass door remembering the kerosene heater the dog and I huddled around as a kid. Im not to worried about the lack of factory flotation. I did some quick measurements of the flotation that is currently in the boat. Im not far off of the cubic inches and as Eric mentioned the location of the foam is above the center of gravity. Still the lack of flotation reinforces the fact that I don't leave the dock without wearing my lifejacket. Not because I can't swim but because I want to be found. If there is a structural component to replacing the foam that must be taken into account though.
Like Steve said, there's only one A in flotation. Seems fitting that today there is only one A in the boat...

 

[Ed L.]

Honestly, when I had a ribbed boat like that, I put a floor in and stacked that pink foam up to the top of the ribs. When I laid the aluminum floor, it gave it a nice support to prevent it from bowing or bending. I used aluminum sheets to keep weight down. It wasnt very thick stuff, so I had to find a way to support it, and stacked pink foam to a 1/4" taller than the ribs compressed down nicely once i riveted that aluminum sheet in.

If you decide not to replace, whats your plan for a floor in this boat?

I did that as well. It was 1446 flat bottom. Today the cost of aluminum is cost prohibited. Im using plywood covered with vinyl.

 

[Scott Gilliland]

When I rebuilt my Arthur Armstrong Broadbill I changed the flotation. In the homebuilt version of this boat it had foam in a closed in compartment in the bow and in 2 compartments midships under the decking on either side of the boat. I kept the forward compartment as is and removed the 2 side compartments I wanted them for decoy storage. I did not want to use 2-part pour in foam - I've had 2 boats that this foam had become completely saturated with water adding a couple hundred pounds to the boat. I used extruded foam for the new flotation. The problem with this foam is that is gas soluble and needs to be protected if there is a possibility of contact with gas. I used 1.5" and 2" foam that I mounted under all the decking (front. sides and stern). I did not incase this foam in anything -- maybe I should have. It did not add enough flotation and I had to add to large pieces of foam that I mounted along either side of the stern of the boat between the floor and the deck. To protect the foam I vacuum sealed it then wrapped it in Tesa tape.

To determine the amount of flotation required I used an excel calculated I found on the Hull Truth site (https://www.thehulltruth.com/boating-forum/14226-calculating-floatation.html). The link to the calculator seems to be broken, I have a copy if anyone is interested. It requires you measure the volume of each material used in the hull to calculate the amount of floatation required (I added a bit more for safety).