Considering adding flotation foam before floors are finished- Double Eagle

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North
Posts: 283
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Considering adding flotation foam before floors are finished- Double Eagle

Postby North » Sun Aug 26, 2018 4:59 am

Hi Folks,
Still using and enjoying my partially finished aluminum 25' Double Eagle!
I am in my 3rd summer of using "temporary" OSB/Cheap chip board floor panels and of course they are getting waterlogged.. This Winter I will use them as templates and will cut out and weld in aluminum floor panels along the port and starboard side and have removable aluminum panels along the middle (for access to steering, hoses, shaft, batteries, etc).

It is NOT required in Canada to have positive flotation in a boat over about 20 feet, but I am considering it for piece of mind... and because it would be a lot easier before welding in the floors.

Realistically, chance of holing the aluminum hull (3/16" sheet), especially with a full keel below, is quite slim..... and I only have 1 thru-hull for the engine's seawater pump - but it has a short standing pipe before the strainer which must put it just above the waterline - I can take the strainer off with the valve open and no water comes in.... but, when the engine pump pulls water it is fine for cooling the engine- lots of flow...

So, I am looking for input - to add flotation or not.... and if so, I am considering pour foam kits (but would need quite a bit as, metal doesn't apparently float as well as wood..) so, also considering placing large soda pop bottles or similar throughout both sides and then pouring foam to solidify everything..

Input please!
Darrell

fyi - here's a fairly recent video - some improvements like more finished gunwhales...

https://www.youtube.com/watch?v=raEzHJ8Y9RA

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kens
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Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Considering adding flotation foam before floors are finished- Double Eagle

Postby kens » Sun Aug 26, 2018 7:01 am

There are many pro's and con's on the subject of floatation foam. I'll merely list my thoughts on the pros & cons.
foam adds weight to the boat
foam is in bottom of bilge and as such always gets dirty, nasty, and waterlogged
foam named as 'does not absorb moisture' is not true
all foam takes on water, it only takes time, time as in years, but it happens nontheless

my personal choice for foam would be foam blocks shaped to fit the bilge, then secured in place by the floorboards. this way the foam blocks could be removed for inspection an cleaning

I have entertained the idea of foam filling the gunnels all the way around, this would be high placement for the foam, but keeps it out of dirty bilge water. same for foam filling between some of the frames above the floor, keeps it dry, and it does not take away storage under floor.

on a metal build, and you say 'weld in floorboards', then consider air chambers. air chambers are lighter than foam, and can be inspected thru a installed inspection plate. inspection plate could be cut in at any later date, if you so desire to look in there.

remember that a empty fuel tank is a air chamber. empty fuel tank is good floatation. it is possible to have a 60 or 70 tank gallon under floor tank, and you never use it, it is always empty air chamber, an you install a smaller say, 25 gal tank that you run on in daily usage. you might be hard pressed to run out 25 gal in a single day with that little Cummins.

I have a 18gallon above floor tank that I recovered from a old donor boat. At first I thought it somewhat of a joke on a 25' blue water fishing rig. But I found out that my favorite fishing spot, 30miles out, only took 16gal, and a 60mile run in a open boat is a long day!!! when will you ever need a 70gallon tank in a day boat?? at a cost of $400 to fill it up, then just merely hauling around 500lbs of fuel, the big tank would make better floatation than useful fuel.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

bobinpowayca
Posts: 422
Joined: Thu Jun 16, 2011 1:40 pm
Location: Poway, CA

Re: Considering adding flotation foam before floors are finished- Double Eagle

Postby bobinpowayca » Sun Aug 26, 2018 3:05 pm

Howdy North,
I just finished my 16' Geronimo and here are reasons why I used pour-in-place foam extensively in my build.
This is a runabout I use for cruising, taking the grandkids tubing sometimes, in the bay mostly. In my boat, I filled the void between the deck (floor) and the hull everywhere except I left a bilge with removable floor about 2' wide from the floor aft.
1. Since I take out kids, and me and my wife essentially can't swim anymore I considered what would happen if you hit a piece of flotsam or a rock. My hull is only 3/8 plywood covered with fiberglass and paint. So suddenly you've got a hole in your hull the size of a dinner plate and the ocean is rushing in. Bilge pump gonna save you?
2. If I do hit a rock or get a big ding somehow, it can be fixed - maybe a little more work cleaning out some foam to make the repair, but definitely repairable - similar to fixing a ding in a surfboard. Also the boat won't be on the bottom of the briny.
3. The weight of the foam is insignificant. The foam I used weighs 2 lbs per cubic foot, almost as light as air. Water (fresh) weighs over 62 lbs. per cubic foot. I forget the amount I put in my boat - but say I put in 15 cubic feet of foam: The foam weighs a total of 30 pounds. The water it's displacing weighs 1872 pounds. That provides 1842 pounds of positive flotation. Maybe I put in somewhere between 10 and 15 cubic feet; at only 10 cubic feet it weighs more than my motor, batteries, and anything else non-buoyant in my boat.
Here are some added benefits I noted with the pour-in-place foam:
1. When I walk around in my boat the floor does not flex - it's solid.
2. When I'm running the boat at speed in choppy waters, I can't believe how violently it slams on the waves, sounds like it's gonna break up and at these times I'm glad I've got the foam in the hull adding rigidity to the hull. I'ts a great design but the frames are far apart.
By the way I did the standard method, I walled off chambers between the frames and did an "in hole " and an "out hole", be sure to keep your eye on the foam's progress, if you cap it off before it's done expanding, or it expands too fast, it'll bust the deck. They use this stuff to pump under roads to lift the slabs. Bob
Attachments
IMG_1213.JPG
IMG_1255.JPG
all but open bilge is foamed under
IMG_0253.JPG
recoilless rifle hole, Navy PBR 1968
Bob
_______________
Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

bobinpowayca
Posts: 422
Joined: Thu Jun 16, 2011 1:40 pm
Location: Poway, CA

Re: Considering adding flotation foam before floors are finished- Double Eagle

Postby bobinpowayca » Sun Aug 26, 2018 5:36 pm

Sorry what a stupid math error. Way off on the net flotation!! So if I have 10 cubic feet of foam at 2lbs per cubic foot I've added 20lbs of weight to my boat. And since water weighs 62 lbs per cubic foot, that foam displaces 620 lbs of water. Thus my foam has given me 600lbs net positive flotation.
Also - realistically - I'm not likely to knock a dinner plate sized hole in my boat but I don't want to sink.
I got the floorboards pretty tight to the hull sides and sealed all the joints with quick faire, so to clean out the salt I can just tilt the nose of the boat up and hose it out, all goes to the bilge and pumped up to the motor box.

By the way, a little girl from Ontario and her family were here in San Diego and went tubing on one of our reservoirs. She was sitting on the nose of the boat when the tube capsized - boat operator immediately put it in neutral, boat abruptly slowed, she fell off and wasn't found for 4 days - 185' of water. She was wearing a life jacket which was found right away. Putting it in neutral slowed it enough to make her fall off but the boat kept going and ran over her. Just thought I'd mention this, same as as my granddaughter who I took tubing 1st time that same day. Keep the lifejackets on properly. I don't let them ride on the bow, hang half way out of the hatch, etc.
Bob
_______________
Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

North
Posts: 283
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Considering adding flotation foam before floors are finished- Double Eagle

Postby North » Mon Aug 27, 2018 4:48 am

Hi Ken and Bob,

Ken - I know it does add some weight, but still question if it may be worth it.

- I can not easily add (sealed) air chambers as the design / my build method has no "wall" or side material running for and aft along each 3rd of the boat, which would be needed to hold air. So, I would have to weld in more material/ weight in order to seal any cavities off - and this is not easy now with the engine in place due to lack of room to work/ weld and I don't really want to weld any more to the bottom/ hull as this would ruin/ blister/ burn the epoxy paint underneath.
- I have a 32 gallon tank and it is all I need - juts fill up more often- I would not want to drag around the weight of 80 gallons of fuel - but to add another real tank juts for flotation would be more cost than foam.
- If I foam under the floors I would (likley) lay down a typar/ tyvek type building material so the foam pours in place and fills most voids, but is not actually bonded to the hull. Of course, this would not add rigidity to the hull like it would if it were stuck/ glued directly to the hull - but would make any repairs easier as I could cut out a piece of floor and lift out / cut out the foam where needed.
- I would NOT be adding any foam to the center third of the boat where the lowest points are and the bilge pump lives. I would only add foam along the sides and then also at the bow and stern/transom perhaps.
- to be clear - my floors should eventually be sealed and self draining - letting rain water and splashed run back out - right now my bilge pump handles rain water but that should stop once floors are welded and sealed - there will be raised lips around the engine well and I will install "tracks" of channel under the hatch panel openings which should route rain water to the self draining scuppers and out.
- I have also thought about cutting out / layering in pieces of rigid foam (building supply / foundation surround type) until the voids are full rather than poured in foam...or perhaps a combination...

Bob- sad story but thanks for telling it as we need to be reminded to be cautious - my kids are 4 and 6 - we still buckle the strap under the legs to keep the life jacket on - riding on the bow seems fun but it's true- you wouldn't stay there if a 3000 lb boat suddenly changes course...

I agree with your choice of foam for your situation and a wooded boat - more chance of holing and not as much foam needed to achieve positive flotation, as the wooded boat only needs a little help floating....the rest of the non-wood parts...

In my case my hull likely weighs 2000 lbs and another 1000 for the engine and misc parts so to float 3000 lbs would likely need about 50 cubic feet of foam so I guess that's about 10 of the Glen L (gallon) foam kits and I guess about 100 lbs of extra weight - and $600 of cost... I would look at other larger kits to save money but I am not even sure if I would have 50 cubic feet of room in the outside runs of floor and the bow /stern...
Though of mixing in empty pop bottles but I read they (air) only have half the flotation of the foam, so more room would be needed if bottles were added with foam poured to hold them together.


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