transom and floatation question

R

Rob_F

Active member
I'm doing a conversion of an old fiberglass hull into a "skinny water" boat. No details yet, because I think the trajectory would get the opinion factor even higher as I wade into the.... INTERNET QUESTION POND :-)

1) flotation: searching this site there seems to not necessarily be a standard specification for foam to use. Any recommendation?

2) flotation: does foam in a sealed chamber float better than plain old air in a sealed chamber?

3) transom: thoughts on plywood vs. board?

I'm not necessarily seeking an answer, but I've picked up a lot from this site and it's members and typically find a combined answer from others experience. When the build is done, I'll post it up, but it might be next spring before it floats.
 
I'm doing a conversion of an old fiberglass hull into a "skinny water" boat. No details yet, because I think the trajectory would get the opinion factor even higher as I wade into the.... INTERNET QUESTION POND :-)

1) flotation: searching this site there seems to not necessarily be a standard specification for foam to use. Any recommendation?

2) flotation: does foam in a sealed chamber float better than plain old air in a sealed chamber?

3) transom: thoughts on plywood vs. board?

I'm not necessarily seeking an answer, but I've picked up a lot from this site and it's members and typically find a combined answer from others experience. When the build is done, I'll post it up, but it might be next spring before it floats.
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1) you want to use a closed cell foam. I would use one designed for marine use. You can use pour in or rigid cut to fit. I like cut to fit because you can remove it and get into the chamber at a later date.

2) foam in a compartment floats worse than air :). The reason you use foam is if the compartment is broken, you still have floatation.
 
Good morning, Rob~

A few thoughts:

1. I have seen posts on this site by a member of the US Coast Guard who provided the federal regs for floatation- which, as far as I understand, apply to commercially sold boats - but certainly provide useful guidance. I do a few simple calculations to make sure my volumes will more than float a fully-laden boat - and try for level floatation if practicable.

2. I have used sealed air chambers (with Beckson Deck Plates for access) and left them empty. (see Gallery 5 at http://stevenjaysanford.com/white-wing-2-man-scooter/ ) They are vulnerable to failure if holed in a collision. A better approach - which I have seen with a number of builders - is to fill such air chambers with pieces of closed-cell foam (NOT Styrofoam or other open-celled foams). The foam pieces would provide buoyancy if catastrophe should strike AND they are removable for access when needed - as for repairing hardware or thatch rails fastened through the deck. The added weight of the foam probably would not alter the trim of the boat.

I do not recommend poured-in-place foam if it is against most wood (because of rot potential). Against 'glass or truly epoxy-encapsulated wood is fine.

3. I am happy using plywood for a transom BUT I would not 'glass it in - where trapped moisture could encourage dry rot. I would put a couple of coats of oil-based primer on the interior face of the transom AND make sure all of the edges are well-sealed - either with epoxy or bedded in 3M 5200 (depending on your construction details).

Hope this helps,

SJS
 
I am currently filling up my flotation chambers with empty water bottles. The new ones are really light weight . I made sure they were cool before I closed the tops to prevent crushing when temps drop. I am not done yet but it seems like a great solution. They are removable and don't soak up water.
Sterny
 
I am currently filling up my flotation chambers with empty water bottles. The new ones are really light weight . I made sure they were cool before I closed the tops to prevent crushing when temps drop. I am not done yet but it seems like a great solution. They are removable and don't soak up water.
Sterny
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In a lot of ways I like that solution. The thing that gives me pause (and it isn't a very big pause) is that in the event of some sort of accident where your liability is in question that could be made to look like you trusted someone's life to empty water bottles (i.e., trash). I think that solution has a lot going for it and it would work well and not absorb water which is a perennial problem with foam. I'm just leery of stepping away from convention with a safety device.
 
I knew a guy who was a very competitive sailboat racer [Lasers] there was a big pihy plate in the bow deck. I peeked inside one day and it was filled with plastic milk jugs. Rich
 
Scott Duckboat started to fill their air chambers with rolled up bubble wrap. NO water absorption problems and still has flotation if punctured.
 
My Phowler is equipped with pink sheet foam as floatation. When I first discovered it, I was a bit distressed. There is always a thread on the mud boat forum about someone's foam becoming waterlogged. They seem to make a hobby out of removing floatation for this reason or no reason at all for that matter.
While expanding the electrical system on my boat, I had to remove a chunk of the foam about the size of my fist. I decided to test the stuff by submerging it under a chunk of lead in a 5 gallon bucket full of water. I weighed it before I submerged it, then weighed it two months later after drying it off with a paper towel (btw if you try this at home, add a little bleach to the water...it gets nasty!). Zero weight gain! I am no longer distressed about the pink foam.
 
Steve,

A very "noob" question, but perhaps a fit for your OCD....

Is every pound of decoys contributive to weight limits?

Nearly all of mine float, even the ones with a weighted keel :-)

Re: Foam~ I may be going pink foam simply from a cost/availability standpount.
 
Rob~

I do not know how the "official" floatation process works. I worry mostly about the heavier-than-water stuff like motors, anchors, tools, guns, ammo, other gear, etc. Obviously, lots of decoys under the decks could keep some boats from sinking. And, while most human bodies are neutral buoyancy, I would want to be able to sit up out of the water if my boat were awash. So, I would include the weight of the gunner(s), too.

If at all possible, round up!

SJS
 
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