Dry tanks for dory

Has anybody installed dry tanks under the NE dory seats for storage and flotation  rather than foam. Does this make sense?

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RE: Dry tanks for dory

IMHO, floatation tanks should be filled with foam and sealed.  Using air for floatation makes them vulnerable to puncture when you most need them.  There are many brands and types of waterproof bags to hold gear.


RE: Dry tanks for dory

IMHO, you need to be very careful about using foam.  This is one of those Ford vs. Chevy arguments that I see all the time in the marine industry.  Keep in mind that once foam gets wet, it will NEVER dry out.  I'd rather stuff pool noodles into a deck plate than pour foam into a buoyancy tank.  I took every precaution to make my tanks air tight on my EP and after I swamped it, it still sloshes to this day, hence my addition of garboard plugs.  If your foam gets wet, it'll add 8# per gallon, which is not inconsiderable, not to mention what that trapped water will do to your epoxy/wood.

My $0.02...


RE: Dry tanks for dory

If the wet foam is closed cell, it will not add 8 lbs/gallon until all the cells have completely broken down - a long slow process. Even then, it will only add weight if the leak is not plugged. Just to be even more pedantic, since the foam weighs about 2 lbs/cubic foot, the added weight will be 7.75 lbs per gallon (*sigh* where's the metric system when you need it?) unless the decomposed foam gets washed out by the water gushing in through the unrepaired leak.

Personally, I've gone both ways and they've worked about the same for me, so I'm neutral in this debate, just want to keep both sides honest :-)

Have fun all,



RE: Dry tanks for dory

   I did a lot of research before making my foam blocks for my dory.  I came to understand at the time that pink (or blue) builders foam sheets will not absorb water where white styrofoam or self expanding foam does absorb water.  I bought a bunch of 3/4" pink foam 4 * 8 boards and glued up the pieces into blocks with Loctite glue intended for that very purpose, then I covered the blocks in epoxy plus a layer of glass on the side exposed to feet hitting it and painted them flat black.  The advantage of this method is that it maximizes the amount of floatation in a given area because each 3/4" piece is larger or smaller than the adjacent piece to match the taper in the hull, completely filling the cavity, something that wouldnt be the case with inflatables.

I also thought about using Taylor fenders as floatation, but again, you wouldnt be able to get enough floatation under each side of each seat.

One option, though, is to put a floorboard in the front and put some floatation under it

Also, do a search in You Tube for Neil Calore and look at his techniques!!





RE: Dry tanks for dory

CLC warns against pouring in foam and recommend cutting sheets of closed-cell builders foam to fill bouyancy chambers.  It's in the manual, guys.

RE: Dry tanks for dory

Yeah, good point Laszlo.  I only meant that any water permanently trapped in the tank will make the boat heavier to manhandle ashore.  I also ASSumed the original question was regarding the two-part foam that a lot of people pour into their sealed tanks before sealing them up.  There are several types of "foam".  In the water, soaked foam has much less effect on the boat since it's displacing so little of the volume of the tank.

RE: Dry tanks for dory

  Ok, so the original question about building a dry tank by bulk heading off the seats and using the space for storage is not a good idea? 

I'm novice, haven't even bought the kit yet

also, what does IMHO stand for

RE: Dry tanks for dory

   IMHO = in my humble opinion

The pink/blue sheet foam which is now purple where I am, is indeed impervious to water. I tossed a slab out behind the shop (garage) last year and with all the snow/rain since it is still dry.

Perhaps kayak style floatation bags would give you more flexability to location.

RE: Dry tanks for dory

First, one should try to provide a means of providing dry air to all sections of the boat so if needed or when in storage these areas can be dried out.or accessed for maintenace if needed. With time bacteria or mold will build up in these areas unless they can be rinsed and dried on a regulaf basis. If the fiberglass should ever get a crack to the wook substrait water will work its way to the wood and do its thing.

Wether one fills this space with extra floatation, uses it for storage, or just leaves it empty is up the the user or builder. There is always a need for storage on a boat for emergency tools or supplies.

How you chose how to use this space is entirely up to you.

I would try to make it as usable as possible by adding an inspection port and then I could not use it, use it for storage, or not use it al all.



RE: Dry tanks for dory

   I have been a power boater for years and watched the construction of my current power boat, a 20' Albury Brothers center console.  Evey boat manufactuer today uses foam in some area of their boats.  On mine they used a spray foam to encapsulate the tank and provide floation.  If the foam is applied correctly it fills all voids and today's foam resists water absorption better than ever.  My thinking, perhaps incorrectly is that sheets of construciton foam will be a lot more prone to trapping condensation and water than a properly applied foam.  After doing a bit of reasearch I found the following from one of the foam companies:  [for the record i am not associated with this company]

Marine Flotation

It is a federal law that boats 20 feet and shorter have level flotation material. The Code of Federal Regulations is very specific about testing for water absorption, resistance to fuel, fuel vapor, bilge cleaner and oil. Versi-Foam® standard foams found in System I, System 15 and System 50 meet these requirements (U.S. Coast Guard Test Data). In addition, polyurethane foams are resistant to polyester resins used in the fiberglass process, making it the most popular flotation material for manufacture and repair of boats and other marine vessels.



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