I bought a piece of okoume from CLC to put in a floorboard that would sit on the mast step, or maybe the mast step plus a 3/4" riser.  The thought was it would make it easier to get in and out of the bow, plus make storage items easier to get at, and also provide floatation.  I was going to make it removable to clean under there.  John Harris said if I did that and put floatation under there that it would be in the right spot (low) in t he boat to aid in getting the rails above water if dumped.  I planned on using a stack of  3/4" pink board, each piece cut to fit the shape at that spot, then glue them all together into one block that could be removed for cleaning purposes.  I personally dont care for expanding foam, but that's just me...if I did use expanding foam, I would line the area with aluminum foil so the block of foam could be removed and not stick to anything in the foaming process.   I never did add the floorboard, ran out of time, but after a summer of sailing I still want to do it.  Never did consider a deck up at the rail level, but would like to hear other builders thoughts on that...I'm pretty sure I've seen a couple that did that.

Let us know what you decide.

Curt

My experience with expanding foam in boats of any size tells me to never use it.  It soaks up water like a sponge.  Curt's thought of using rigid insulation (pink board) would work well.  It adsorbs significantly less water.

Closing off this entire area for flotation seems a bit excessive.  It would make a great place to store gear and have some flotation.  You cold even make it water tight to keep everything dry.

Nick

   I would need more information to give an opinion as to whether this would be a good idea for your case. What is goal, specifically?

The negatives, in any case, include adding weight, expense, and potentially windage. The weight is in the worse possible place, too. Boats, and especially open boats, do best if they can easily ride up the face of lumpy water. This also speaks against much storage of heavy things up front.

There is also potential for rot with adding foam which is enclosed. Enclosing any area allows moisture to linger, then adding foam just contributes to this scenario by impeding air flow even if an inspection port is opened. Do not assume epoxy will solve these issues easily; it is nearly impervious to water but not entirely.

. The suggestion to use rigid pink insulation is a good one; this insulation is nearly immune to holding onto water and becoming water logged. In contrast, white styrofoam can become so waterlogged it will sink! Some expanding foam is like styrofoam in this regard.

As to positives, floatation is there, potentially making the boat easier to bail out and harder to swamp beyond recovery. There are lots of other options if this is the goal. Dry storage is another possible benefit. Other options there as well. Dry bags come to mind as giving both of these options if well secured in the boat.

Not sure why everyone's hating on the expanding foam. I've been using it for well over a decade and the boat still hasn't rotted or sunk :-) Maybe folks are thinking of the stuff in the spray cans from Home Despot.

A 2-part Coast Guard-approved structural foam is designed for this use. It's closed cell, so it won't "soak up water like a sponge", even if you punch a metal spike through the wood.

It's meant to be a structural component, so it can handle compression loads, unlike the pink foam which is meant to be a non-structural insulation.

It's also deliberately designed to stick to the sides of the compartment that it fills. Lining the compartment to make it not stick defeats this and accomplishes nothing.

The weight is 2 lbs/cubic foot. The buoyancy is 62 lbs/cubic foot. My sailing dinghy, which uses the same idea that jabbot is proposing (raised floor with foamed space, sheer-level deck and closeable  area between) has no trouble riding over 3-foot waves. And there's no way that anything that stays below the sheer line can add windage.

The downside of this setup is that it would cost more money (especially if the correct foam was bought) and add time to the build. I've not regretted doing it on my boat.

Have fun all,

Laszlo

   Thanks for the opinions everyone.  I am still a ways off from needing to decide on an option here, so I will think on it a bit longer.  I guess my reasoning for considering this is really three points: 1) to add more flotation for safety not to mention a splash guard  2) to create a more permanent fixed mast partner 3) looks - I think it would look pretty sharpe going into a thicker inner rail that I have planned

Thanks all -

John

   I like those reasons other than the splashguard; skeptical it would do much given the freeboard and hull shape. That also sounds like it could be adding windage.

Dow pink foam is 25psi rated for compression, can be used under home foundations

I concur with Laslo. . . I have been using "Mix & Pour" foam floatation for many years in boat builds and have never had a problem with water, gas or oil absorption. I don’t think I can name brands here but I use one that specifically meets USCG Title 33, Chapter 1 Subpart 183 criteria.

I will definitely be using it in my upcoming Skerry and / or Northeast Dory Build.

JP

Mind if I offer a couple of things to consider?
The Dory is pretty sensitive to trim. Blocking the entire bow, if I understand your plans, would prevent moving gear up front to balance things. It’s also a really handy place to get gear out from underfoot. All manner of pesky gear lives up there in my Dory.
You’d also pretty much sacrifice the the front seat, unless you sculpted a seat back into the deck, which would be totally cool. But then it won’t be able to incorporate the mast partner. If you Only plan to sail this point is moot.
The thing that gives me pause though, is having that entire chamber full of flotation way in the bow. Wonder what effect it would have on the boat’s attitude in the water after a flip? Is it conceivable that it would lift enough to submerge the stern, making getting the water out impossible? Is there enough flotation under the stern seat counter? Would it be better to bring the top of bow flotation only to the same line as stern floatation? There are a couple of people on this board much more qualified to answer those questions though.
ev

   If you look at the Skerry, you'll see that forward and aft seats are the the tops of sealed compartments with waterproof access hatches. There is no need for foam because the compartments are sealed and air weighs less than foam. I have as one of my projects, a Boston Whaler. These boats are full of closed cell foam and what has been discovered over the years is that unsealed screw holes and degraded thruhull fittings admit water which does a fine job of migrating throughout the foam.  Older whaler owners (the boats, not the owners) have taken to weighing their boats to determine how much water is in there. You can find a lot of info. on closed cell foam absorbing water at the whaler central site.  My point is that CLC didn't see the need for foam in floatation compartments so I think it would be an unnecessary expense and a loss of storage space. 

The OP mentioned putting on a deck and and enclosing an area under this deck for flotation foam. He never said anything about filling the entire area under the deck with foam, nor did he mention anything sticking up above the sheer line.

That being the case, there's no windage issues and there's still plenty of storage space (which is now out of the sun and any direct splashes).

Good point Eric about balancing the flotation between the bow and stern to facilitate bailing.

One big advantage of foam-filled vs. air-filled compartments is that a foam-filled compartment will keep providing flotation after a puncture.

CG certified closed-cell foam takes years to break down enough to start absorbing water. It has to be exposed to extreme vibrations and/or large temperature cycles and/or UV. On a boat like the Dory, neither of the former  is likely to be a problem and a sealed compartment takes care of the UV, Unsealed screw holes and degraded fitting are a workmanship and maintenance problem, not a foam problem. It's like blaming the motor oil when the filter hasn't been changed for 200,000 miles.

Have fun all,

Laszlo

https://www.youtube.com/watch?v=bGTnauBC3Dw

You have to look closely but in this video of Neil Calore sailing you can see that he has air bags both fore and aft...but he's doing serious expedition sailing.  I would think if you want serious floatation (like filling the bow with air or foam would bring), air bags would be the way to go, because you can remove them as needed, and if you do one end, do the other end too. 

 For me, I intend to stay relatively close to land and the storage in the bow and the possibility of rear seating kills the idea of massive floatation in the ends for me.  I still want to do the floorboard in the bow with floatation underneath but for me a deck would block the ability to hang gear from the inner rail slots in the bow area.  

Here's another idea if you want floatation...what about putting one of the foam beach rollers on the outside ends of the seats and bungying them down to the seats?  (getting the floatation down low where they would be underwater if swamped)  Neil tied pool noodles to the rail, but I'm talking about mounting the beach rollers lower in the boat.  Thought on that idea?

Curt 

   As a dory owner, here's my two cents. 

Deck over forward part:  might be pretty handy as it would provide a nice dry area to shove stuff, and it would add a bit of water deflection in heavy seas.  I have to admit that the only time I have ever taken any water over the bow in my dory was in pretty extreme conditions of 4-5 foot seas steepened by shallow water, and the bow managed to dig under a wave only occasionally. Having a deck up there would have helped. Don't bring it as far aft as, or connect it permanently to,the mast partner though:  you need more room for a forward rower's back to move into if you ever want to do two person rowing (which requires removing the mast partner).    But enclosing ighe bow area completely would be a bad idea.  One of the big advantages of the dory over the skerry is the completely open hull gives you lots of places to put stuff, or people.  I wouldn't want to give that up. 

Additional flotation:  I thought about this a lot before embarking on a week-long trip on the Maine coast in my dory.  

First, the dory is hard to capsize.   It's not that hard to take some water over the rail by healing too far, but as long as your sheet isn't cleated, You can correct before you take on much water.  It's not a catastrophic tip over like on a 420 when you tip past the balance point.  

Second, there are more flexible ways to keep flotation low in the boat when u need it but be able to remove it when you don't.  I epoxied multiple tied own points along the garboards just above the deck plank and along the top of the garboard. Use those to tie down two big rubber fenders with 1" thick nylon webbing straps, one on each side just aft of the amidships thwart. They serve triple duty as beach rollers, comfy fore-and-aft seats for sailing (transverse thwarts are not comfy for sailing!), and very floaty things low in the boat if u did capsize.   Use those tie down points also to tie down big dry bags if you're on an expedition.  Sure , those dry bags seem heavy when you are schlepping them down the dock, but they are light compared to the amount of water they displace. As good as flotation.  (I made my tie downs from scrap Spanish cedar left over from cutting the thwarts, they look great). 

   Ask the man who owns one.  Liked that last answer a lot.