Aluminum boat rebuild and float foam question

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wildman_bill
Posts: 1
Joined: Fri Sep 17, 2021 10:38 pm
2

Aluminum boat rebuild and float foam question

#1

Post by wildman_bill »

Hey everyone. New poster. I'm rebuilding a 14 foot, 1986 Mirrocraft Northport Troller. It's my first rebuild. The hull is gutted and stripped to bare aluminum. I've used Marine-Tex epoxy to fill any obvious holes and fill dents. I used West Marine 2 part epoxy in a caulk tube to fill long seems. I have 1 gallon of Gluvit liquid epoxy to seal the entire bottom of the boat; inside and out (2 coats on rivets). I plan to use the proper primer and paints (2 coats) inside and outside of the boat. After all of this I should have several solid layers of leak prevention.

Now I'll start to get to my question. I've been researching float foam for weeks and the threads on this topic are frustrating. Here are some facts. Generally, boats under 20 feet, float foam is not optional. Since 1972 Federal law requires horizontal flotation. That means under your deck. Since 2018, horizontal and vertical flotation are federal law. Your boat needs to comply with the manufacture date.

Now my question. Should I assume I can prevent salt water intrusion, and use closed cell pour foam? Or should I assume I cannot prevent saltwater intrusion and have a removable deck with sheet foam underneath?
kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24
Posts: 1735
Joined: Mon Aug 18, 2008 1:37 am
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Location: Kenai, Alaska

Re: Aluminum boat rebuild and float foam question

#2

Post by kmorin »

Bill, welcome to the AAB.com Forum.

We don't see that many smaller skiffs here, the main readership is focused on welded plate boats, that usually implies a little bigger hull but I'll try to reply to your post.

Don't know West Marine's 2 part epoxy so I can't speak with much surety.... does it dry/cure/'kick off' hard or does is remain flexible? My concern would be that a 2part epoxy would become hard, so used as a bilge seam calk? instead of being flexible to move with the boat's seams - it might be rigid and crack or even stiffen the seams to the point they'd experience cracking? Key would be the final state of that particular 2part epoxy.

You can't assume or really even insure you won't have water in the bilges or an open skiff- unless there's some real deck sealing going on.... like welding and air testing; If you're in salt water, there will likely be some salt water in the bilge (wind drift, spray, slop over the gunwales) so I'd plan assuming some water will be in the bilge.

Pouring & spraying foams can break down more readily than cast foams (in molds). Urethane is usually less stable than a polystyrene type of foam- so if you can make panels of sheet foams and insert those you'll likely have less problems that if you spray our pour. (IMO) Any metal boat should have some means (even w a saw!) to get to the hull's inner surface to inspect and maintain. So I'd vote for the removable deck and sheet foam cut into pc. that will fit snugly into each framing section. Some are using 'pool noodles' as they're non-reactive, conform to odds shapes with little work, and last well in the bilge.

I have no idea if your area of the world is policed by the DHS/CG/DOT enough to find out if you have any flotation in your skiff? If you feel you need the flotation then it's your rebuild to add or skip as you see fit. I don't think a refit/rebuilt/re-manufactured really falls under mfg. laws but then I don't know for a fact.

If I were putting in flotation in a small skiff I'd want it higher in the profile than the bilges- to avoid the flotation turning the skiff upside down when it is swamped. Freeing ports sufficient to drain this size skiff would be a fairly challenging task to build and 'rivet' on just above the final deck level. If level flotation is important (?) then what about adding some 'box-like' structure to the gunwales and put the foam there? then the flooded stability of the hull is higher than it would be empty?

Hope you'll take pictures and post them- boat work in progress is always interesting to the Forum.

Cheers,
Kevin Morin
Kenai, AK
kmorin
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