Polyurethane vs Polystyrene in Hulls

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MurrayM
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Polyurethane vs Polystyrene in Hulls

#1

Post by MurrayM »

I've put many miles under the hulls of sea kayaks, but basically none in larger boats. It's time to move up in comfort and speed. Aluminum boats in the 18' to 22' range appeal to me for their rugged 'let them dry on a protected cobble beach and go photographing till the tide floats it again' hulls. Scooting up rivers and creeks on the high tide to tie off on sand and gravel bars would also be on the agenda.

While researching the different boats available on North America's west coast (I'm from BC's north coast) I found the following bit of information on an aluminum boat manufacturers website, and was wondering what the collective wisdom here thought about it;

All hulls need to be built with rigidity and support. However, this can be achieved by using a method that leads to hull corrosion, or by using a method that PREVENTS hull corrosion.

Method #1: Creates Hull Corrosion

The least expensive method of providing the needed rigidity and support is by installing only the longitudinals and then spraying the hull with polyurethane foam that then hardens. The only problem with this method (and trust me, it can be a huge problem) is that polyurethane absorbs water rather than allowing it to drain out.

When water is absorbed by polyurethane, the two components react together to cause corrosion inside the hull which can then lead to HUGE repair bills. As well, since the foam absorbs water, it becomes heavier over time. This causes the deck to sit lower, and will then require a bigger engine to drive the boat, thus consuming more fuel.

By now you're probably thinking that there shouldn't be any water inside the hull. Ideally, there shouldn't be; however, we live in the real world where water always manages to find a way into areas it shouldn't. A couple of ways it does this is through condensation, and seepage through mounting holes.

Method #2: Prevents Hull Corrosion

The proper and best way of outfitting a hull is with both longitudinals and ribs (see diagram 1). This provides the hull with the rigidity and support it requires, and then polystyrene is added to comply with Transport Canada Regulations. Since the polystyrene is cut and fit into the hull rather than sprayed in, any water that may get into the hull is free to drain down to the water tight inspection hatch.

In this way, the hull is kept safe from corrosion so it can be used for many years without worry.


Sorry, couldn't find a picture of the ribs they're talking about, but figure they're welded in pieces of aluminum plate perpendicular to the longitudinal axis of the boat.

What do you think? Is this salesmanship, or based on solid fact/experience?

Murray
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Re: Polyurethane vs Polystyrene in Hulls

#2

Post by Chaps »

What kind of boat are you talking about and what is the hull thickness?

What does Transport Canada require as far as flotation specs in 18' boats?

I'm generally in agreement with the statements made above as far as styrene being a better flotation choice if flotation is required . . .
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Re: Polyurethane vs Polystyrene in Hulls

#3

Post by pjay9 »

I have used Polyethylene sheet material and pool noddles in previous boats and RV's. I will be changing out the bead board (white) used in my boat in a year or two when I work the deck over. Capt PJ
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Re: Polyurethane vs Polystyrene in Hulls

#4

Post by MurrayM »

That was a quote from Ironwood Boats. They use 1/4" for the hulls and transoms.

http://www.ironwoodboats.com/index.php

This stuff is all new to me. I'm really early in the research stages of looking for a boat, so I'm unsure if this way of building (which probably adds quite a bit to the building costs) is worth the extra cost, if it would make the hull significantly stronger, or if water absorption into aluminum boat hulls is even a problem at all.

Murray
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Re: Polyurethane vs Polystyrene in Hulls

#5

Post by Chaps »

Well, with 1/4" hulls the rigidity or strength is not going to be affected one way or the other by foam of any type so its a confusing statement. In fact I find it unlikely that Ironwood puts any foam in their boats unless it's required up there by law . . . nonetheless, sprayed in or poured in foam should not be down in the bilge of any boat IMO. Have you looked at or seen any boats that are built that way?
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Re: Polyurethane vs Polystyrene in Hulls

#6

Post by steve-r »

Here is the Transport Canada link describing floatation requirements....looks like it applies to vessels under 6 meters ( 19 ft 8 inches ) .
http://www.tc.gc.ca/eng/marinesafety/tp ... -flot-test
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Re: Polyurethane vs Polystyrene in Hulls

#7

Post by Chaps »

steve-r wrote:Here is the Transport Canada link describing floatation requirements....looks like it applies to vessels under 6 meters ( 19 ft 8 inches ) .
http://www.tc.gc.ca/eng/marinesafety/tp ... -flot-test
Well I guess that explains why Ironwood doesn't show any boats on their website shorter than 20' :thumbsup:
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Re: Polyurethane vs Polystyrene in Hulls

#8

Post by Jay Perrotta »

Balderdash and horsepuckey..

"The least expensive method of providing the needed rigidity and support is by installing only the longitudinals and then spraying the hull with polyurethane foam that then hardens. The only problem with this method (and trust me, it can be a huge problem) is that polyurethane absorbs water rather than allowing it to drain out."[/i]

I don't know of anyone manufacturing alloy boats today that either uses foam as a structural component or claims that foam is a structural component to "provide rigidity". This is called a straw-man argument. First you put words in you opponent's mouth and then show the error of their ways. Who is using foam as a structural element?

The second contention that polyurethane foam absorbs water is a bit true and a bit untrue. Closed-cell polyurethane foam in an "as-poured" state (no cuts, damage) is highly resisitant to water absorbtion. I know this not from literature but from direct experience. Having said that if you crush or cut polyurethane foam you can get water absorption at the margins and if this held against aluminum it can cause corrosion. I'll address this further in a minute...

When water is absorbed by polyurethane, the two components react together to cause corrosion inside the hull which can then lead to HUGE repair bills. As well, since the foam absorbs water, it becomes heavier over time. This causes the deck to sit lower, and will then require a bigger engine to drive the boat, thus consuming more fuel.[/i]

Ummm... I'd like a reference to where in the literature on corrosion or any other place a reaction beteween polyurethane foam and aluminum alloy is mentioned and also what exactly is this "reaction". Fact is there is no "reaction". I'm sure what they're talking about is a corrosion called "poultice" or "crevice" corrosion"... has nothing, absolutely nothing, to do with the type of foam or even foam in general.

The one place people often see aluminum corrosion is when an aluminum fuel tank is foamed in-place. Boston Whaler is the most famous example. The corrosion found on foamed in-place fuel tanks isn't from some scary, fictional "reaction" between aluminum alloy and foam but rather a completely known, completely avoidable form of corrosion, again, called poultive or crevice corrosion. Poultice corrosion is a reaction between de-oxgenated water and aluminum - not foam and aluminum.

The beauty of marine-grade aluminum alloys and especially 5086 and 5083 (5052 to a lesser extent) is that when exposed to oxygen and saltwater and the environment it forms an oxide layer (aluminum oxide) that is the second hardest naturally occuring substance in nature. This is a form of corrosion but is helpful and good because unlike steel's corrosion is doesn't fall off and continue deeper into the metal. It is hard. It is tough. It protects the metal for an almost indefinite time (longer than we'll live!). The main ingredient necessary for this great corrosion is oxygen. Aluminum needs oxygen to protect itself.

On foamed-in fuel tanks water gets between the foam and the aluminum and then starves for oxygen. It becomes an acid and then corrodes away the tank because the surface of the aluminum tank has no access to oxygen to form its protective coating.

To prevent this corriosion one needs to either coat the aluminum with a substance that is impervious to this acidic water (i.e. Coal Tar Epoxy) or give it access to free and abundant oxygen.

On our boats that have foam in the hulls we (on purpose) allow any water that would be in contact with the foam and the hull the ability to drain away and for oxygen to circulate.

This statement is harmful and misleading in that it might make a buyer/home builder think that this poultice corrosion is particular to a polyurethane/aluminum interface (because of that darned "reaction"). The buyer/home builder then uses polyethlene or polystyrene as flotation and (if he doesn't allow free flowing oxygen) - guess what - poultice corrosion.

Hard to be more wrong in one statement.

"The proper and best way of outfitting a hull is with both longitudinals and ribs (see diagram 1). This provides the hull with the rigidity and support it requires, and then polystyrene is added to comply with Transport Canada Regulations. Since the polystyrene is cut and fit into the hull rather than sprayed in, any water that may get into the hull is free to drain down to the water tight inspection hatch.

In this way, the hull is kept safe from corrosion so it can be used for many years without worry."


Ummmmmm. What?

Many great boats are built with mainly longitudinal framing (including Pacifics). This form of building stated in the Pacfic Northwest and is commonly called "free-form" building. Done correctly it is a great, great way to build boats. (for more information the book to read is read Stephen Pollard's Boatbuilding in Aluminum.

Building boats in the more traditional way with lateral and longitudinual framing (egg crate construction) is also a completely reputable way to build boats.

For both methods, though, it is important (as in any engineering endeavor) to design in strength enough to accomplish the boat's mission. If you badly engineer an egg crate boat it can break and if you badly engineer a free-form boat it can break. The engineering is very, very straightforward and the calculations easy to make strong boats out of aluminum alloy in either way.

To say that building with "both longitudinals and ribs " "...provides the hull with the rigidity and support it requires" is absolute, complete and utter nonsense. If you make those ribs of the wrong material, or put them too far apart or they are supporting a skin that is too thin or of the wrong grade material then you would, in NO way, be providing the boat with the rigidity and support it requires.

There is lots of marketing talk on the internet... "Best riding, best built boat on the market!!!" We all take these sorts of claims with a grain of salt but when someone starts publishing quasi-scientific mumbo-jumbo and making statements that don't begin to hold-up to scrutiny then that frustrates me.

The plate aluminum boat industry in the US is still in its infancy. To get our boating brethren to switch from flammable, cracky GRP we need to do two things:

1) educate on the benefits aluminum alloy boats in a straighforward and honest way.
2) build great boats.

We do not need misinformation, disinformation, scare tactics, etc.
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Re: Polyurethane vs Polystyrene in Hulls

#9

Post by MurrayM »

Hey Jay,

Thanks for chiming in and giving such an informative, lengthy reply. You're right in saying the Internet is full of balderdash and horsepuckey...which is exactly why I joined this forum to post my question!

Again, thanks!

Murray
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Re: Polyurethane vs Polystyrene in Hulls

#10

Post by JETTYWOLF »

Murray.....

Have ya heard the one about,

"Two guys go fishing.....one owns an heavy duty alloy boat, the other doesn't. He owns a 1982 Bayliner, ya know...before they changed the name to Trophy boats?? While out there, they get checked by the fish & game nazi's. And are asked for their fishing licenses. The owner has his in a packet of info he keeps on the boat, and produces it quickly. The guest roots around in his tackle box, can't find it. Then looks in his wallet, can't find it.....Eventually remembers that he stuck it in his front pocket of his cordoroy's and pulls it out, crumpled and folded. And hands it to the officer. While doing so a penny falls outa his pocket the change he recieved back from buying a cup of joe earlier in the morning at the zippy mart. The penny rolls around the deck, and some how finds a spot to fall deep down into the bilge. The bayliner owners says, we better hurry and get that penny out there!! I don't want it burning a hole through the boat and us sinking out here, today."

:rotfl: :rotfl: :rotfl: :rotfl:

Myths, whoa how they fly around. I hear them all the time. My favorite is that I'm a lightning rod on the water, and why would I want a boat that attracks lightning?

Thanks Jay. I appreciated reading your essay. :thumbsup:
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Re: Polyurethane vs Polystyrene in Hulls

#11

Post by pjay9 »

Jay well said and explained for all of us to understand! THX!!

I had a Hewescraft (alloy) I bought used and tore it apart as the deck was mushy. I found poured in foam that appeared OK... BUT in fact it had so much water stored in it that when I took a test bore it filled with water about two inches from the top. I removed all of it and when I filled a 30 gallon trash can with foam I could not lift it over the gunnel, I had to unload the can some and then sit it outside and load the foam over the side. Beware of poured in foam! The old Tiderunner (a NW built Glass boat)I was going to rebuild had the foam and it was water logged as well, what a mess...I guess tearing both those boat apart made me make some decisions to get a new or near new boat and it was ALLOY to the top of the list.

As we all know all boats are compromises...some more or less than others. You buy what you can afford and go from there, BUT being an INFORMED buyer is the great and this AAB place does just that! THX everyone! Capt PJ
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Re: Polyurethane vs Polystyrene in Hulls

#12

Post by Jay Perrotta »

pjay9 wrote:Jay well said and explained for all of us to understand! THX!!

I had a Hewescraft (alloy) I bought used and tore it apart as the deck was mushy. I found poured in foam that appeared OK... BUT in fact it had so much water stored in it that when I took a test bore it filled with water about two inches from the top. I removed all of it and when I filled a 30 gallon trash can with foam I could not lift it over the gunnel, I had to unload the can some and then sit it outside and load the foam over the side. Beware of poured in foam! The old Tiderunner (a NW built Glass boat)I was going to rebuild had the foam and it was water logged as well, what a mess...I guess tearing both those boat apart made me make some decisions to get a new or near new boat and it was ALLOY to the top of the list.

As we all know all boats are compromises...some more or less than others. You buy what you can afford and go from there, BUT being an INFORMED buyer is the great and this AAB place does just that! THX everyone! Capt PJ
Thanks, Pjay.

Poured-in foam.

Funny - the only part of the OP's first post that gave me pause is the poured-in foam absorbing water part.

Just like your story I have heard of completely saturated, heavy, blechy foam in boats. Although Ive never seen it myself it is prevalent and first person acoounts like yours that always makes my claim that we don't have problems sound like the above mention horsepucky and balderdash.

Story...

Pacific Boats makes and uses "boatholders" that are made from the same foam that is injected into the boats. They make a "form" with the same deadrise as the boat - pour-in the foam, let set and then remove. These pure polyurethane holders are light, easy to handle, don't damage the boats - they're great!

I had them send me some with a load of boats and dutifully put them out in the yard. At various times they are holding boats, being rained on, frozen in snow and ice and after nearly 10 year they are as light and dry as the day I got them.

Certainly there is something wrong between your observation of mushy, water-logged foam and my observation of dry light foam.

I am no foam expert at all and am not familiar with various different types of polyurethane foam but the discrepency between what my eyes have seen and the stories I hear bother me.

If I read your story pjay I don't think that I would want to buy a boat with foam in it - sounds like a heavy mess...

Another quick story...

Had a gent email me one time from the Florida Keys - he wasn't requesting literature although he greatly liked the boats and was in the market for a boat.

You see he explained that although aluminum alloy boats might be great in the northeast and northwest the salinity, growth and "electrolysis" in his area would preclude having an aluminum alloy boat. The conditions in his area would cause the hull to corrode away. Further, he explained, he was an airline tech and was very familiar with aluminum alloy so I shouldn't try and tell him that he was wrong - he knew what he was talking about. The letter was friendly and open but his mind was clear and made up.

I've learned (mostly by having a wife and kids!) that arguing with someone who already has their mind made-up is a foolhardy task. Especially where I am suspect since I make money selling aluminum alloy boats my goal is always assumed to be money and sales rather than hard truth.

So instead of arguing with this gent I suggested science. An experiment....

I sent him 8 sample pieces of 5086 aluminum alloy roughy 1.5" x 1.5" in size. Also included in the package were 4 stainless steel nuts and bolts and 4 small, round outboard zincs.

I asked him to put these over the side of his dock in the following manner:

1 Alloy piece sitting on the bottom with no zinc bolted-on.
1 Alloy piece sitting on the bottom with a zinc bolted-on with the SS nut and bolt.

1 Alloy piece midwater with no zinc bolted-on.
1 Alloy Piece midwater with a zinc bolted-on with the SS nut and bolt.

1 Alloy piece in the intertidal zone (dry at low tide and wet at high tide) with no zinc bolted-on.
1 Alloy piece in the intertidal zone with a zinc bolted on with the SS nut and bolt.

and finally,

1 Alloy piece suspended in the salt air with no zinc bolted-on.
1 Alloy piece suspended in the salt air with a zinc bolted-on with the SS nut and bolt.

We would leave these pieces for a year and take them out and photograph them on the first of every month.

This seemed a good experiment - protected and un-protected aluminum alloy in his home waters under every conceivable condition.

This gent was amazing. He set the experiment up exactly as I described and even sent photos of the set-up. On the first of every month the photos would dutifully arrive of the pieces - high-def images. He left them for a year and returned the pieces along with a water sample and the exact lat/long of the experiment.

So what happened?

Nothing. The metal was just as good as the day I sent it in the mail - absolutely zero change other than color.

Funny thing was I asked him if the experiment had changed his mind because he had been so adamant at the beginning and had not made any comments on the experiment's result as he dutifully sent back the monthy, then annual results.

I was very disappointed that he came back with some malarky about how his dock had no stray-current, etc which was not what our discussion had been about at all. He changed the parameters of the disagreement when the results didn't fit with his already made-up mind - arrrgh! He had clearly and indisputably said that the salinity, growth and "electrolysis" in his area of the world would preclude alloy boat ownership - not stray current. Bad form in my mind.

Well anyway - this is a long way of suggesting a second experiment - does closed-cell foam (like we use in our boats) absorb water and become significantly heavier over time.

I make the argument that the foam when poured in-place and allowed to have water drain down and away from the foam to be removed remains, over time, virtually dry. I make an allowance for any cells on the surface which migh be broken and accept water.

Pjay - what if we send you 6 plastic cups filled with the exact same foam we inject into the boats. We'll letter each of the cups and get an exact weight on each to start.

You'll then place them thus:

A) 1 Foam/Cup unmolested and kept submerged in water.
B) 1 Foam/Cup with a steak-knife driven into the topskin and removed then submerged in water.
C) 1 Foam/Cup unmolested floating in water but not kept submerged.
D) 1 Foam/Cup with a steak-knife driven into the topskin and removed floating in water but not submerged.
E) 1 Foam/Cup unmolested and simply left out inthe elements (Tacoma is pretty rain, no?)
F) 1 Foam/Cup with a steak-knife driven into the toppskin and removed the left out in the elements.

You'll take each and weigh it on the first of each month and at the end of 1 year.

The results should give us a pretty good idea about whether the closed-cell, polyurethane foam we use absorbs water - shouldn't it?

None of these set-up reflect exacly the situation in a boat but we should get results that are informative.

Mythbusters comes to AAB!
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Re: Polyurethane vs Polystyrene in Hulls

#13

Post by Chaps »

Jay, I work on boats, whatever comes in the door. The older plastic boats with plywood decks and foamed hulls are always saturated and rotting. Just about every Whaler I work on has water in the hulls that cannot be removed. But even if one uses a foam that doesn't absorb water its pretty tough to keep the boundary layer between a metal hull and foam well adhered and dry. Such conditions can lead to oxygen depletion and corrosion, no? Or did you already cover that above . . .
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Re: Polyurethane vs Polystyrene in Hulls

#14

Post by Jay Perrotta »

Chaps - is there a place in these hull (I know that there isn't on Whalers) for the water to go?

Does the foam sit in the very bottom of the boat - surrounded by water or can the water move down - away from the foam to be removed.

I know that the foam we use is USCG approved and has passed their "immersion" test - I'll have to look up the test and post a link.

I believe that their test has a maximum absorbency rate for a defined period of time. It may well be that if you simply leave the stuff immersed in water indefinitely it absorbs.

Again, I'm not sure if there are different types of foam or if the difference is that we allow any and all water to be able to follow gravity downward to an empty bilge but no problems whatsoever.

I'm no expert and I want to learn as well. I'm not coming at this with an "I know the answer" attitude - I'm trying to learn...
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Re: Polyurethane vs Polystyrene in Hulls

#15

Post by pjay9 »

Jay, I am not a person with a mind set and I think your experiment with the gentleman was admiral but I didn't think you would change his mind. I have been around the block a few times too. I suspect that the foam you use form what you are saying is better and you treat the initial set up differently.

The foam Ii refer to had adhered to the aluminum, wood GRP or whatever it contacted which to me says it was poured in ans swiped off especially as it didn't always meet the swipe surface, top of stringers. Since the adherence the weep hole being very small were plugged. Plywood screw down decks, so what happens water goes thru any possible opening and stays put. Granted the chambers forward had less water but the ones aft were to the top, just because the boat sat that way on the trailer.

So my conclusion is as follows: With a CLOSED CELL foam there should not be absorption unless there is a deterioration of some kind, incorrect install and is allowed to sit in water 24/7/365, little over exaggeration but you get my drift...you have wet foam!!

So allowing free draining (not in my experience with these boats) and correct installation and handling the foam can stay dry. Agreed! Does all of that happen industry wide NOT AT ALL!

My boat has white bead board, bad stuff doesn't hold up to gasoline and can create black smoke. The saving grace it is not in contact with the bilge water therefore water drains and air circulates...As I said that white bead board is gone when I get around to it!

Your experiment is not needed from my point of view as I accept your experiences, practices and value your input. Thx for sharing! Maybe someone else will take up the challenge. Again thanks for letting us see a better and different way of accomplishing tasks and requirements. Hope to visit with you on my next journey! Capt PJ
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Foam is not always FOAM

#16

Post by kmorin »

I'm coming late to the discussion but one point not made which we found critically important when we built and repaired full time. It's important to remember that my work was a while back and that's a critical factor in my point.

There are several types of foam that is 'brownish- yellowish', mixes and pours and foams up and 'seals'.

One is Urea Formaldehyde (UFFI) and another is Polyurethane (PUR) which is sprayed or poured. Both products come in different densities even though UFFI isn't used as much anymore because it is a little toxic.

Both products are/were often called just "urethane" even though neither is what a chemist would call urethane!

I don't know the chemistry well enough to explain well, but I do know that UFFI is cheaper by far and was commonly sprayed for years under the generic term -urethane foam. UFFI's formaldehyde component will break down into formic acid and if it were foamed into a bilge that foam would react and create one mess of those areas where it could mix with salt or bilge water. In fact well mixed and catalyzed UFFI has a free formic acid component, probably only in the smallest percentage but surely enough to begin acid corrosive cells.

PUR, or SPF when sprayed, isn't the same 'stuff' chemically and is much more stable after its catalyzed so Jay's explanation of poultice cells from de-aerated and therefore acidic water explains PUR's potential damage to alloy hulls.

However, UFFI which WAS used by many pressed formed boat mfg.'s -cost effective solution to CG reg.s- will decompose with water and literally destroy a thin hulled boat. I've tried to help recover some boats from this fate and business associate the Chemical Engineer has explained some of these basic differences to me.

Its possible our discussion isn't apples to apples and foam to foam? I don't think the UFFI fill is as widely used but I do know what a few boats in our area looked like when we removed the decks that has sprayed foam below and no air pressure test of the welds!

One last item about UFFI it will pick up water and retain it, PUR won't hardly at all.

RANT:
As long as I have the soap box out, and keyboard handy, I'd like to complain about the idea of any foam except as cushions under my overly round stern. IF foam is used for sound deadening, then I'm not discussing that here.

Why is foam used in metal boats? The main reason for small boats <30' to have foam is to display water in a case where the hull is awash. In that case the displaced water's mass is not added to the awash displacement (sinking it) and the boat may float at the surface because of the relatively lighter density of the foam replacing heavier water.

In the case of <20' boats, I think CG requires level flotation, and foam is preferred because CG won't permit (purely) air chambers or voids in the hull at those sizes? I don't actually have that regulation at hand; but that is my understanding. I personally view this poorly conceived or perhaps senseless regulatory concept as ill informed about welded metal boats. However, I can understand in press formed boats of materials that are not welded foam would serve this purpose adequately.

But, as I mention above, if the UFFI foam is used results would be different than if a PUR or SRF were used.

My complaint [part one] is to allow fully welded boats to fall under the same foolish waste of building effort just because they're <20'. If you build the boat of welded materials and have foam under a welded deck (?) why is that foam there? If the deck is air tested after construction and vented correctly when the boat is finished; there is no reason to have foam!

To keep water out of the foam compartments you'd air test! why have foam in a pressure tested, welded metal chamber? What am I missing? Jay there must a good reason for Pacific to foam? I just don't know it yet?

Unfortunately, I've built hundreds of skiffs in the <28' LOA class that have welded in air flotation chambers in them. There is no foam in any of them, they're still fishing and many have been landed with four tons of sockeyes in a following sea on a gravel beach and plenty of them filled, rolled, swamped and were driven over by large boats. The air kept them up, saved them or popped them up in the wake of the larger boats. No foam, no fuss, no corrosion, no problems- why foam?

Again, I'm not discussing the press formed boats of lighter material with riveted or screwed in decks, I'm ranting about all welded boats.

Cheers,
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Re: Polyurethane vs Polystyrene in Hulls

#17

Post by trouty »

I'm glad Jay answered this, because it saved me a lengthy missive.

I'll just add this.

With styrene n any gas powered boat - spill one teaspoon of gas into that styrene and you no longer have any flotation foam - you have a bilge full of sticky black goo.

Don't believe me get a styrene foam coffee cup and add a teaspoon of gasoline and let me know how you get on - better still take some photo's and post them here.

When your boat catches fire - good luck with that styrene! Maybe add a match to your styrene foam cup and lets see how that gets on too.

The original post was unmitigated crap.

When I built and put my alloy 16 fter thru commercial passenger survey - I was required by the survey / marine safety authorities to use:-

High density, closed cell, fire retardant, Polyurethane foam, encapsulated.

This means blocks cut to fit between stringers and cross members / bulkheads, encapsulated in heavy inert plastic sheeting sealed with 100mph waterproof tape - i.e. each piece wrapped like a waterproof Chrissy present and hand fitted into the hull. Option 2 was to NON ALLOY encapsulate the foam blocks - which is what my surveyed 25 foot charter boat is fitted with.

The sealed foam blocks are supported on inert PVC half pipe up off the bottom and side sheets of the hull to allow water to flow to the bilge pump/s and to prevent any crevice corrosion.

Whoever posted the first bit about canoes and styrene and tried to apply that principle to an alloy gasoline powered vessel, has been drinking the coolaid from the shallow end of the gene pool. (OK Its Canada everyone knows we have to make allowances for them - must the be the snow & ice maybe).

High density foam because if the hull is ever swamped - you don;t want low density styrene because it compresses under water pressure and no longer displaces sufficient water to provide adequate positive buoyancy.

The reason to encapsulate it is because the specified polyurethane is a crumbly nature material and those foam crumbs could be carried on any water in the bilge to the bilge pump/s and block the screen/s and burn it/them out running dry.

Hope this helps clarify whats no doubt already been posted (I gave up reading after page 1).

The Alloy boat building Industry needs to defeat such plain plastic boat oriented marketing crap, by posting the correct information and allow buyers to make their own decisions.

Cheers
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Jay Perrotta
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Re: Polyurethane vs Polystyrene in Hulls

#18

Post by Jay Perrotta »

Kevin,

Thank you for the reply - and, as usual, you are smarter, by far, than me. We're lucky to have you on this board.

Why does Pacific foam? As silly as it seems I have never really thought about the question before....

Now that I've thought about it...

When I began working with Pacific I asked if they could build a 19' "V" bottom center console out of alloy. At the time they were building 20' and 22' skiffs for Alaska which had no foam, no real deadrise, no cleats, no running lights. They must have read the regulations on boats less than 20' which clearly must have foam flotation. (All boat less than 20' must have positive and level flotation - sealed air voids can be used but are not allowed to be "integral" to the hull - thus you would have to make metal air tanks and install them in the belowdeck voids - quite a bit of work and a pretty silly requirement as Kevin has already pointed out)

So Pacific was making a V19 and a V17 and to fulfill the requirements of the USCG they inject foam in the outboardmost voids and leave the centerline void (which holds the fuel tank) foam free. If and when water gets belowdecks (which should be a very rare thing) the water would be able to easily desend to the lowest and foam free portion of the hull for removal.

When the line was extended first to 22' and subsequently 23' and 26' our current customers expected and knew the boats BACK SIDE as unsinkable, foam-filled boats. Since we've never had a foam "problem" there was no reason to change. The foam also does have the great effect of making the hulls much quieter.

We have had customers request the boats without foam and we've been happy to do so (over 20').

Foam and weight add expense to the build. There is something like 7800lbs of foam flotation on the 23' hull - overkill and about $800 worth of foam. Maybe we should make it an option?

Wouldn't make sense to spend more time, effort and money to make a heavier boat that has weight gain and corrosion problems - does it?
Jay Perrotta
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Re: Polyurethane vs Polystyrene in Hulls

#19

Post by Jay Perrotta »

Hi Trouty!

I was typing while you were replying - good to hear from you again - missed you when you left THT!

Be gentle to our Canadian friends they make great beer, great hockey players, pretty women and HUGE trout:

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Re: Polyurethane vs Polystyrene in Hulls

#20

Post by Jay Perrotta »

Pjay - thank you for being open minded.

Also from: http://www.uscomposites.com/faq_foam.html#14

Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case with all after market closed-cell polyurethane foams and even manufacturer installed foams.
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Re: Polyurethane vs Polystyrene in Hulls

#21

Post by keith »

Kevin,
I always enjoy reading our posts as you have a tremendous amount of knowledge to share. There is one part of your post that I'm confused about though. You state that if the deck is pressure tested after construction and vented correctly when the boat is finished, there is no need to have foam. What is the purpose of venting an air tight chamber? If a vented chamber is compromised below the water line wouldn't the vent allow it to fill with water? Thanks for your input.
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Re: Polyurethane vs Polystyrene in Hulls

#22

Post by kmorin »

Keith,
positive pressure will vent into pressure leaks that are common to MIG overlaps or cold fusion toe and top of welds where a third piece of parent metal is added to the topsides to deck weld joint- corners, over a gusset, over a under deck transverse member for example.

In these areas the weld may 'chill' lowering fusion and an air test can catch those spots, easily repaired with a TIG torch by simply floating most of the cold fusion or higher porosity areas.

Pressure in a void in a hull will vary with temperature. PV/T= P1V1/T1 or pressure times volumes divided by temperature (in the first case) equals pressure times volume divided the temperature in the next case. This relationship or ratio stays constant.

If these relationships stay constant, lets agree (if you're will?) that the volume of the tank or chamber is almost constant- I'm ignoring the alloy expansion and contraction for this illustration; so we can ignore the volume as a constant. That means the pressure divided by temperature is a ratio that is the same/constant; regardless if the air is at 60 degrees F or 80 deg F. But to keep the RATIO the same- the pressure will increase or decrease controlled by the temperature of the air in the chamber.

Doing ratios you'll recall we know the pressure of one side and the temperature AND temperature of the other - 14.65psiA/60 F = X (psiA)/80F to solve you multiply 80 times 14.65 and divide by 60 to find X 19.5 psiA. Now, you need to subtract the ZERO pressure of 14.65pisA to get positive pressure or psiG (gage)- that means 19.5 psiA -14.65psiA is 4.85 psiG which is gage pressure. That 20 degree change in the chamber's air temp. will make a pressure gage rise in temperature by 4.85 PSI on the gage. The gage will read "0" at 14.65 psiA - or pressure absolute. But we didn't want to have to fiddle with a zero in the equation so we used absolute pressure instead of gage pressure.

OK, where are we? If the boat's air void chambers/tanks/ compartments are absolutely sealed in the shop at 65 degrees then any 20 degree temperature change up or down, in that air will create a 4.85 psiG difference inside that chamber. One square foot has 144 square inches so this force inside the tank is 4.85 x 144 = 698.4 lb. of force per square foot on the tank walls.

That adds up to some pretty impressive forces if the deck is 6' wide and 20 long (roughly) 120 sq ft. x 698 lb. is 83760 lb. of FORCE! this starts to add up quickly!!! Now consider this is against the bottom (120 sq ft) the deck (120 sq ft.) the topsides of about a foot wide strip between chine and deck up the topsides (40 sq ft) and a completely sealed deck can become a very powerful force within the boat's design. :!:

When you air test a chamber you usually test to 2-3 psiG but perhaps 1-2 psiG in huge deck areas? This tests the welds for not only pressure leaks but their opposite number. [ And very importantly confirms the fusion of 90+% of the welds inside the entire deck area]

How does most water get into a sealed deck? Vacuum. The sun goes up the boat gets wet and the deck is warmed- Jettywolf's deck is warmer than mine by far but they both get some sun. Now the air in the tank/chamber is forced into pressurization and will find or release out any vents/leaks/hatches or other release points. The sun goes away, at night or it gets cloudy and the temp goes 20 deg neg. of the daytime temp so the pressure drops 4.85 inside- vacuum. This will pull water (and fish gurrey) into welds/ through welds and into the bilge or chambers with a vacuum that is a about 10 inches of Mercury! 9.8in Hg.

The companion design feature to sealed air chambers is a vent to allow the air pressure to equalize with temperature changes- otherwise this method of construction will eventually cause flexure fatigue by differential atmospheric pressure pushing in and out on the tack/chamber walls as internal pressure varies by internal air heat expansion and contraction.

I use a small diameter half a pipe coupler welded to the decks, the put a SS tubing fitting bedded in Teflon pipe dope and use a goose neck riser of SS tube. this allows the deck to 'breath' and remain at a constant pressure during a season's use. I use a half a pipe coupler usually 1" or larger diameter at the low point of the transom/bottom seam to drain the bottom chamber in case of water in the bilge, and this SS socket recess pipe plug is removed any time the boat is out or the water- if desired.

For chambers that are along the topsides, bow, bow deck above the welded decks, transom or engine cantilevers I use a piece of pipe recessed into the side wall with a tapped plate in covering the recessed pipe. Into that tapped hole I thread another SS fitting and leave the tube cap loose and the chamber will vent and draw (breath). I've used Schrader valves (tire rim stems) and they work OK but require the owner to tend them for venting both directions.

The size of the tank vents is small; water can't fill the voids fast in any case- even if they were broken off underwater or removed. If the deck is awash and the gooseneck underwater it won't ship water at any fast rate, and all the other voids have similar volume to opening relationships so they won't 'fail' or fill in short periods.

Hope this clears up my earlier statement and adds more to the methods I've used to build safe metal boats since the late 70's?

Cheers
Kevin Morin
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Re: Polyurethane vs Polystyrene in Hulls

#23

Post by pjay9 »

blacklabmarine wrote:Pjay - thank you for being open minded.

Also from: http://www.uscomposites.com/faq_foam.html#14

Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case with all after market closed-cell polyurethane foams and even manufacturer installed foams.

You are welcome! The above paragraph states many factors, one being "submerged in water permanently"...that requires a definition of what the length of time is to be called permanent...in the case of the two boat it was obvious that the time period was just that...throw in the bad install procedures and lack of care by owners it turned out to be a disaster for the foam and surrounding structures. From this discussion it has become apparent that Pacific is a builder that does it right and therefore the foam stays as it should a DRY floatation material.

Again, Done right it is right! Now we move onto a different plane of understanding. Capt PJ :highfive:
2009 Raider 185 Pro Fisherman, 2005 90Yamaha, 2012 Yamaha9.9HT, 2008 EzLoader roller, 2004 Dodge TCD dually, 2005/2015 Lance1161
keith
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Re: Polyurethane vs Polystyrene in Hulls

#24

Post by keith »

Thanks for the reply Kevin. I wasn't thinking about expansion and contraction. Companies like ACB must make their compartments small enough and design in enough rigidity to overcome the flexing and fatigue issue.
trouty
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Re: Polyurethane vs Polystyrene in Hulls

#25

Post by trouty »

missed you when you left THT!
Who left Jay - I didn't leave I was banned by that mongrel dog Wiley - about a week after I paid my $25 capts club "lifetime membership!" Guys nuthin but a thief.

Whats it cost to put a contract out on someone in the USA these days and who do I see - the hells angels? :thumbsup: :clap:
:rotfl:

I've been banned from better establishments than he runs! :rotfl:

Good to catch up with you to Jay - I'll ease up on the canukistanians. :deadhorse:

Cheers
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