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Author Topic:   Removing Wet Foam

ChumLine posted 04-26-2009 09:20 AM ET (US)
I [recently bought] a [1987] Outrage 18 that sits low in the water at the stern. With its 150HP four-cycle motor, two batteries in console, and a full tank of gas, the water line is above the transom drain tubes and the splash well has water a couple inches deep when at the mooring. Prior to a recent re-powering the boat had a Johnson 150-HP with batteries and oil in the splash well. Static trim was about the same: above the [spashwell] drains. In both cases the boat handles great but the well gets slimey. I guess I could plug the drains but don't like the idea of that from a safety perspective. I want any additional water to self evacuate.
I replaced all the thru-hull drain tubes and found the foam around the starboard sump drain to be wet. Not dripping wet, but clearly wet to the touch with some water dripping out. Tried to dry it out over the winter with the drain tubes out.
I've seen posts by members who have cut open the boat hull from the bottom and removed and replaced large sections of wet foam. I've also seen posts from members that have cut out sections of floor decking on smaller whalers to access and remove wet foam from above. In both cases I believe they were happy with the improvement in static trim. I'm considering trying to remove and replace some of the wet foam but feel acess from either the bottom of the hull or the deck would not be ideal. I will likely replace the under deck fuel tank later this year. My thoughts are that when the old tank is out that I could cut through the rear floor of the tank cavity to access and remove wet foam. Refill with new foam and patch the acess hole in the tank cavity before installing the new tank. With tank back in and deck screwed back in place the repair would be completely out of [sight], and no cosmetics to worry about.
Any thought from the Outrage experts? How much space is there between the hull and the fuel tank cavity and would there be sufficient access to get old foam out, particularly reaching back under the splash well?

HAPPYJIM posted 04-26-2009 10:08 AM ET (US)
That sounds like more work than any benefit gained. If the boat handles fine while underway, use it as is. You can adjust static trim by adding weight to the bow. Add more chain to your anchor or just place a sand bag (like the type they use for flood control) in the bow locker.
jimh posted 04-26-2009 11:05 AM ET (US)
I would not start cutting into the hull because the foam surrounding a drain tube was damp.
If you are concerned that there is water retained in the foam between the inner and outer hull, the next time you have the boat on the trailer for an extended lay-up, drill a 0.25-inch hole into the hull in the region where you suspect there is entrapped water. Observe the hole for any outflow of water.
Peter posted 04-26-2009 06:27 PM ET (US)
I would not remove any foam which is not only there to keep your boat from sinking but also has a structural function.
Keep in mind although the approximate 100 lbs of batteries were moved to the console your Outrage is carrying about 100 extra lbs on board than it was due to the fact that the 150 4-stroke is about 100 lbs heavier than the Johnson 150. That will make it sit lower in the water even though the weight at or near the the transom is about the same.
Finnwhale posted 04-26-2009 09:16 PM ET (US)
I've been lurking on this website for the last year or so, and I also, have an 87 18' Outrage. Last year I noticed that (probably one of the few advantages we have here in the Northeast) condensation (observed earlier in the "spring") appeared on the bottom portion of the hull about 6' from the stern to the stern. So, I drilled a hole about 6" from the stern and got about 3 quarts of water out of the hull. By the way, the bilge drain tube as well as all three drain tubes in the transom were clearly leaking.
This year, I removed a portion of the shelf in front of the motor (after removing the motor) and removed about 10 cu ft of foam. It's interesting how water migrates in the urethane foam; it migrates along the foam to polyester resin boundary. I've also removed all the wood from the transom through the top and poured Nida-bond into the excavated cavity. I have already purchased the replacement urethane foam and plan on pouring it over the next couple of weeks after I reinforce the bottom with fiberglass woven roving and epoxy.
So, in answer to your question: yes, you can remove the foam from the top. It's a lot of work where you'll end up making some specialized entrenching tools and you'll end up using a mirror to see what you're doing.
Next year I'll probably remove the deck and the gas tank to get at the rest of the wet foam, but I don't think it'll be as onerous as the work I've already done...
ChumLine posted 04-27-2009 09:28 AM ET (US)
Thanks for all the responses.
I'm certainly looking for the most minimally invasive long term solution to what apprears to be abnormally low freeboard at the stern (with the weight of the 4-stroke considered) and will try temporary forward ballast and will weight the boat this summer to try to confirm or rule out trapped water. If I do try to remove foam I would certainly refill the void with new foam for the boyance and strucural support.
JimH - Great site! Thanks. I did drill drainage holes in the keel over the winter with very little water coming out but based on all I've read on this sight my understanding is that the foam retains most of the water in it as opposed to it pooling in the bottom of the hull for easy drainage.
FinnWhale - I'm interested in what you found when you opened up the splash well from the top. Lot's of questions for you:
1. Is there a large open cavity from the bottom of the hull to the underside of the splash well and forward from the transome to and under the fuel tank cavity, or are there structural supports/divider?
2. Was your foam soaked throughout or just damp? In other words do you think there was much water weight entrapped in the 10 cu. ft. you removed.
3. Do you have any pictures you can post before you foam it back in? It would be great if you could document what you found.
4. Would you come at it from the top again or consider tunneling aft from the fuel tank cavity rear wall as the patch would be easier to hide.
Thanks very much
Finnwhale posted 04-27-2009 05:24 PM ET (US)
In answer to your questions:
1. Yes, there is 14” of space between the top of the splashwell and the keel. Once you get to the gas tank and “bilge” area, the separation between the deck and hull can get as small as 2 or 3 inches. There is a “support” that was clearly installed prior to the hull being poured; it’s made up some kind of spongy open cell foam encased on two sides by fiberglass woven roving that, I surmise, was used to keep the two shells of the boat separated during manufacturing. With the poured in foam, it doesn’t really add any integrity to the boat structure. I ended up cutting them out (rather easily) with a sheetrock saw.
2. The water concentrates on the foam to fiberglass boundary. The1/2” next to the foam seems to be where the water concentrates (and the funky “support” I removed with the open-cell foam). The center of the foam was quite dry. That being said, there were “veins” of saturated foam. It was either saturated or dry foam. The funny thing is that you can be digging through absolutely dry foam, and then run into a wet vein of saturated foam. I would assume it’s because of the closed cell nature of the urethane foam. I also think that the freezing cycles we get here in the northeast don’t help much either.
3. I actually weighed all of the foam I removed and, unfortunately, some of the wet transom wood was mixed in. I removed over 200 lbs. of foam/water/wood and I anticipate I’ll be replacing the material I removed with about 80 lbs. of material (i.e., Nidabond, fiberglass/epoxy and pour foam). I do not know how much water I removed through evaporation; I made up a little “dehumidifier” with a muffin fan, light bulbs and a tray of calcium chloride. Sigh, I’ll get the pictures up on the web, eventually…
4. I would definitely do it from the stern, the way I did it. The shelf is quite wide and afforded me access to the very back of the boat where I could pick away at the wet foam next to the transom. As I said in my previous response I intend on going in from the fuel tank cavity next year and completing the wet foam removal.
By the way, the wooden transom is entirely encased within fiberglass, which made use of the Nidabond very appropriate (I actually “excavated” the foam before I found that out, I thought they wouldn’t bother with the fiberglass encasement for the entire transom).
95Outrage17 posted 04-27-2009 09:25 PM ET (US)
Finnwale,
Great info! It would be really great to see pictures. I did somewhat of a restoration to a 1987 Outrage 18 this winter. I'm just finishing it up now. The boat has been kept in the water some of it's summers here in Nova Scotia and "dry sailed" others. It has been farily well kept, but used hard (some stress cracks at the transom, etc). I noticed last summer that the actual water line was about 1" above the painted water line at the transom. It has a 1998 Yamaha 150 2-stroke. At rest there was standing water in the two outer transom drain cutouts, but not on the "floor" of the splashwell. One of the first things I did once the boat was out of the water was drill two holes at the V just ahead of the transom. Water has dripping from these holes off and on all winter (the boat has been inside). Next I removed all the thru hulls which had been leaking. I dried the foam/wood around the thru hulls with a heat gun over time, enlarged the holes (for the new larger thru hulls) and lined the holes with epoxy. Then I installed the new thru hulls with lots of sealant. I used plastic Whaler press together thru hull in the bilge and anchor locker and heavy duty bronze screw fittings for the transom (they look great). I found a couple spots of osmosis and damage (nothing real bad) on the hull bottom and dried/repaired them. I will soon fill the drilled holes in the hull. They still drip sporatically every week or two. I will fill them while they are dry.
In relation to this; I pretty much stripped the whole hull including replacing the fuel tank. Very few fittings on the boat were sealed from the factory. I'm sure this contributed to the water ingress. A lot of the problem appears to be improper assembly at the factory. In contrast, most of the fittings I have removed from my 1995 Outrage 17 have been properly sealed with the exception of the plastic bilge thru hull which allowed water in. I removed most of it using a small hole near the thru hull with heat, vaccume and time (few weeks). My boat sits high, even with the big 4-stroke on the transom. It always has though. I have noticed condensation on the hull bottom as you did. Maybe there's still some water in there. I wouldn't say it's of any concequence though.
Getting back to the Outrage 18; I did similar work to a 1991 Outrage 17 last winter with good results when it was launched last summer. The boat sat 1-2" higher in the water and actually felt different (lighter) while underway. The owners and I were very pleased. I'm hopeing for similar results from this Outrage 18, although it was in better condition to begin with. On both boats I have made every effort to ensure that all fittings, thru hulls, screws, etc are properly sealed. I think this will greatly reduce future water intrusion. There are so many points of entry, that it's no surprise to me that there's often a water intrusion problem. Even trailered boats that are kept outside uncovered, likely take on water through unsealed fittings on the deck.
- Chris
jimh posted 04-28-2009 09:22 AM ET (US)
In a Boston Whaler boat, the laminate of the outer hull skin and inner hull skin are not very thick. As a structure, without the dense foam filling the area between the inner and outer hull, the strength of a Boston Whaler boat is very low. The strength of the hull comes from the bonding of the outer hull and inner hull laminates to the dense foam core as a single structure--the Unibond hull.
If you cut out sections of the foam and replace it with much lower density foam that is just sprayed into the void, the structure that results will not have the same strength as the original.
I recommend you carefully read the instructions from Boston Whaler which are reproduced in the REFERENCE section, particularly the area under the subheading Large Structural Repairs.
http://continuouswave.com/whaler/reference/repairInstructions.html
In this case we have the further problem that the area being rebuilt is the transom. The transom has to be the strongest element of the boat's structure. It seems reasonable to me that if it is necessary to cut away a lot of the foam in this area, the structure be reinforced with some new laminated stringers or knees to add strength.
ChumLine posted 04-28-2009 03:21 PM ET (US)
Jim,
I agree with most of what you are saying and really appreciate your advice. I'm simply exploring options and want to be as knowledgable as I can be when I speak with the repair shop about what can be done to dry out a stern heavy Whaler hull. I’ve been told that the high density polyurethane foams (4 to 16lbs. per cubic ft.) are more dense than the pressure compressed lower density foam used in a Whaler and will bond just as tenaciously to the hull and the original foam as it expands. I know, that is likely the repair shop’s sales pitch to get my business. I’d need to confirm with the foam manufacturer if they agree. I do see from the link you provided that the large repair instructions suggest working with shaved down blocks of previously cured foam but I would think that would eliminate the advantage of the 2-part foam’s bonding strength as it expands in the void and permanently affixed to all surfaces. It could be that on the repair shown in the link that the unsupported fiberglass skin surrounding the opening in the hull could easily bulge out under pressure of the expanding foam.
My thoughts were that if one could access the stern area foam from low in the rear of the fuel tank cavity, essentially tunneling in and removing only the lowest couple of inches of foam above the keel toward the transom (and presumably the most water saturated), then replace the foam with a high density 2-part expanding polyurethane foam that would bond to both the hull and all surface areas including the remaining original foam structure, one could to some degree, create an internal “unibond patch” with rigid, high density foam bonding to all surfaces. While the access area is opened up and before applying foam, I would have a humidifier and fan trying to remove any additional moisture that could be entrapped. I believe the key with this approach would be to leave as much of the existing foam in place, removing only the wettest areas and proving a tunnel for air circulation to dry out the remaining foam before foaming back in.
It’s only a theory!
Finnwhale posted 04-28-2009 04:54 PM ET (US)
Chumline:
Your thinking is very similar to mine when I started. First of all, the concept of the hull's strength is through the use of a "high density foam" and a "light skin" is probably inverse to what is actually going on. If we refer to an interesting article: boatdesign.net/articles/foam-core/ where the "sandwich principle" is outlined:
"it is apparent that the core material does not directly contribute to the stiffness of the panel or beam, (at least in lower density cores) but it's the distance between the skins that is the overwhelming factor. Increasing the "d" variable will have a much greater effect on the flexural rigidity than any other component in the equation, since every other variable has a linear contribution. When dealing with higher density cores (usually > 5 lb/ft 3 ) and thicker skin laminates, the full equation must be used in order to properly predict the stiffness properties."
The whaler foam is clearly not a high density foam; indeed, it is most definitely a 2 lb/ft3 density material. So, the majority of the stiffness of whaler hulls is due to the distance between the inner and outer skins. For the 87 18' Outrage, the distance from the keel to the skin of the shelf is 14"! I'm sure that the design driver in this area of the boat was driven more by keeping the deck above the waterline then the contribution to stiffness. In addition, the polyurethane "pour foams" which I'm planning on using have approximately 2-3 times the compression and tensile strength as the "spray" foams. As Chumline has stated, the bond between the polyurethane and the skin of the hull will be "tenacious" so worrying about shear effects should be pretty minimal.
That being said, after digging around in my own transom, the idea of going back from the gas tank recess to the stern sounds painful. I had a hard enough time getting to the "bilge" area from the shelf area....
Just my two cents worth...
arctic cruiser posted 04-28-2009 05:42 PM ET (US)
where do you get the polyureathane foams you are talking about?
Finnwhale posted 04-28-2009 07:45 PM ET (US)
There are a number of sources:
www.jgreer.com/Foam%20Page.htm?gclid=CPy9lrHy3JgCFSPaDAodxSX7cg
www.uscomposites.com/foam.html
Personally, I'm using the jgreer foam since it's effective at lower temperatures (it's not that easy to get 80+ degree working conditions here in the northeast during the spring!)

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Author	Topic: Removing Wet Foam
ChumLine	posted 04-26-2009 09:20 AM ET (US) I [recently bought] a [1987] Outrage 18 that sits low in the water at the stern. With its 150HP four-cycle motor, two batteries in console, and a full tank of gas, the water line is above the transom drain tubes and the splash well has water a couple inches deep when at the mooring. Prior to a recent re-powering the boat had a Johnson 150-HP with batteries and oil in the splash well. Static trim was about the same: above the [spashwell] drains. In both cases the boat handles great but the well gets slimey. I guess I could plug the drains but don't like the idea of that from a safety perspective. I want any additional water to self evacuate. I replaced all the thru-hull drain tubes and found the foam around the starboard sump drain to be wet. Not dripping wet, but clearly wet to the touch with some water dripping out. Tried to dry it out over the winter with the drain tubes out. I've seen posts by members who have cut open the boat hull from the bottom and removed and replaced large sections of wet foam. I've also seen posts from members that have cut out sections of floor decking on smaller whalers to access and remove wet foam from above. In both cases I believe they were happy with the improvement in static trim. I'm considering trying to remove and replace some of the wet foam but feel acess from either the bottom of the hull or the deck would not be ideal. I will likely replace the under deck fuel tank later this year. My thoughts are that when the old tank is out that I could cut through the rear floor of the tank cavity to access and remove wet foam. Refill with new foam and patch the acess hole in the tank cavity before installing the new tank. With tank back in and deck screwed back in place the repair would be completely out of [sight], and no cosmetics to worry about. Any thought from the Outrage experts? How much space is there between the hull and the fuel tank cavity and would there be sufficient access to get old foam out, particularly reaching back under the splash well?
HAPPYJIM	posted 04-26-2009 10:08 AM ET (US) That sounds like more work than any benefit gained. If the boat handles fine while underway, use it as is. You can adjust static trim by adding weight to the bow. Add more chain to your anchor or just place a sand bag (like the type they use for flood control) in the bow locker.
jimh	posted 04-26-2009 11:05 AM ET (US) I would not start cutting into the hull because the foam surrounding a drain tube was damp. If you are concerned that there is water retained in the foam between the inner and outer hull, the next time you have the boat on the trailer for an extended lay-up, drill a 0.25-inch hole into the hull in the region where you suspect there is entrapped water. Observe the hole for any outflow of water.
Peter	posted 04-26-2009 06:27 PM ET (US) I would not remove any foam which is not only there to keep your boat from sinking but also has a structural function. Keep in mind although the approximate 100 lbs of batteries were moved to the console your Outrage is carrying about 100 extra lbs on board than it was due to the fact that the 150 4-stroke is about 100 lbs heavier than the Johnson 150. That will make it sit lower in the water even though the weight at or near the the transom is about the same.
Finnwhale	posted 04-26-2009 09:16 PM ET (US) I've been lurking on this website for the last year or so, and I also, have an 87 18' Outrage. Last year I noticed that (probably one of the few advantages we have here in the Northeast) condensation (observed earlier in the "spring") appeared on the bottom portion of the hull about 6' from the stern to the stern. So, I drilled a hole about 6" from the stern and got about 3 quarts of water out of the hull. By the way, the bilge drain tube as well as all three drain tubes in the transom were clearly leaking. This year, I removed a portion of the shelf in front of the motor (after removing the motor) and removed about 10 cu ft of foam. It's interesting how water migrates in the urethane foam; it migrates along the foam to polyester resin boundary. I've also removed all the wood from the transom through the top and poured Nida-bond into the excavated cavity. I have already purchased the replacement urethane foam and plan on pouring it over the next couple of weeks after I reinforce the bottom with fiberglass woven roving and epoxy. So, in answer to your question: yes, you can remove the foam from the top. It's a lot of work where you'll end up making some specialized entrenching tools and you'll end up using a mirror to see what you're doing. Next year I'll probably remove the deck and the gas tank to get at the rest of the wet foam, but I don't think it'll be as onerous as the work I've already done...
ChumLine	posted 04-27-2009 09:28 AM ET (US) Thanks for all the responses. I'm certainly looking for the most minimally invasive long term solution to what apprears to be abnormally low freeboard at the stern (with the weight of the 4-stroke considered) and will try temporary forward ballast and will weight the boat this summer to try to confirm or rule out trapped water. If I do try to remove foam I would certainly refill the void with new foam for the boyance and strucural support. JimH - Great site! Thanks. I did drill drainage holes in the keel over the winter with very little water coming out but based on all I've read on this sight my understanding is that the foam retains most of the water in it as opposed to it pooling in the bottom of the hull for easy drainage. FinnWhale - I'm interested in what you found when you opened up the splash well from the top. Lot's of questions for you: 1. Is there a large open cavity from the bottom of the hull to the underside of the splash well and forward from the transome to and under the fuel tank cavity, or are there structural supports/divider? 2. Was your foam soaked throughout or just damp? In other words do you think there was much water weight entrapped in the 10 cu. ft. you removed. 3. Do you have any pictures you can post before you foam it back in? It would be great if you could document what you found. 4. Would you come at it from the top again or consider tunneling aft from the fuel tank cavity rear wall as the patch would be easier to hide. Thanks very much
Finnwhale	posted 04-27-2009 05:24 PM ET (US) In answer to your questions: 1. Yes, there is 14” of space between the top of the splashwell and the keel. Once you get to the gas tank and “bilge” area, the separation between the deck and hull can get as small as 2 or 3 inches. There is a “support” that was clearly installed prior to the hull being poured; it’s made up some kind of spongy open cell foam encased on two sides by fiberglass woven roving that, I surmise, was used to keep the two shells of the boat separated during manufacturing. With the poured in foam, it doesn’t really add any integrity to the boat structure. I ended up cutting them out (rather easily) with a sheetrock saw. 2. The water concentrates on the foam to fiberglass boundary. The1/2” next to the foam seems to be where the water concentrates (and the funky “support” I removed with the open-cell foam). The center of the foam was quite dry. That being said, there were “veins” of saturated foam. It was either saturated or dry foam. The funny thing is that you can be digging through absolutely dry foam, and then run into a wet vein of saturated foam. I would assume it’s because of the closed cell nature of the urethane foam. I also think that the freezing cycles we get here in the northeast don’t help much either. 3. I actually weighed all of the foam I removed and, unfortunately, some of the wet transom wood was mixed in. I removed over 200 lbs. of foam/water/wood and I anticipate I’ll be replacing the material I removed with about 80 lbs. of material (i.e., Nidabond, fiberglass/epoxy and pour foam). I do not know how much water I removed through evaporation; I made up a little “dehumidifier” with a muffin fan, light bulbs and a tray of calcium chloride. Sigh, I’ll get the pictures up on the web, eventually… 4. I would definitely do it from the stern, the way I did it. The shelf is quite wide and afforded me access to the very back of the boat where I could pick away at the wet foam next to the transom. As I said in my previous response I intend on going in from the fuel tank cavity next year and completing the wet foam removal. By the way, the wooden transom is entirely encased within fiberglass, which made use of the Nidabond very appropriate (I actually “excavated” the foam before I found that out, I thought they wouldn’t bother with the fiberglass encasement for the entire transom).
95Outrage17	posted 04-27-2009 09:25 PM ET (US) Finnwale, Great info! It would be really great to see pictures. I did somewhat of a restoration to a 1987 Outrage 18 this winter. I'm just finishing it up now. The boat has been kept in the water some of it's summers here in Nova Scotia and "dry sailed" others. It has been farily well kept, but used hard (some stress cracks at the transom, etc). I noticed last summer that the actual water line was about 1" above the painted water line at the transom. It has a 1998 Yamaha 150 2-stroke. At rest there was standing water in the two outer transom drain cutouts, but not on the "floor" of the splashwell. One of the first things I did once the boat was out of the water was drill two holes at the V just ahead of the transom. Water has dripping from these holes off and on all winter (the boat has been inside). Next I removed all the thru hulls which had been leaking. I dried the foam/wood around the thru hulls with a heat gun over time, enlarged the holes (for the new larger thru hulls) and lined the holes with epoxy. Then I installed the new thru hulls with lots of sealant. I used plastic Whaler press together thru hull in the bilge and anchor locker and heavy duty bronze screw fittings for the transom (they look great). I found a couple spots of osmosis and damage (nothing real bad) on the hull bottom and dried/repaired them. I will soon fill the drilled holes in the hull. They still drip sporatically every week or two. I will fill them while they are dry. In relation to this; I pretty much stripped the whole hull including replacing the fuel tank. Very few fittings on the boat were sealed from the factory. I'm sure this contributed to the water ingress. A lot of the problem appears to be improper assembly at the factory. In contrast, most of the fittings I have removed from my 1995 Outrage 17 have been properly sealed with the exception of the plastic bilge thru hull which allowed water in. I removed most of it using a small hole near the thru hull with heat, vaccume and time (few weeks). My boat sits high, even with the big 4-stroke on the transom. It always has though. I have noticed condensation on the hull bottom as you did. Maybe there's still some water in there. I wouldn't say it's of any concequence though. Getting back to the Outrage 18; I did similar work to a 1991 Outrage 17 last winter with good results when it was launched last summer. The boat sat 1-2" higher in the water and actually felt different (lighter) while underway. The owners and I were very pleased. I'm hopeing for similar results from this Outrage 18, although it was in better condition to begin with. On both boats I have made every effort to ensure that all fittings, thru hulls, screws, etc are properly sealed. I think this will greatly reduce future water intrusion. There are so many points of entry, that it's no surprise to me that there's often a water intrusion problem. Even trailered boats that are kept outside uncovered, likely take on water through unsealed fittings on the deck. - Chris
jimh	posted 04-28-2009 09:22 AM ET (US) In a Boston Whaler boat, the laminate of the outer hull skin and inner hull skin are not very thick. As a structure, without the dense foam filling the area between the inner and outer hull, the strength of a Boston Whaler boat is very low. The strength of the hull comes from the bonding of the outer hull and inner hull laminates to the dense foam core as a single structure--the Unibond hull. If you cut out sections of the foam and replace it with much lower density foam that is just sprayed into the void, the structure that results will not have the same strength as the original. I recommend you carefully read the instructions from Boston Whaler which are reproduced in the REFERENCE section, particularly the area under the subheading Large Structural Repairs. http://continuouswave.com/whaler/reference/repairInstructions.html In this case we have the further problem that the area being rebuilt is the transom. The transom has to be the strongest element of the boat's structure. It seems reasonable to me that if it is necessary to cut away a lot of the foam in this area, the structure be reinforced with some new laminated stringers or knees to add strength.
ChumLine	posted 04-28-2009 03:21 PM ET (US) Jim, I agree with most of what you are saying and really appreciate your advice. I'm simply exploring options and want to be as knowledgable as I can be when I speak with the repair shop about what can be done to dry out a stern heavy Whaler hull. I’ve been told that the high density polyurethane foams (4 to 16lbs. per cubic ft.) are more dense than the pressure compressed lower density foam used in a Whaler and will bond just as tenaciously to the hull and the original foam as it expands. I know, that is likely the repair shop’s sales pitch to get my business. I’d need to confirm with the foam manufacturer if they agree. I do see from the link you provided that the large repair instructions suggest working with shaved down blocks of previously cured foam but I would think that would eliminate the advantage of the 2-part foam’s bonding strength as it expands in the void and permanently affixed to all surfaces. It could be that on the repair shown in the link that the unsupported fiberglass skin surrounding the opening in the hull could easily bulge out under pressure of the expanding foam. My thoughts were that if one could access the stern area foam from low in the rear of the fuel tank cavity, essentially tunneling in and removing only the lowest couple of inches of foam above the keel toward the transom (and presumably the most water saturated), then replace the foam with a high density 2-part expanding polyurethane foam that would bond to both the hull and all surface areas including the remaining original foam structure, one could to some degree, create an internal “unibond patch” with rigid, high density foam bonding to all surfaces. While the access area is opened up and before applying foam, I would have a humidifier and fan trying to remove any additional moisture that could be entrapped. I believe the key with this approach would be to leave as much of the existing foam in place, removing only the wettest areas and proving a tunnel for air circulation to dry out the remaining foam before foaming back in. It’s only a theory!
Finnwhale	posted 04-28-2009 04:54 PM ET (US) Chumline: Your thinking is very similar to mine when I started. First of all, the concept of the hull's strength is through the use of a "high density foam" and a "light skin" is probably inverse to what is actually going on. If we refer to an interesting article: boatdesign.net/articles/foam-core/ where the "sandwich principle" is outlined: "it is apparent that the core material does not directly contribute to the stiffness of the panel or beam, (at least in lower density cores) but it's the distance between the skins that is the overwhelming factor. Increasing the "d" variable will have a much greater effect on the flexural rigidity than any other component in the equation, since every other variable has a linear contribution. When dealing with higher density cores (usually > 5 lb/ft 3 ) and thicker skin laminates, the full equation must be used in order to properly predict the stiffness properties." The whaler foam is clearly not a high density foam; indeed, it is most definitely a 2 lb/ft3 density material. So, the majority of the stiffness of whaler hulls is due to the distance between the inner and outer skins. For the 87 18' Outrage, the distance from the keel to the skin of the shelf is 14"! I'm sure that the design driver in this area of the boat was driven more by keeping the deck above the waterline then the contribution to stiffness. In addition, the polyurethane "pour foams" which I'm planning on using have approximately 2-3 times the compression and tensile strength as the "spray" foams. As Chumline has stated, the bond between the polyurethane and the skin of the hull will be "tenacious" so worrying about shear effects should be pretty minimal. That being said, after digging around in my own transom, the idea of going back from the gas tank recess to the stern sounds painful. I had a hard enough time getting to the "bilge" area from the shelf area.... Just my two cents worth...
arctic cruiser	posted 04-28-2009 05:42 PM ET (US) where do you get the polyureathane foams you are talking about?
Finnwhale	posted 04-28-2009 07:45 PM ET (US) There are a number of sources: www.jgreer.com/Foam%20Page.htm?gclid=CPy9lrHy3JgCFSPaDAodxSX7cg www.uscomposites.com/foam.html Personally, I'm using the jgreer foam since it's effective at lower temperatures (it's not that easy to get 80+ degree working conditions here in the northeast during the spring!)