expanded foam in hull question |
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captpete
Newbie Joined: May-11-2008 Location: United States Status: Offline Points: 31 |
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Posted: May-20-2008 at 6:49pm |
Yet another question for you experts. I removed all the foam from my '86 Nautique and have reinforced the inside of the hull with additional glass cloth and resin -especially along the area where the chine meets the bottom. Stringers are good. I am going to replace the floorboards with PT plywood. Is that foam structural and does it have to be replaced? If so do I have to fill the complete cavity below my floor boards ( I know the original floor was glass over foam, which I removed). By the way, the old foam was soaked and weighed a ton! A situation I would like to prevent in the future. I also intend to glass over the new floor prior to carpet installation.Thanks guys.
Peter |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Peter, The foam is for flotation and isn't structural. The stringers are. How did you check the condition of the stringers? What's going on with the chine area?
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captpete
Newbie Joined: May-11-2008 Location: United States Status: Offline Points: 31 |
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I can drive a large nail into solid wood and the engine mount bolts are turned in tight. There are some cracks in the gelcoat along the chines on each side running about two feet about midship; one piece of gel is actually missing (about the size of a quarter). When I removed the carpet I noticed the glass floor had separated from the hull sides which prompted me to remove the floor and found the soaked foam. My guess is this allowed the gel coat to flex and resulted in the cracking. New floor will be glassed into the sides. Thanks for your prompt reply.
Peter |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Pete, Im not convinced that the foam isnt structural, at least in the newer, wider boats. While the hull of my Tique doesnt bend and bow under my weight (no floor), my '90 would depending on where I stepped. The foam provided a sandwich keeping it all solid.
You also missed an important point- you neglected to tell Peter not to use pressure treated wood! |
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80 Ski-Tique
Newbie Joined: November-21-2007 Location: United States Status: Offline Points: 38 |
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I know we all have discussed to foam or not a hundred times now but I have talked to and seen proof of that the foam does provide strength to the hull. It helps keep the bottom from deforming when hitting waves. The hull can be used with out it but you are more likely to have issues pounding in choppy water and this can lead to stress cracks. This was from a nautical engineer. I hate the water getting in the foam but I am re-foaming anyways because I have enough issues with the boat pounding as is.
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Peter, Tim's correct that I missed the "PT" abbreviation you used for pressure treated ply! If you go the plywood route, you are better off coating the wood with epoxy resin. The chemicals in the treated cause bond failure with ether polyester or epoxy. (do use epoxy)
Before you get too far into this project, I'd like you to make sure the wood is ok. Many times the tops will be good but the bottoms will have rot. Small 1" (hole saw) pieces of glass can be removed off the stringers close to the hull. You had lots of soaked foam so I'm just concerned. The foam being a part of the structure of the hull is still open to discussion! The guys are correct that the newer hull are thinner. The gel cracking along the chine/floor has several theories to the cause. Stringers, foam problems as well as having extra weight from boarding sacs. |
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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if you look at it this way, was it put in for safety or was it put in for structure?
i would say it was put in for safety and the only minimal benefit would possibly be some structural quality in using it, it has no grain so its not for adding strength.....it has no use, if the gunnels were double walled like a whaler then pumping a sealed cavity i could see its benefits. it sounds like a double edge sword...in a CC its for safety in a Boston Whaler it is a combination of both |
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"the things you own will start to own you"
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captpete
Newbie Joined: May-11-2008 Location: United States Status: Offline Points: 31 |
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Your comments are helpful. I will check the bottom of the stringers this weekend. My plan now is to add two layers of fiberglass to the hull where the foam was ( what about glassing in 1/8" luan between the layers?) for strength. The boat will not be subjected to excess pounding if I can help it. I really can not see how new foam will not become water logged again.
I will also use 1/2" plywood coated with resin and then the upper part, once installed, will be glassed. Interestingly, I really enjoy this working on boats! Most of my time on the water has been as a captain on my 31' fishing charter boat - of which I am now selling because of fuel prices. I guess this project is my "hot rod" that I always wanted to build in high school. Anyway, great being a member of this site! Peter |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Peter, Are you adding the 2 layers of glass between the stringers because you feel it's needed for hull support without the foam? Just wondering!
Adding the luan is not agood idea. First, I don't feel it's going to add structurally and also luan is a very poor choice from the standpoint of rot.(just in case you get water in it) |
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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2 Pete's... its to early
not to often do these boats take a pounding, they are flat water boats and 98% of the time they are in flat water and the the benefits of foam are non existant except for safety purposes, actually if you make the cavities pretty much air tight it is sufficient enough time for the boat not to sink and have the rescue helicopter come and plop you out from the 300 acre lake or river. in the long run foam does more harm than good. if these were ocean going vessels i surely woud consider foaming because you may be floating a little longer out there lol |
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captpete
Newbie Joined: May-11-2008 Location: United States Status: Offline Points: 31 |
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Well, that was my idea. Overkill? or How can it hurt. Scratch the luan. The two layers would be between the chines down to the first stringer.
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Im not so sure, Eric. The hull of my '90 would oilcan under my own weight in certain places. I would imagine that would make for some interesting handling on the water. It has no such tendencies with the foam and floor back in. |
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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im looking at it a from a different angle cause i could think of 10 other ways to make a boat more structurally sound than using foam, it is required and the hulls were designed around its use, since it is required why not use it as part of the structure and build the boat in this fashion, lets skimp on real ways to make a boat sound and use the foam which is required and to some extent does add a compression factor and not a twist factor, im not doubting it as to be part of the structure, but because it was required it was used as an addition to the structure,
if the foam was not required then the engineers i would guess never would use it because of cost and tie in the hull in other ways and make the hull more rigid |
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David F
Platinum Member Joined: June-11-2004 Location: United States Status: Offline Points: 1770 |
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IMHO, the foam had four original purposes in order of importance:
1. Meet USCG flotation requirements to prevent boat from sinking. 2. Provides support for the fiberglass floor. 3. Prevent oil canning of hull bottom and thus... 4. Reduce sound transmission of wave hitting bottom of hull. The boats are structurally sufficient without the foam, but why not put it back in? Today's modern foam is closed cell and will not soak up water like the old stuff. It might however trap it in places it should not be, just seal it up well and you are fine. Remember to seal all screws penetrating the floor. |
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behindpropeller
Platinum Member Joined: July-31-2006 Status: Offline Points: 1810 |
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Quit half-assing the job and put new stringers in. Why do all of that work and not replace the stringers?? |
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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to foam or not to foam, that is the question...its personal preference, and it could go either way
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"the things you own will start to own you"
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captpete
Newbie Joined: May-11-2008 Location: United States Status: Offline Points: 31 |
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I guess I opened up that "can of worms" with my question on foaming! I appreciate all the feed back. My next go around will be engine related so get ready.
Capt. Pete |
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jon4pres
Senior Member Joined: September-19-2005 Location: United States Status: Offline Points: 275 |
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I did not refoam mine when I redid it. I decided that there was no way to keep it completly dry in there. For reinforcement I glassed in some lumber to help give me a place to attach the plywood floor too.
I have been very happy with mine and have not noticed it being any louder or hollow sounding. |
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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I thought about it for a while and if you take some 3/4 ply and build 2 boxes approximately 1x2x3 square fill one with foam and one without foam and with not knowing which has the foam, and jump up and down on them with your body weight, will you know the one with the foam? and if you make them both air tight and throw them in the lake will they sink???this all of course after you glass all the corners and epoxy both sides.
what would your answer be? |
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BuffaloBFN
Grand Poobah Joined: June-24-2007 Location: Gainesville,GA Status: Offline Points: 6094 |
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I say both would float and you would be able to pick the 1 with foam!
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Yes you could tell the one with the foam only because it will float lower in the water. The foam is 2lb per cu. ft. and will add to the weight of the box. I'll still say that the foam isn't needed as a structural component of the hull. Even though we have all seen some of the "engineering marvels" of CC through the years, I'd hate to think they counted on the 2lb density foam. 2lb is not a structural foam. The Whaler construction example is totally different. It is a closely spaced inner and outer skin both acting as tension or compression members. It's hull was engineered as a system. Someone else besides Tim (was it you Greg?) mentioned months ago about the oil canning of the hull while walking in it stripped. You really need to consider that the PSI of a persons foot is a lot more than the hull sees sitting or running over the waves. The surface area of the hull really spreads out the boats weight. We also haven't heard (maybe someone else has) about a older CC with soggy shot foam with absolutely no structure left causing a hull to come apart. Gel cracking yes but is it from bad foam or rotten stringers? |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Pete, don't worry about it. This is the way we talk all the time!! We get some pretty good conversations going. Nothing lately requiring the sites administrator to step in!! Even some of our more "verbal" members have been pretty quiet lately too. |
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BuffaloBFN
Grand Poobah Joined: June-24-2007 Location: Gainesville,GA Status: Offline Points: 6094 |
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Pete, Eric said jump up and down on both boxes. I say the 1 with foam will be easy to pick out...by more than the sound. I'd even go so far as to say that whatever exact weight dropped from a given height that would break the empty box would not break the foam filled box.
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21169 |
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Pete, when the hull would deform, it would not take my full weight to do so- it didnt take much pressure to oilcan at all, actually. This was right in the area of the hull offcenter from the keel where the water would break on the hull when on plane. I really think that without the support of the foam, the handling of the boat would have been affected. My Tique has no such tendency, btw. Probably due to a thicker hull and narrower beam. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Greg, I did see that Eric mentioned jumping up and down on the boxes but felt he was talking about doing it in the water. Eric - In the water? I don't think you could tell. a 2' X 3' piece of 3/4 ply is pretty stiff.
Now, as far as the drop test, I think we could use the pumpkin patch for it. What do you think? I'll pitch in for the crane! |
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80 Ski-Tique
Newbie Joined: November-21-2007 Location: United States Status: Offline Points: 38 |
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I think with the box that small and using 3/4 ply it would be more dificult to tell, but build the same box and use 1/4" ply and even a blind man could tell. The less strength you have to begin with, the more difference you can tell with the foam. A Correct Craft is not underbuilt, don't get me wrong, but it is not overbuilt by any stretch of the imagination. That's why they are comparitivily light to many boats their size. I am sure there are better ways to do it but who am I to argue with nautical engineers. I have the floor out of mine right now and I must say the hull is not very stiff without the foam in there, the boat even with the soggy foam felt more solid than it does now. I even took it out once over the winter without the foam and floor in it, granted the floor adds a lot of structure also but mine had separated all the way around anyways, and the boat flexed and twisted so much that I made my mind up then to put the foam back and glass the floor in better than it was. Just my two cents.
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Alright, I'll give in and go along with the foam being part of the engineering CC did!!
I remember I had a friend with a 14' Shell Lake with I think a 60 outboard on it. This was the very early days of glass. The hull bottom was so thin that on real sunny days you could see through it to the lake bottom. Talk about flexing when going over rough water! It was actually scary! |
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BuffaloBFN
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Pete, when the patch is finished you can drop the whole crane in there...it'll bounce!
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BuffaloBFN
Grand Poobah Joined: June-24-2007 Location: Gainesville,GA Status: Offline Points: 6094 |
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Besides...it's original?!!?
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eric lavine
Grand Poobah Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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so if you dont use the foam, can you deviate from the masterplan and add more ribbing to ensure the floor doesnt "oil can"?, with this information it is possible to re-inforce the floors as if no foam was needed?
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"the things you own will start to own you"
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