Wood Vs Foam stringer question

[Tail_Gunner]

Recently ive just foamed my boat with 8lb two part foam. This stuff is so incredbily strong and stiiff iam just wondering why this type of foam is not used as a complete replacement for wood stringers.<br /><br />I guess i am also a bit worried if the strength of the foam is going to create some type of over kill in the boat ( structal failure) there seems to be no flex what so ever. I assume there should be some type of flex avaible?

 

[dmarkvid2]

Re: Wood Vs Foam stringer question

As strong as that foam appears to be, I think there is a good chance that it would snap under pressure, where as the wood stringer would give and flex.

 

[BrettNC]

Re: Wood Vs Foam stringer question

There are some manufacturers that are doing just that. Depending on the configuration, the fiberglass sheathing is where most of the strength is derived from anyway.

 

[bigbad 4cyl x2]

Re: Wood Vs Foam stringer question

im thinking with the 4lb i'll be getting better impact resistance and better water intrusion protection from a small hole or somthing . as well as " locking in the stringers " for strength.

 

[Purduebarry]

Re: Wood Vs Foam stringer question

I've read your posts on this from some other topics and it seems that you are bummin a bit and now wished you used the 4lb. <br /><br />Is there anyway to cut some expansion joints in the foam. I got to thinking about this and using the mentality that concrete (hard like 8lb.) has expansion joints to control the expansion and contraction etc. If so, you could provide some flex in critical areas where you think you should have some. Not just a slit but ream out a 1" or so. You could then use the 2lb. (from home cheapo) to fill in the gaps (joints) so you don't "squeak" across the water. <br /><br />You could use a really long bit to route the joints. Like the kind they use to rough in plumping and electrical on homes. Just be careful to not go too deep with a cut and get into the hull, glass etc. This could be done eaisily enough with some type of homemade depth gauge. They also have long razor type knives at commercial caulk suppliers. They use these to remove glazing and caulk joints on commercial structres. Might be safer than power tools provided you have the access you need to the areas you want to "cut out" a joint or two.<br /><br />Just a thought...hey I'm I guy, we always try to come up with solutions , ask a woman and you might get a different answer. They probably like stiff boats ! <br /><br />On the other hand, call up one of the techies from a performance boat manufacturer, Fontaine etc. Ask them about your situation, hull stiffness, flex, they might use the 8lb or harder to provide structural integrity. You may have built a damn high performance hull and don't have anything to worry about !!!

 

[bigbad 4cyl x2]

Re: Wood Vs Foam stringer question

 

[Chief101]

Re: Wood Vs Foam stringer question

In over 6 years of using 7lb. foam I find it extremely water tight and strong. I don't know what your boat is or how much you used but I am sure if you used the right amount and applied it correctly it will do the job. I havn't done the testing to know how much you need to use so you are an experiment in the works. Chief

 

[Tail_Gunner]

Re: Wood Vs Foam stringer question

Frankly im a bit to reactionary,and i read far to much. In replacing my stingers i was concerned with hydrolic vibration so i set them in 1/4 in bed of a urathane type product (3m 8609) both the bottom and top of the stringers. After that i bonded the bottom of the stringer's to the hull with west system's using it a peanut butter like form (thanks to realgun) Now i thought that was a very competent design. Then i used the 8lb foam, i tied the deck or screwed it down to the center stringers leaving the outside edges free. Snapped a chalk line on the sides that was level and watched the foam raise the edges level and just stood on them to keep the foam flowing where it needed to go.<br /><br />Now here come the amazing part, the floor is so stable or rock hard it worries me, it indeed is like concrete. and i have not even glassed it, normally that would be a good thing. But now i have a light weight cement hulk in my boat.The only thing that seperates it is a thin skin of fiberglass (hull) and i cant help but wonder what that might do to the orignal design of the stingers.<br /><br />Im sure there will not be any weak part in the frame or the foam but, what will happen to the fiberglass skin or maybe the overall design and the hull.

 

[Purduebarry]

Re: Wood Vs Foam stringer question

Did you make that call yet??? Stop second guessing and just finish it. I'd rather have too little flex than too much. In your mind this thing is going to slam a wave and bust all to pieces. Look at it on the bright side you'll have a nice hunk of foam to hang onto if it does happen. What do you think makes Whalers unsinkable? I'd bet it is 8lb. foam framed in glass, probaly isn't a darn stinger in the thing!

 

[Terrulle]

Re: Wood Vs Foam stringer question

Yes, Boston Whaler uses two Steel molds attached together. A top inner boat mold and a bottom hull mold basically bolted together. The steel molds have vent holes where they are connected(where the rubrail is placed). They are then injected with high density foam. The foam is constricted so that it only fills the void between the two laminates and excess flows from the vent holes making it an even more dense foam that bonds the two laminates together.making it one solid hull. You shouldn't have any problems. T.

 

[Chief101]

Re: Wood Vs Foam stringer question

Wear your pfd while you're out on the water if you like, but I think you will be just fine. Chief

 

[Tail_Gunner]

Re: Wood Vs Foam stringer question

Originally posted by Chief 100:<br /> Wear your pfd while you're out on the water if you like, but I think you will be just fine. Chief

You can be sure of that. Talked to some engineering types...........No problem....

 

[Purduebarry]

Re: Wood Vs Foam stringer question

One last jib, since I'm considering which lb to use myself I've spoken to several "experts" in the area. When I asked about your overkill 8lb, they said so long as the rigidity is consistent throughout, meaning stiff in one void and soft in another would create an imbalance and different rates of flex. Bam, not good! However, you did the whole boat this way so you have a big firm boat now and should be good to go. <br /><br />Id be interested to know if your ride is smoother or more choppy. Stiffer cuts better or worse, sort of like riding on tires with too much air?