Grinding hull for new stringers

[Baylinerchuck]

Well conventional stringers will run you less than 1/2 that cost. Time savings would not be that much IMHO due to still needing to prep the hull properly and then glass in the Prisma Stringers. :noidea:

Interesting, I have never seen these composite stringer systems before, (not that I was looking). In some of the pictures and descriptions of this system they come with the tabbing? So basically it looks like you wet it out with resin and your done? It looks expensive, but I want to do some further investigation.

 

[ImJohnnyKelley]

Interesting, I have never seen these composite stringer systems before, (not that I was looking). In some of the pictures and descriptions of this system they come with the tabbing? So basically it looks like you wet it out with resin and your done? It looks expensive, but I want to do some further investigation.

Yeah, you can build your own for less than wood would cost, but it does take more glass and resin so the savings are lost. If you buy the prisma ones they have the tabbing already on them and even a felt like material on the underside to actually adhere the underside (sorta like bedding in a wood one). Speed and ease is the biggest reason to do it. You also save a bunch of weight and they can't rot. I know they are more expensive, but I am still considering it. If I do it, I may just end up building my own foam stringers instead of buying the preformed ones. Just need sheets of closed cell and a foam heat knife. I have done a lot of building with foam in the past and would be confident in that part of it. Probably will still end up with wood, but definitely considering the foam.

 

[ondarvr]

The weight savings would be minimal, resin the same, they may not rot, but they can still become waterlogged. Nothing wrong with them, but I'd use hollow stringers before foam core.

 

[ImJohnnyKelley]

The weight savings would be minimal, resin the same, they may not rot, but they can still become waterlogged. Nothing wrong with them, but I'd use hollow stringers before foam core.

Closed cell foam can get a small amount of water, but won't become waterlogged unless the individual cells are damaged. Voids and vapor can allow a small amount, but by most standards it is only about 6-7% of what an open cell would do.

 

[ondarvr]

Closed cell foam is the waterlogged foam everyone is digging out of their hulls, it deteriorates over time and absorbs water, the foam in these stringers is no different. The likelihood of it becoming a problem is less though because it's protected a bit better, and there is less of it.

​The foam doesn't offer much strength, just a shape, so the laminate needs to be a little stronger than what's used over wood because wood provides a good deal of support on its own. The problem is if you use the woods strength and reduce the laminate, then when the wood rots you have a weak stringer system, if you don't use the wood as a structural component, and only a shape (like the foam), then if it rots away it doesn't really matter.

​If you use a hollow stringer there's nothing to protect or rot, it can be drilled or cut with no downside, it's also easy to make openings anywhere so water can drain to where you want it to.

 

[ImJohnnyKelley]

Closed cell foam is the waterlogged foam everyone is digging out of their hulls, it deteriorates over time and absorbs water, the foam in these stringers is no different. The likelihood of it becoming a problem is less though because it's protected a bit better, and there is less of it.

​The foam doesn't offer much strength, just a shape, so the laminate needs to be a little stronger than what's used over wood because wood provides a good deal of support on its own. The problem is if you use the woods strength and reduce the laminate, then when the wood rots you have a weak stringer system, if you don't use the wood as a structural component, and only a shape (like the foam), then if it rots away it doesn't really matter.

​If you use a hollow stringer there's nothing to protect or rot, it can be drilled or cut with no downside, it's also easy to make openings anywhere so water can drain to where you want it to.

From what I have read, the foam used for many years wasn't closed cell, but open cell. That the standard in boats didn't become closed till the 90's. My boat is from the mid-70's. I could have been wrong about the type of foam, just don't see anything to say that the closed cell gets waterlogged like you are saying. I am a newbie though, so I really don't have any real knowledge on this stuff yet...it's why I am asking about it. How would you make a hollow stinger? And is the water logging the only reason to make one instead of foam filled?

 

[ondarvr]

Every bit of foam used in boats for flotation has been closed cell since day 1, the problem is that over time the cell walls break down and it more resembles an open cell product. Open cell foams are also known as sponges, probably not the best thing to use for flotation.

You can either pre make a stringer shape and install it, or make a shape from something like cardboard and glass over it. Builders use a pre made grid assembly made for that exact hull, for an application like this you would just make a hollow shape.

​You can nail a couple of 2"x12"s together, wax it up, stand it on edge, then use it as a mold and make the stringers on. Remove them from the wood mold, and since they are just a couple layers of glass they are easy to handle and cut. You would use these three sided hollow shapes as the form for the stringer, cut them to fit the hull contour and glass over them, the laminate would need to be heavy enough to support all the stress. You can do the same thing over a wood stringer, only it won't be hollow, but if the wood rots away it doesn't make a difference.

 

[tpenfield]

Closed cell foam . . . lots of Internet folk lore about it being open cell, because it absorbed water . . . they forget to include the fact it took 10+ years of water immersion, winter temperatures, etc. to become that way.

 

[ImJohnnyKelley]

From what I am reading there is also a big difference between the closed cell foam of the old days and the new plastic closed cell foam and the cell structure being much much stronger and less resistant to breaking down. Like I said from the beginning, probably just gonna go with plywood stringers, but always looking to see the different stuff available and whether to use it or not.

 

[ondarvr]

There is little to no difference in the foam, the newer foam has a lower VOC content though, this tended to make it a little harder to use and maybe a little less durable.

​People look at a 40 year old boat and a 1 year old boat, then make things up as they go to fit what they think they see.