Another floor/stringer question to add to the mix

[mikemerrill50]

So, i've read about stringer repair, and I know how to spot rot, which is why i assume almost all of the stringers are bad in this picture:<br /> http://image57.webshots.com/157/1/89/60/530718960RAleIG_fs.jpg <br /><br />When I kick the stringers from the side, they are all sturdy to about 2ft. away from the stringer damage you see in the picture.<br /><br />According to www.rotdoctor.com, the point of the wood in stringers is to form a mold for the fiberglass to be laid on, not necessarily for structure. I don't know if this is true, but it seems to make sense. When I make an automotive speaker pod, which may be a layer or two of fiberglass, I can jump up and down on it without it breaking. So, the 5 stringers in this boat, even if they didn't have wood in them (or the wood was rotted), should easily support the floor with just fiberglass.<br /><br />Anyways, what I am wondering is, instead of replacing or removing all that wood, would the stringers be structurally sound by simply roughing up the stringers and adding several coats of fiberglass to them? I am also thinking of doing the floor in two layers, for a total of 1.5" or so, for added support.<br /><br />For more pictures, go here:<br /> http://community.webshots.com/album/530653041gHTxRa/0 <br /><br />Thanks, guys. Yall have already been a big help.

 

[JasonJ]

Re: Another floor/stringer question to add to the mix

I would not recommend running a floor that thick, it is not needed. You plan on foaming, the foam will add the support and be considerably lighter that that thick floor. My floor is 1/2 inch thick and the voids underneath are fully foamed. Rock solid with no flex is the best way to describe my floor. <br /><br />You could, in theory, get some Seacast and fill the voids where the stringer wood was and have a rot free structure, but that is a bit of cash to spend. In the end, the cheapest most effective structure would be to put new wood in, and make sure it is actually bonded to that stringer glass. Unless the stringer glass is at least 1/4 inch thick, top to bottom, it is unlikely that the stringer glass alone will give the same support as the stringers with wood. Good luck...

 

[BillP]

Re: Another floor/stringer question to add to the mix

That is called a "hat" stringer...the name was coined by Owens Corning in the 1950s. The core is used only to shape the glass and strength is 100% from the glass. Weight, cost and labor are generally higher than using wood stringers. That's probably the ONLY reason it isn't the standard way stringers are made in production boats today.

 

[epresutti]

Re: Another floor/stringer question to add to the mix

Mike,<br /><br />There are two things I see in your pictures, first it looks like there is a lot of water penetration into your stringers, this is going to definately add weight. The second is up by your steering the stringers have no continuous glass along their length. I would think at the point where the roving stops (where the gap is) and before it starts again would be a weak point.<br /><br />I am not a structural engineer. It appears to me if you slam the bow down you could fracture the hull at that point.<br /><br />BillP and Jason, what do you think?<br /><br />These are my thoughts.<br /><br />Peace.<br /><br />Ed.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

yeah, up to about a foot back from the messed up roving, if i kick, the stringer bends. I am planning on trying the "hat stringer" idea. does anyone know the pros and cons of hat stringers? also do you think i should use fiberglass cloth, mat, or roving? i would like to do several layers of whichever i decide on. i have never used roving before, but I have worked with cloth and mat. the example i used above of being able to jump up and down is with cloth or mat. if i do 2-3, or even 4 layers of mat, I think it would definitely be strong enough, but I'm no boat expert. it seems roving isn't as strong when nothing is under it. mat and cloth, however, do fine, at least in automotive applications.<br /><br />thanks!

 

[epresutti]

Re: Another floor/stringer question to add to the mix

Mike,<br /><br />I used double Biased stitched matt for my stringer repair. It is basically woven roving that is stitched to matt, the double bias is woven in two directions, really tough stuff. Hard to wet out though, really soaks up the epoxy. You can encapsulate the stringer in a single application.<br /><br />I don't know anything about the "hat" stringers, sorry.<br /><br />Peace.<br /><br />Ed.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

above, BillP said a hat stringer is simply a stringer that uses the fiberglass for support instead of the wood. the wood is mainly used for the mold, and the fiberglass is layered itself to protect the floor.

 

[BillP]

Re: Another floor/stringer question to add to the mix

Do a cross section of a glassed stringer. The glass looks like a hat...top, sides and brim. That's where "hat" comes from.<br /><br />Mat is measured in oz per sq ft (1.5oz mat is 13.5oz per sq yd)and roven woven measured in oz per sq yd. Mat is cut random fibers and stiff compared to woven roven. Mat conforms and adheres to surfaces better than woven roven. Woven roven is continuous strand and strong on that axis. Use both together in alternating layers for stiffness and strength. You can rotate the woven roven to get the same effect as biaxial.<br /><br />I couldn't tell much from the pics except that you have a lot of stringers and can see woven roven (probably 18 or 24 oz) over them. It is a lot of work to pull the stringers out (especially if they aren't totally rotten), grind the hull smooth, fit-cut-install new wood stringers and glass them in. <br /><br />This boat might be a good candidate for using the old structure as a form and glassing around the old stringers "hat" style. If the wood is wet you can drill 1/2" holes down into the stringer tops to air dry and put fans on 24x7 for a week or two. Use masking tape (or anything you can think of) to seal the hole tops before glassing...glass adhesion isn't a factor here. <br /><br />Glassing over the stringer tops is a PITA with thick glass if you try to do it with one piece. I do the sides with one piece and and then glass the tops and overlap it down on the stringer sides. How much and what type glass can be done many ways. I prefer to bulk up for glassing stingers so my choice is old tech 1.5 oz mat and 18 or 24oz woven roven in alternating layers. On a boat like yours it would be 1.5 mat, 24oz woven roven, 1.5 mat and 24 oz woven roven around each stringer...no less and maybe one or two more layers. Biaxial works too but you need to take more care in glassing with it.

 

[JasonJ]

Re: Another floor/stringer question to add to the mix

I don't know, if it was me (and it was), I would cut it all out, grind it smooth, and glass in some fresh meat. You could have it all out in a day or so, and having fresh meat is the ultimate peace of mind. On the other hand, Bill's way will definately get it done quite well, you'll just really need that wood to be dry or you'll always have it in the back of your mind that there is festering wet stringers under your feet.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

do you guys think i should keep all 5 stringers? i imagine I should, but i figured i should ask. i'm looking for good, cheap sources for fiberglass materials. any ideas? also, for 5 18' stringers, how much epoxy resin do you think I would need?<br /><br />thanks again, mike

 

[epresutti]

Re: Another floor/stringer question to add to the mix

mikemerrill50,<br /><br />You may want to consider using polyester resin, I used epoxy for my entire rebuild and have come to the conclusion that I should have used poly, this is mostly due to cost and ease of sanding, epoxy is a bear to sand. Additionally, you can certainly get the strength you need, this is how the boat was put together in the first place.<br /><br />Further, once you use epoxy, you cannot use poly, it will not stick to it. Also epoxy will not take a gelcoat and should be painted.<br /><br />You should definately keep the structure as was design, removing parts will change the structural integrity of the hull (good or bad who knows).<br /><br />I use Fiberglass Coatings Incorporated for my supplies.<br /><br />Peace.<br /><br />Ed.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

ed, thank you for that extremely informative reply.<br /><br />my likely process is as follows:<br />fiberglass up the sides, cut the cap off, remove the rotted wood, the fiberglass a cap on.<br /><br />i am thinking of using 1 layer of 1.5 oz. mat tape, one layer of 18 (or would 24 be better) roving, one layer of 1.5 oz. mat tape, and then a final layer of roving. is that a good process? is the roving really necessary? I'm wondering if it would be better (it's definitely cheaper) to do 4 layers total of mat tape instead of 2 tape / 2 roving. i would prefer to do 4 layers of mat tape, and i imagine it would be good.<br /><br />how much resin do you think i would need to do 4 layers of fiberglass in 5 18 ft. stringers (actually the outer ones may only be 12 ft.)? i was just gonna go with lowe's, but i'll check out that website.<br /><br />thanks!

 

[JasonJ]

Re: Another floor/stringer question to add to the mix

I would stick with the same number of stringers. If you use less stringers, you have less structure, and that is not a good thing. Good luck..

 

[BillP]

Re: Another floor/stringer question to add to the mix

You can use all mat on stringers but it is more brittle than roving woven...many boats were built this way in the early days. The combination of mat and roven is best.<br /><br />The amount of resin you need is calculated on how many oz of fiberglass you use. Baseline 1 oz of resin for every 1 oz of fiberglass. Remember that mat is measured in oz per sq FT and woven roven measured in oz per sq YD. Measure the area and convert to sq yds OR sq ft, total them and that is how many oz of resin to use. Depending on your glassing style (wet or dry) it can be more or less. Benchmark yourself on the first glassing area and use that for your formula.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

it has woven roving now that's a bit soft, but i am going to cut the cap off. what i might do is run some resin over the remaining part to stiffen it. then i'll do one layer of mat, one layer of roving, and then one more layer of mat. what i will eventualy have is about 3 layers on top and 4 on the sides. or, i might do an extra layer of mat just to be sure. I have about a week of spring break to work on this, so if I don't finish it, I can always resand the stringers and add more in another 2-3 months, right?<br /><br />thanks again, guys! this forum is tons of help.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

also, i'm looking on http://www.uscomposites.com/polyesters.html <br /><br />which do you think would be the best resin to use? i was thinking the 700 Vinyl Ester Resin or B-440 Premium Polyester Layup Resin seem to be the best. but would the cheaper EB General Purpose Polyester Resin do just fine?<br /><br />thanks!

 

[BillP]

Re: Another floor/stringer question to add to the mix

Vinylester sticks best but costs a lot more. I would go epoxy before spending the extra on vinylester. If money is an object use the general purpose laminating resin...that's what your boat was made with. Make sure it IS "laminating" resin and not "finishing" resin. Laminating stays tacky for weeks and requires no sanding between coats. This lets you do a little work at a time without the pain of sanding. For prepping, use styrene to wipe the surfaces down before glassing. It chemically links the old and new resins together. Some people use acetone but it is only a cleaner. Styrene is superior for this application.

 

[mikemerrill50]

Re: Another floor/stringer question to add to the mix

on the website i mentioned, the vinylester is cheaper than the epoxy, so I'm gonna go with vinylester. it's about $37 a gallon on the site, and the epoxy is more like $50.

 

[BillP]

Re: Another floor/stringer question to add to the mix

Vinylester is mostly used as for boats that sit in the water full time and are subject to osmosis. Even though is is more tenacious, there really is no other major gain in using it instead of general purpose poly for trailer boat projects. If you prep well, do standard poly, if you don't prep well and need gap filling/gluing properties, use epoxy.

 

[Mark42]

Re: Another floor/stringer question to add to the mix

BTW, old Chrysler boats from the 60's and 70's were made without any stringers. They attached the floor to the hull and then filled the space under the floor completely with foam. Foam has good adhesive properties and "glues" the hull and floor together. Light, rigid and unsinkable. <br /><br />If you were to go this route, I would suggest top grade 3/4" marine ply for the floor. Epoxy it to the hull. Also make sure the inside of the hull is completely clean and roughed up so the foam will stick well. <br /><br />You will have to compare the cost of foam to the cost of epoxy/resin for making the stringers to see if it's cost effective.<br /><br />Kind of a neat and proven alternative to stringers in boats that size. Something to think about seriously.<br /><br />I think that's is the Manatee I had my eye on at the liquidator. Nice to see its being overhauled.<br /><br />Good luck and keep us posted.