How to section stringers?? fiberglass boat

[stantonxr7]

What is a good way to section in a new section of a stringer to an old section of stringer?

I've cut out the bad part of the stringer which was from the transom forward about 50"

My current plan is to do something similar to shortening or lengthening of truck frames. My technique is to cut a vertical down half the height of the stringer, make a cross cut of a certain length (around 8") and then cut the rest of the way down the stringer. This makes a shape close to a "Z" that I would then match the profile to the new stringer section.

I would fasten the two pieces with gusset plates and fiberglass the whole works.

Is this acceptable? There's plenty of discussion on if the plywood stringers actually offer any strength to the hull or if they're there simply to create a beam shape for the fiberglass; that is in some viewpoints considered the strength of the hull. I've read about scarf beveling and don't think this an option for me.

Hoping to do this tonight and would appreciate some quick feedback. Thanks.

 

[gm280]

Stanton, when I was building my stringers I actually made lap joints for every place that I added the plywood to another piece. However, I was told that really wasn't needed and simple butt joints would be as strong. It isn't that actual joint that creates the strength but the fiber glassing you apply after the stringers are in place. So most any type stringer joint will offer a supporting setup. I know it doesn't seem that way, but when the fiberglass and risen setup, it becomes one piece anyway. So most any way you want will work. however, I know me and if I had to do it all over again, I would make the lap joints for my piece of mind even knowing it really isn't needed. Just my stupid way of thinking. :facepalm:

 

[wellcraft-classic210]

WOG will likely be along with some expert advice but borrowing from another recent post you may want to try ;

Lap joints with 45 degree angles so you can glass them //glue & screw with deck screws every 4 inches // the added pieces ( scabs ) can be as thin such as as 1/4 to 1/2 if placed on both sides.

 

[stantonxr7]

okay, thanks!

Is it preferred to use plywood as a gusset plate so that it replicates the flex of the plywood stringer? Or would it be okay to use steel plates with screws as the gusset plates?

The gas tank is a tight fit in-between the two inside stringers that I'm patching and don't probably have enough room even for 1/4".

 

[stantonxr7]

I was thinking about using the galvanized joist nailing plates that you can use for rafters. I understand this might all be overkill considering that the fiberglass is what derives the strength

 

[Ned L]

"My current plan is to do something similar to shortening or lengthening of truck frames". ............Nope, not what you want to do. Wood and steel are very different. With Steel you can take a bunch of little pieces and when you butt weld them together you can end up with the strength of a single piece. Not so with wood.

With wood, ideally you would want just a 12:1 tapered scarf. If properly glued there is no need for gussets or additional pads on the sides.

For stringers that are glassed in place you could get away with about an 8:1 tapered scarf. ------ 45? angles are too short a taper and I would not recommend that.

As far as stepped, or a "Z" shape that will not add any strength. I don't see a problem with a very small step in the middle of the scarf ONLY to keep the sections from sliding past each other when they are clamped.

Something like this when looking down from the top.

 

[Ned L]

Don't bother with 'joist nailing plates' they will do nothing. Scarf the new sections of stringers on with proper tapered scarfs and you will need nothing else. it WILL be as strong as a one piece stringer.

 

[stantonxr7]

No Title

Thanks Ned, which would be correct then? I am hoping "A" as I don't think I could cut straight enough for "B"

 

[kcassells]

Lots of opinions and options.
http://forums.iboats.com/forum/boat...-joint-vs-butt-joints-for-laminated-stringers

 

[Ned L]

"B" would be preferred. You can do it as "A", however it will require a longer scarf.

With method "B", a 10:1 scarf for a 1.5" thick stringer would require a 15" long scarf.

With method "A", a 10"1 scarf for a 6" high stringer would require a 60" long scarf.

I don't know if you do any woodworking at all. Method "B" is not really that difficult with a descent chisel and careful work. A couple of years ago I had to replace the forward 4ft of stringers in a retired raceboat of mine and "B" worked just fine (70 MPH flat bottom inboard with a 350 Chevy - not a place where I wanted problems with the stringers).

 

[Ned L]

Lots of opinions and options.
http://forums.iboats.com/forum/boat...-joint-vs-butt-joints-for-laminated-stringers

I have some problems with a number of the suggestions here. ........ Some examples of "a little knowledge is a .....".

 

[stantonxr7]

Doing scarf "B", my stringer is 1" wide by 8" tall. Scarf would be 12" long. I'm struggling to think of how one would chisel a stringer 8" deep that is still in the hull of the boat to match the new portion being mated to it.

 

[Ned L]

ahhh, ...... Hmmmmm, ....... ok, .. I understand your dilemma. I have to think about this a bit for you. In addition to being the best from a strength perspective, with a big sharp chisel or a slick, method "B" really is also the easiest and fastest way.
Let me think about some options.

How about a quick rundown on the tools you have available and what your skill & confidence levels are.

 

[stantonxr7]

I am competent enough to tackle any task with proper setup. I don't have a hand planer, or hand belt sander which i feel this method requires to get a proper fit.

I do have, circular saw, sawzall, 3" cutoff wheel, die grinders, 4-1/2" angle grinder with cutoffs, hand saws, jig saw, mudhog (8" DA), 6" DA,
Basically any mechanics and bodyman's toolset I have something.

 

[jbcurt00]

Pix of the boat and stringers would be helpful too.

 

[stantonxr7]

No Title

here is a pic of what I'm working with.

 

[Ned L]

it looks like you have lots of working space around the area. Unfortunately I'm not coming up with other easy ways to get to the 'method B' without buying a good size chisel and doing a bit of practice work on a piece of scrap 2x8 to get the hang of it. One advantage of epoxy is that it is fairly forgiving with the fit of the glue line, it doesn't have to be perfect.
Sorry, If I were close I'd be glad to stop over and make quick work of it.

 

[jbcurt00]

Based on that pix of the engine and gas tank bays, 50in of removed stringer (from the transom forward) and motor mounts doesnt look like it'd be enough

 

[gm280]

More pictures would be nice because I can't see too much from that one. But want I did see looks like you have a lot of grinding to do before replacing anything in my opinion. And I guess I didn't read what type resin you are going with. are you planning to use epoxy or polyester? Just wondering. The material you will use with either of those will be determined by the type resin you pick as well. Knowing that actual fit doesn't have to be perfect, the better you can make them match up the easier it will work out. If there is only going to be one piece of wood, then most any joint you like will work. However, if you have a few pieces of wood to joint, do stagger the joints, whatever type you chose, for a stronger setup. JMHO!

 

[kcassells]

Well then..
People learn more on their own rather than being force fed. -- Socrates (469-399 BC)
Everyone is ignorant only on different subjects. -- Will Rogers (1879-1935)
Example is the best precept. -- Aesop (c.620-560 BC)
Knowledge is power. -- Francis Bacon (1561-1626)

And here's a lot more detail from what are the usual techniques from IBoaters;

http://forums.iboats.com/forum/boat-...ice-a-stringer

At the end of the day like I said there are various options and techniques to skin your cat.