Boat stringers

[dancudayo]

Hi all, I got a question about putting new stringers in on my 73 MFG tri-hull. Does anyone have any tricks to cutting the stringer to match the shape of the hull? I've tried making a cardboard templet but that doesn't help me much for including the angle for the shape of the hull. Also, can they not physically touch the hull surface? I've read somewhere to use some sort of foam underneath the length of the stringer so any force on it won't crack the hull. If this is true would I do the same for perimeter of the floor? I have a west system manual that doesn't mention any of this, just to use heavy kind of epoxy from stringer trailing edges to hull, and to shape them so they round out, would this along with glassing help distribute the forces? Also, what kind of wood might you recommend for stingers: pressure treated plywood, pressure treated what I belive is pine, or I saw today some kind of pvc composite that won't rot. Any ideas would help me get this baby done, thanks all, Dan

 

[tashasdaddy]

Re: Boat stringers

exterior grade or marine grade 3/4 ply for the stringers, and sister them together at the joint. i use card board. and just use a peanut butter paste to set them in once fitted. this fills the small voids.

 

[dancudayo]

Re: Boat stringers

Thankyou for the advice Tashasdaddy, what do you mean by sistering them together? and the cardboard, doesn't it get wet or do I saturate it with epoxy to seal it up? I was thinking about using styrofoam and sanding it down to fit the contour of the hull then laying my stringer on top and glassing it in. Is that too much work or the right remedy? also, would you recommend epoxying the entire inner hull to prevent any leaks? This is my first real boat and I am enjoying doing the work, just hit a road block from lack of knowledge now and again, but heck that's how you learn the ins and outs!

 

[wildmaninal]

Re: Boat stringers

I believe Tashas Daddy means joining/sealing or (sistering) the joints (if you have any joints to be sealed. Lay paste down to fill any gaps before you lay the stringers, lay the stringers on top of the paste, if I'm not mistaken. I don't know if a protractor would be of use in cutting the angle of the stringers or not. I was lucky enough to have a piece of the old stringer intact to were I used it as a template. I used a level in my 13 ft boat to assure that they were plane or even and no humps when I replaced the stringers in it. I layed resin on the on the inner hull. Good luck on the project.

 

[dancudayo]

Re: Boat stringers

Thanks wildmaninal, how many coats of epoxy did you use on it? I tried the protractor method, but I used my nieces school one, lol. I imagine there is a better protractor for this job. I was just trying to eyeball it, not a good way for a quality job huh. thanks again, keep them coming!

 

[wildmaninal]

Re: Boat stringers

I only applied one coat of resin to the inner hull, didn't apply to thick, and you don't want to leave a spot for water to get trapped. It was my first time replacing the stringers and I am not done with that boat yet still got the transom and paint. I used a presure washer on the inner hull to clean any old dirt that settled in there, but that was my method, if you do the same watch how close you get to the hull because you can blow it to pieces. I'm racking my brain trying to figure out a solution on measuring the angle of the stringer .

 

[Nandy]

Re: Boat stringers

Ohh, God, let me try to help you with my broken English. To make a template you will need a piece of wood, like a 2”x1”x6’, a marker and cardboard or any other material you want to turn into the template. If you took the upper deck off the hull this template material should be around a foot wide and should be as long as the stringer you are trying to replace. If you are not taking the upper deck out make sure the template material will fit into the boat perpendicular to the hull thru the length of the stringers. This will make more sense later.

Let’s say we are working in the middle stringer that has no wood left on it. Your stringer is 4 inches deep and the slot (where the stringer wood was sandwiched between the epoxy or resin walls) is 2 inches wide. Grab that 2”x1”x6 and cut it to a foot long. Then measure 5”from the bottom up and place a mark in the 2” side making sure the mark is centered to the sides. It doesn’t have to be perfect but get as closed to perfect as you can. In that mark drill a hole the size of the diameter of the marker (if you are drilling the hole correctly you will be goring thru 1 inch of material, not 2). Stick the marker on the hole and secure it by glue or any other way. Make sure the marker tip is not more than ? an inch past the 2”x1”x1’. This will be your tracing tool.

Lay the side of the template material perpendicular to the hull and make sure it is also touching the outside of the stringer wall (it will be parallel to the stringer wall). Got to the transom and stick your tracing tool inside the stringer slot, with the marker touching your template and making sure your tracing tool is leveled. Start moving your tracing tool towards the bow, making sure it is in constant contact with the hull, tracing material and very important, it is leveled. This will trace the shape of your hull in to the template material. You will have about an inch at the beginning of the template and at the end where you can’t trace due to the 2 inches wide of your tracing tool but you can surely follow the trend of the trace and finish it off. If you understood the concept you can just make a slimmer tool, as wide as the marker and that will take care of those 2 inches.

Once you are done with all the stringers this way, you can use the same technique to trace the shape for the new deck. The only difference is that you will have two templates, one for starboard and one for port and you will have to add material later to make that template as wide as it needs to be so the two sides will touch the hull.

I hope it is clear…

 

[Bondo]

Re: Boat stringers

Ayuh,.........

Another way to build a Pattern is to pull a String Line from the top point at 1 end of the new stringer to the top point at the other end,.......
Then just measure down to the hull at whatever intervals will work for you,.....
1 inch where the change is steep, to maybe every 6 inches where it flattens out......
Then just transfer the measurements to your New Wood, or Cardboard Pattern...................

 

[seasprite]

Re: Boat stringers

I used polyurathane foam under my stringers when I replaced my floor on my 70 seaspite filled any gaps plus acted as glue to help hold them in place floor is solid as rock good luck

 

[Robj]

Re: Boat stringers

I used the string method and it worked great. I bedded mine in peanut butter, so any small voids were filled by the mixture. As far as the angle, which one are you referring to?

Have a great day,

Rob.

 

[dancudayo]

Re: Boat stringers

the angle I'm talking about is from side to side of the stringer where the hull curves up to the walls of boat. It's not the same from end to end of the stringer, guessing it's like maybe 30 degrees near the back of the boat, and as you work your way to the front it climbs to about 45 degrees. So the peanut butter won't make the hull to rigid? Does it have some give to it or something? I appreciate everyones techniques!

 

[wildmaninal]

Re: Boat stringers

Post some pictures of the inner hull if possible dancudayo, this might help these guys in helping you better. It might shed some better light on the subject. Was I right on the resin coating guys? Just my 2 cents

 

[Robj]

Re: Boat stringers

No, the peanut butter will not make the hull too rigid or create hard spots. A hard spot is really a stress concentration point, the hull flexes and hits something hard that won't flex. Think of poking a balloon with a pin, it will pop it. Now poke it with something that is larger, like your finger, it takes much more force to pop it. Same idea with hard spots, eventually it will cause the hull to crack at the area. If you use the peanut butter method, the peanut butter fills the gap and distributes the forces over a large area.

As far as the angle goes you can get a good estimate using trig, measuring the rise, and the run of the angle and then using the inverse tanget function on a scientific calculator. If this sounds too complicated, get a few pieces of wood and then cut them at different angles, starting at maybe 15 degrees and then increasing each piece at 5 degree increments. Use to determine the angle at 6 inch intervals along the hull. See which piece fits best and use that as your angle. An angle measuring device used to measure drive shaft angles in automotive applications would also work. They should be avaialble at most auto parts stores. The angle does not have to be that precise. Remember to leave a bit of a gap between the stringer and the hull which will be filled with the peanut butter mixture.

When you make your stringer, leave about a 1/4 inch gap which will be filled with the peanut butter, and also leave some allowance to glass over the top of the stringer.

Have a great day,

Rob.

 

[wildmaninal]

Re: Boat stringers

No,
If this sounds too complicated, get a few pieces of wood and then cut them at different angles, starting at maybe 15 degrees and then increasing each piece at 5 degree increments. Use to determine the angle at 6 inch intervals along the hull. See which piece fits best and use that as your angle.

Rob.

I was thinking about that exact same tactic myself, cut it till you get it right. Just get you a piece of scrap wood how ever long you want it, this way you won't ruin a good long piece that you have planned on using for the stringers. Cut it like he mentioned then use it for a template. I have done that myself in different types of carpentry work I have endured in the past.

 

[penst8grad]

Re: Boat stringers

Here's how I found the contour of my stringers since the originals were mulch.

Since I cut the floors out, there was a mark where the floor previously attached to the hull. I had several pieces of 3/4 inch lumber left from a remodeling project. I laid one of them across from port to starboard touching the old floor mark.

From there, I laid my 4' level from the front bulkhead to the previous 3/4 in a T-shaped arrangement. Again this used the old floor mark on the bulkhead. Using the level as a locator for the stringer I took depth measurements every inch along it's length and subtracted 5/8 in for the thickness of the new floor.

I then transferred the measurements to a piece of WELL DRIED 1x6 pressure treated lumber. The new stringer fits almost perfectly. I had access to fiber reinforced poly filler so I laid the new stringer into a thin bed of this filler.

That alone holds the stingers in much stronger than I can pull them out. When I get some free time I'm going to glass them in with 6oz fabric strips and epoxy resin.

Hopefully this arrangement will outlast my ownership of the boat.

 

[Robj]

Re: Boat stringers

Unfortunately with boat stringers, there is always the possibility that there will be some water ingress. With the peanut butter mixture it will prevent the water from spreading. With your poly filler mixture it will turn to muck. I would not use that stuff to bed stringers. Use peanut butter, which is a mixture of resin, cabosil and chopped fibres, mixed until it reaches a peanut butter consistency.

Have a great day,

Rob.

 

[dancudayo]

Re: Boat stringers

WoW!!! You all have been extremely helpful! I don't know about that trig. stuff, I'm just a produce clerk, lol. The methods should definitely give me a leg to stand on. I have some of that poly-fiber epoxy stuff, it's mostly used for auto body but I was thinking I could use it for my peanutbutter, what do you all think? I will try to put a picture on here one of these next days, I just need sometime to figure out how to do it. Thank you much everyone!

 

[rebuilt]

Re: Boat stringers

Don't know about the pre-made goo, but US Composites was a great source for 1/8", and 1/4" milled glass, as well as Cabosil. Home made peannie butter. Nice folks, good service. Oh, yeah, their pourable foam prices beat the livin daylights out of what iboats prices theirs at. Another 2 cents worth. K

 

[dancudayo]

Re: Boat stringers, update

Re: Boat stringers, update

Hey all, I got my stingers cut looking much better, not perfect but I belive the epoxy with cabosil will fill it in nicely, would you recommend some fibers or is the cabosil enough to thicken it up? I also decided to cut out the old transom for replacement, it wasn't horrible but might as well do it while I got her all broken down. Let me just say, the angle grinder is a man's best friend! Before I purchased this I was spending forever using my air rotary sander with 24 grit paper, forget about it! I went to ace and got a cheapo angle grinder for 20 bucks and some of them 24 grit discs that overlap each other, it was like cutting through butter! Thanks again for your help!