To bed or not bed stringers that is the question
 

I sent out a post earlier about why stringers are not touching the hull and received some explanations. I get it about hard spots and stress points which are why stringers, bulkheads are not directly in contact with the hull. So I have a couple of question I could use some help on.
First in reading up on replacing stringers from different post and sites it seems like there are two trains of thought. One method is where stringers/Bulkheads are suspended with a gap under them and then glassed to the hull using vinyl ester resin with 1708 cloth.

Second way I keep reading about is where the stringers are “bedded” in some type of compound from liquid nail all the way to “peanut butter” made out of carbosil and resin and then covered in 1708 and resin (vinyl ester) So if stringers are bedded on this manner are they not hard spots or stress points? Working with resin and carbosil makes for a hard compound when cured.

Third what is the best way to support the boat when cutting stringers and bulkheads out. Granted in my case there is not much there, as they are rotted out however the glass coming up from the hull is acting as some kind of support I would assume. The trailer has full length bunks three per side (older picture when I was working on gel coat)
Thoughts ?
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Cabosil and resin, and use a plastic spoon to do a fillet on either side of the stringer. Or a flexible plastic spreader cut to the fillet radius you like.

i use CoreBond to bed in stringers and transom. You should always bed them in, never been a fan of "suspending" anything or any sort of gaps in a build. When i fit superstructure theres very little gaps anyway. 3M makes a real nice version of corebond thats only like $135 for a five gallon pail and it works well. Easy to use with a long pot life. I use to use Cabosil but its just to easy (and better anyway) to use a per mix.

I built everything so tight that I never had to use a shim to hold anything in place and I went with the cabosil mix to make a nice radius. Good point by Dave on the core bond being easy to use I would recommend that as well, I just used what I had on hand and cabosil/resin is time consuming to mix up but its not cost effective since a 5 gal of vinyester resin is $180 vs corebond at $135

I never understood the thinking on leaving "gaps" so theres no hard points on the hull, theres no need for suspension built into your structure

I left boat on a myco trailer to redo stringers and everything is fine, you want boat sitting in most natural state if its possible

As long as i have been doing this i never followed the "hard spot" thing either. My guess is it was a way to justify poor sloppy build techniques in budget line boats where they were floppy fliers anyway. The hard spot thing really applies best to deck repairs where you want to keep good surface continuity, which is essentially your goal with any repair (continuity and control)

for those of us who are barely able to follow this conversation what do you guys mean when you talk about hard spots?

Hard spots. I think there are more qualified people on this post than me to explain, but I will give it a shot. If you (I did) go out on the web and type in replacing stringers, or look at some other posts, on other sites, there is talk about not letting the plywood touch the hull because it can create a stress point along its length, or if there is a high point on the wood stringer, that point would be a “hard spot” that would, or could (as explained by others) create a stress point on the hull that could (again by others) create a fracture or failure point. I pasted an excerpt from the website boat builders central to help explain the "hard spot" comment.


There are two points to pay attention to when installing the stringers in the hull.
There should be no hard spots and the top of the stringers must be in the same plane.
Hard spots are points where a part pushes hard on the hull. (This happens only with plywood stringers.)



Hard spots concentrate loads and are dangerous. They can lead to cracks or hull failure. A stringer should distribute loads evenly all along it's length. The ideal way to install stringers is a little bit above the hull. Builders should start with a stringer that follows the shape of the hull within a 1/4?. They can use small pieces of foam to lift the stringer from the hull and fill the gap with epoxy putty while building the fillet.

Guys,

Thanks for the help. I did not realy get the suspended stringer concept. Thanks for clearing that up as "not "a good idea. Anyone work with (Meranti/Keruing Mahogany "Hydrotek")plywood. It is supposed to be or carry the BS 1088 stamp for boat building. Or is there better materials to work with?

If you do decide to use resin and cabosil, pre-mix a bunch of it so you only have to add catalyst to it later on. It takes quite a bit of cabosil and thus mixing and time to get the thicker consistency, eventually I just took the last couple gallons in a pail and used a drill mixer to mix up a big batch. Keep it covered and then just scoop out what you need, when you need it.

Nothing wrong with that wood other than the $127 a sheet price. Regular marine ply runs around $80. Decent Arauco plywood runs around $40 at Menards, these are all 3/4" prices.

Keep this in mind, most likely your boat was built with the cheapest wood they could find, and built as fast and cheap as possible, obviously not properly sealed which is why you are replacing it, and it lasted for 25 years (assuming the boat in your info). Decent Arauco properly prepped and sealed will easily last another 25, and will be 1/3 of the price.

Hey LarryL - please keep posting more pics of your project - I'm doing the same thing on a 22' boat and since GlassDave hasn't published his book yet I need all the input I can get! That was a friendly 'jab' to GlassDave to get movin' on the book - by his past postings - he is a HUGE wealth of knowledge and has been very helpful to a lot of guys doing 'projects'!!!!!!

Its funny this topic should come up.....i just got my Boat Builder Mag last night and theres an article in there on a military boat they are building/testing. I haven't read the whole article yet but skimming over it they mention that the bulkheads are attached to the sides of the hull and then bedded with a flexible mastic...the only place they have stringers in in the engine compartment. This idea is to allow the hull to flex during running...they say it flex's several inches!
In my mind no matter how the stringers are bedded down to the hull you will have a "hard spot" under it as the sides around it can "potentially" flex....

This information is a great help. c_deezy you make a great point about being built fast and cheap. And yes it is the boat in my info. Glass Dave mentioned in one of his other posts that they were not the best built.
Arauco plywood? looked that up and it is supposed to be pine based and I though that pine was not a good wood to use due the oils in it. Lots of comments about using only doug fir (yes I know it is in the pine family) plywood or the expensive stuff Meranti/Keruing Mahogany "Hydrotek. I dont know just asking questions. and yes I would like to keep costs down however, for he amount of work it going to take to replace most of the stringers and bulkheads, there is not going to be a second time in this boat.

Ok I was searchng the web for CoreBond and that name seems generic. or I am looking in the wrong place. I was able to find 3M Nida bond core bond is that what Dave is talking about? Even in that product line there are two types, 3M Composite Bonding Compound, All Purpose 11110 or 3M Composite Bonding Compound, Radius Filleting 11113. The only other one i seem to come up with is ATC Core-bond 70 Adhesive.
Thoughts?

On the light weight jet drag boats I bed the stringers but float the bulkheads on the side and deck so they don't photogragh

I've heard/read about pine and the oils, don't really recall what the general consensus was.

When I redid mine, the original stringers were dimensional 2X lumber, and the transom was exterior grade plywood held together with staples. There was about 3 layers of glass on the transom stringers, 2 layers on everything else and even with the wet spots and rot that glass was still stuck to the wood after 20 years. I did use marine ply on the transom, Arauco everywhere else. The failure/rot that necessitated the replacement wasn't from the wood itself, the failure(s) stemmed from not sealing cutouts in the wood.

There is nothing wrong with wanting to use the best materials you can find, I was just suggesting an alternative thought or option. I would suggest you cut it apart first and see what the factory used, then order your materials and improve upon what was done originally.

As far as the hard spots go I think its more of an issue with a non-cored, thinner glass layup.

For example, take a look at this thread by a boat being layed up by the legend. That bulkhead looks like its right up against the hull to me, and very little fillet under the tabbing.

http://www.offshoreonly.com/forums/g...ml#post4027756

Hard spots are caused by too little contact area. Think of a piece of window glass laying on a flat surface, you could walk on it and chances are it wont break. Put a pebble under it and walk on it and it will shatter. If an inexperienced person were to fit a bulkhead and it only made contact in a few places, it would most likely cause stress cracks on the outer gel over time. If it is fit correctly and not forced into position, it should be snug and also filled to eliminate any gaps. As far as the lines you notice on the outside of the hull from bulkheads, that is generally caused when it is in the mold being built.

Yep 3M NIDA Bond is what i use, bad habit i use the term CoreBond generically and that is the ATC product. I pay $135 for a five gallon (more like four in it hough lol) and it is is the general purpose composite bonding compound.

For wood i use a simple marine grade Douglas fir i get from a local higher end wood supplier. You can use stuff from the big box stores but it is not ideal and its is true pine has oils that can cause problems ( i would just stay away unless your just trying to get a few more seasons out of your beater Bayliner lol) Your choice of wood is not near as important as how it is put in and maintained, heck I could do a boat in OSB that would out last a poorly installed Lloyds certified Okoume :D.

For what we are doing it is still best to use traditional methods, old school for the most part. Fit is everything when doing stringers and bulkheads, balanced laminates. One of the things i also do to help minimize "hard spots" or stress risers is stagger the laminates or tabbing graphic (below). The ends of each layer are shorter then the last and the final two layers of tabbing are offset so you dont need two different widths of tab tape. This will help minimize telegraphing but will not eliminate it.


The mil spec boat mentioned is a pretty sweet rig, just saw that in PBB but keep in mind that is one highly engineered structure as a whole. I havnt read the article yet but i believe the hull acts as a suspension system.

Thanks glassdave. I get the picture. Fitment and the installation is the key over everything. (I included some pictures of the lack of fittment [in spots it is up to a 1 insh gap] which we will correct I agree the best materials in the world will not make up for sloppy craftsmanship. Thanks for taking the time to explain. :) I’ll bet that picture of the stringer layup is in or will be your book! Put me on the reserved list for first edtion!:)

Katanna, Thanks Good explanation using the glass example about the hard spots. Makes sense when you think about it in that way.

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If other want I can post some pictures. Right now all I have is ones that show the damage. Don't know if I should carry the rebuild here or ??? I agree the glassdave and others provided great incite on how to go about this project.

Thoughts?

If you would like to document the thread, I would say start a new thread. It helps to document rebuilds so other guys can see the work done and possibly attempt something similar on their own.

For example - http://www.offshoreonly.com/forums/b...ld-thread.html

Hey LarryL - can you confirm which 3M bonding compound you ended up using 3M 11110 general purpose or 3M 11113? Thanks and any more pics of your project?

I use 11110, sorry i didnt catch ya on the other thread just been super busy in the shop.

So how much does a typical transom need? I suspect its only sold in 5 and 55 gallon barrels only. Stuff is $$$$$$$$! Shipping cost and it's a hazmat product.

maybe two gallons for a typical transom and bilge stringers, sometimes as little as a gallon though for just a transom. where are you located? I get a five gallon pail for $135 and dont pay hasmat when truck freight FedEx but I am usually getting several items on a full pallet.

Thanks Dave! I'm in Phoenix Arizona and haven't been able to find any locally. Any ideas? If I could order a 5 gallon pail from where you get it, that would be awesome, although prob not as you are getting it bulk.

THANKS for the clarification GlassDave!!!!!! Still waitin' on the first issue of your book!!!! LOL!
Any recommendations for using this product this time of year (we're averaging about 65 - 68 degrees) during the days.....Not sure if the instructions give clear details on amounts of hardener for various temperatures

Hi Glass Dave, Where do I get Corebond?

Sent you a PM regarding where I located it fairly reasonably priced. Cheap HAZ MAT shipping as well.

Hey Borgie - I'm not sure if you were sending me a PM regarding where I can purchase the Corebond bedding compound, but I've been reading your posts and would appreciate any recommendations for the 'bedding compound' you used on your transom repairs I'm in Sacramento, California - Thanks!

This is the cheapest I was able to find online. Very reasonable shipping!

https://www.apdmro.com/mobile/Produc...de=70006474343

Hey Borgie - THX!!!!!

You got it! Looking forward to seeing your project!

Thanks! I'm doing a 1985 22' Vaughn - (we restored one almost two years ago and posted the restoration on RiverDavesPlace) that turned out AWESOME!!!! It was originally set up as a outboard that we reconfigured into a BBC with Bravo 1 drive. It looks and rides just like a 24' Schiada. Hope to start grinding out the old wood on the transom next week! Thanks for the lead on the 3M product!!!!!

Here's a few pictures of my stringers which I bedded in on the floor side with 3M Corebond, and used West system 404 adhesive filler on the back side and at each end.

http://i1140.photobucket.com/albums/...psv1imz5tl.jpg

http://i1140.photobucket.com/albums/...psmknx8qsv.jpg

http://i1140.photobucket.com/albums/...psgnucxxjx.jpg

WOW! Nice job!! How much Corebond did you use for the transom and stringers?

Thanks! When all is said and done with transom, stringers and fillet work, I will have used 4 gallons out of the 5 gallon pail. Corebond is a way better choice vs cabosil for fillets IMO, glassdave turned me onto this idea. I really like the 3m Corebond, and West System 404 adhesive/filler. The bond of these products can be summed up in one word "tenacious". So glad I didn't do this the traditional way!