LarryL

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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c_deezy

iTrader: (1)

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.

glassdave

iTrader: (1)

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.

Pokher Ace

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

glassdave

iTrader: (1)

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)

pstorti

iTrader: (2)

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

LarryL

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.

LarryL

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?

c_deezy

iTrader: (1)

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.

MooresWarlock

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'!!!!!!