Wally

iTrader: (1)

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....

LarryL

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?

lightning jet

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

c_deezy

iTrader: (1)

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

Katanna

iTrader: (1)

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.

glassdave

iTrader: (1)

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 .

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.

LarryL

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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LarryL

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?

c_deezy

iTrader: (1)

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

MooresWarlock

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?