68/69 Mustang Resto

I don’t wish to start the right and wrong argument I am only looking to document my progress.

There are many options out there on material selection and each has its pro’s and con’s. Coosa, Seacast, laminated ply, LVL, white oak, southern pine, cypress, and a host of others have all been used successfully in marine construction. Factors such as price, availability, rot resistance, strength, weight, bond ability, fastening ability, personal preference and more goes into this selection.

I encourage anyone looking to tackle a project such as this to perform their own due diligence and make a sound decision based on their particular situation.

Below is a link to a discussion held in mid-October regarding material selection. Additionally; searching “stringer” on CCfan or any other boat repair site will present you with a host of options to consider.

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=23871&KW=stringer&PID=300784&title=span-classhighlightstringer-span-wood#300784

Mike,
I am watching your thread pretty closely because I am doing a stringer replacement, but am a few steps (OK a lot of steps) behind you. My concern with the plywood is screwing lag bolts or other fasteners into the vertical plwood and splitting the laminated layers apart. I'm no expert and you have more experience than I do (I used to belong to iBoats and saw your Bayliner project) but when a guy with 17,000 posts asks about "flexural modulus ", I pay attention.
Good luck, I will be watching and learning.
Wes

8122pbrainard wrote: mountaineerminer wrote: I encourage anyone looking to tackle a project such as this to perform their own due diligence and make a sound decision based on their particular situation. So, how does the flexural modulus of the ply compare to the original Doug Fir? Did you calculate it at the butt splice as well where you will only have one layer of ply? BTW, your link didn't work for me.

This would be an interesting experiment. As finding this info online would be next to impossible. Once you are done with your stringer put it on two blocks at the ends and apply pressure to the center to see how much it flexes. The old three point test. If you had a press with a pressure gauge it would be the most accurate. I think it could hypothetically work but I would worry about possible delamination over time rather than its ability to hand the load.

Are you interested in the steering wheel? Let me know, the price is right.

John B,

Send me an email @ mcurry@alphanr.com

TIM,
If only the factory built them with the quality of your workmanship and your attention to detail!

I wasn’t going to make any reference to the post’s regarding my shoddy workmanship and incompetence only because I wished to keep my thread on topic and not get lost in hostility that is all too popular on most message boards. It is quite apparent that my selection of material goes against the convention of this forum and I will not likely find any supporters within the community. I politely alluded to a two page thread on material selection where this debate could be archived and useful for future reference. This does not mean that I do not appreciate your comments; I fully encourage constructive criticism and helpful suggestions that are delivered in a professional manner.

That being said I chose to use laminated ply to construct my stringers over dimensional lumber for couple of reasons. This was not decided on in haste or to save money. If you consider the cost of the plywood, epoxy, cloth, fillers, and time it is probably a wash if not slightly more expensive than using dimensional lumber. I view the wood of the stringers as the core a composite that works as a system of reinforcement. That system is reliant on all of those pieces working together.

The plywood is much less likely to shrink, swell, cup, warp, or split. Additionally, I have had more success in bonding glass to plywood than to dimensional lumber. I am not sure if this is due to moisture content, surface finish, or density.

I was a little confused by the statement regarding the flexural modulus of ply vs. douglas fir. I thought this is why engineered joist are considered superior to dimensional lumber, even when made of OSB, as already stated. The moment is applied to the edge, not the face. If properly supported along the face and loaded along the edge it would be hard to argue that dug fur is substantially less resistant to deformation. This proper support is provided to the face by the glass that ties it to the hull and the cross braces to the outer stringers. I plan to use layers of CSM and 1708 biax on both the inner and outer stringers. On top of the stringers will be a ½” plywood deck that is covered both top and bottom with CSM and Glass mat and secured with 5200 and SS screws.   

As for the strength of the lap joint, the wood itself will fail before the glue joint; in addition those joints will be wrapped in glass. Also, AC ply has 7 layers in a ¾” board, leaving 3 ½ layers on either side of the joint.

Yes, marine ply (AA) would be superior, but in using AC for many other projects I have yet came across an voids while cutting rabbits and such. I am not saying it is completely absent of voids, but is much better quality than the BC ply typical used. My problem with marine ply is availability. The closest supplier I have found is in Charlotte NC.

The other concern I have in ply as was mentioned is the pull out strength. I know this will not be as great as with white oak or douglas fir but feel it will be more than adequate.

Below are pics of the factory installed “clear pine” that was completely delaminated the entire length of the board, significantly cupped, and contained numerous knots.

I am not saying that this method is superior to any other method, including the use of douglas fir, but I do not feel that it warrants being considered cost cutting deplorable construction.

There is more than one way to skin a cat and if stepping outside of the generally accepted practice is so abhorrent I guess I owe everyone an apology. I feel confident in my construction and have duly noted everyone’s thoughts. Feel free to make additional comments as to how poor my assembly is in the above mentioned thread.

I probably just took it the wrong way and everyone was only trying to help. It is sometimes the way things are written that they are interpreted differently.







Mike

Mike - Keep posting pictures of your project. You might be changing the paradigm here.

mountaineerminer wrote: There is more than one way to skin a cat and if stepping outside of the generally accepted practice is so abhorrent I guess I owe everyone an apology. I feel confident in my construction and have duly noted everyone’s thoughts. Feel free to make additional comments as to how poor my assembly is in the above mentioned thread.

I dont think anyone has questioned your assembly... you havent started rebuilding yet, really. I think we were questioning your plan, but again, without understanding the basis for the choices you made, I think thats to be expected. Now that youve explained your rationale, its pretty clear youve put some thought into this- so bravo. I still wouldnt go down the same path, but I do understand your approach.

I will say that if you were mainly interested in using ply for shaping the stringer core, there may be other choices out there that wouldnt rot. I know Joe built one foam-cored stringer boat, not totally unlike how CC builds boats nowadays. As far as lagging into the end grain, Id avoid that... maybe drill a larger diameter hole and fill with thickened resin, then drill a pilot for the lags... Pete has suggested this in the past when lagging into weaker materials.

I think that all discussions are good as it aids the flow of information between interested parties. As mentioned there are many reasons to choose one material over another.
If CC had done the job properly back in the 80s then we wouldn't be having this discussion....... However at that time they used their best knowledge and went with it. 25 years later we can tell them that they were wrong. But we don't know what the design life was for the boat. Look at modern cars, anything over 10yrs old needs attention.

The answer to the argument will be to meet back here in 25 years time and see how all the different materials used in replacement stringer jobs have faired!

That's my twopence worth.

Planning a stringer job for next winter so I have a vested interest in the reasoning behind different materials. Not to alienate a member because he is outside the perceived box.

Morfoot wrote: uk1979 is restoring his CC by going all composite and coming up with some really neat ideas and thinking WAY outside the box in his methods. It's a neat thread to follow. Keep up the good work and drive on. Thanks for the thread and the updates on the progress. I like your boat hoist and the cradle for the hull. Pretty Crafty!

Wow thanks for the bump Tim that’s quite something coming from a composite expert.
As for this approach this just how I view ply and sure it would work if done well with glass between the layup and extra build around it, all comes down to is it worth all the effort and still have the risk of delam years later the problem with ply is you can only seal (CEPS or thinned epoxy) the outer veneers and different depths across the edges as the glue in the ply will prevent deeper penetration so will leave the middle layers unprotected from moisture along with some layers will be cross grain and more moisture absorbent, the hole build up will need to be very well coated in epoxy maybe wrapped in cloth before fitting to the hull for some piece of mind, using solid timber warming first then CEPS it all over should give a deeper penetration over ply all round along with no delam issues, both methods are reliant on how well the restring is carried out in an old hull for a long service life.

If you won’t to build a wood base stringer system may be better to build your own ply using constructional veneers CEPS first then lay up with epoxy/cloth and clamp long flat bed just a bit wider than the stringer width then trim to size, down side to this is the wood will become neutral bayonet and will be heavy, I have found that using this method and placing under water for three weeks with no epoxy coating just sawn edges and sanded faces
The ply stood up well with just a .3mm or 2.8% increase in thickness and no delam.

I’m not sure if your just using the cradle to move the hull around but when it’s time to refit the stringers may be good to support the hull off the cradle at the transom and each side at the chine, I know it’s a small boat but there may be a small risk of the hull flexing in once all the old stringers are removed which would give it more hook and a slower Mustang which is not aloud here.

Keep up the great work and thanks for saving another CC.              

mountaineerminer wrote: "when it’s time to refit the stringers may be good to support the hull off the cradle at the transom and each side at the chine" uk, This is a concern I had and plan to look into a better way to support the hull. Do you think I am better off trying to support it from the chines and transom area or building 4 or 5 bunks that run parallel to the transom? I am not sure how to describe this all that well; I might just need to describe in a picture. -Mike

Mike The way I see it supports each side of the transom and 2 each side of the chine in line with the windshield should be fine some add a support to the keel as well just before the pylon its up to you, making up ribs would work too but allot more work and ensuring the hull is true and level could be a pain to do.
There is the argument that depending how big a guy you are you will push the hull out with your weight which is a fair point but my guess is the hull would run faster.
My self I took the sub stringers out first and replaced then took the main stringers out one at a time and replaced using the old to hold the hull shape while the hull was up on 4 stands this way will take allot longer to do but you can use the old to register/brace the new,if your going for a all out approach I do feel leaving 2 or 3 small tabs of the old glass sticking up 1/4 or so on the stringer runs make life easier registering the new.   
With your set up of lifting if you clamp some timber across the deck and plum down at marked points to the hull then lift and plum down again we can see how much flex there is once all the stringers are removed as I have not see this data on here and would be a great help for the flat bottom boats.

Long time no post,

Since my last post I have completely ground out the hull and most of the sides using both a 4 1/2" angle grinder and a 7" angle grinder both affixed with a flap wheel. All the old gel in the bilge was removed as well at the unwetted glass under the old stringers. I roughed up the entire hull, but will do a final sand with a DA prior to glassing. This process seemed like an eternity and took place over about three weekends.   

Before rolling the hull in the garage I laminated the stringers using US Composites epoxy and two layers of glass cloth, cut, and sanded to final dimensions.

Below are some pictures of the glove box, console, and controls that I picked up from John B and Aaron.

The brown console on the right is supposedly from a Barracuda SS. Its definitely different than the Mustang console as it was made to run into the motor box with the battery directly behind the console. I purchased this console for the controls.



John,

The holes in the corners of the glovebox fit up exactly; I take this to mean that this boat was originally equipped with the glove box and it wasn't an after thought some time in the last 40 years. I will just have to fill the holes that the aftermarket box was installed with.




Gary,

I have finally taken some measurements of the knobs for you.

Diameter of the ridge around the knob


Measurement from the flat threaded end to the round top


The next 2 images show the closest measurment I could get of the full diameter of the knob minus the rigde and flat spot.



Mike

Thanks John...I might need to make my way to the windy city again. Last time I was there was 7 years ago when my father and I went to pick up parts for an 88 Toyota supra turbo. It was a good trip, only our Yankee asses didn't realize we changed time zones!!!

A BIG thank you.I didn't realize they had a ridge,don't think I'll be able to find them but diameter will be easier now. Just like everything else CC they must have had different consoles over the years,heres mine out of a 'Cuda,it's just taller.John brought your white one over on his visit. If I cut the lower portion off,it's identical.