mustang #1 pictures

eric lavine wrote: on a foam core boat or even a balso core they are not relying on the bonding, they rely on ecapsulating the material for integrity. in most cases a little of both are used on stringers, the wood is simple a filler and the glass around it is the strength...dont get me wrong the wood too helps.

Eric,
The basic principle of a balsa core boat in the core maintains the spacing and the glass skins are under compression/tension. The same method used for "SIP's" (structural insulation panels) in home and light commercial building. This is a different principle from the typical wood stringered glass hull.

Here's a Boston Whaler with wood skins!!!!

farmer wrote: I think I remember seeing a stringer project on a Ski nautique(?) where the stringers went side to side and not front to back. The hull would be supporting the load in that instance.

Gary,
This method was used on the Torino/Separator with a V drive engine/trans but just like Joe mentioned, these were V hulls with the V giving the hull strength.

Joe,
Lets not forget with the flat bottoms of our ski boats that the stringers maintain alignment between the engine and the strut too. Eric would be real busy with bad trans's without the stringers there!

as progression evolved, so too did the thoughts on the strength of glass, on the old Chris roamers in the early days of glass the transoms were 4 inches thick, if you go onto a newer Sea-ray you can actually see sun through the side hull. glassing hasnt changed much over the years but the thoughts on its strength have..one on one cases on such as the boats use will be factored in, you would think the strongest boats would need to be the go fasts wave hoppers, they are actually the lightest and least structural built boat, if any boat was to snap in half its one of these. alot of overkill is built in for liability reasons cause one good lawsuit could kill a company, thats factored in...many variables, obviously in an mid engine you want the most structure in the middle in an aft engine you want the structure in the rear because in the non weight baring areas they rely on the fiberglass...of course when you rebuild a boat you too build in overkill as you should whether it be wood or coosa........anythings better than rotted wood that supported the boat for a few years prior i would imagine

I am not a naval architect, I rarely build or repair boats for a living, however as a card carrying geek sometimes I do FEA on old ski boat hulls before I rebuild them. However, since I am not a navel architect or a designer with years of research and experience building boats rather than assume I know all the loads that could be applied and the ways a boat could fail I instead endeavor to produce a structure that is equal to or stronger than what was originaly designed. Its a basic standard of care that would also be applied when one does something like automotive frame repair.

Of course I do also think about the loads, ... the stringers in some fiberglass boats are there to hold the engine perhaps, in the design of a flat bottom correctcraft that is clearly not the case. The southwind, BFN, or seperator/torino is a different case as it relies more on the V hull shape to bridge the two upright sides and counteract loads that would are applied between the stern and the bow. Those loads include but are not limited to the weight of the engine and anyone/thing in the boat when lifted by the lifting hooks, the dynamicly applied weight of the boat and engine etc while on the trailer, or god forbid when you put the boat on a rock, or into a wall. In addition Ski boats are also a special case where the pylon in the center of the boat needs to be able to hold rediculous louds and transfer them to the prop. What about the load of an 800lb engine when the boat goes from 50 to 0 in a power turn, bolt it directly to the hull without stringers and see if the hull ends up with holes in it. Don't compare the structrual needs of a stern drive, outboard, v drive, etc to a flatbottom inboard its a whole different ball game.

I have taken the stringers out of an older mustang, and broke the hat shaped section in half by hand without a lot of effort, and yes the fiberglass is thicker than the later wood stringered boats. But it was nowhere near the rigidity or strength that it would contribute to the structure of the boat anywhere near what the wood did. I know because I measured and did the calculations and designed a foam cored (not coosa) stringer system that would have the same strength as the wood and fiberglass I took off, and then I added the fiberglass that held it down. Now on an old mustang, which had thicker fiberglass on the stringers, had thicker hulls, and had less flat floor area to span between the vertical walls of the boat and had a pylon that would pull out before you could really load it up, as well as less powerful engines you probably wont die as easily.

However don't get a good bond to a wood stringer on an 80's ski nautique and use the same amount of glass the factory did and then go out and treat it like a ski nautique and you will be lucky not to end up tearing the hull apart.

Bottom line is you can build a similar v8 inboard skiboat boat out of wood without any fiberglass and it will work just fine. Build a pre 93 fiberglass correct craft with everything exactly the same construction except no wood and I dont want a ride.

I think I remember seeing a stringer project on a Ski nautique(?) where the stringers went side to side and not front to back. The hull would be supporting the load in that instance.
This was discussed awhile ago and the general concensus was that the older boats had heavier fiberglass layers around the stringers and could support the majority of the weight.The wood stringers were just an attachment point for the motor mounts.

David F wrote: JoeinNY wrote: No offense David, but that is some of the most dangerous advice I have ever heard. Just curious as to what dangerous advice I gave. Did I tell anyone not to install the stringers...NO. Are you sure you know what the purpose of the stringers are in a boat, or just guessing?

I certainly do not feel Joe is guessing. He went through the strength modulus figures before he did his Coosa board stringer job. Have you? The "advice" you stated was that the fiberglass does all the work and we certainly do not feel that is the case.

David F wrote: It is the fiberglass around the stringers that provides the rigidity for the hull.

The glass and the wood works as a combined system.

JoeinNY wrote: No offense David, but that is some of the most dangerous advice I have ever heard.

Just curious as to what dangerous advice I gave. Did I tell anyone not to install the stringers...NO. Are you sure you know what the purpose of the stringers are in a boat, or just guessing?

The strength value of the wood itself could be tested by putting in wood under the engine only.

Anybody brave enough to test that theory? Look how much materials cost you would save!

When I have to do stringer rebuild (I am sure it's coming), it's overkill for me!

Something does look unusual with the way those stringers came out so easily you can see two small places where the fibreglass adhered. Is there something different about the timber (maybe treated ?). Without the stringers adhering to the hull they would not have been providing very much structural integrity.

Looks like it would be a candidate for "Seacast" as the shell is almost complete.

I really couldn't see how the stringer failed to bond to the fiberglass unless it was intentionally done that way somehow. If I didn't have the floor up to remove the soaked foam,it looks like the stringers would have been okay for a few more years.Water under the bridge now.Anyway I'll feel better knowing exactly what I've got after I'm done.
I'm going to freshen up the fiberglass that's there with a grinder and see how it looks.I called Smith's CPES and talked to the man himself.He told me that I could use it on questionable fiberglass to "fortify" the old glass.I don't think he was just trying to sell me the stuff.He seemed pretty straight forward when talking to him.I used it on the bottom of this boat before the epoxy layers and it really seemed to soak in.

This is a picture of the bottom with Smith's before I had finished the filler coat.

I wont take it the wrong way. And if you re-read my earlier post, the stinger does prevent the hull from oil canning and thus effects the ride over chop/waves. And yes, I did not think of how it would effect how the boat sits on a trailer...yes it will provide support in that situation. But, rotten wood might be stuck to the fiberglass, but it is not adding any structural integrity at all.

I guess we can agree to disagree. I am not sure what sparked this discussion now, but if it was me, I would remove the old fiberglass (around stingers) and start fresh. But, I would not worry about whether or not the fiberglass/resin was going to bond to the wood, because it will anyway...any type of wood other than pressure treated.

It won't fold or collapse. The wood is there is resist in one direction or the other and the sides are connected together topa and bottom. Again, the hull does not even need the stringers for rigidity along its length as the sides of the hull prevent bending. So, no real bending flexing loads on the stringers anyway. Think about it, have you ever heard of a boat bending or breaking in half due to rotten stringers...I bet you have not. And certainly, the fiberglass is not bonded to rotton stringers. Aint gonna happen.

I am going to say that I do not think adhesion between the wood and fiberglass is all that important. Here's why:

The wood stringer serves two main purposes:
1. Solid mount for the engine.
2. Form for the fiberglass surrounding the stringers.

It is the fiberglass around the stringers that provides the rigidity for the hull. This is evident in all the boats running around with rotten stringers...without hull failure. I will even go so far as to say you do not even need the stringers or fiberglass around the stringers for hull integrity. But, the hull would then oil can terribly and you would get stress fractures eventually.

So, IMHO do not worry about adhesion. But in the photos above, I certainly would remove all the old fiberglass that was around the stringers and start new from the hull up. Don't worry too much about evenly the wood stringer rests on the hull, you can always fill the voids with thickened epoxy (epoxy resin and saw dust works well). Shoot getting the stringers out in one piece like you did means you had a few years left

farmer wrote: the stringers lifted out in one piece.Is that right?

Nope, that won't work! As I have learned from this site, a big part of using d fir is for the adhesion. My old stringers had to be scraped to be burned. The old glass was still stuck on good after 20 years...even in the rotten spots!

Well I finally got around to the stringers on this boat.A couple of things have me confused.I cut just the top of the fiberglass encasing the stringers expecting to have to dig out the wood.But when it was all removed,the stringers lifted out in one piece.Is that right?I thought they were fiberglassed in and attached to the hull.I don't know if they were replaced before.
I also was looking for the post about the proper orientation of the grain in the stringers.If these were replaced at one time they may not have the grain running the right way. Here are some pictures.



They look original to me but I don't know for sure.I also noticed that the angle on the bottom of the sringers remained constant even though the angle of the hull flattens out at the back near the transom. Gary