Implications of Bonded Structural Grids in Production Boats

[Manateeman]

RayR. Precisely. It is sometimes difficult to have clean roughed up surfaces both on the grid and on the hull in a OEM environment. It doesn’t take a lot of dust or wax or dirt or silicone to defeat the best adhesives.
Mark

[RaymondR]

Originally Posted by Manateeman

RayR. Precisely. It is sometimes difficult to have clean roughed up surfaces both on the grid and on the hull in a OEM environment. It doesn’t take a lot of dust or wax or dirt or silicone to defeat the best adhesives.
Mark

If one was building a large hull from steel one would use fairly large T sections fully welded to the hull plate to form the grid and those welds would be put into shear when the I beam formed from hull plate and T section were put under bending load.

Consequently just gluing the inverted U shapes to the hull without any continuity of the roving in the composite in a doubtful quality join would appear to me to be poor practice from a structural integrity viewpoint.

[boatpoker]

Originally Posted by RaymondR

Consequently just gluing the inverted U shapes to the hull without any continuity of the roving in the composite in a doubtful quality join would appear to me to be poor practice from a structural integrity viewpoint.

Never seen an "inverted u shape".
I have seen top hat sections.

[TeddyDiver]

Originally Posted by boatpoker

Never seen an "inverted u shape".
I have seen top hat sections.

What comes to the cross section of that grid on the video, it wasn't a "top hat section", as the dimension of the flange is too narrow. So it's flanged U and now you have seen it..

[RaymondR]

Whether you call it an inverted U or top hat section and whether laid over cardboard or timber or polyurethane forms they should be installed as part of the original hull lay up as an integral part of the hull shell and not just glued in later. Whilst this would require a greater labor input it would provide greater hull integrity than just glueing in a moulding.

[Seabeau]

Originally Posted by jtsailjt

“Stronger” doesn’t tell the whole tale and it would be interesting to know what sort of boat you consider to be the best fin keel boats.

If you’re talking about even the best high aspect fin, there’s no getting away from the tremendous concentrated forces that the combination of a long moment arm and a small cross section yields. I’m sure you’ve seen these boats with the aft part of the keel rotated right up into the hull and cracking it like an eggshell. Some end up on the bottom shortly afterward but some make it to a nearby boatyard and are repaired at great expense. Ive seen these hauled out and some were very expensive, high performance yachts that many would consider to be “the best.”

More moderate fins with lead ballast bolted on are probably the best for withstanding hard groundings with minimal damage just as long as the keel bolts are inspected to ensure they haven’t developed microscopic cracks that could lead to failure, but very few are inspected because keel bolt failures are infrequent and it’s an expensive process. These keels have some of the groundings energy used to transform the shape of the lead and the remainder is spread over a much larger area than with a more aggressive fin. The damage from even a hard grounding can usually be repaired with some filler and paint.

Encapsulated ballast boats with fins usually have a shape similar to a moderate bolted on lead keel but with the ballast completely encapsulated there is zero chance of bolt failures allowing it to break loose and the boat sinking as a result. However, the damage from a hard grounding can be much more expensive to repair, especially if sea water penetrates into any voids around the ballast, and doubly so if the ballast used is a ferrous metal.

So, for as an owner/skipper responsible for paying the boats yard bills, for a hard grounding I think I’d rather be in a boat with a moderate fin with bolted on ballast, but if I wasn’t going to have to pay for repairs I think I’d choose encapsulated ballast as the safest. Even the best boats with aggressive fins are much more vulnerable to catastrophic damage from a hard grounding than are the other 2 types.

Then there’s another option I can think of and that’s a design where the boat has no keel and instead has ballast encapsulated in the bottom of the hull with a large bronze centerboard that is both ballast and fin but would flip up in a hard grounding, minimizing damage. Ive only seen one of these, a Ted Hood design that was a 49 footer and the owner said it sailed very well.

I cruise the extremely shallow waters of the US Southeast Coast. My Presto 36 is a true centerboarder with no external keel and designed in 1884 by Ralph Middleton Munroe. She was designed to "take the ground upright". The vast majority of it's ballast is in the form of a long lead "grounding shoe" and my rudder, a barn door type , lies behind deadwood. Subsequently, I worry not about bumps nor crab pot lines. Carter, Seguin and a few French firms, also make/made great sailing centerboarders. Purchase a vessel for the conditions in which you sail.

[boatpoker]

Originally Posted by TeddyDiver

What comes to the cross section of that grid on the video, it wasn't a "top hat section", as the dimension of the flange is too narrow. So it's flanged U and now you have seen it..

At what specific width does a flange make the member a "top hat" ?

[TeddyDiver]

Originally Posted by boatpoker

At what specific width does a flange make the member a "top hat" ?

Equal width with the other planes.

[boatpoker]

Originally Posted by TeddyDiver

Equal width with the other planes.

I believe that would be a stetson

[TeddyDiver]

Originally Posted by boatpoker

I believe that would be a stetson

I'm not going to argue more about something as trivial, just if you like to make a real life test go and buy some hihat extrusion and see what you get..

[RaymondR]

Anyway it looks likes the folks in the video know what they are doing and are now going to glass the grids in properly.

[Manateeman]

I love silicon bronze and I haven’t thought of the Ted Hood boats for years.
So I was thinking about all the people who are sailing boats who just know or have seen boats identical to their boat being repaired while the owners watch their money evaporate. So I proposed struts...maybe just two. But...maybe silicon bronze plates are easier.
You don’t have a problem bending or welding. I’ve used button head bronze bolts underwater and they still look new. So right at the keel / hull joint you could fabricate a keel support system and use backup plates inside the hull and bolt everything together.
If the hull looks a little weak, clean it up and lay in some glass in epoxy.
Some owners know they own a boat which will be very expensive to repair if it hits something but I don’t see a discussion of how to correct the problem.
It would be nice if boats were designed and built correctly the first time but the original post seems to open a wide subject matter.
Bunny rabbits I shot and fin keel boats I built come back to haunt me in my dreams...LOL.
Take them away.
Happy trails to you.
Mark and crew.