Implications of Bonded Structural Grids in Production Boats

[Dockhead]

Originally Posted by Manateeman

Lead will take some of the impact but not anything significant. Where the impact occurs ...tip or mid keel is a big difference. I’ve looked at a number of fin keel hits and the stub idea made it possible to cover the keel to hull joint with a flat band rather than glass at 90 degrees which is much stronger. I worked for one of the first OEMs to change the way the keel was bolted to the hull. The hull stub was remolded with a rabbet so a vertical band of glass in epoxy could be applied after the keel was bolted on. The lead had a similar rabbet so the thickness of the band was accounted for and the finished band made the joint flush. This vertical band did help keep water out of the joint and did add strength.
Worked better for day sailor boats but as the vessel size increased, it became clear the forces needed to be spread out much further in the hull. The “bend” where the glass in the hull rolled over into the stub became the crack prone area. The stub and vertical rabbet band helped. This was at the time...pre computer engineering...a lot of work and money for builders. Not a big selling point. One poster on this forum said it well. They were still selling boats, why add costs or change.
I do think post construction improvements could be engineered.
Happy trails to you.
Mark and his manatee crew

A strut would certainly help spread out loads, but do you realize that water is almost 1000x denser than air? No matter how streamlined the shape, even a slender strut is going to have substantial hydrodynamic effects, and you can bet they won't be good ones. Not just drag - a streamlined strut leading from the keel shoe towards the bow would be a very high aspect wing which would strongly pull the bow to windward when you're beating - weather helm.

Very creative idea! But I think much better results to just buy a well-built boat in the first place.

[Jim Cate]

Not a structural engineer nor a NA, but didn't they give up on struts in aircraft quite some while ago and go to cantilevered wings, etc? And that in air, not water...

Jim

[coopec43]

Originally Posted by Jim Cate

Not a structural engineer nor a NA, but didn't they give up on struts in aircraft quite some while ago and go to cantilevered wings, etc? And that in air, not water...

Jim

I'm certainly no expert either but just doing a little research I came up with this. I think you are right.

[double u]

while the concept of bonded matrices/liners/grids certainly has some scary elements, one aspect seems to have been missing in this here discussion:
it is practically impossible to find an affordable, say, 40' boat, 7 years & younger without bonded grid-frames...
the discussion is similarly academic as a discussion about the desireablity of saildrives, wheel-steering, swept-back spreaders, spade rudders, ...

[RaymondR]

Originally Posted by Jim Cate

Not a structural engineer nor a NA, but didn't they give up on struts in aircraft quite some while ago and go to cantilevered wings, etc? And that in air, not water...

Jim

Engine power had a lot to do with it. The Wright brothers had bugger all horsepower so had to build an aircraft with very large airfoils to get the required lift at slow speeds. Consequently spindly construction with truss structures. In designing these truss wings they also tended to use wires for tensile members, some of which were airfoil shape to decrease drag as were the compression members. As the power available and speed increased lower wing areas were required in order to generate the required lift but as speed increased form drag became more significant, the square of the velocity thing which appears to intrude in all fluid flow equations. Cantilevered beam structures also were handy to put fuel tanks and machine guns in fighter aircraft.

Practicalities often intrude on theory. Long high aspect ratio wings do the lift drag thing best but are buggers of things to drive without knocking the ends off in airport taxiways etc.

There's no practical reason why a skeg or spade cannot be designed to be as strong as each other once one departs from hanging the spade on a skinny shaft.

[sailorboy1]

If the thread is about grids being dangerous the question is who here can afford a completely custom boat that doesn't have one? I think saying a hard grounding caused a grid to come loose isn't enough info to say bonded grids are bad. After all you are talking a VERY hard grounding which didn't rip off the keel or sink the boat.

I believe Hickley is doing bonded grids now.

[Manateeman]

Let me be very clear as to my experience base. I learned my fluid mechanics from a gentleman who designed fighter aircraft at a laboratory behind MIT.
The manatee crew has no need of further instruction.
If you disagree, please also state your education, background and experience both in fluid mechanics and yacht design/ construction.

Weather helm. “Substantial “? I disagree. A single fwd strut might not be needed at all. The greatest damage usually occurs at the trailing edge BUT this is not always the case. Interior reinforcement during the design / build could deal with this but its...obvious...there are a lot of boats out there where this structural strength is inadequate and reinforcing the entire grid properly, becomes very expensive and difficult.
Compression struts are still used in aircraft design.
Clearly there is no substitute for good engineering and careful construction as pointed out in a prior post. But to dismiss a conceptual suggestion out of hand is unfair to those who have less than ideal fin keel / hull structure.
The free exchange of information and ideas without vague generalizations and dismissive snipes would benefit the forum members who are looking for answers or even suggestions as to how to protect their vessel from turning into a total wreck. If one has ANY suggestion on how to help, we welcome it. We see boat after boat with fin keel / hull attachment issues. Videos of complex and extremely expensive repairs. Perfectly fine vessels cut up because the repair cost exceeds the value. Maybe there are some who would rather loose a bit of speed rather than all their investment. Some people have a very high emotional attachment to their boats. There is a builder on Cape Cod who painstakingly rebuilds old Herreshoffs for several times what a new similar size boat would cost because the family wants to see great grand father’s boat sail again.
Please...let’s dial back the negativity.
Happy trails to you.
Mark and his “a face only a mother could love” manatee crew.

[double u]

Originally Posted by sailorboy1

If the thread is about grids being dangerous the question is who here can afford a completely custom boat that doesn't have one? ....

I believe Hickley is doing bonded grids now.

Exactly! Let's worry about parameters that we can influence/have a choice in!

[robert sailor]

Originally Posted by sailorboy1

If the thread is about grids being dangerous the question is who here can afford a completely custom boat that doesn't have one? I think saying a hard grounding caused a grid to come loose isn't enough info to say bonded grids are bad. After all you are talking a VERY hard grounding which didn't rip off the keel or sink the boat.

I believe Hickley is doing bonded grids now.

Hinkley is doing bonded grids BUT not like production boats...their grids are infused glass grids that are basically part of the hull...they are not held together by a bead of glue.

[sailorboy1]

Originally Posted by robert sailor

Hinkley is doing bonded grids BUT not like production boats...their grids are infused glass grids that are basically part of the hull...they are not held together by a bead of glue.

sure they are, they are just calling it epoxy or something, all fiberglass boats are held together by "glue"

[robert sailor]

Originally Posted by sailorboy1

sure they are, they are just calling it epoxy or something, all fiberglass boats are held together by "glue"

Well if you want to view glass and resin as glue your certainly free to do so but let's put it another way....Hinkley's glue is multi times stronger than the glue in production boats.

[Breaking Waves]

Originally Posted by robert sailor

Well if you want to view glass and resin as glue your certainly free to do so but let's put it another way....Hinkley's glue is multi times stronger than the glue in production boats.

Hmm, actually, properly applied plexus generally has a stronger bond strength than epoxy. The problem here is that the grid structures are often poorly placed, leading to big gaps between the pan and the hull, leading to either no bond or a thick bond that is quite brittle.

So, 'the initial problem' is not the glue used but rather the process has very sloppy QA.

With much bond area missing and/or too thick/brittle bonds, it does not take a catastrophic grounding to crack the bonds. The brits found some boats which had (they believed based on owner interviews and keel inspections) had only what the owners thought were mild groundings (nothing they felt to be concerned about) but the pan bonds were in fact cracked.

After the initial problem, after the bond has failed, then the pans have a follow-up disadvantage which is both difficult to inspect all the bond area (without destroying much of the boat) and also difficult to fix all the cracked bond area. With an integrally infused grid those follow up problems would still exist to some degree but would be more minimized/localized.

I do know a Morris built boat, that eventually had to have its whole bottom cut off. They took a chainsaw and just cut the boat around the waterline, and a new structure was designed and whole new bottom was glassed on. The designer and the yard each said "not me - it was him who messed up".

[sailorboy1]

Originally Posted by robert sailor

Well if you want to view glass and resin as glue your certainly free to do so but let's put it another way....Hinkley's glue is multi times stronger than the glue in production boats.

Super special glue only know to them made by the super best and biggest glue maker for the major profit market to them of Hinkley boat building.

Got it. Stupid me as normal

[TeddyDiver]

Originally Posted by sailorboy1

Super special glue only know to them made by the super best and biggest glue maker for the major profit market to them of Hinkley boat building.

Got it. Stupid me as normal

Can't find a way to comment that without being banned

[RaymondR]

Dies not matter how super the glue is since they are only bonding to the resin.