440: Hull Thickness

[cll2]

On occasion I've seen questions about hull thickness of Lagoons in CF. I recently replaced an AC inlet on the forward port side of our boat and while the through hull was out I measured the thickness at that point with a caliper. It is, of course, solid glass below the waterline. The measurement was 0.625 inches, or right at 16mm. This is a 2006 440.

[arsenelupiga]

my wild guess is hull thickness is not uniform. Bigger where statistically more chance of impact.

Finite element analysis and statistics of past hull impacts is included in decision on thickness at particular hull point.

I guess thickness behind fin keel is less than in front of keel.

Hard to see how impact between fin keel and rudder can happen. But easy to see impact in front of keel.

i can live with that.

[minaret]

How about a pic of the inside? Sure there's no backing plate included in that thickness? I posted my similar pics with caliper in place, inside and out. Can you do the same? Doesn't mean much otherwise.

[UNCIVILIZED]

Nothing like 5lbs/sqft of fiberglass to keep a boat svelte & unsinkable.

[BambooSailor]

When I replaced through hulls on my previous Lagoon, fiberglass midship was only 3-4mm (1/8") thick, but more than an inch in front of keel just a foot or so away (I drilled a new hole there for a transducer). Maybe (I hope) they ran finite elements analysis

[cll2]

These pictures were taken several weeks ago. The new seacock is already installed. The original did not have a backing plate and these pictures do not include one. I did add one to the replacement Groco seacock. Sorry I don't have any pictures of the interior during the installation. I took these pictures and the measurement out of my own curiosity and decided someone else might be interested. I realize the thickness almost surely varies depending on location and it makes sense that this would be one of the thicker areas. I also don't have any pictures with the caliper in place, but I have no reason to misrepresent the measurement.

[eyschulman]

As noted by others thickness may vary based on need of stiffness. The type and quality of the lay up is often much more important than thickness. Some times thickness is substituted for inadequate engineering and quality of lay up. The ultimate thickness for stiffening is when thick foam or balsa is used and when done right with good bonding nothing wrong with that.

[arsenelupiga]

if one complains about lagoon weight and how heavy it is... like 3 T over competition.

and on the other side about hull thickness - way too thin.

And of course competition has thicker hull and 3 T less.

Hum, yeah, of course.

[minaret]

Originally Posted by arsenelupiga

if one complains about lagoon weight and how heavy it is... like 3 T over competition.

and on the other side about hull thickness - way too thin.

And of course competition has thicker hull and 3 T less.

Hum, yeah, of course.

Cored vs uncored construction. No core, needs thickness to provide panel stiffness and prevent oil canning. Add core, and voila! Thicker, stiffer, lighter, stronger, more buoyant. Solid glass certainly has its advantages over cored, but not for this type of construction.

[Cheechako]

Originally Posted by BambooSailor

When I replaced through hulls on my previous Lagoon, fiberglass midship was only 3-4mm (1/8") thick, but more than an inch in front of keel just a foot or so away (I drilled a new hole there for a transducer). Maybe (I hope) they ran finite elements analysis

Surely that must have been cored if only 1/8" thick?

[neilpride]

I doubt very much those 16 mm are the real hull thickness, most likely a backing plate to, the pic show a 440 hull cut out for trhu hull installation... far from 16 mm ....

[colemj]

neilpride, where on the boat was your hole cut? The OP's thruhull is right in the area of both the turn of the bilge and the main beam/bulkheads tying the two hulls together and supporting the mast.

It is quite possible you both are correct, but looking at different parts of the elephant.

Mark

[neilpride]

Originally Posted by colemj

neilpride, where on the boat was your hole cut? The OP's thruhull is right in the area of both the turn of the bilge and the main beam/bulkheads tying the two hulls together and supporting the mast.

It is quite possible you both are correct, but looking at different parts of the elephant.

Mark

Is not in the turn of the bilge as far i see, several inches below the waterline in the Op Pic, the other one is a Brand new cut out trhuhull in a Brand new Lagoon without antifouling below the waterline if i remember well from a Lagoon owner blog, cant remember well if is for AC Air cond wáter pump or something related, one thing is for sure , a 440 hull thicknes is far from 16 mm right there, in the real turn of the bilge could be but not in the Op picture... 16mm or more is quite usual in the bridgedeck layup,,, maybe im wrong but fixing several of those Lagoons i never see something far from 8 or 10 mm....

[Panope]

I couple years ago, I made two videos that depict crude testing of boat building materials.

In this video, I beat the snot out of some fiberglass panels of similar thickness that is being discussed here. I have since learned that the material used is probably G-10. G-10 is a high quality fiberglass and epoxy product that is manufactured in a controlled environment. It is likely stronger than a comparable thickness hull lay-up. How much stronger? I have no idea.

Also, In the video I mention that the "birds mouth" that is cut into the glass panel is causing a stress riser and is "unfair". I will note that the aluminum panel that I tested also has a birds mouth so maybe it was not so unfair after all. I will certainly place a birds mouth in any future material I get the opportunity to abuse.

Admittedly, These are not scientifically administered tests. However, as someone previously noted, there has never been a scientific test of a boat on the rocks either.

Steve

https://www.youtube.com/watch?v=siiMRfvs1GU

[arsenelupiga]

Originally Posted by minaret

Cored vs uncored construction. No core, needs thickness to provide panel stiffness and prevent oil canning. Add core, and voila! Thicker, stiffer, lighter, stronger, more buoyant. Solid glass certainly has its advantages over cored, but not for this type of construction.

well, not ideal either. quick search produced this:

Why It's Risky to Buy a Cored Bottom Boat

The risk of water entry into a cored bottom is obvious to most experienced boat owners. It's like having a water-proof watch. Even my Rolex Submariner will, over time, experience the seals aging and going bad and water leaking into the watch. That has already happened twice. Of course, a boat bottom is not built with the precision and care of a Rolex watch, so how much more is it likely to leak? The answer is so much more so that water ingress into the core is almost inevitable over time.

Cored Hull Bottoms