Implications of Bonded Structural Grids in Production Boats

[Dockhead]

Originally Posted by robert sailor

The average new sailboat buyer is not all that sophisticated when it comes to construction details....they tend to be impressed with CE ratings and the layouts....the manufacturers are very aware of this so it's very unlikely that they will be rushing to improve the current construction methods. By and large these boats are built to a price and there is nothing wrong with that as it allows people to buy a lot of boat for the money. Accountants are busy saving nickels and dimes, certainly not interested in spending more money.

Building to a price is market economics 101. It's driven by buyers who want more boat for less money. Group B and Hanse etc. are only giving people what they demand. The great majority of sailors don't need a really good structure. They don't use their boats much and they go out in benign conditions. In many cases, it's more efficient to repair an occasional hard grounding (on insurance money) than to build every boat to withstanding hard groundings.

So it is what it is.

Nevertheless, I for one wouldn't own a boat built by any of the mass production yards -- just doesn't suit how and where I sail. This story will make your toes curl:

https://www.cruisersforum.com/forums...ds-248854.html

Apparently 5% (!) of all of these boats have had failed bulkheads -- i.e., major structural failure.

Another boat built by this yard, the B57, was not all that cheap and was apparently intended for more ambitious sailing, but also suffers from structural problems. Pushing the limits of the structure seems to be in the DNA of the mass builders. I guess it must make business sense.

It didn't use to be that way. The Bens and Jenns of 20-25 years ago were pretty strong (if not maybe the Bavs). I think also the price difference was less in those days, too, though.

[Elie]

These grids solutions for structural support of hulls is a very economical way of reinforcing the hull. Taking into account that the molded hull do not have any rigidity to start with. This grid system implanted and strongly bonded to the hull before it it extracted from its mold, add much rigidity that will be complemented when the deck structure is added. But, the fundamental flaw of this kind of grid systems is that it is strongly glued(using polyurethane glue to a much less strong layers of the hulle made of polyester. When grounding occurs, the weakest bond will break, That is often the first layer of hull moulding(where the grid is attached only) , or the polyutethane bond itself, if not well made to start with. The grid is very large, and making a perfect bond demands skill, good method, and attention to details and skill from workers. When grounding, once the grid is separated from the hull, it is almost impossible to repair, without significant dismantling the boat interior... Very expensive!...

[ktbaker]

In the early 80's I had a Westerly Ocean lord.
sailing in a squall I hit HARD at full speed.
I think I removed a couple of barnacles maybe.
it was slow and heavy and overbuilt BUT that boat would go anywhere and I never worried about grounding.

[Breaking Waves]

something I have always been a bit puzzled about this manufacturing process is that you have two molded parts (the hull and the grid). The molds should be pretty high precision. So the two parts should fit together quite closely. But they seem to often end up with like 50mm gaps. Seems like it should be relatively easy to get these two parts to fit with only like 1 or 2 mm gaps.

I wonder if the problem is that their glass layup in the molds is so sloppy that they can't control the height to 50mm - that seems unlikely - would be so sloppy they would have other problems. Or if they just go too fast when fitting the grid and if they just took like 5 minutes longer when fitting the grid they could get it to the actual place where it fit properly? IDK, just seems like a pretty bad production flaw somewhere.

They don't seem to care much about 50mm gaps/misalignments. I know an owner that had a new boat delivered and they were puzzled looking at it from the dock and when they got a surveyor to measure it they found the deck was offset 50mm to port (from where it should have been). When they contacted the manufacturer they were told that was within their manufacturing specification and of no concern.

[MJH]

Originally Posted by Dockhead

Interesting video. The guy had a hard grounding in an almost new Hanse which required extensive structural repairs.

Caveat emptor (Let the buyer beware).

For sailboat buyers it is a case of selecting the proper design that was created for the type of sailing you intend to do. That should please all parties if they are informed and truly knowledgeable of the tradeoffs and limitations of the design...but that is unlikely to happen in many purchases. When owners change their sailing objectives it would be prudent to revisit their current boat design features and see how it matches up to their newly proposed use.

The current mass production and marketing of sailboats says more about meeting popular hedonistic desires than seaworthy construction, craftmanship, and practicality...an adjunct of the throwaway society. There are the time proven methods of hull design and construction and then there are the shortcuts (tradeoffs) done to achieve other goals, some of which have nothing to do with sailing.

Caveat emptor (Let the buyer beware).

~ ~ _/) ~ ~ MJH

[Dockhead]

Originally Posted by MJH

. . . The current mass production and marketing of sailboats says more about meeting popular hedonistic desires than seaworthy construction, craftmanship, and practicality...an adjunct of the throwaway society. There are the time proven methods of hull design and construction and then there are the shortcuts (tradeoffs) done to achieve other goals, some of which have nothing to do with sailing.. .

Well, just to play the devil's advocate here -- what else than "hedonistic desires" is sailing, as a sport, about? Of course ALL recreational sailboats are built for the purpose of meeting "hedonistic desires". That's the "pleasure" in "pleasure boat".


A boat used for short coastal jaunts, and which may even be used mostly in its marina berth, does not need to be extremely seaworthy.


Most of these boats do NOT end up with broken bulkheads or unbonded grids. So I think there is an argument that they are entirely fit for a certain purpose.


It's not MY purpose, but for many people, it might be just fine.

[MJH]

Originally Posted by Dockhead

Well, just to play the devil's advocate here -- what else than "hedonistic desires" is sailing, as a sport, about? Of course ALL recreational sailboats are built for the purpose of meeting "hedonistic desires". That's the "pleasure" in "pleasure boat".

A boat used for short coastal jaunts, and which may even be used mostly in its marina berth, does not need to be extremely seaworthy.

Most of these boats do NOT end up with broken bulkheads or unbonded grids. So I think there is an argument that they are entirely fit for a certain purpose.

It's not MY purpose, but for many people, it might be just fine.

Exactly, their limitations need to be realized.

~ ~ _/) ~ ~ MJH

[robert sailor]

People have circumnavigated on Catalina 27's and Cal 25's.....others have rowed across oceans so if you sail in the lowest latitudes and you operate in a manner that's easy on the boat and gear it's highly likely you'll make it in one piece.

Production boats as we discuss them are certainly built down to a price and you shouldn't kid yourself when you make your sailing decisions however many of them are safely crossing oceans.

Grounding is one activity that really brings the worst out in production boats so its wise to treat groundings with a great deal of caution as if a liner breaks the glue joint it compromises the whole structure.

These boats are really designed for coastal cruising which is what 99% of modern sailors partake in but they certainly can cross oceans. They are probably not the best choice for long term ocean voyagers who are visiting higher latitudes and crossing oceans on a whim.

Just do a walkthrough on a new modern production boat and they have amazing room both inside and outside with huge amounts of natural light as well as large heads and galleys.
I certainly can see a new potential owner getting very excited about spending time on such a boat.if I was shopping for a new boat for coastal cruising I'd take a serious look at one of them myself.

The downside is when you cross oceans you really work the boat and overtime the fixed ports start to leak....those beautiful SS fridges just like home are really the best for local coastal cruises and marina living but sailing on your ear offshore they are the second best ideas. Some of those beauties are 16 feet across with little to hold onto, one slip and you can be badly hurt. I could go on and on but you get the point...

Modern high production boats are designed and priced to meet the needs of 95% of their purchasers so don't be upset with the manufacturers or their products as to produce products any other way would be foolish from a business perspective.

[C420sailor]

I genuinely wonder how much more expensive a boat would be with a properly laminated/tabbed-in grid instead of using adhesive. $10k? $20k?

[Kaimana]

My opinions on hull material and construction for sinkable boats

I was in Taiohae in Nuku Hiva in 1976 on my 37-foot trimaran Spice when I met a French couple on a 45-foot steel ketch, and a Belgian couple on a 55-foot steel ketch. Back then the Galapagos was still open to casual yachting visitors, and both these boats had visited there, then sailed for the Marquesas.

About halfway to the Marquesas, they had both seen killer whales, then been attacked by them. A single whale had rammed each boat about 3 feet underwater on one side, causing her to heel over; while the crew in the cockpit each saw a second whale, which had been intending the same maneuver from the other side, and sheered off because of the alarm sounds from the first whale.

Both boats had bulges, or indentations, about 6 inches deep in the steel plate sheathing between frames; the 45-footer, of 3/16” plate sheathing, and also the 55-footer, of ¼” plate sheathing. In both boats, the steel deformed but held, and there were no leaks. If this had occurred in a wooden or fiberglass boat of the same size and general sturdiness, they would have had 3-foot diameter holes in the hulls, and would have sunk within ten seconds.

Because we “know” that killer whales attack large whales this way, I thought that only monohulls, because of their similarity to large whales, would be susceptible to this kind of killer whale attack. This theory disappeared when I heard about a 36-foot trimaran that got attacked 3 days south of the Big Island on her way to Tahiti. The killer had rammed the boat just aft of the bow, and left a huge hole.

Fortunately, it was in the vee-berth area, below the berth level, and the owner had never gotten around to cutting an access panel into the area below the berth. He’d just hole-sawed a bunch of 2-1/2” holes in the vee berth bottom for ventilation. He had a box of oranges on board, so he stuffed oranges into the holes, put a piece of plywood on top of them to hold them down, and put sticks up to the underside of the deck to hold the plywood down. Then he pumped the forward cabin out and sailed her back to the Big Island for repairs. Sad, he never did make it to Tahiti.

I talked to a salmon boat fisherman in San Francisco Bay once; he’d had a 45-foot steel salmon troller and had been going out under the Golden Gate in the fog when he was rammed amidships by a destroyer escort. He didn’t have a radar on his boat, and the DE might not have been watching theirs. He was piloting from the flying bridge on the boat, and said he got pushed nearly underwater by the collision.

After popping back up and grinding along the side of the DE for 250 feet or so, he rammed both engine throttles home, spun the boat around, turned on all his bilge pumps and headed for the Sausalito mudflats next to the haulout yard. One of his two engines didn’t respond, but one did. He reached the mudflats just in time for the boat to sink: at high tide, right next to the haulout yard’s marine railway.

When they got the boat out they found that one of the two engines had been sheared entirely off its mounts and pushed into the other engine by the collision; that’s why it wasn’t functioning. The other engine had two of its four mounts sheared off, but stayed functional until beached and turned off. Although there was a terrible crushing on the side of the boat that got the collision, the only actual hole was a tear about 6 inches long and 1 inche wide in the steel.

Again, if this had been a wooden or fiberglass boat, this guy would have been swimming home.

If I go to sea on a sinkable boat, it's going to be made out of the MOST sinkable material available: STEEL!

With Warm Aloha, Tim

[robert sailor]

Originally Posted by C420sailor

I genuinely wonder how much more expensive a boat would be with a properly laminated/tabbed-in grid instead of using adhesive. $10k? $20k?

Good enough question but you'd be introducing a labor intensive job right in the middle of getting the hull out of the mold. Without the liner bonded to the very thin hull it would be like a gummy's candy and the manufacturer wouldn't be able to remove it from the mold which would stop production. They have production down to a science....if you want a stick built boat you just have to write the cheque...one reason they cost alot more...big labor bill and much more time to produce the boat. That's why liner boats are so much cheaper.

[Manateeman]

I’m disappointed no one is commenting on the strut idea. There are a lot of owners who have fin keels. The focus of the thread was the structural grid inside the boat. Well it's kind of obvious there are a lot of boats out there where the grid to hull bond is...let’s call it...less than ideal.
So why not substantially increase the strength of the fin keel by struts from the bottom of the keel to the turn of the bilge where most grids attach to the hull.
The wetted surface area isn’t large and if airfoil sections were used, the fluid turbulence would be minimal.
We use chainplates as the base of large loads to keep the mast in column.
Four struts ought to substantially increase the survivability of the vessel.
It’s the aft knife edge of the keel that’s pushing up against the hull/grid.
Add two struts pushing up against 1/2 a square foot exterior hull plate which is bolted to an interior backing plate...or ideally the grid. You have a huge increase in the surface area to spread the load.
Maybe it would only take three struts. One on the center line angled forward.
Seriously.
Sailors come here and they have questions. The full keel vs fin keel debate has been covered again and again. The manatee crew has a well worn copy of Principles Of Yacht Design by Larsson et al. The inspiration for the Strut Fin Keel comes straight from aircraft design.
We all have seen fin keel issues. We know the advantages. Why not discuss methods to reduce the damage rather than argue over OEM constructions.
The boats are sold, now sailing.
Look at the cost and time in this repair. Let’s assume it is as strong or stronger than before. He hits another object. What’s really changed.
Are struts the answer? Well we know the OEMs are not going to spend money .
The manatees have put their beer down and are drawing something very secretly and measuring a fin keel boat surreptitiously.
Why don’t I have a normal crew.
Happy trails to you.
Mark

[robert sailor]

I'm no engineer however I know from experience that if you glass in the floor grid or floor timbers and the boat is built with a keel stub and the keel is made from lead that type of construction can absorb some substantial grounding loads without damage because it spreads the load out over a large area. Obviously no one can make a fiberglass sailboat that is totally impervious to grounding damage but they can be made a heck of a lot stronger than they are currently made.

[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

[HansChristian33]

Stringer grids ie transverse and longitudinal frames if laminated outside the boat then bonded in can have excellent strength it just depends how they are designed and how they are installed and the materials used to install them. Many of these new boats have infused hulls after the bag has come off and consumables removed the area where the stringer grid is going needs to be ground up. Next the stringer grid to hull bottom distance needs to be checked to ensure it’s not more than the adhesive can fill in any area. Good quality methacrilate adhesives like needs to be used. Once the adhesive cures then the join to the hull is glasses over with quad. It is important that the design of the stringer grid allows for wide flanges where the grid meets the hull to ensure stresses are over a wide area and the is sufficient surface area for a good bond. Most boat building methods can be done really poorly or really well just depends on the skill and knowledge of the person building the boat.