Hull flex on modern production boats

[rognvald]

I would agree with Zippy and check the furniture tabbing before I condemned any boat. It is very likely that it is the cause of the noise. Also, all boats are built for a particular market and when people buy a production boat of any size, they need to understand what market that boat had as its target. And, every coastal sailor and around the buoys racer wants a solid boat capable of a circumnavigation but they want to pay production boat prices. The majority of sailors, I believe, on this Forum ,and others, will never do any serious sailing so what's the point with an overbuilt boat? To sail along the coast harbor hopping with your 40-60 foot Brontosaurus? I have always been an advocate of a proper tool for every job. Why use a jackhammer when a Dremel will do the job? Good luck and safe sailing. Rognvald

[Polux]

Originally Posted by Dockhead

That sounds very interesting. Please keep us informed.

I have more information on my blog about several boats of the C line. In fact with the help of a Croatian friend I was able to be the first to publish on the net photos of the new Bavaria C45, a well guarded secret that should only be revealed at Dusseldorf.



That spoiled a bit the business for Bavaria that is selling now the last Bavaria 46, that was European boat of the year in 2015, at incredibly low prices.

It can be a good deal for the ones that are looking for a main market produced boat and are low on the money. I have heard that they are selling it at the same price other shipyards are selling smaller boats. It is not going to last.

European Yacht of the Year

[daletournier]

I have a Catalina in 470. Solid glass below the water, balsa above. From hull samples ive see it's quite a decent layup.

At anchor or underway I hear no creaking. The boat does not drip water at all, 10 deck hatches and eight opening cabin side portholes.

I was in a very strong gale one night last year with large swell, running at approx 7k with no sails up, surfed 16.3k once recorded on wind instrument. This is the only time I've had leaks on the boat. Those little lewmar side portholes over my sea berth started dripping, boat was obviously flexing abit as I've never had a drip before or since.

Now the inmast furled sail flopping around at anchor, that's another thing... Grrrrrrrr.

[john61ct]

In researching blue water boats under 30', I have learned that boats built in the early days of plastic (generally, late 50's to early 70's)

have much "better bones" than later on.

And by then the market was much more focused on comfort below, and realized bigger is better for safety, so that market segment shrank radically.

Not precisely relevant for those with new boat money, but a data point for us poors.

[SV DestinyAscen]

This is called survivor bias.

Bad builds and design that didn't past the test of time didn't survive, so it gives the illusion that things were better built in the past. Find that in housing too. Bad homes built in the 1800s got torn down. The stuff that remains are exceptional and gives illusion that homes were better built.

Boats too.

[Peregrine1983]

Originally Posted by SV DestinyAscen

This is called survivor bias.

Bad builds and design that didn't past the test of time didn't survive, so it gives the illusion that things were better built in the past. Find that in housing too. Bad homes built in the 1800s got torn down. The stuff that remains are exceptional and gives illusion that homes were better built.

Boats too.

Now there's some food for thought.

[john61ct]

Very true.

But often the difference shows in the very same boat model from the same factory.

Familiarity with the materials grew, they never intended to build a boat that would last 60+ years.


plus price competition, lots of the ones that maintained their quality standards got priced right out of business.

[Dockhead]

Originally Posted by john61ct

In researching blue water boats under 30', I have learned that boats built in the early days of plastic (generally, late 50's to early 70's)

have much "better bones" than later on.

And by then the market was much more focused on comfort below, and realized bigger is better for safety, so that market segment shrank radically.

Not precisely relevant for those with new boat money, but a data point for us poors.

Well, it's also my experience that older boats -- certainly through the '80's -- are much more heavily laid up. That is often explained with the idea that when GRP was new technology, designers didn't really understand how to engineer GRP structures and so used massive overkill in the layup to be sure it was strong enough. Sounds plausible to me.

But does that mean they have "better bones"? I'm not sure. They are certainly stronger and stiffer than boats like, for example, some recent Beneteaus, but they are massively heavy and this really hurts sailing performance. I like to sail and I prefer very light, very strong hulls. That excludes the "cheap" side of the design values tradeoff tripod. Owned boats with these so-called "better bones", and I wouldn't want to go back to them, to be honest.

[Dave Humphreys]

Originally Posted by Cheechako

As most Bene's now are cored hulls, you wouldn't think flex would be much. A bit disconcerting to hear that though... at anchor! It will be flexing a lot more under sail. Of course today, many boats are built with a interior liner that supposedly reinforces the boat. However, one wonders if "pasting" that liner into the hull on top of adhesive goo is as good in reality as the idea looks on paper. You cant really see under there to know. Maybe the liner is moving in the hull making creaking noises? Would you buy a boat that the deck is simply pasted in place onto the hull instead of thru bolted or fully laminated?
My 47'er was traditionally built, but cored to the waterline. It also had two large rectangular stringers glassed longitudinally in the hull below the water line on each side. The hull was a shy 1.5- glass at the keel/hull tapering to 3/4- at the waterline. When I bought a hydraulic backstay tensioner, I was between sizes so bought the big one for up to 55 ft boat. The reality is I could bend the boat with that adjuster and the headstay would not really tension up much. So with normal tension in 15-20 knots of wind, the headstay furler would sag maybe 10" to leeward. With a lot of tension it would do the same. I tried to figure a way to measure what was bending but I know of no way to do that. I just decided it must be bending the boat hull banana shaped.

Most Benetaus are not cored hulls (the 474 is definitely not cored) and they are built with a rigid internal stringer floor system that insures stiffness. It is more likely that the boat you were on was damaged at some point. Was this a rental fleet boat? If so, who knows what abuse it has experienced. If a properly maintained and surveyed 474 interests you, have no fear!

[Peregrine1983]

Originally Posted by Dave Humphreys

Most Benetaus are not cored hulls (the 474 is definitely not cored) and they are built with a rigid internal stringer floor system that insures stiffness. It is more likely that the boat you were on was damaged at some point. Was this a rental fleet boat? If so, who knows what abuse it has experienced. If a properly maintained and surveyed 474 interests you, have no fear!

Yes, it was a rental fleet. So you might be right. Honestly though, I wouldn't hesitate to buy this boat (was a 473 actually) with a good survey and maintenance history. Sailed great. Tons of space, good ventilation, easily maneuvered in tight quarters, and nice-looking to boot.

[Exile]

My boat is definitely "old bones" (or maybe "old school"), with a heavy, thickly laid up non-cored hull, and cored decks. But guess what, I've always had creaking going on in more boisterous conditions (but not at anchor). I kinda doubt it's significant hull flex since all 16 portholes, 7 deck hatches & numerous interior doors, etc. have never leaked or failed to align. Probably should just go around checking the fasteners holding down all the furniture as has been suggested. I know that many modern production boats use glue in lieu of fasteners for interior fittings, but not sure which way that cuts.

[boatman61]

I've always assumed its the internal moulding that cause's much of the creaking in boats like the Bendi's..

[a64pilot]

I think old boats had very thick hulls for a couple of reasons.
First resin and glass was cheap, so why not?
Secondly there was very little or more likely no real engineering done, all based on what they were comfortable with.
I see this even in aircraft, things are sometimes built with the idea, “ I know this won’t break” it’s not even designed much less Engineered, just built.
Just about everything now is designed /Engineered to a design specification that has an accepted model of loads and cycles.
Some models have more “fudge” built into them than others, and it’s usually those that earn the reputation of being very stout, well built whatever’s, cars, airplanes, boats.
Some think of cored hulls as being better, and in some ways they are. Right now I have been fighting with interior condensation that I bet if my hull was cored, I wouldn’t have.
However some are nervous that the skin can become compromised or through a joint water can intrude, just like it does in decks, and we stay away from cored hulls.
Some can afford new, and intend to buy new every few years. They are usually more tolerant of risks, some can only afford to buy once, they are usually more conservative.

[SV DestinyAscen]

Originally Posted by a64pilot

I think old boats had very thick hulls for a couple of reasons.
First resin and glass was cheap, so why not?
Secondly there was very little or more likely no real engineering done, all based on what they were comfortable with.
I see this even in aircraft, things are sometimes built with the idea, “ I know this won’t break” it’s not even designed much less Engineered, just built.
Just about everything now is designed /Engineered to a design specification that has an accepted model of loads and cycles.
Some models have more “fudge” built into them than others, and it’s usually those that earn the reputation of being very stout, well built whatever’s, cars, airplanes, boats.
Some think of cored hulls as being better, and in some ways they are. Right now I have been fighting with interior condensation that I bet if my hull was cored, I wouldn’t have.
However some are nervous that the skin can become compromised or through a joint water can intrude, just like it does in decks, and we stay away from cored hulls.
Some can afford new, and intend to buy new every few years. They are usually more tolerant of risks, some can only afford to buy once, they are usually more conservative.

So true. You can build the empire State with bolt beams and concrete. Or build the Taipei 101 with I beams and tuned dampers. Whatever works!

[nwdiver]

Originally Posted by Peregrine1983

I just spent over a week on a 47' Beneteau built in the mid 2000's. At night on the hook we often had some high winds (30kts plus), but even when it was relatively calm I could still hear the wood in the furniture (specifically the long settee) in the salon pretty loudly creaking.

I realize that all boat hulls are designed to flex, but I'm curious to know if more flex is an attribute of these boats in general. I have only owned older (pre 1990) grp production boats, so I'm imaging this may be an attribute of more modern boats with lighter construction and thinner hulls - something like a modern sky-scraper in an earthquake.

I am just asking if this is the norm because I've considered purchasing a mid-2000's boat like this. This is not a knock on Beneteaus. This boat sailed beautifully... pointed very high and felt perfectly safe in 2.5-3 meter waves and 25 plus kts.

Just curious if this flex is the norm or not.

Thanks

It may have been the mast working a bulkhead a bit causing the movement in the furniture, the mast is a big lever when at anchor, eh........