Hull strength

[Oscarpop]

In my constant and unyielding comparisons of different yachts, I am once again playing Top Trumps with Southerly Vs AWB.

This one pertains to the manufacture, strength general seaworthiness of the hull.

As far as I can see, they all have hand laid GRP hulls, ( Hanse is now epoxy as standard). They all seem the same thickness. They have balsa cores where needed.

So what is the difference? Is there any? Does A Malo,HR,Southerly have huge amounts of increased strength over the AWB.

Thanks.

 

[Tranona]

Not sure that "strength" of hull is a particularly big issue. There are different methods of construction and variations in materials, but most modern boats are well engineered in this respect. I say most, because you do get the odd failure such as Joker's Huzar which was written up in one of the mags recently (and fequently discussed here).

Some hulls look more substantial than others because the boats are heavier displacement and carry heavier loads, but design now seems to focus on engineering to take the loads rather than just slapping in more material. It is inevtable that builders will emphasise features of their constuction - Bavaria and Jeanneau use of Kevlar, Hanse the option of epoxy, Elan use of resin injection techniques and so on, but the variety suggests that there is no definitive "best" . Indeed, one of the most expensive boats, Nauticat still builds hulls out of solid GRP - no cores for them.

Many of the newer techniques are used because they reduce the amount of materials used, reduce production cost and increasingly to meet demanding environmental legislation. It is inevitable that there is more than one solution to building strong reliable hulls, and one can construct an argument in favour of different approaches, but not entirely sure that any one stands out as markedly superior to another.

 

[aardvarkinvader]

Strength, now there is an intersting question and one you will find acres of answers on the interweb to do with composites; tension, compression, shear, load paths, fibre orientation etc etc. Initially "plastic boats were built using masses of resin and chopped strand matt to gain "strength" from bulk, but over the years designers have found out much more about "composite" materials and structures and can really accurately calculate loads and how to design in strength rather stick it in. Most modern boats are very cleverly built with "strength" where it is needed and light weight where it is not. That said, they don't always get it right as a quick flick through many a sailing magazine will testify; hulls falling apart, skin fittings fizzing away, keels dropping off, the list goes on. But all the boat yards you have mentioned are at the high end of the market producing quality designed and built craft. You do get what you pay for.
Really a bit of a red herring this question methinks, but a final point in favour of the Southerly swing keel. If you strike a submerged object, be it shipping container, rocks, log, whale, mermaid or any of the miriad of possibilities, with a "conventional" bolted on or even lifting keel, you run the risk of at least seriously stressing the hull and keel bolts, but at worst ripping it off. The swing keel however just clunks and swings up out of the way then drops down again when danger is passed. Now on any scale of physics that won't count as "strength" in any way shape or form, but the boat will sail away from a potential sinking with nothing more scaped antifoul and new underpants.
Finally, pay a visit to Northshore, watch them being built and talk to the craftsmen; that should put your mind at rest.

 

[Tranona]

That said, they don't always get it right as a quick flick through many a sailing magazine will testify; hulls falling apart, skin fittings fizzing away, keels dropping off, the list goes on. But all the boat yards you have mentioned are at the high end of the market producing quality designed and built craft. You do get what you pay for.

What alarmist claptrap! Of course there are failures - but nowhere on the scale you imply. And some of the most spectacular cases of major failure have involved boats from the "top end" of the market.

Of course one should take note of the failures -but by concentrating on those you are ignoring the hundreds and in some cases thousands of similar boats that do not give any trouble.

You do indeed get what you pay for - but this does not mean if you pay more you are automatically getting a better product.

 

[Norman_E]

My view is that all modern yacht hulls are built strong enough for purpose. I have related before how I saw a new charter Bavaria 38 rammed stern first into the concrete jetty at Dirsek, and survive bouncing off it with little more damage than a bent strip of stainless steel. The hull flexed and sprang back.

At the other end of the scale I have seen a big Oyster with a 3 foot hole above the waterline on the starboard bow, where its owner had rammed it into a rock at 8 knots, motoring in the dark.

In other words even an economy yacht will survive considerable abuse, but nothing is going to stop you holing any yacht, if you try hard enough.

 

[GrahamM376]

My view is that all modern yacht hulls are built strong enough for purpose. I have related before how I saw a new charter Bavaria 38 rammed stern first into the concrete jetty at Dirsek, and survive bouncing off it with little more damage than a bent strip of stainless steel. The hull flexed and sprang back.

I've also seen a Bavaria which hit a Victoria 34, transom to transom, when the Bavaria's gear cable fell off when he was reversing into a fuel berth.

The Victoria had some gel coat scratches whereas the Baviaria's boarding ladder was ripped off, the lid broken and the transom cracked - £1,500 damage.

I should think most modern boats are fit for purpose and won't fall apart when sailing within the design criteria but, just like cars, some survive impact damage better than others.

 

[doug748]

As far as I can see, they all have hand laid GRP hulls, ( Hanse is now epoxy as standard). They all seem the same thickness. They have balsa cores where needed.

Now, I would go a long way to avoid a boat laminated around balsa wood.

Not that you need worry, I am sure it delivers a lot of advantages when new, and when looked after. As a twenty year old secondhand proposition the outlook is not so bright. A depreciating asset, a sort of teak deck buried inside your hull.

 

[jackho]

Perhaps a to simplistic approach

A good question and one i always wondered about. A while back i did a rough calc. (now not in any way technical) on the differences between the new HR37 and a 37ft AWB (the HR being slightly heavier)
When I allowed for the heavy density teak interior vs. light wood, teak decks vs. standard, bigger engine vs standard the actual hull weight seemed about the same.
While this is only a ball park exercise there does seem to be some sort of standard weight/build/length relationship !!??
I'll leave it to the experts to enlighten me.

 

[Twister_Ken]

Better boats have Dyvinicell rather than balsa, coz it doesn't rot if water gets into it. But the real purpose of the hull is to keep the water out - stresses from rig and keel are taken onto a galvanised steel frame...

...oh sorry, just realised I'm talking about Arcona again!

 

[aluijten]

Better boats have Dyvinicell rather than balsa, coz it doesn't rot if water gets into it. But the real purpose of the hull is to keep the water out - stresses from rig and keel are taken onto a galvanised steel frame...

...oh sorry, just realised I'm talking about Arcona again!

Which ends up in another discussion about the bonding between a galvanized frame and the polyester hull itself.
I've spoken to boatbuilders that say there is a real risk of delamination if the keel hits something.
Personally I don't know. There are just too many variables at play.

 

[fireball]

I've also seen a Bavaria which hit a Victoria 34, transom to transom, when the Bavaria's gear cable fell off when he was reversing into a fuel berth.

The Victoria had some gel coat scratches whereas the Baviaria's boarding ladder was ripped off, the lid broken and the transom cracked - £1,500 damage.

I should think most modern boats are fit for purpose and won't fall apart when sailing within the design criteria but, just like cars, some survive impact damage better than others.

Ah - but what you don't say is exactly where the impact occured - knowing Bavarias I would hazard a guess that the impact was with the boarding ladder - this could easily create point loading on the Bav whilst spreading the impact on the Vic34. This would result in more significant damage to the Bav.

 

[fireball]

Better boats have Dyvinicell rather than balsa, coz it doesn't rot if water gets into it. But the real purpose of the hull is to keep the water out - stresses from rig and keel are taken onto a galvanised steel frame...

...oh sorry, just realised I'm talking about Arcona again!

Yer - but have you seen my galvanised launching trolley ... it's all rusted and needs to be cleaned back and re-galvanised .... alternatively I can buy a new trolley ...

Only kidding ... I'm sure your frame won't get the seawater bashing my trolley does!

Swings and roundabouts - I bet your galvanised steel frame holds shape far better than those without - which should aid you getting more power from the rig....

 

[GrahamM376]

Now, I would go a long way to avoid a boat laminated around balsa wood.QUOTE]

Cored decks don't worry me, Westerly, Moody and many other makes of boat from 1970's onwards (maybe even earlier) have balsa cored decks and problems are few, considering how many thousands are around.

Having heard about the expensive problems when cored hulls are damaged, I wouldn't want one of those.

 

[Twister_Ken]

Which ends up in another discussion about the bonding between a galvanized frame and the polyester hull itself.
I've spoken to boatbuilders that say there is a real risk of delamination if the keel hits something.
Personally I don't know. There are just too many variables at play.

Rock bashing is an everyday hazard for Baltic boats, which is where Arconii come from, so I guess they have a very superior glue!

 

[Sailfree]

At present my lottery boat would be a Southerly. I own an AWB.

When studying boat costs, weights, quality a few things struck me. Malo & HR etc are quality boats that originally were a lot lot heavier than AWB's but they were still dearer £ per kg than AWB's yet masts, winches & engine still come from the same manufacturers as AWB's.

All boats are strong enough and with better understanding of structural strength the weights have reduced (even on HR's).

Quality boats still have a strong hull (some with a sandwich construction for better insulation above the waterline). Apart from the thickness of the GRP hull the next thing to consider is giving the boat its rigidity/stiffness. They all started with GRP ribs and stringers bonded to the outer hull but with the need for even cheaper construction Beneteau led the way and created an internal hull like a waffle that when bonded to the outer hull gives great strength. Its cheap effective and works and the only downside that I can see is the difficulty of assessing any debonding after an impact or grounding. X boats looked at the structure and put in a galvanised steel frame taking the keel , mast and shrouds - structurally very sound. Arcona copied this idea. Both have the hull effectively sandwiched between the internal frame and keel and the main stresses on the hull are imposed only by forestay and backstay. As a Structural Engineer I like this idea but was surprised when a 46's keel struck a rock in a harbour (the skipper/owner insists it was a slow/slight impact) and the inner frame moved and had to be unbolted and repositioned! One slightly misleading point about this form of construction is that X boats counts the internal steel frame as ballast which results in a false ballast ratio - as if it was GRP it would not be considered as part of the keel weight! Not sure what Arcona do.

The quality boats AFAIK still do the GRP ribs and stringers bonded to the hull while the trend is for the AWB's to now follow the Beneteau inner waffle GRP hull for cost reasons.

I have a 2005 Jeanneau 43DS and frankly would not buy a waffle constructed boat but lots are made and are adequate so frankly its probably a bias on my part that is not logical.

Southerly AFAIK still do the inner ribs and stringers so you can inspect the structural members beneath the floor. There are cost implications and thats why a Southerly to me is my desired (but lottery win) boat. I am hoping that Arcona bring out a DS version and drop Volvo engines in favour of Yanmar but as any long keel enthusiast will confirm we are all prejudiced to some extent. Until then I am sticking with what I have as the cost difference to step up in quality from my current boat is IMHO far too high.

Last point - just read what Ken posted. Most baltic boats are built with the risk of rock bashing in mind so many have an internal bulkhead in the bow section so that damage can be sustained but noticed via a small bleed hole but stop the boat from sinking. Exposed frames and ribs are therefore essential for easy damage assessment and ease of repair. Look at a Finngulf for this.

 

[Twister_Ken]

At present my lottery boat would be a Southerly. I own an AWB.

When studying boat costs, weights, quality a few things struck me. Malo & HR etc are quality boats that originally were a lot lot heavier than AWB's but they were still dearer £ per kg than AWB's.

All boats are strong enough and with better understanding of structural strength the weights have reduced (even on HR's).

Quality boats still have a strong hull (some with a sandwich construction for better insulation above the waterline). Apart from the thickness of the GRP hull the next thing to consider is giving the boat its rigidity/stiffness. They all started with GRP ribs and stringers bonded to the outer hull but with the need for even cheaper construction Beneteau led the way and created an internal hull like a waffle that when bonded to the outer hull gives great strength. Its cheap effective and works and the only downside that I can see is the difficulty of assessing any debonding after an impact or grounding. X boats looked at the structure and put in a galvanised steel frame taking the keel , mast and shrouds - structurally very sound. Arcona copied this idea. Both have the hull effectively sandwiched between the internal frame and keel and the main stresses on the hull are imposed only by forestay and backstay. As a Structural Engineer I like this idea but was surprised when a 46's keel struck a rock in a harbour (the skipper/owner insists it was a slow/slight impact) and the inner frame moved and had to be unbolted and repositioned! one slightly misleading point about this form of construction is that X boats counts the internal steel frame as ballast which results in a false ballast ratio - as if it was GRP it would not be considered as part of the keel weight! Not sure what Arcona do.

The quality boats AFAIK still do the GRP ribs and stringers bonded to the hull while the trend is for the AWB's to now follow the Beneteau inner waffle GRP hull for cost reasons.

I have a 2005 Jeanneau 43DS and frankly would not buy a waffle constructed boat but lots are made and are adequate so frankly is probably a bias on my part that is not logical.

Southerly AFAIK still do the inner ribs and stringers so you can inspect the structural members beneath the floor. There are cost implications and thats while a Southerly to me is my desired (but lottery win) boat. I am hoping that Arcona bring out a DS version and drop Volvo engines in favour of Yanmar but as any long keel enthusiast will confirm we are all prejudiced to some extent. Until then I am sticking with what I have as the cost difference to step up in quality from my current boat is IMHO far too high.

Arcona doesn't count the backbone as ballast.
Arcona uses Yanmar engines in some models.

 

[Sailfree]

Arcona doesn't count the backbone as ballast.
Arcona uses Yanmar engines in some models.

Just need a DS version and I will be reaching for my cheque book!!

 

[Twister_Ken]

Just need a DS version and I will be reaching for my cheque book!!

Sorry, no info on future product plans!

 

[pvb]

Now, I would go a long way to avoid a boat laminated around balsa wood.

Not that you need worry, I am sure it delivers a lot of advantages when new, and when looked after. As a twenty year old secondhand proposition the outlook is not so bright. A depreciating asset, a sort of teak deck buried inside your hull.

Hallberg Rassy boats use Divinycell rather than balsa - doesn't absorb water, doesn't rot.

 

[doug748]

Hallberg Rassy boats use Divinycell rather than balsa - doesn't absorb water, doesn't rot.

Good show. Now there is only one thing left stopping me buying this boat:

http://www.yachtsnet.co.uk/boats/b57811/b57811.htm





.........Poverty :-[