SailNet Community

SailNet Community (
-   Boat Review and Purchase Forum (
-   -   the concept of unsinkable yachts (

Johnno 07-01-2005 04:53 AM

the concept of unsinkable yachts
If you are in the market to buy a new yacht then think long hard before you part with your hard earned dollars or pounds or whatever before you lay them down for a boat that makes a claim to unsinkability.

The concept itself is nothing new. Sadlers used it years ago. Etap have legitimised it even more with certification. There are also several ways it can be done and there is plenty of material out there on the Net that discusses the use of foam, floatation bags and even closing compartments.

Sadlers and ETAPs though use double skin technology with GRP. It is not to be confused with Whipple shield technology in spacecraft either - in that sense it is very low tech!

It is easier to provide unsinkability on glass boats. Remember the Boston Whaler. It is certainly more difficult on a steelie or even a heavy timber or even aluminium boat. Although some of the other methods are more appropriate with those materials. One noted marine architect I spoke to said it was easy enough to do in any boat and I agree with that - his reason for not designing such safety into all boats was the lack of interest. Maybe it is like cars years ago when the manufacturers claimed "safety does not sell" as their excuse for not including it in all vehicles.

What the boat manufacturers do not tell you if you are buying an "unsinkable yacht" and worst still when you approach them are not prepared to say is what happens when the keel sheers. The truth is it happens and when it does the results can be disasterous in any boat.

Why it is important to understand the limits of unsinkability in the buying decision is that boats that are being sold as "unsinkable" come at a premium so if you are going to pay the extra you may as well know that the concept of unsinkabilty is limited to just that.

When the keel sheers an enormous weight is suddenly removed from the boat. When it happens, and recent Sydney-Hobart yacht races show that it does, most boats either sink or just turn turtle.

It is all very well for marketers like ETAP to say their boats are unsinkable but the reality is that is not much comfort when the boat is upside down and you are trying valiantly (usually in heavy seas) to hold onto what little grip or flat section there is on the bottom. The boat certainly won''t right once the keel is gone and indeed with so much floatation low down in the hull the thing will turn turtle very quickly. Hey even I learnt that in the bathtub!!!!

The reality is that "unsinkability" is just that - there is no guarantee that the boat will stay upright. So do not be seduced by the claims that it can still be sailed when it is flooded. That does not happen in all circumstances. Even though the brochures and deliberate floodings described in them are designed to make you feel warm and fuzzy about such things.

There is a lot of obstacles out there in the ocean, some living, some not, and a keel is not made to take that much impact. You don''t have to be a rocket scientist to understand that any pressure at the bottom of the keel translates into a lot more pressure at the top with fin type keels. It is all to do with leverage. And I am not talking about dingies here - I am talking about craft that weigh or displpace many tons.

Whatever the manufacturers claim the bottom line is and history has shown that fin keels just cannnot take that sort of punishment.

Maybe it is time ETAP too considered longer keels otherwise all cruisers who want that concept will be better off to resort to other boats with inflation bags or closing compartments to stem the flow rather than opt for foam core plastic boats which despite the claims are still delicate in such circumstances. Remember steel has about 27 times more impact strength than fibreglass of the same dimension.

That does not even take into account that the present foams all take on some water albeit some less than others. There is also the nasties that love to eat that stuff. They too are matters that the manufacturers don''t want you to know.

At least if you buy an unsinkable boat after reading this you will know that they do in fact have limitations and what to expect. For most of us though I wonder whether all that hype is really worth the extra expense. I for one don''t think so. Probably the reason why ETAPs are not volume sellers either.


Jeff_H 07-01-2005 06:03 AM

the concept of unsinkable yachts
With all due respect I think that your post is way too much of an over- simplification and in some ways is a bit misleading in some of its apparent implications.

For example it is a bit of a non-sequitor to say that "You don''t have to be a rocket scientist to understand that any pressure at the bottom of the keel translates into a lot more pressure at the top with fin type keels. It is all to do with leverage"

and then to assume that means:
"Maybe it is time ETAP too considered longer keels";

The reason that I say that is that in most long keel boats the ballast keel of the boat is placed at the leading edge of the keel and for any given hull form the ballast keel itself rarely extends any further aft of along the keel than it would in a fin keeler. That happens because in designing two boats of equal design except for the keel, there is only one right place to place the ballast and that is set by the 'statics' of the boat.

In a frontal impact on a long keel, given the rigidity of the ballast keel, the ballast keel itself tries to rotate up through the bottom of the boat, independent of the ''deadwood'' portion of the keel, with pretty much the same impact force that a fin keel generates as it tries to rotate up through the bottom of the boat.

In other words, a more accurate conclusion is that you might then argue that deep draft is a bad idea from an impact standpoint, but of course that would be counter to what is ideal from a motion comfort and seaworthiness standpoint.

And if puncturing of the hull is your primary concern then I would also caution against boats with encapulated keels because they are especially vulnerable to puncturing the watertight envelope in a frontal impact to the keel.

I also think that your statement "Remember steel has about 27 times more impact strength than fibreglass of the same dimension"; is also very misleading. That is only true if the dimension is thickness. If the dimension is weight, that is totally eroneous.

To more realistically represent the reality of the situation, the statement should have said something to the effect of "Remember that pound for pound a moderately densely cored, vinylester resin glass hull with a minimum of non-directional material is roughly 8 times more resistant to puncture than a A36 steel hull, and a vinylester resin and glass sheathed cold molded cedar/fir hull is roughly 11 times more resistant to puncture than an equal weigh A36 steel hull."

It is often neglected in discussions of the relative strength of materials that the density of steel is so high compared to glass (roughly 4 times denser) or typical wood planking species (roughly 17.5 times denser), that steel plating and structure of equal weight is way thinner than either fiberglass or cold-molded construction, and so despite steel's superior cross sectional properties, steel is actually way weaker than the other two materials on an equal weight basis. Of course this last point somewhat complicates the discussion a bit because few glass or modern wooden boats are constructed with hulls of an equal weight to a steel hull.

Lastly, I also think that the discussion of full floation in a cruising boat is an extremely complex one. In my mind the real issue with trying to get full floatation is the weight and placement of that weight of the floation material, as well as the volume of the boat that is given over to that create that floatation. If sinking is so important to you then it probably makes more sense to look at the puncture issue rather than the floation issue. Using modern materials and careful engineering, it is possible to achieve puncture resistance at any impact speed that a sailboat is likely to sustain in collision at sea. If you really are concerned with seaworthiness then it would make a lot more sense to push towards engineering for a higher impact load resistant design on both the hull and keel. That can be achieved with less of a cost, weight and carrying capacity penalty than trying to achieve full floatation.


WHOOSH 07-02-2005 02:36 AM

the concept of unsinkable yachts
Hanging out here all by itself, Iīm left to wonder what generated this post in the first place. Having said that, here are a couple of addīl observations in addition to Jeffīs more technical analysis:

I see no correlation between a boat (letīs presume itīs an Etap) with in-built flotation and a lost keel. None. So if we back up to the larger data base, of all boats that are sunk, rolled, dismasted, clobber reefs, go aground and otherwise experience a terminal event, how many keels fall off? Virtually none relative to any kind of longitudinal statistical analysis. So most of this post, which involves follow-on effects from a lost keel, strike me as irrelevant to the topic of unsinkability specifically and design issues, generally.

Sadlerīs brand name has been recently resurrected but Sadler has not built boats with in-built flotation for many years now, so Iīm not sure how their product is relevant to todayīs boating world except where the potential buyer is in N Europe and wants one of the relatively small percentage of Sadlers that were built with flotation. Similarly, bagged floation has been commercially attempted in the past, only to fail at meeting even the simpliest criteron, that of keeping the Mother Ship afloat, and the vendor had to abandon the idea this topic also seems essentially irrelevant in todayīs market.

To my knowledge, Etap is the only builder of a range of offshore sailboats with in-built floation, and the only builder that then meets certification for the boat to be *sailed* in the totally flooded condition while still retaining acceptable stability. The fact that these boats may also inhibit catastrophic flooding due to a colision, depending on the location of the hull strike and what is hit and what speed, isnīt promoted by Etap but I think itīs worth considering as a potential, additional safety feature.

''Unsinkable'' boats are not UNcatastrophic Event boats, and so a fire may still require the crew to abandon the boat...but thatīs a small portion of the issues faced by an owner today. Beyond this, Iīm not sure what motivated this post.


JeffC_ 07-02-2005 05:57 PM

the concept of unsinkable yachts
Mr. T, you''re going to have learn to distinguish bettween a post and a rant.

And, Jack posted:
<blockquote>So most of this post, which involves follow-on effects from a lost keel, <u>strike me as irrelevant</u> to the topic of unsinkability specifically and design issues, generally. (emphasis mine)</blockquote>

Lost keels from submerged objects. <em>Strike you</em> as irrelevant. Very droll indeed.

Johnno 07-06-2005 12:49 AM

the concept of unsinkable yachts

I would be interested to know what you say the apparent implication of the post was?

Over simplification is one thing but I am not too sure that we are on the same wave length.



Jeff_H 07-06-2005 06:48 AM

the concept of unsinkable yachts
Hi Johnno

I am not sure that I came to a conclusion about the "apparent implication" of your post. I think that there were several aspects of you post that seemed to suggest an apparent conclusion that perhaps warranted further clarification or discussion. My post pretty much discussed those aspects of your original post that I thought suggested dubious implications or conclusions. Those areas that I was concerned about included the likelihood of a fin keel vs a long keel of breeching the hull in a grounding or collision, the relative strength of steel vs. fiberglass (or wood), and the issues of designing a boat for full floatation, vs designing a boat to resist impact damage in the first place.


thorJ30 07-07-2005 03:59 PM

the concept of unsinkable yachts
whats this all about .;.;.

lets recap in plain english ....
etaps unsinkability sucks, because they loose the keel ? ( and than you have to climb above and hold on for dear life ...

havent heard to many boats loosing their keel.... forget the canting race wonders for a second, which nobody of us are going to sail anyhow .....

I dont like etap, because they are trying to reinvent the wheel( literally) and come up with all kinds of new ideas... see the funky steering for example. I dont like them cause the foam is so thick, you loose a lot of room inside ... But for some people unsinkable boats have their merits... so let them go ahead and buy them.

if you like unsinkability you can also go with a catamarane .... lol
a whole new can of worms is about to open ...



h20ski 07-07-2005 07:37 PM

the concept of unsinkable yachts
sounds like Johnno is a yacht salesman and possibly lost a recent transaction to ETAP and wants to gripe about it here by attacking them. ETAPS are fine boats for real sailors.

Silmaril 07-07-2005 09:14 PM

the concept of unsinkable yachts
It''s late but I''ve been away for a bit... I saw this one hanging out there and had to comment...

Losing a keel? Come on... Let''s see, my fiberglass boat has a fin keel, that is attached to a pretty darn massive steel hull matrix (a grid about 7'' long and 7'' wide, 1/4" steel tabbed directly to the hull and bolted into stringers and bulkheads) Figure I could hit a coral head at 15 kts and not break it loose.

The modern interpretation is the matrix used by X-Yachts.

I HAVE been onboard a 47'' Nautor when it hit a submerged granite rock at 6 kts. No damage.

A well designed and built vessel with a fin keel is reinforced for just such occurances. At least all the ones I would want to be out on.

Etaps are just too goofy for me, anyway. I get the whillies whenever I see "Picture Windows" on a salon. Thoughts of sun damage induced failure down the line are not something that would give me the warm and fuzzies on a crossing.

Other types of flotation have been tried. Anyone remember "Yacht Saver". Airbags that would deploy inside the boat. Two problems, 1) where''s the crew going to get out of the elements. 2) better be pretty damned sure the hull/deck join would stand the stress of supporting the hull (not something it was designed to do most of the time)

I guess that''s the lure of video games these days. Gives you the mental challenge without the risk. Well, maybe carpal-tunnel.

Just get out there and sail... Be prepared, and accept the concequences of your decisions.

928frenzy 07-08-2005 03:38 AM

the concept of unsinkable yachts
I doubt all seaworthy sailboats can survive hitting a submerged object. There may be some that can, and maybe you''ve been on a few of them, but most sailboats are not built to withstand catastrophic collisions.

Etap has an interesting design. Perhaps their improved safety will become more popular as more families go cruising. (Keep in mind, automotive safety only became popular after the sixties, as more women started driving and long distant family vacations became easier as a result of new interstate highways.)

~ Happy trails and sails to you ~ _/) ~

All times are GMT -4. The time now is 12:10 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
(c) LLC 2000-2012

For the best viewing experience please update your browser to Google Chrome