Interesting aluminum design

Discussion in 'Multihulls' started by Stutts, May 30, 2009.

  1. brian eiland
    Joined: Jun 2002
    Posts: 4,948
    Likes: 179, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Yes I was familiar with David de Villiers website and dwgs. I just had not seen that photo in the water. I thought maybe you might have shot it. I now see it came from the builder's site.

    I met the American gentleman who is building the vessel, and only recently ask him for an update on the project and some photos. Haven't got anything yet.
     
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    "...To keep the weight down we are using Sealium alloy which is 15 to 20% stronger than the conventionally utilized 5083 grade.."

    Well, that is fine when comparing proof strengths and as-welded strengths,yes Sealium is better than basic 5083. BUT, and this is where all these claims tend to fall down is that once you crunch the numbers on what is an allowable thickness for example hull plating, the change using 5083 will go from say 5.15mm to 4.85mm in Sealium. So what do you buy if using 5083, you still buy the 5mm. What do you buy when using the Sealium, get 4.85mm...no, you buy 5mm, as its 'off the shelf'. So any weight gains are so minor it is not worth even considering!

    Gone through this experience myself so many times...
     
  3. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    Well thickness for thickness don't you at least get a 15 to 20% stronger boat with Sealium if using 5mm? No harm in that surely.
    A lot of heavy duty work boats, big police and coast guard boats are built in alloy nowadays, not steel of glass due to modern construction techniques in alloy that are light weight and as strong as buggery. Wouldn't you rather bounce around on a reef or hit something in alloy than glass? Glass is strong but also brittle. Not so alloy.
     
  4. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    No you don't generally get an "increase" or "decrease" in thickness, certainly not on smaller boats. If you're up in the 60~90m size, then yes as you can shave off 1mm or if you're lucky 2mm here and there.

    A boats strength is not just the material and what its properties are when tested. It comes down to how well it has been designed, load paths, shear paths, redundancy in the structure, arrangement of the details, removing stress concentrations, good access for the welder etc etc.....blanket statements of comparing one alloy to another does not take into consideration all the 'elements' that go into a well designed boat...

    If the boat has been designed and built properly, doesn't matter when hitting a reef, it is all the same...however, if there is no structural redundancy and the designer has used the calculations to the max with no margins etc etc...doesn't matter what the material is, ...it'll fail!
     
  5. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    Out of interest, I put the question to the 62' designer about possible weight savings using Sealium and another question on my mind about glass cats floating and if an alloy cat is more likely to sink in the event of a capsize. His reply:
    -----------------------------------------------

    "Thanks for your email, which raises some interesting points. Briefly my answers are as follows":

    1. I agree with what you have heard in regard to Sealium plating but on the 62’ design we were able to use 5mm in place of 6mm in several areas and ditto with 4mm instead of 5mm so we did make some weight savings. At the end of the day performance was a big issue with the client for the 62’ cat so we decided not to compromise.

    2. I do not agree with the statement that glass cats will float if capsized and alloy ones won’t. Assuming the glass hull is cored there is obviously a bit more flotation available but not enough to keep the boat afloat. Rather, air gets trapped in areas of the hull and this prevents sinking. A similar thing would happen with an alloy cat design.

    3. In actual fact my 62’ cat has watertight subdivision whereby the forepeak and aft engine room are totally separate from the rest of the accommodation and therefore this boat would be less inclined to sink after a capsize than a glass cat with no subdivision.

    With kind regards,
    David de Villiers
    ---------------------------------------------

    Monohulls that capsize also float due to trapped air when they lose their keel [Tony Bullimore, Sth. ocean] and if they don't, they mostly would self-right. Tony was lucky that he was inside the hull and also wearing a survival suit. If he had been outside in the elements, he would have quickly been swept away from the boat and died. Ditto on an upturned cat in bad weather too I guess. Especially anywhere cold.
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Stutts

    "...we were able to use 5mm in place of 6mm in several areas and ditto with 4mm instead of 5mm so we did make some weight savings..."

    So they ahve justified to themselves that 5mm meets their design requirements in-place of the 6mm...that's fine. I suspect the boat is not built to any Class, just their own in-house codes. However, if it is built to Class rules (ie designed), then perhaps their original 6mm may have been too heavy to start with on the previous design since changing from 6mm to 5mm on such a small boat simply by changing the alloy (Sealium from 5083) is not possible when building to Class, only on larger vessels. They qualified this by saying ..." in several areas..." ie not carte blanche the whole boat such as the whole of the hull plating. If they told you the exact weight saving as a percentage from Sealium to 5083, i am certain it is not in the 15~20% as is implied owing to the change to Sealium.

    In DNV for example, they class the difference as 145MPa to 125MPa. But when 'designing', the actual allowable design stress is taken from (200 x F1) and the F1 for Sealium is the same as 5083. Therefore the "increase" is only for minor not major.
     
  7. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    You have moved the argument I think. The original claim from the designer was: "...To keep the weight down we are using Sealium alloy which is 15 to 20% stronger than the conventionally utilized 5083 grade.." Hardly a claim of 15-20% weight saving. 'Some weight saving' was the claim from the designer, which is a reasonable claim I think.

    Considering the boats intended purpose, I'm sure the boat was not built to class rules.
     
  8. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Stuttts

    With respect I haven't. It is called marketing!

    They use the Sealium and its 15~20% improvement in strength as a "claim of major weight savings"...when in reality it isn't as i have noted. It is just marketing, which you have been 'sucked into' as many are which is why this approach in promoting a design as 'being better' is taken by many. QED.
     
  9. Zed
    Joined: May 2009
    Posts: 232
    Likes: 13, Points: 0, Legacy Rep: 179
    Location: Australia

    Zed Senior Member

    The boats lines remind me of Chris Whites Atlantic series.
     
  10. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    I think you have still moved the goal posts here Ad Hoc. You have the designer claiming things [in quotation marks too] he never claimed and then calling the claim a marketing pitch I've been sucked into.

    You have turned a claim by the designer of 'some weight saving' into a claim of 'major weight saving' [BIG difference] that are your words, not his and have then gone on to accuse the designer of presenting a marketing pitch based on words your putting into his mouth. Now that's shifting the goal posts!
     
  11. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Stutts

    You're missing the point totally.

    By saying "..'To keep the weight down we are using Sealium alloy which is 15 to 20% stronger than the conventionally utilized 5083 grade.", they have juxtaposed the notion of "weight saving" alongside that of an alloy that is 15~20% stronger.

    This plays on the notion that you equate weight saving with the use of the Sealium. This is simple marketing (To think it as anything else is just ignorance). They haven't told a lie, since they can save 1kg and legitametly say they have saved weight using Sealium.

    But how much?

    By further enquiry they say "...we were able to use 5mm in place of 6mm in several areas and ditto with 4mm instead of 5mm so we did make some weight savings...."

    In other words, they are still being vague.....but so what, doesn't matter. They don't want to say how much. Because all those like you have been taken hook-line-and-sinker into the subliminal notion of using Sealium = weight saving.

    To make a statement of "I am using Sealium, I am saving weight"...requires some justification. Their justification is Sealium is 15~20% stronger. Ok...so how much have you saved...well, don't ask, because just saying we are using Sealium, with it improved mechanical properties, leaves one with the impression it is a pro-rata 15~20% saving in weight, with the improvement in strength. Which it obviously isn't but they don't want to say that.

    To suggest that their intention is anything other than that, just indicates naivety on your part about materials, their usages and benefits in structural deisgn and how people sell boats by being vague with such methods for clever marketing.

    And then because you don't understand this you say the goal posts are shifting....!!! Go figure...
     
  12. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    Ad Hoc,

    Are you always like this?

    You seem to be laboring a point and trying to prove things. That you know more about design than I do? Well that is obviously a given and makes me an easy condescension target [which your last post was quick to deploy in it's final paragraph] and also allows you to do a bit grandstanding as well I think.

    Perhaps you should direct your arguments to the navel architect involved [not me as an easy target] and tell him he's all sales pitch and no sincerity and that you know more about boat design than he does. You seem to be laboring to prove a point of disagreement with the designer that you have created. Not created by me, nor him.

    As far as the final weight of the boat [or supposed marketing], regardless of what alloy he used, I couldn't give a rats arse as I'm certainly not buying an expensive 62' cat anyway and the designer knows that already, so he's 'marketing' me nothing. I'm certainly not replying to any more of your posts on the subject, as you are directing them to the wrong guy.
     
  13. Ad Hoc
    Joined: Oct 2008
    Posts: 6,564
    Likes: 583, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Stutts

    "...You seem to be laboring a point and trying to prove things..." I have no idea where you obtain that assertion from, I'm just questioning your replies which you appear not to like for some reason.

    You started the whole thread with "...I'd love to hear some opinions of this design..."

    Of which there have been a few, mine included. Opines do not mean they must agree with your position. When they do not you can choose debate why or choose to ignore it.

    However, When aluminum was discussed between myself and another you piped up with a quote from the designer about using Sealium....again, not sure why, but you choose to enter into this deviation of the debate.

    You asked "...Well thickness for thickness don't you at least get a 15 to 20% stronger boat with Sealium if using 5mm?.." which i replied above in post #19.

    But you for some reason decided to go to the designer again for a more 'in-depth' reply, again not sure why you kept asking the "forum" if you already have direct links with the designer. I can only assume you perhaps were not happy with my blunt assessment of using Sealium, so you wanted to hear from the designer. However, these are questions you asked the designer, no one else did.

    You are taking someone else's position without understanding why, when the reply is not as you expect. You then seem to draw illogical conclusions based upon the posts that " You seem to be laboring a point and trying to prove things". If you read above it is clear you are asking the questions, no one else.....had you not asked the questions to me, i would not reply. But you persisted in asking more questions so i answered. Again see the pattern, you are asking the continual questions, no one else. You then asked the designer as if that justifies your stance, there is some logic there, somewhere...???

    As i said way back in post #2
    "Every design has an objective...doesn't mean we must all like or agree with it!....So long as the design satisfies the client requirements, what does it matter?"

    well...it seems to matter a great deal to you for some reason.

    As for "..That you know more about design than I do.." I do not know you from a bar of soap, and you have no idea of my background either. I could be 15 year old kid with high speed access to the Internet for quick replies. But for a debate like this, it doesn't matter, because you asked for opinions.

    An opinion is simply that, take it or leave it....or is that not what you meant in your post #1?
     
  14. brian eiland
    Joined: Jun 2002
    Posts: 4,948
    Likes: 179, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member


  15. Stutts
    Joined: Apr 2009
    Posts: 22
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Australia

    Stutts Junior Member

    Thanks for the heads-up Brian [Your in Tazzie arn't you?]. I am looking for a new boat to replace my monohull and from 30 odd years of past experience with the Oz coast, I think a cat would be ideal to save some money on some mooring fees and to explore many of our shallower waterways and reef anchorages . I was thinking around 44 to 50' for my wife and I with a low cruising weight with moderate performance and a safe design. A cutter rig though, not ketch.

    I'm trying to avoid glass production boats that seem to cater for far too much accommodation [read caravan charter cats] but did like the 62' David de Villiers alloy design. My [only] em to him was mainly inquiring whether a scaled down version of the plans were possible. No, a complete new design would be required at considerable cost, so that's that in that department.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.