Cosmetic strakes on welded aluminum hull?

Discussion in 'Boat Design' started by Winign2, May 24, 2013.

  1. Winign2
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    Winign2 Junior Member

    On this welded aluminum hull are the eight uppermost ridges purely cosmetic and intended to resemble the strakes on wooden hulls?

    Those are spray rails parallel with the bottom of the anchor, right?

    This looks like an S-bottom hull rather than a soft or hard chine hull, right?

    The boat is a 1967 Crestliner Norseman 19 Day Cruiser.

    [​IMG]
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Welcome to the forum Winign2

    Whilst there are a wide range of experts and specialist on this site, one expertise/skill we do not have is ESP.

    You're going to have to provide some pictures and/or drawings to clearly explain what it is you are attempting to describe. Without such...no one has a clue I'm afraid!
     
  3. Winign2
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    Winign2 Junior Member

    Sorry about that. Photo added to original post.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    It looks like purely cosmetic to "look like" a wooden hull.

    However looking at this sales literature:
    http://www.retrocrestliner.com/1967norseman19.pdf

    It appears to suggest that it is indeed made up of "strips" of ally. Not only to resemble a wooden boat, but made like one too! (Crest-weld lapstrake aluminium)

    I'm not familiar with this type of boat, I suggest you contact forum member PAR whom is far more knowledgeable on these type of boats than I am.

    Yes, below the anchor is a spray rail.
     
  5. Winign2
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    Winign2 Junior Member

    Thanks Ad Hoc.

    Just noticed it has two additional riveted on pieces under each side of the hull which I think are lifting strakes.

    [​IMG]

    [​IMG]

    Transom dead rise seems fairly flat compared to the bow.

    [​IMG]

    Prior owner suggested the high center of gravity and I suppose the hull means it is best in smaller waves.
     
  6. Petros
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    Petros Senior Member

    while the hull is made to look like a wood lap strake design, it also serves the purpose of making the hull more stiff, saving weight. there is be minimal effect on the performance since the lap strake part of the hull is well above the water line.

    It is a clever design actually, traditional look but uses modern construction, and likely saves weight as well.
     
  7. DCockey
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    DCockey Senior Member

    My guess is the ridges were intended to make the boat resemble a wood boat, stiffen the sides, and also make any waviness in the sides less obvious.

    I looked at the sales literature link and didn't see anything which indicated the sides were made from individual strips and did not see any reference to "Crest-weld lapstrake aluminium". There are several references to Crest-weld aluminum" and a sentence "Crestliner's exclusive CREST-Weld unitized hull . . . already a leader in the field of welded boats." The "weld" probably refers to welded joints at the stem, keel, chines and transom edges rather than riveted joints which were used by some other north American builders of aluminum recreational boats.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    See here:

    Lapstrake.jpg
     
  9. Winign2
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    Winign2 Junior Member

    The prior owner added sound deadening material along the hull so I don't think I can pull it off and take a look until I'm ready to replace the material.
     
  10. tunnels

    tunnels Previous Member

    i cant believe it !!

    Those bits of wood called lifting strakes planted on the bottom of the hull would be about as useful as **** on a bull !! the amount of lift generated at any speed the boat would be traveling at wouldn't help at all with lift!!
    Why do people do such silly things !! if anything they probably slowed the boat down !! :confused:
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Bits of wood :confused: I don't see what you see ! :p Pressing or swagings of thinner gauge sheeting is the perfect way to stiffen and "beautify" all at once. It is standard practice these days for small aluminium boats. As is the use of extrusions along the chines, keel, and gunwales. Unfortunately your kidneys may be re-located nearer to your shoulder-blades in practical use. :D
     
  12. PAR
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    PAR Yacht Designer/Builder

    I haven't seen one of these in a long time. The topsides are stamped, not welded, though the chines, centerline, transom, etc. are. The simulated strakes do as David suggested, stiffen the unsupported areas and of course look like strakes. They also help a great deal in knocking down spray, so a bit more then just cosmetic in nature.

    The hull is a warped bottom with a touch of "arc" worked into the bottom. This again was to stiffen the hull shell, prevent "oil canning", decrease internal stiffener requirements, remove some of the hollow in the WL's, etc. It's not the best approach for high speed craft, but these hull forms are limited to about 40 MPH anyway, so it's a moot point. The deadrise on these is slightly deceiving, because of the arc bottom approach, but this boat has sufficient "grip" that she could easily handle some chop fairly comfortably, certainly more so then a flat plane version of warped bottom.

    Strakes do help considerably Tunnels. Nearly every single powerboat design in the last half century, has them and do you really think a manufacture would install them, if they could save the money in materials and labor, because they weren't needed? It's simple math really, take a 2" wide strake and calculate the lifting area on it's length and multiply by the number of strakes. Yep, suddenly it all makes sense. Strake design can be critical in high speed craft, but not so much on a boat as drag limited as this one. No, they speed the boat up Tunnels. The surface area, stripping action and flow control all contribute to decreasing drag, wetted area, etc., which are serious things to consider, on high speed craft. For example, this boat's speed i limited purely by the drag it's hull creates after it reaches certain speeds. You'll need an atomic reactor to go much faster, so if you can install some strakes, to decrease drag or increase the drag limit threshold, well it's an easy decision to make, again, once you do the math.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Still looking for these "bits of wood". Are they stealth strakes ?
     
  14. tunnels

    tunnels Previous Member

    What are strakes really used for anyway ??

    Strakes are on the bottom of the hull !!!
    Strakes on that kind of boat will have very little if any lift that would be noticeable , Strakes anything less than 50mm wide does nothing except makes lines in the wake as it goes along !

    The placement and length along with the width of strakes can be very important to change and make a hull perform a lot different !!
    :D:p
     

  15. PAR
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    PAR Yacht Designer/Builder

    Your last comments serve to illustrate that first, you've contradicted you're previous statement in this thread and second, that you haven't a clue about the dynamics involved with strakes. These strakes serve several roles, some solely, while participation in other aspects of the hydro package as well (it's more then just lift Tunnels). Admittedly, the strakes on this hull don't offer much, but they do offer some and with their removal, there would be a performance detraction.

    BTW, Tunnels, the strakes on this hull are aluminum alloy, not wood and are riveted in place.
     
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