Aluminum Extrusions

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Steelhead
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Aluminum Extrusions

#1

Post by Steelhead » Sun Aug 28, 2016 9:42 pm

I'm considering building a 21 ft open sled for bay trolling for salmon, and was I'm wondering where I could find the chine extrusions? I have built a couple alum drift boats a few years ago and one 21' rib rigid dive Boat. also been a welder for 30 years.

Any help or links to others who have done the same would be great. I did read the one about the new sled build by reel song and that's the direction I would like to go.

Thanks Ray

Chaps
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Re: Aluminum Extrusions

#2

Post by Chaps » Sun Aug 28, 2016 11:35 pm

Most chine extrusions are proprietary to individual builders so not typically available but you might try Alaska Copper & Brass in Seattle as they may still sell some profiles
1987 24' LaConner pilothouse workboat, 225 Suzuki
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kmorin
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Re: Aluminum Extrusions

#3

Post by kmorin » Tue Aug 30, 2016 1:44 pm

steelhead, some remarks about building with insertion extrusions at the chine. These extrusions are a double edged sword- there's some gain and some potential for loss to the overall structure of the boat.

The gains are; #1 the conveniences of a finished edge at the chine without a weld on the outer most edge,
#2 a heavier cross section at the chine where impacts in shoal water is most likely to happen,
#3 a reduction in the level of panel edge curve fairness needed in cuts and prep; due to the finished/cut edges being inside the extrusion,
#4 and aid to forming to the tacked-up state since the edges are held by the insertion into the extrusion's slots.

One the other hand there are some losses to using chine extrusions that could be mentioned too.
#1 the extrusions are almost always 6061 and the hull 50 series so there's a small difference in alloys that leave the welds less malleable in bending if impact occurs. I've repaired sleds with major rock damage where the chines' welds failed and similar damage on sleds where the bottom and topsides just bent where only 50series was involved- no chine extrusions. Not all impacts will result in bends sufficient to fail welds- regardless of construction. A very heavy chine extrusion will, of course, help stiffen the chine to resist impacts, so that would act to counter the alloy differences by adding mass.***

#2 The extrusion chine design creates the need for twice the number of welds- four instead of two when using an extrusion- ( back stitching inside to avoid a continuous weld there will only result in crevice corrosion inside the extrusion even though its done by some Major name builders !) This increases (or can increase) the heat contraction distortion depending on the weld sizes and pattern the welds are added.

#3 Unless air tested the extrusions' sheet slots can act to promote corrosion: the sheet edge can become a source of corrosion due to water intrusion into the void around the sheet edges. Again, repair experience ; I've seen a few boats where the chines were welded inside and out (four welds) and when a section was cut out there was water caused crevice corrosion beginning inside the extrusion's pockets.

#4 in pocket type instead of 'edge' type extrusions the design of the sheet insertion part of the extrusion has to be much wider than the sheets to accommodate the variable angle between the topsides and the bottom along the chine. At the stern bottom to topsides may be at or close to 90-100 degrees orientation in the Body Plan (Section View). However as the hull lines/chine seam is viewed in cross section going forward- the angle gets to be greater where it approaches 150 deg. So the sheets need some 'slop' or tolerance in the two recesses of the extrusion to be able to accept the side and bottom over this change in angle. So that increased inside volume relates back to the other points about long term effects of this chine design.


steehead, just a review of the concept of incorporating a chine extrusion in any boat's design; there are pro's and con's. I've never used them- always relying on a sheet edge to edge fit and one weld inside and one outside. I've only done a few river sleds (inboard 454's w/ Jet pumps) and they've been out of contact for so many decades that I can't really report on their chines after the last 40 years? All the salt water skiffs, both commercial and recreational, have done OK without chine extrusions but then beach landing is not the same as river sled running as a test for structural design and performance of chine joints.

**** I recently looked closely at a very well built production boat (offshore 30'er sled type hull) that has chine extrusions which were so massive that I was amazed. These chine bars (obviously products of a proprietary extrusion plate) were almost 2" x 2" in size of almost solid aluminum!! This boat was rolled off its trailer in a highway accident and the chine had taken the impact along the after 4' of the hull. The total impact to the hull was so slight that you had to get down and look under the boat to see a very small deflection of the hull seam. So chine extrusions of this extreme size can be a very positive design element.


IF you have building experience then I'd say your boat will end up fine without extrusions in the chine joint? As Chaps has mentioned most of these extrusions are not for general retail sale as the design and plates are part of licensing process with the extrusion mills.

Cheers,
Kevin Morin
Kenai, AK
kmorin

ReelSong
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Re: Aluminum Extrusions

#4

Post by ReelSong » Fri Oct 07, 2016 1:37 pm

Steelhead,

While I aprreciate and respect everything Mr. Morin has to say and have gleaned much from him, Iwill add my two cents,

If I were building an open river sled like a few I have built, I believe extrusions defintley simplify the process and have there place as most all of the big production shops use them. Yes, most own there own rolls or the rights to. that being said I have purchased some chine and gunwale extrusions through Ryerson. If I were planning on bay and salt water use, the double and or quadrouple full welded chine are the king. Yes more work, but as bullet proof as an alloy boat can be. Kevins comments are right on.

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