Feedback needed on a chambered boat design

General boating discussion
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Feedback needed on a chambered boat design


Post by alumioforte »

Hey everyone, and especiall kmorin because of your experience-
We've had a lot of people asking Silverback if they can make a 16' or so aluminum chambered boat with a 25" transom and foam filled chambers. We've come up with some drawings and renderings that will work on our CNC machines. However I'd like to get feedback from others because this is a relatively unpopular design in America, at least in comparison to the aussies and kiwis. Thoughts? Heres what I have so far. Hopefully this image shows up I still struggle with figuring out how to upload photos.
<img src=" ... -rev-1.png" alt="copper-mettalic-clipped-rev-1" border="0"> ... -rev-1.png

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Re: Feedback needed on a chambered boat design


Post by kmorin »

I'm an old marine traditionalist- so segmented hull forms are not appealing to me. The mitered sections of a press braked hull sponson is so unappealing to me that I term his entire effort "agricultural" and I mean it as a disparaging term.

"If it floats it should flow"; the shape of boats should be sweet to the eye, not necessarily true of a corn combine- so I'm the last guy to ask about this purely fabrication oriented faceted hull shape.

To give my reasoning, for my view point I'll start with the foam to get that out of the way. If a hull has a void, and the void is filled with any kind (including non-reactive styrene) foam - there better not be any water in that compartment- so.....
The welds creating the compartment need to be air tested and the void has to be vented to prevent vacuum egress of water or other fluids.

As I have stated countless times while attempting to address this design concept (utter; total; and complete ignorance portrayed in a design idea) if you air test a void- how will it get water inside? Except for #1 condensation- therefore these voids should have drain fittings & #2 collision/penetration at which time the foam will be used to maintain some flotation.

#1 is simple and has been shown, dealt with and discussed quite a bit- but we can go over it again if needed? #2 is solved by asking this question:

CAN anyone, anywhere, at any time, provide a picture of a welded aluminum boat with an actual TEAR of the metal in the hull due to impact??? So far all I've seen are 3rd, 10th and 20th strike images of 5052 river sleds with big block inboards running in single integer inch deep, gravel bed of a river strewn with rocks..... at highway speeds for a family SUV!!!!!

Let's restate that: I have seen one or two hull tears from the 50mph+ river sled hull impacting rocks for the umpteenth time- usually only slight tears too! But I don't know of any saltwater skiffs with holes from impact??

In other words: the idea that a void in a hull, especially a topsides, needs to have emergency collision foam insert is about 1/1,000,000,000,000,000,000-ish! If anyone can show a picture of a hull of 5086, pierced by a rock, in any normal running condition- THEN, I might have some reason to discuss this (otherwise) absurd idea.

I know the CG regs call for foam, but i refuse to follow idiots' direction as they have more experience than I do at being ill informed. And, if any bureaucrat/CG person will show me their couple hundred still running skiffs- I'd be willing to discuss facts with them... until then: I consider them spectators only- and anyone can buy a ticket to watch.

In the meantime- let's try on my experiences of the past few decades (again)? I've built a series of set net skiffs (more than a dozen dozens) that were 5', 6', and wider at the chine that landed 4k to 10k of salmon in following seas onto leeward gravel and rock strewn beaches and have done so for 40plus years.

They are all still doing that job, and have no holes in them except those worn in by sanding off the bottom thickness by dragging these boats with tractors and trucks on that same gravel beach! No holes by impact after landing countless tonnes of salmon onto rocks in sometimes a dry break onto the beach!

So.... back to the idea of adding foam in a air tested chamber? What kind of ill informed buyer would want to buy a boat that was made of a metal they just didn't comprehend? ( I know that the CG wants foam in a mfg'd boat less than 20'LOA)

What I did was to keep a .357 and some wad cutter ammo in the shop. And out back the shop's lot butted a big open swamp where nobody lived... so when I got the "how strong is this stuff" question?? - I'd take the newby out back. Hand them the pistol and ammo, then show them a series of 1/8", 3/16" and 1/4" plates hung in frames and offer them the opportunity to "become informed".

The wad cutters will stop in 1/8" at 80' (depends on how hot they're loaded) and all the others perform more impressively... and that is at quite a bit faster rate of travel than a skiff!

Then, for the really ignorant; I had put some 3/16" plate, cut in a circle an 18" a circle- over a tire laying loose on the ground.. I'd hand them a 8lb hammer with a long handle and offer them to 'break through the plate'.

I'm not sure what else you can do for boat buyers who're so ignorant about aluminum alloys except to allow them to bring some wood and glass fiber samples to compare their performances?

Foam in a void is just plain silly, IMO. Anyone who thinks differently is either listening to the totally absurd 'gummint' regulations - where regulations are apparently based on purely open form, pressed parts, metal boats of the stamped out type- ie. no voids sealed by welding (!) OR... they're just plain ignorant of the physics and history of welded metal boats.

MY take is that a boat with segments, foam inserts and all the rest will cost more to build than a nicely shaped 20'er- so why bother with a 16'? that costs more to build and is terminally ugly? (Ugly to my eye, perhaps not to others?)

"A thing of beauty is a Joy forever".
"Combines are for harvesting corn, on dirt."

the littlest/shortest/smallest skiff I've done recently is here

I'd prefer to offer some "looks" over the segmented, bent section panels that you're showing?

Kevin Morin
Kenai, AK
Last edited by kmorin on Mon Jan 14, 2019 6:42 pm, edited 1 time in total.
Reason: typos

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Re: Feedback needed on a chambered boat design


Post by Krisinak »

i would prefer to sink than have a foamed boat. its wrong for a host of reasons. rant/off

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Re: Feedback needed on a chambered boat design


Post by alumioforte »

Ideally I wouldnt do foam, rather just an airtight chamber- but I'm within driving distance of the local Coast Guard inspector, and if I dont pass, we get it on our record-literally. We asked him why other builders get away with not having to have foam galore on the less than 20' boats- the answer was "they're too far a drive or geographical distance from available factory inspectors". Oh well, such is the outcome of building right in Seattle.

A lot of people like the Stabicraft and euro style builds- its definitely not the norm over here. I guess time will tell.

Thanks for the input, this is going to be an interesting market test!

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Re: Feedback needed on a chambered boat design


Post by Chtucker »

Count me in for 10' version.

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Re: Feedback needed on a chambered boat design


Post by alumioforte »

Interestingly, this thing has been almost wildly popular so far. :clap:

Today we sold a 14' version, so I guess smaller sizes in this design are appealing from a safety perspective. chtucker, if you want a 10' I think we can do that, would it be 20" or 25" transom? same width, or narrower? email me at and I can send you drawings.

Sea word
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Re: Feedback needed on a chambered boat design


Post by Sea word »

Glad to hear the general opinion on foam here. In wood boats it’s a death sentence, and it seems to me that it was cooked up by boat mfg to get the coast guard to require them to put it in. Why? Well, so that boats wouldn’t last forever. Gotta sell new boats right?

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