10'-12' aluminum outboard skiff

[lwight]

I'm looking for plans and CAD cutting files for a small runabout. Finding lot's of 16' plans but very few small boats. Any suggestions?
Larry

[kmorin]

Larry,
There are most likely very few plans or outline shape files for this size because of two market forces.

Almost any skiff this size would be thin- say less than 0.080" bottom and topsides. This thickness material is most often riveted and most riveted hulls are manufactured to justify the jig and fixture costs. Lund, Gregor, Starcraft, Monark, and other riveted skiff builders aren't interested in publishing their designs.

So one reason that smaller thin skinned skiffs aren't as likely to be available is that the people who design and build them aren't in the business of explaining to others how they make that product.

The other reason I think there are few plans available for this size is the lack of welder who want to build very thin hulls. Welding 0.080" or less aluminum, even 0.100" aluminum can be a challenge to keep the sheet material fair and clean.

So the next reason I believe there are few small skiffs offered is that the skill level needed to effectively weld thin alloy reduces the number of possible sales for this plans package. With very few builders interested in working this thin, coupled with the somewhat increased time needed to work in thin material, I'd guess designers spend more time on the 20' or larger sizes where there is a larger market for plans packages.

I believe Michael Kasten has a small welded aluminum boat plan at his web page.

Another method would be to convert a plywood design to metal. With very few exceptions you can simply copy the hull panels in metal as long as you provide an edge-to-edge fit instead of an overlap that might be found on a ply skiff.

I'm assuming that a one-off skiff would be welded (?) but you may plan to rivet (?); in any event, there are few of ANY aluminum plans available let alone smaller and thinner scantling skiffs. I think these reasons are part of why that is true.

I've attached a few images of a 14' skiff in welded aluminum that I've done recently. The reason to show this skiff is to suggest that you consider downloading Delftship Pro and create your own design? This skiff was cut to the output files or outlines laid down in D'ship Pro which proved accurate.

Unfortunately, I didn't have access to NC cutting affordably but the day or so it took to cut the skiff with power tools wasn't much of a slow down considering the layout was generated by the software not a plate model.

The blue painted skiff is 10' long and was built of 0.080" about 20 years ago (these pics show a face lift and rework). This skiff is just flat bottomed but is the type I think you've remarked about here? This type is an example of what you'd get if you copied one of the many plywood skiff plans available.

Once you get a plywood plans package you could get cutting files taken off by either the NC service or most CAD services (*.dxf, *.dwg, files are common types used) if you don't do that type of work yourself.

Good luck, with your project.
cheers,
kmorin

[lwight]

I'm downloading Deftship even as I type this! Thanks for all the great advice. I know you are right about the thicknesses; I may abandon this and build a slightly larger skiff but I'll explore Delftship a bit first.
Thanks again,
Larry

[kmorin]

lwight@sjisd.we,

Thinner metal requires a smaller cross section weld bead but the distortion/contraction in any group of welds isn't directly proportional to the size of molten mass or weld cross section. This fact makes the related rate of travel, arc length, arc cone size, mode of welding and wire feed very critical.

This extremely critical balance of variables becomes more and more exact as the weld size and parent metal get smaller. In 1/4" material with a 0.45" or 0.65" diameter wire the balance between all the weld factor variables is much more tolerant of one or another factor being heavy or light in the overall ratios.

However, that same tolerance drops to 1 or 2 percent when the weld is 0.100" or 0.080" using 0.030" or 0.25" wire to weld. In fact, many welding authorities and authors on the subject of metal boats will routinely claim aluminum MIG will not work on metals less than 0.125" thick.

While not [absolutely] true, this represents the widely held conventional wisdom on the subject. These welds are not that hard to do once the welder is aware of the real variables and learns to adjust for them. I'm not trying to discount the skill required, nor to make light of others' experiences or knowledge about these aspects of welding; but I've done work in thinner materials for a long time and can assure you that MIG work in metal as thin as 0.030" is mainly a matter of practice and self-education.

The real challenge is to keep the final boat hull's panels 'clean' ,fair, and smooth after they are welded. Welding is part of this issue but the design and build sequence are more factors than the welding by itself.

Good luck with Delftship. I've created a series of 'beginners' lessons for the software, written for friends that are learning to use Delftship Pro, and while they aren't published, I'd send them to you if you need some help getting up to speed with your skiff project.

iisco@acsalaska.net

Cheers,
kmorin

[lwight]

I so appreciate this advice. Let me take a rain check on the tutorials; let's see how far I get alone.
And I certainly appreciate the 'thin metal' points. I've been considering 3/32 or smaller metal so your caution (and encouragement) was very timely.

Thanks again,
Larry Wight

[dick stave]

www.metalboatkits.com (Trident welding in Richmond B.C.) have the cutting files for a 12 ft. skiff for $110.00 usd. Construction is .125" welded aluminum.

[kmorin]

dick stave, lwight,

A 256lb. - 12' skiff? Wow she won't be very handy on the beach for young people, can't be hauled on deck without rigging- even by a grown man, won't slide on the ramp, without a few men, can't be manhandled in a swell as it weighs more than a 'man-weight'.

The 10'-11' foot skiff shown above (blue) weighs about 100 lb. and an 8hp moves it much faster than needed.

I can easily understand some reasons why the kit is offered for 1/8" sheet, as mentioned above, but I'd wager not may of these 'tanks' have been made?

Seems pretty heavy wt. for so small a boat, I'd think she could be done in less than half that wt. - but the welding would have to be scaled to thinner material in order to accomplish that.

I've attached photos of a 17' gunning dory that has a 3" hollow [flotation] bottom and hollow double wall 'ends' and only weighs 155lb. I think 260lb. for a skiff as small as 12' is to much for that size boat.

Cheers,
kmorin

[dick stave]

Up here in CANADA, we consider this about the lightest boat a man would handle. you asked.

[lwight]

I posted my initial inquiry after seriously considering building exactly this boat. I, too, was concerned about its weight. I may build it anyway but first I'm going to consider using 1/16" instead of 1/8" stock. I've been alerted that the welding would be tougher!!

Thanks all

[dick stave]

It could be built in .100 gauge, although I would prefer pulse mig for that thin.
Proper weld sequence and down hand wherever possible to minimize distortion. 080 Ga. would be extremely tricky.