15' skiff plans, boston whaler like?

[bkcorwin]

Hi everyone. I have been researching building an aluminum boat. I have been looking for plans for a boat that is something like a 15' boston whaler, or a small boat, designed for remote steering (read not tiller). I am thinking I would like a design that doesn't require cnc cutting, but that can be easily laid out on sheets and cut manually. I have seen the typical plan vendors on google, but was curious if there are any designs floating around the forums that have been built a few times, or have a good history of builds that may not turn up on google? Or if anyone has recommendations for suitable models?

I've considered something like this. http://metalboatkits.com/?product=16-foot-skiff. but honestly I am curious about other choices

Thanks for any suggestions.

Brian

[kmorin]

Bkcorwin,
welcome to the AAB.com Forum, there's a lot of territory to cover in your post so I'll address the points, but; I end up with a question of what boat are you looking for?

a boat that is something like a 15' boston whaler,

is a very complex shape with lots of 'chines' separating the various hull panels or surfaces. The bottom is gull winged or cathedral shaped with a central V, and a set of 'tunnels' then two side V's with some flats and ridges in between these three V's. In welded aluminum these would all be hull seams, welded joints between pieces of the hull cut in long 'fishhook' like "J's".

The reason this hull shape is not going to be found in any kit is the extreme welding skill, and time, it would take to weld such a hull without distortion so the result even resembles the plastic molded shape of the original. Next, the aluminum boat would not be as worth building because it would weigh about 1/5 or less the original plastic molded boat. Therefore the skiff would pound like it were flat bottom so; why bother to do all the hull shaping work if the result didn't provide a good ride and was so hard to build?

or a small boat, designed for remote steering (read not tiller).

This is kind of a wide open field, moving from the Whaler shape to 'or a small boat'! That means that almost any online plywood plans package for boats in the size range you describe could be a candidate for your project? If a plans package if offered for sheet ply construction, not ply wood planked or carvel hull forms, they could be converted to aluminum in most cases. It is often the case, however, that the conversion is not the simplest set of steps for the first time builder.... So staying with a metal boat kit may be the safest path.

NC cutting;

I would like a design that doesn't require cnc cutting

No hull HAS to be cut with NC equipment. All metal hulls' parts can be cut by hand after layout of lofting of the parts. I'm not trying to split hairs just making sure you do realize that NC cutting is a time savings in the build due to laying out or lofting being done by the computer and the cuts being done at higher than human speeds to lines not drawn full size? So any metal boat's parts can be laid out, cut, fit and welded by hand since that's how they all used to be done; however that was pretty expensive in time so NC saves time and reduces skills required to attain a high quality build.

but that can be easily laid out on sheets and cut manually.

Online use of terms like "easily" when describing sheet line layout makes for confusion. For example, if you're already familiar with layout grids for curve batten points, line-to-curve transitions, and curve fairing (?) then using that term 'easily' may be applicable, but if you have to learn those concepts, followed by their theory and practice.... well those steps could be seen as very difficult?

Hope to help you refine your thinking a little in regard what's implied selecting a design and planning the skills needed to build a welded aluminum skiff?

Cheers,
Kevin Morin
Kenai, AK

[bkcorwin]

Hi Kevin,
THanks for all the great feedback!

I will clarify my goal isnt for the multi chine hull of a whaler, but more the size of boat, with a remote helm, and for the same purpose, inland water, lakes, sounds etc. A shallow V hull of some sort would work great.

I'm actually really familiar with layout, and the application of NC technology. I own a bridgeport style CNC vertical mill as well as own a CNC router. However, the router is onlyt 4 foot square and its in my basement making bringing sheet goods down difficult. I am a classically trained mechanical engineer who has gone through a lot of time with drafting, layout, etc. My main thought behind easily cut by hand is that things with complex compound curves take way more layout time and for the goals of the boat, which are function over form, seem unnecessary.

So in closing the goals are simple shaped hull with a shallow v.

[kmorin]

bkcorwin,
With your post I can see that replying with a bit more in depth details could help along your project.

First since we're discussing a sheet form boat, there are no compound surfaces all curvature is flat, cylindrical or conic and even the tiny ( a few sheet thicknesses of the material) bit of convex 'bulge' of a V bottom in the forefoot and the topsides forward as the come to the bow stem; the compound development doesn't change the flat 2D (essentially) Bezier curves of the panel outlines or the frame edges when they're out of flat material (sheet goods). Therefore, because the hulls are (99%) developable surfaces there is no compound cutting, forming or shape.

Some boats, usually in the 26' and over class will have some English wheeling or even planking in the bow sections to achieve a compound shape but in a "5 panel skiff" this is not the case.

Minor reminder regarding "terms of art" that in a well designed welded metal boat, form is function; (while) function is form. I do understand you don't want to add 1959 Cadillac tail fins to a simple utility skiff, and I'm not suggesting that's worth considering, but I do note that the best designed skiffs many functions are performed by one piece of metal.

An example the kit boat you've linked to; the thwarts are air/voids/flotation and they are transverse ribs, and they are seats and they are potentially stowage, and they are bilge containment (if needed).

One item to further the discussion about NC vs hand cutting. The panel outlines or lofting is considered a big deal by most new builders, with your background a 'best fit' batten through a series of points will not be that much of a new builder fear; I've worked with new builders where curves drawn with aluminum extrusions as fairing battens to best fit a point set; was considered a big deal because of their fears.

However, once you have the panel outlines as curves that you can layout by hand, I'd observe, putting them into a CAD file for output to G-code is not nearly as much work, time, effort as laying out by hand. So emailing these curves tool paths to an NCshop.... is becoming more and more prevalent instead of hand layout, battening fair, and cutting and dressing the cut edges.

The five panels implied by the simplest version of the boat you're describing are the two bottom panels since you've specified a V and not a camber with a warp to (only) form a V forward. Then two topsides which will look like long slow, very flattened J's with the lower curve as the chine and the upper one the sheer. Finally a 5th panel is the transom, regardless of which of the several stern arrangements you choose.

The first complication is to add horizontal chine plates (reverse chine flat?? terminology?) and next being a flat at the sheer (sheer clamp/guard deck/gunwale plate??/ terminology?) and finally considering which interior and exterior structural elements that you'd use?

So far the "metalboatkits" 16's sounds like it has most of what you're discussing? I think you can see how to invert the midships thwart panel outline for your center console modification? Instead of walk-through or step-through seat; you'd put the center console there in amidships and walk around it by lowering the seats down to frame sections you could stand on/walk over.

What this means is taking the stock cut files you'd leave the outside profile of the seat thwart panel and change the inside lines to fit the new shape of a raised center console with lowered side frames to walk around the console.

Cheers,
Kevin Morin
Kenai, AK

[bkcorwin]

Good points all around. I have press brake and shear capabilities but do not have an english wheel so not needing one is great.

Yup no tail fins, but i think we are saying the same thing. I want something simple, and efficient. Which is much inline with what you said about form is function.

I have a few calls in to a local NC shop to get some estimates on cut time. I am not averse to paying to get it cut, and I may well, but there is some satisfaction to doing it by hand. I cnc mill parts all the time yet theres something to be said for doing it by hand on the old manual mill. Its not for production, its for fun.

I may go ahead and make a 12' skiff from theirs as a first check of how the drawings look and everything lays out. I can let my kids play with it when its done anyway.

I am curious how efficiently there drawings are nested, and in general what format they provide me with. I have a lot of money tied up in cam software so modifying their drawings to accomodate a center console is no big deal.

I have been doing some reading into the coast guard floatation requirements that you mentioned in another post. I had not been aware of those actually. I am going to email them and make sure that they have documentation etc to verify such requirements are met.

Thanks

[kmorin]

bkcorwin, I'd like to make a remark hoping you understand this is not directed at you in a disparaging manner, I'm making an observation that I've probably made approaching a hundred times on all sorts of metal boat building web sites, not to mention the pure welding sites.

Making a small skiff is not an easy ramp up to making a large skiff.

Now, if you make a 1/8" plate skiff that is 12' long; therefore totally not proportional scantlings, that is a different case. But what is the proportional scantling of plate for a 12' boat when a 24'er uses 1/8 or 5/32" topsides? I'm NOT inferring this is a linear 1/2 proportion but I am suggesting that the Lund, Gregor, Tracker, Starcraft hulls of this size range are 0.060" and in some cases less!

Will you be welding a 0.060" 12' boat? I know it can be done, and I'm not saying it can't be... what I'm noting for all our readers and remarking to you is; that a good beginning welded boat is 16 to 18' and I'd say wait 'til you've got a half dozen of those under your belt before moving down to thin materials.

Of course if you build a 'battleship' skiff; that is- 12' LOA and 1/8" thick ? ... OK fine... but it will weigh more than any 12'er ever needed too. That skiff will be like a 22' er made or 3/8" plate... not much framing needed- check; not any flotation possible- check; stop a .38 Special at 15' - check; need a 15' boat trailer and 4x4 to pull- check.....

So, I'm noting for everyone that "small" in welded aluminum is not easier. Smaller in welded aluminum is harder, due to the weld quality and control needed in proportional scantlings. Thinner than 0.125"-1/8" aluminum is harder to weld by twice for every few thousands you remove. Remove half of a 0.125" sheet down to 0.060" or even 0.080" and welding becomes "somewhat more challenging": let's call is a non-trivial event?

I've posted here on the site some smaller boats, including one that is 30" long, so I'd encourage you to read a bit on the site as we've beat around similar bushes before. Not many have posted their builds in this class, except me -somewhere here? but I'd sure welcome others' input and experience in regard my advice that thinner scantlings are more work!

Peter Eikenberry's (Ike) http://newboatbuilders.com/ site is worth reading, he's not a metal boat guy per se; but has lots of facts there and links to so much more that words can't describe. Ike's career was as a Coastie, I think he's told me before? So his links will take you through an immense labyrinth of links to the underlying reg.s on all sorts of topics.

Size MAKEs a BIG Difference if the Scantlings are Proportional
Brian, I'm primarily addressing the ( misconception IMO) idea that a small welded aluminum (<16') boat is a good warm up for a bigger one... the best warm up in welded aluminum is 16-20' in at least 1/8" or thicker metal. (and) If you don't have the first thousand hours of arc/hood/welding time; then going thinner doesn't really work as well as it might appear. Welding is not proportionally scalable due to the heat transfer rates versus the thickness of the materials' inducing a criticality of bead size and travel speed.

Welding Scalability
If you spend a few minutes looking at the calories/wattage it takes to melt a 0.060" or 0.080" sheet and its transfer of that by conduction away from the weld zone (freeze rate) and contrast that to twice or more thickness of that same material it will become apparent the speed of travel has to increase at rates that are difficult to perform without wire feed or robotics; which is why there are no welded products/boats offered in that scantling range.

Cut Files
I'll assume that all cut files will be *.dxf in order that each NC vendors' table drive software will be able to input and generate paths from that common format?? Nesting is not addressed in my remarks because I'm not viewing any given layout.

I've done my share of smaller skiffs in thinner materials and have noted my experiences on different threads here, so you can look at those images and decide if this info helps? I offer some 'been there and done that'; but surely not the last word, just my experience in building.

Cheers,
Kevin Morin
Kenai, AK

[Challenge]

I have a boat that was designed by Bill Lincoln at Response Marine and built by Viking welding in New Hampshire. It rides better and is much more stable than any 15' whaler that I've been on.

here is a link:

http://www.responsemarine.com/images/223/index.htm

I'm not sure if Bill would sell you the plans and cut files but you can ask, he is a great guy.

Let me know if you have any questions

Cheers


Rick W.

[kmorin]

Challenge, the Resonse/Lincoln multi-chine hull you link would be quite a challenge as a first skiff! To keep the hull from tripping in a tight, high speed turn, Bill has added a nice looking plank just above the outer chine reducing the angle of the topsides to a skidding turn stopping the hull from chine tripping, or flipping over as was evidently found to be a bad habit in the Hickman Sea Sled? So this is where the planking aspect of my previous remarks could make this boat harder for a newer builder to build.

I like the boat, but I'd have rounded the bow instead of leaving the pram bow shown. But it's just more than a first time builder is going to get done -well. If there were lots of welding experience, and the entire boat was NC cut... not laid out by hand and cut... the boat would likely end up giving good working performance as everything from Bill's hand does.

However, I'd recommend a simpler 5 panel (or even a 4 panel flat bottom skiff) hull for a first build. That first few skiffs is quite and education from most builders!

Your link left me to wander the Response site to see more of Bill's fine lines. (He) Sure does have a great sense of proportion, and subtle lines.

Cheers,
Kevin Morin

[Challenge]

Hi Kevin,

Thanks for your insight on build difficulty.

I get immersed on Bill's site for an hour or two at least once a month, He designs some great boats

Rick