Anyone know of plans for a CNC boat kit that is riveted NOT welded together?

[wannarivet]

Good Morning,

I searched google and this forum but could not find any link to a website where could build my own 27 foot (8.2m) aluminum boat CNC kit that is riveted together. There are lots of plans for a welded aluminum boat but none for a riveted boat.

Why rivets?

Well, 1) aircraft are riveted because welding distorts the metal and removes the heat treat, causing fatigue cracking behind the welded area. 2) I can't weld. 3) I want substitute carbon fiber honeycomb for aluminum sheet.

I know that using carbon fiber will cost 5x as much as aluminum but it is half the weight and 5x stronger. The cost of making a really good mold, laying up the carbon fiber and vacuum bagging it all is just too way high for one boat. A good CNC machine can cut carbon fiber just like aluminum and steel.

I found some boat plans for a riveted boat on *************** but no way to see what kind of boat. I'm looking to build a trailerable hardtop cruiser and light weight is very important to me.

I'm guessing that making the keel rib and lots of brackets would be challenging.

Any tips and links would be greatly appreciated.

Thanks.


P.S. I'd love a step hull but that might be out of the question.

 

[gonzo]

Carbon is not an overall stronger material. There are different ways of measuring strength. For example, tensile, compressive and shear. Many of the "high strenght" fibers do badly in shear. That is why sheaves for kevlar lines have to be of large diameter. Also, toughness is also a very important characteristics. Aluminum or steel with dent or deform, while carbon will break. The first has a larger margin of safety.

 

[Barry]

Good Morning,

I searched google and this forum but could not find any link to a website where could build my own 27 foot (8.2m) aluminum boat CNC kit that is riveted together. There are lots of plans for a welded aluminum boat but none for a riveted boat.
As one would expect as you can easily say make a welding 90 degree or 45 degree joint by just welding aluminum sheet together but if a plan is available for riveting in aluminum in thicker sheet thickness, you need to make the joints overlap. So how would you accomplish this without expensive tooling to be able to vary the overlap angle say from the transom to the bow?

Why rivets?

Well, 1) aircraft are riveted because welding distorts the metal and removes the heat treat, causing fatigue cracking behind the welded area.
Some of this is sort of true. Welding on thin aluminum CAN cause issues but not always. The use of thin material in airplanes to keep weight to a minimum is due to the fact that
it costs money to move heavy objects through the air and the cost per air mile per pound impacts an airlines bottom line. The factor of safety in airplanes is much smaller than say cars to keep weight to a minimum. The engineering in airplanes is a large component of the cost of airplanes to ensure safety at minimum weight
The material thickness that you would normally consider in a 27 foot boat in aluminum would not lend itself for riveting, easily. Often in smaller aluminum boats, the manufacturers will install a mastic sealant, similar to a two sided tape, to make the joint water tight. And the thickness is such that the rivet will deform the thin material to make up a tight joint. Tens of thousands of boats under severe usage are made of welded aluminum and have stood the test of time. If you are thinking that a riveted aluminum boat would be better than a welded aluminum boat, I think that you are on the wrong track.

2) I can't weld.
You don't have to do the complete welding on your hull. No matter what material that you will be using, comp, aluminum, ply, etc, you will have to have a certain skill set to build a jig and form the surface material and internal structure to form your hull. In the course of half a day, a welder would be able to teach you how to make tacks so that you could fit up the components at your own pace, tack them in place, then merely hire a competent welder to do the final welding. The actual welding time is not a huge factor in a hull but the fitting can be. And there are many books available to help you with plating etc. ie you do the time consuming fit up and hire a guy to do the final weld.
The advantage of aluminum is that the joints are easy to make. You can easily join 1/8 inch sheet to 1/8 inch sheet without backing support. The joint will be strong and last a lifetime.


3) I want substitute carbon fiber honeycomb for aluminum sheet.

I know that using carbon fiber will cost 5x as much as aluminum but it is half the weight and 5x stronger. The cost of making a really good mold, laying up the carbon fiber and vacuum bagging it all is just too way high for one boat.
The comment above contradicts itself. I sounds like you are prepared to spend 5 x as much for carbon fibre, as aluminum but then say building the mould is too high for one boat. Which it is. Is your goal the absolutely lightest boat that you can build irrespective of the cost, or a compromise in weight at a reasonable cost.

A good CNC machine can cut carbon fiber just like aluminum and steel.

I found some boat plans for a riveted boat on *************** but no way to see what kind of boat. I'm looking to build a trailerable hardtop cruiser and light weight is very important to me.
Weight is an issue in a boat but so should be the cost. Without knowing exactly what you are building but knowing that a 20 foot open aluminum jet boat will cost about $25,000 powered and suggesting that your 27 sedan could cost $35,000 - $60,000 (obviously much more if you are buying diesels or high horsepower outboards) trying to save 500 pounds but adding in many thousands of dollars of cost, difficulty of build, and an unproven, to a point, design, seems like you might be taking a chance.

I would suggest a bottom thickness of maybe 1/4 inch aluminum. You could go to 3/16 inch but then you might need more stringers ie more weight to make the bottom stiffer. The sides 3/16 would be fine, 1/8th then you need more side stiffeners, ie more weight so often there is little weight savings.
Many of the sites that sell aluminum designs can provide the weight of the finished hull, aluminum only,


I'm guessing that making the keel rib and lots of brackets would be challenging.

Any tips and links would be greatly appreciated.

Thanks.


P.S. I'd love a step hull but that might be out of the question.

 

[gonzo]

I think that riveting is probably harder and requires more skill than welding. A poorly fitted plate can be fixed with a fat bead of weld. With rivets, that would mean discarding one or more plates and redoing them.

 

[valery gaulin]

I did built an aluminum trimaran all riveted, the thicknest was 0.06 in 5052-H32 aluminum.

Here is the link.

Aluminum Trimaran on the Water | Small Trimarans http://smalltrimarans.com/blog/aluminum-trimaran-on-the-water/

If you have any questions let me know.

 

[Magnus W]

Riveting is challenging, although I haven't any experience with said tech on boats but I do on aircraft and seaplane floats.

One thing to consider is that riveting requires tools which may, most likely, be of greater cost than a really good welding equipment. Especially if you're upping the size from what's used on aircraft.

Also, riveting takes time. And not only for you but for the friend that needs to be on the other side of the hull.

While a welded construction can be said to be in one piece", a riveted cannot. Airplane floats have sealant between the parts that are riveted together and they still leak (but in all honestly they are quite fragile). It's more common than not to see corrosion between the rivets and the holes, maybe not on a new float but surely on one that's been around for a while. Because the joints move, ever so little, and that will let oxygen in and so it begins.

All modern floats are FRP and even the aircrafts are moving away from rivets to fiber/matrx, composite, glue, whatever. For a reason I'd suspect.

 

[Barry]

Magnus, what is the typical thickness on the aluminum sheet on floats? and perhaps airplanes wings
Valery looks like a nice completed project. I don't think that a .06 inch thickness would not be sufficient for a 27 foot sedan

 

[Angélique]

. . . . I can't weld . . . .

There's a nice suggestion on the thread: Kiribati 36 opinions ---> post #2

. . . . If you are not a welder, hiring one will save you a lot of time and the boat will end up with a better quality. You can assemble parts and tack them in place, then the welder can finish.

 

[gonzo]

The average hourly pay for a welder is about $25 canadian dollars. If you pay cash, $20 will do it.

 

[Magnus W]

Hmm, I don't know for sure. On floats .06 seems about right for the bottom but I reckon thinner on the sides. Fuselage skin is also less than .06, at least for a non pressurized fuselage. Maybe .06 on the leading edge of a wing but in general thinner.

 

[gonzo]

Airplanes don't get pounded by waves, so the skin is much thinner than a boat of the same displacement.

 

[valery gaulin]

Airplanes don't get pounded by waves, so the skin is much thinner than a boat of the same displacement.

Sorry Gonzo, think about this one more time! Wave at 6 - 10 knot versus birds, ice, snow, etc. at 200-400 km/hour with 120 to 400 passenger. Which one needs to be stronger?

 

[gonzo]

The boat hull. The density of water is about 750 times that of air. Birds can cause major damage on an airplane. Also, the leading edge of a wing or fuselage is reinforced and not the gauge you are discussing. I can cut my way into an airplane with my pocket knife.

 

[Angélique]

. . . . think about this one more time . . . .

return to sender​

Wave at 6 - 10 knot versus birds, ice, snow, etc. at 200-400 km/hour with 120 to 400 passenger. Which one needs to be stronger?

Aircraft are not designed to fully withstand these kind of impacts like ships and boats deal with their normal impacts, since this would make aircraft far to heavy for any economical operation or to fly at all. So aircraft are designed to have no more than survivable damage in these occasions, which makes repairs or at least inspections after every kind of aircraft impact standard procedure in aviation.

This in contrast to ships and boats which don't need, nor would this be acceptable, to go to a repair yard after every heavy wave impact, which heavy impacts aircraft don't have to endure due to air having a so much lower density than water.

Displacement aircraft like balloons and zeppelins are even weaker than planing aircraft, otherwise the displacement type would be to heavy to float in such a light medium with such a low density as air.

 

[wannarivet]

Hi, thanks for the many responses to my inquiry.

I've since given up with my idea to rivet the entire boat, but still believe that boat plans designs for sheet aluminum that can be cut on a CNC machine can be used to cut a composite sheet that will be half the wight and 2x as expensive as alu. The 5x figure comes from having to buy peel ply, resin mat, vacuum bags, hoses, etc. That was just my cost estimate for materials NOT including a mold. A boat mold runs $1,200 a foot and then if you want a mirror finish, add $8,000. Allmandboat has a mold calculator. $125,000. And you need 2. One for the hull and one for the upper deck. All I would want to rivet now would be the keel rib and 2 chines under the waterline to help lateral stability and strengthen the boat's bottom. The transom and other structural cross members could be fastened to the inside of the hull with epoxy and carbon fiber bent like angle iron where as aluminum would be welded. That's how the fiberglass boat builders do it.

The issue that I'm running into now is that no boat builder wants to sell me enough data to be able to create my own design with the intent to modify it and no one really understands what I'm trying to do.