Overbuilt vs Overengineered

I have a feeling that gelcoat and CSM technology should be reserved for bathtubs and shower trays.

I'm sure I can make a boat half as light with plywood, epoxy, and fabric strips, and 10 times lighter using appropriate composites and/or aluminum elements.

Boats are overbuilt because of what Ondarvr wrote , CSM technology is "heavy" and flimsy. The structural safety factors require a high mass.

 

Mass is not always a bad thing, depending on the purpose of the boat. I have a feeling an ultralight tug boat ten times lighter might be useless.

 

Of course, light weight isn't always helpful. When navigating waves, heavy weight can be helpful.

But in my opinion, small boats tend to be lighter.

For example, a 33' cat float with only 180 lbs.

 

There are flaws in the way we think about boat design in general.
I fall into the trap of traditional thinking myself.
I don't understand why a 22' aluminum boat has to weigh 2800 lbs.

I don't buy it. The numbers don't add up.

 

The budget is the start of the discussion on the project. The engineer should be able to have a ballpark figure. It the client is unrealistic, the engineer should be honest, not take his money, and walk away from the project.

Absolutely no. If you have seen his posts it would answer your question. Probably you wouldn't be asking it.

You overengineer an item by wasting time, resources and money on the design and construction. For example, if I engineer the floor for a house I would use a value of 1/320 for the floor deflection. To get the value for the joist I will use the tables from the manufacturer and the building code. I then enter the span and the loads, which gives me an answer. That is proper engineering. Overengineering would be to buy joist and test them for their E value and breaking strength. Then design the floor from first principles. I can save some weight on the floor joist, but is and inane endeavor.

 

You can make it lighter with different materials and no interior. There is no mystery there. We use to build 30 foot cargo canoes certified for 13 passengers that weigh 200 Kg (441 lbs). I also believe you are not calculating numbers and adding them up, which would be proper engineering.

 

Always felt overbuilt was needless use of additional material while overengineered meant system complexity that introduced user or maintenance weakness not necessary for a primary function.

Seems like I see over built a lot in home builds and back of the napkin designs. With glass projects it seems like all manner of reasons end up with heavier and overbuilt.

Over engineered seems to show up in a lot of electrical systems. Work on a few very expensive conversions vans, with 5 figure power systems, very few take in the reality of use. Favorite was a van with solar, lithium, and multi fuel appliances... for a guy who plays predominantly in winter near the artic. System we dropped in was based around pragmatism, way simpler, and based around on ground reality as opposed to perceived optimum use case. A 5 gallon jug of gas and a Honda eu2000 for a couple days use is awesome when in temps that make lithium, propane, and solar moot.


Have a 16 foot work skiff that is several tons, so wont way in to that discussion....


My favorite over build is schedule 40 aluminum railing. For some reason we can get it cheaper per stick than sch 10, and it allows me to be rougher when roll bending without kinks. End up with a super beefy rail, but other aspects make it work.

My boom was engineered for average use case, we ended up going significantly larger... knowing full well it would get radically over used in a pinch every few years.

 

A large margin of safety is adequate for applications where there is an expectation to occasionally exceed the working loads. that is different from overbuilt. An example of overbuilt is a 12 foot dinghy with 8 2x4 frames, like someone built some time ago. A hull built with a chopper gun will be heavier than a vacuum bagged carbon fiber, but also a lot cheaper. The weight penalty for a weekend use runabout is reasonable and good engineering because low cost is a major factor.

 

My least favorite example was putting a through-hull in an '80s 44' sailboat that was anchored out. The through-hull had 2 1/2 inches of threads, but it wasn't enough I had to grind out a pocket for the flange - after I had already got the hole drilled. "Erm, hold this rag in the hole - I'll be back in a couple hours with the tools I need". They were putting $50 a drum resin on with string mops back then. If it looked a bit dry, they poured five more gallons into the mold and just kept mopping it around.

Of course, this was one of the three hulls I know of that survived Hurricane Andrew anchored oceanside. All three were built by Canadians, if that means anything.

 

The Spruce Goose - Evergreen Museum https://www.evergreenmuseum.org/exhibit/the-spruce-goose/

What say ye? Which one, both, or neither?

 

Went to a formal dance there about twenty years ago, it was superbly well built/engineered for being a prop at a dance...

 

That was a proof of concept prototype. It did generate a lot of valuable data.