Quick question about construction method and weight

Just a quick question, while i was browsing some plans, i found a particular boat that can be built using 3 techniques, metal, composite wood and fiber.

Now my question is, each method will result in a different dry weight for the boat. Does this mean i would fit a small engine to achieve the same speed as a heavier technique? or will i have better fuel efficiency?

Or is the displacement weight the determining factor regardless of boat overall weight?

 

Something you haven't considered is that the ballast is probably adjusted so the boat displaces the same amount...regardless of the hull material. You wouldn't want to play with the DWL that much for the same design.

 

Thx lewis! So in reality it is adjusted to give the same specs by ballast.
If it wasnt adjusted then would my earlier statement be true? A lighter boat will have less DWL therefore can get away with a smaller engine? (figuratively speaking again )

 

I would suppose...in theory...except the skeletal scantlings would not be the same for each method of building so there may not be a whole lot of difference once everything is accounted for. If you use 30 mm thick wood, vs 12 mm thick fibreglass vs 7 or 8 mm metal...and the ribs, frames and keel are also varied accordingly there may not be any difference in the final result at all. I would expect you would need to have the plans and scantling BOM in front of you to compare. A lighter boat usually needs a smaller engine...but then again if the difference is only a couple of hp...what's the point?

 

Makes sense i guess ... choosing the construction plan is a group of mental questions for me, and i thought there would be a weight advantage so i will have another criteria to influence my construction method choice along with the other variables.

Its a mental exercise in my twisted mind that keeps me awake at night with excessive thinking
Thx lewis should i get some sleep tonight it would be thanks to you

 

Depending on the size and intended use of the boat, typically for recreational size boat, optimized designs for each construction method ends up pretty similar. Each material has advantages and disadvantages, it is up to you to determine which are more important. Cost, labor, available skills, tooling and technology (welding, vacuum bag, etc.) are all trade offs that usually determine what you choose.

Very high tech materials will save weight, but at a high cost. Typical materials and methods do not have any clear advantage one way or the other.

 

Yah ... indeed .... it seems after i hopefully get and finish my boat i have a huge @$$ can of worms i need to open to get a glimpse of boat design!

Funny thing really, the more i learn about boats the more i feel that my knowledge is nothing at all ...... If only i could read in my sleep ....