William Jackson seaskiff stretch

Any one see any major issues with stretching this design to 17 ft? I’m looking to make a good sized utility skiff that can row, sail, and motor. It doesn’t need to be a champ at all three. I promised myself I wasn’t going to build another flat bottom skiff and also that I wouldn’t do another jigless boat. So this is what I’ve been able to find.

 

Looks like 24% growth by length...

 

Tops thanks. What software did you use?

 

Rhino3D, taking 2D curves off the PDF (sheer, chine, keel) and projecting them into 3D to start building the surfaces.
The stem throws this off a bit but for the sake of a quick mock-up I let it ride.

Edits: If the stations were drawn in, and curves struck through them, the panels would be more fair as well.

I have casually read that +10% in length is a guideline before other things need to change like adding frames, etc.

 

Not only frames, but also longitudinal girders should be checked, not to mention the reduction in stability.

 

Tansl,

It will be a sturdy build, I plan on adding extra frames, heavy rails, 1/2” plywood, fiberglass everything, etc.

 

Don't be confusing "sturdy build" with stability.

 

With the same width and height, the stability increases directly proportionally to the length,

 

I have always read and understood what Gonzo said, that length increases stability.

 

In short, no, that cannot and should not be stated (if we're talking about transverse stability).
Another thing, what does height mean to you in this context?

 

Very good idea. Do not place more than necessary, nor less.

 

The total stability is the sum of the stability of all the sections. If you add more sections there is more total stability

 

Great theory! I'd never heard of it before. You always learn something new.
To apply it to my projects, I just need you to explain how to calculate the stability of each section. Once calculated, do you simply add up all the sections, or do you have to distribute them proportionally to the stiffness of each one? (I know you also know a lot about beam stiffness.)

 

Murky There are some trolls in the forum that will say square if I say round. The explanation is easy, even for someone completely ignorant of engineering principles. Start with a simple shape like a square float and it has a stability of 100 lb to list 5 degrees. If you tie two together and apply 100 lbs to the side, each float gets 50 lbs of force, therefore the now longer float will list less.

 

@Murky Deep indeed, there are members (or member) on this forum who troll Gonzo, but who know about naval architecture. But, beware! there are also very good people who don't know about naval architecture, who, unaware of their own ignorance, will give you, with the best of intentions, advice that could ruin you.
Telling someone he is wrong, even sarcastically, isn't trolling at all.
If you want serious and truthful help, I'd be happy to discuss it with you.