deriveur integral (internal ballast sailboat, ala: alubat, feeling..etc)

[samh]

Do these particulars, other than the loa/lwl of 1, look way off spec? This is for an internal ballast type sailing yacht, meaning no ballast keel.


LOA 28’ 0”
DWL 28’ 0”
BEAM 9’ 10”
DRAFT 1’ 7” / 6’ 6”
DISPLACEMENT 6,600 lbs
BALLAST 2,650 lbs
SAIL AREA TBD

LOA/LWL 1
LWL/B 2.87
BALLAST/DSPL .4
DLR (D/L) 129
SA/V2/3 TBD

[sharpii2]

Hi Sam

Seems a little on the light side, but is probably ok. Other than that, there dosen't seem to be enough information. I have four questions.

1.) What will the boat be used for? Local cruising? Coastal cruising? Deep water cruising?

2.) What is its midship freeboard? Is it closer to 2.5ft or is it closer to 4ft?
With the lower number, it will be able to carry more sail.
With the higher number, it will have a greater range of stability.

3.)What is its midship cross section? Is it round? Is it "V"? Or is it flat on the bottom with great flair to its sides?

4.) What will you use for ballast? Water? Sand? Concrete (with steel reenforcemt or punchings)? Iron (or steel)? Or will you use lead?
Water and sand are the least expensive but are also the least effective (though they are easier to remove)
Iron and lead are the most expensive but the most sffective (can also be removed).
Concrete (with punchings and/or reenforcemet) is in the middle cost wise and in efectiveness (but usually can't be removed).

Answering these four questions will probably tell you a lot about your design. But always answer the first one first.
The other three, you can take in any order you like. They are, of course, inter related.
Thats what makes this so fun

Bob

[samh]

Your comment that she "seems a little light," is the major issue for me. The other points will be addressed in the 'design basis statement' which I am working on.

As an aside I am leaning towards lead ballast - concrete being an interesting option that I don't know much about. (Can you point me towards any references on that subject?)

So here we go on the subject of her displacement:

A parametric study and trend-line analysis of the displacement versus waterline lengths of all the deriveur integral (what is the pleural of this?) that I could find produces a magic displacement length ratio number of 246 or thereabouts. Now that would give, what is in my mind, a really heavy displacement of 12,096 lbs for a waterline length of 28'.

Per the suggestion of another forum member, I did a parametric analysis of Displacement versus LOA. A fairly simplistic analysis of these numbers produces a D/LOA [D/LOA=(DSPL/2240) x (.01 x LOA) ^ (3)] of 129.
This would give us a displacement, for LOA = 28' of 6,343 lbs. At 6,600 lbs, my design is a bit heavier than this.

In my meager experience though, I haven't really ever heard of anyone comparing displacements based on the length of the hull though, rather than the length at the waterline. The boats in the parametric study aren't really radically shaped, with huge overhangs.

Looking over your post, you raised some other questions, like her intended use and hull form. I am working on a design basis statement that should address some of that.