J-class hullform

Thanks Robb,

 I used to skipper those old B-40's and know all about the centerboard housed in the keel. Never knew the old ones were wood and that would make for a fat board. The keel root fillet was very generous on those boats and may be what I'm seeing in one particular image of yours. How did the hydro and stability work from your reverse engineered model go and what did you use for that analysis? 
 My favorite boat to skipper in our fleet was the big sister to the B-40 which I think was simply designated the H-48. It was a Tripp design pretty similar to the 40 with more of a flush deck without the full length cabin trunk. It had more of a blister like doghouse aft over the galley and the hull was deep enough to not need the trunk forward over the salon for headroom. It had a very similar keel centerboard to the B-40 and was a fine sailer.

B-40 Righting Arm.pdf (245.7 KB)
The attached file is a PDF of the righting arm curve. I did not make a PDF of the excel spreadsheet taken from the ORCA plug-in but her displacement was pretty darn close to that of the Tripp claimed displacement. You sure can tell a Bill Tripp boat from miles away!

Thanks Robb. Looks good from my house! Was your client happy with the efforts?


Yes the client is in fact thrilled. He wanted to see with the weight savings in the deck structure just what would happen to stability. The righting arm curve crossed the “0” line a bit further to the right as it were and he was of course, quite pleased. I explained to him just what was going to happen when a few hundred pounds of unnecessary weight is removed from the deck structure and thanks to ORCA and it’s sensitivity to the VCG, the righting arm looked a bit better than the “as built” deck which was a hodge podge of the following ingredients: (against the deck beams) 10 gage copper sheet and yes I was amazed as anyone, but I learned a long time ago that to be surprised is often not very surprising! Next: 1 1/2" mat + 10 oz. cloth set in polyester resin and yes, it was not attached to the copper but in a few tiny patches here and there and finally a teak overlay that was the only part of the deck with any structural integrity: the boards were 2" x 1/2"! I followed scantlings based on a spreadsheet I designed a few years ago this is comprised of the formulas found in Dave Gerr’s “Elements of Boat Strength” using the "sandwich construction part of the scantlings. My deck was considerably lighter and much stronger with far greater attachment to the hull, deck house, beams and cockpit coaming than the original home made deck.

I should quickly point out the this boat was built on a hull that Henry Hinckley produced and sold along with a few other in an effort to raise money to pay off the tooling costs of the b-40 or so I was told. Someone bought a hull and created that bizarre deck structure likely from materials he had on hand.

I have a ton of such stories but all for now, and cheers, Rob and PS: the attached is my future boat that I shall build for Kellie and myself using my lottery winnings!

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Sweet, I’d like to run your hull through ORCA3D and compare the stability results, let me know if interested. Kellie’s boat looks great!

First I would like to apologize for not reacting on the discussion I started begin of this year, but family affairs took all my spare time.
I picked up where I ended, but, probably because English/American is not my own language and I’m not so good with Rhino, I still didn’t understand what Pascal meant.
After a lot of searching, I finally found a very instructive video from Simply Rhino, “Creating and Controlling a Transition Surface in Rhino3d”, and now I understand what Pascal was talking about. Thanks all of you, and Simply Rhino.