Ultimater versions of the Prism

Free plans and building instructions

Ultimater?

Ultimater? Wasn't the Prism in the previous section already ultimate?

Hey come on! I work for the software industry, I know the vocabulary. After the Ultimate there come several versions of the Ultimater, followed by Ultimatest, followed by several versions of the Ultimatester, followed by the Ultimatestest, followed by Ultimate AT, followed by Ultimate 6.0......

The new versions are based on the first ultimate maximum volume ones, enhanced by some of the findings in the previous "Stability section.".

Dory 82

This one is the dory, or rather box shaped one that gave the highest "work to flood" figure for the two-chined hull forms. The bottom width is 28", sides 10" high, inclined at 82 degrees.

The maximum displacement (just before swamping) is slightly above 800 lbs, so it's not bad, although not close to the absolute maximums.

The original Prism ideas apply when cutting the plywood sheet. Note, however, two slight differences:

• The measurement A is longer than measurement B. Hence the points of the bottom strip and side strips don't meet, as they did on the original Prism. Instead, a small triangle from the bottom strip point extends beyond the ponts of the sides. A couple of square inches of plywood wasted ;-(
• The sides are inclined at such an angle, that it causes the points of the bow and stern to rise above the straight sheer line. This, of course, adds to boat looks, but slightly decreases the maximum displacement.

Otherwise the hull is assembled just like the original Prism. The beam on the sheer is 30.8". See also the corresponding .hul file..

You can also set the sides to 90 degrees, if You prefer square boats, thus getting the 28" bottom box shape that also reached very good righting moment figures.

Circular 18

On "Aqualung" Jethro Tull sang "Who would steal a candy from a laughing baby's mouth, if he could steal it from the money man?"
Likewise, I now ask "Who would build a box, if he could build a boat?"

"A boat" in my dreams would surely be something traditional like this one, built in 1932.

But that's round bottomed. How do You build round bottomed single sheet boats?

By letting the number of strips on the Prism grow towards infinity.

Cut only the zig-zag pattern, not the straight strips. A suitable height of individual zigs and zags may lie in the range 2"-4".

Then attach the outer ends of the original plywood sheet together.

Bend the uncut area of the resulting piece to the desired radius, bend and glue the end strips together, and You have a round bottomed single sheet boat.

This one is the 18" radius semi circle bottom that gave good results in the righting moment calculator. And quite nice looks.

The corresponding .hul file.

Circular 22

A semi circular cross section with a 22" radius also gives very good righting moment results.

She looks a bit strange, however. Somewhat "Egyptian" with that high rising bow and stern.

The .hul file. for the 22" radius boat.

Moth

But traditional boats that I have in mind don't have identical ends.

	Bows are wide.
	Sterns narrower.

So why not bend a different radius to both ends of the uncut ply? Like around 15" to one, around 22" to the other end.

Couldn't resist turning her upside down...

...and calling her "Moth".

The Moth .hul file.

The question unanswered so far: "Can this be done?"
We'll see!