Deep V-bottom

[Willallison]

Originally Posted by gonzo

Volume and displacement are not related.

I must have missed something...? Or is there something that you know that Archimedes didn't?

[Tim B]

Based on the quoted volume being 8m3, I think the comment was with regard to the relationship between the quoted enclosed hull volume (which has little or no meaning) and the immersed volume (ie. displacement).

It's interesting that this is not actually ground-breaking research. Making a boat longer reduces the pitching motion for certain wavelengths, by changing the pitch moment of inertia and the pitch moment for any given angle (back of an envelope calc if you know your dynamics). And making it narrower reduces the wave drag, which has been known since the dawn of time.

The reason that boats have evolved as they have is that often length is constrained (usually by the owner for fiscal reasons), which forces the beam to get the stability, accommodation and maneuvering control. The deep V form is not easily powered, but it does possess fairly good handling characteristics. Often this is more important, especially in deteriorating conditions.

The actual interaction here is much more subtle than is first apparent, so I would be careful of making such bold claims. I would also be slightly wary of quoting student testing as backup, unless you can also produce the test report, which should detail how everything was done (down to the equipment used, block diagrams of the test setup, specified locations of the equipment etc.), with time histories of recorded data (at least as graphs), and an amount of analysis, to arrive at the final results. These documents are often a minimum of 100 pages and generally take no less than three weeks of testing. Call me skeptical, but I've rarely seen reports which come up to standard, even from professionals.

Best of luck,

Tim B.

[HJS]

These two boats have the same interior volume, living space, load capacity……………and about same weight and therefore displacement.
But different length and beam

The boats compared in this sea test are 6.6 x2.0 deadrise 13dgr and 6.2 x 2.2 20 dgr, total weight 1350 kg including crew.

There will come a full report when I have the energy to translate it into English.

But the report shows that the calculations where right, some results are even better than calculated.

js

[HJS]

It has all be done in the way you say. The equipment and procedure was the same as in tests for the highest standards for the Swedish navy patrol boats.
It was a lot of work, it took six weeks for six students and resulted in a short report of 52 pages, excluding all background calculation and test data.

At least I am convinced that there is a big difference when I travel in these boats in these conditions. I was also skeptical when I begun with this project. After the measuring the vertical acceleration, I am convinced.

You are welcome with your own equipment for a test ride whenever you want.
It is your choice.

js