bertram31.com

I should know the answer to this question. What is the Gross Tonnage of a B-31 Sportsfisherman? Walter

Walter,

As a general rule of thumg for boats smaller than 50' & larger than 20', figure 1,000 lbs per foot of displacement. At just under 31' the B31 figures to 30,500 lbs, or 15.25 tons. However, that total displacement weight could & probably would put your scuppers underwater... For CG classification, the 15 ton figure would stand.

Br,

Patrick

Capt. Patrick,

would there be that much difference between the Sportfish and the Bahia Mar?
My survey says displacement of 9700 lbs.
My CG Documentation says, 10 gross tons.
Just broke out my notebook from Sea School.
The formula for Gross Tonnage is length x beam x depth divided by 100 x .67. (depth = top of gunnal to bottom of keel)
30 x 11 x 4.5 divided by 100 x .67 = 9.9495

I guess 9.9495 is close enough to 10 GT.

Harv,

That's a lot more accurate formula than the rule of thump I posted... All B31s should fit that bill.

Br,

Patrick

Harv's formula is correct as far as determining a vessel's "tonnage", but tonnage as used in calculations for a CG issued license is not the same as a vessel's displacement. Tonnage when considered by the CG technically refers to the vessel's theoretical cargo carrying capacity, and the term "ton" is actually volume of 100 cubic feet of cargo carrying capacity. This is probably a holdover from the old days, hence the calculation of volume. Weight. as in displacement, does not enter into the calculation when the CG determines your license limits.

Tonnage for CG documentation is nothing like displacement at all. It has more to do with "cargo carrying capacity." BUt then it isn't really all about that either....

Confused? It is confusing!

Here is a link to a document that talks about the CG tonnage calculation. There is a simple formula given a few pages into the document that can be used to calculate your boat's tonnage. Or you can submit a form and have the CG do it for you.

Note that if the deck house volume is less than the hull volume it isn't used in the calculation. Also be sure to use the correct shape factor.

CG Tonnage


If anyone has a documented 31 it would be a simple matter to look on the paperwork and post the number here with a sticky at the top of the page. It would be one of those little bits of information that is a lot easier to copy from someone else's paperwork than to have to calculate each and every time.

Peter

I tried that link in "Preview" and it worked, but then after I posted it didn't seem to work.

Here is the url in link form:


http://homeport.uscg.mil/cgi-bin/st/por ... 635aa15561

In case that doesn't work here it is in raw form. You can cut and paste it into your browser address bar, then add
"HTTP:// "
at the very beginning of the address


homeport.uscg.mil/cgi-bin/st/portal/uscg_docs/MyCG/Editorial/20070514/Guide_Simp_1.pdf?id=93fa277580e8b7e52073e79f032e7d635aa15561

Peter

Peter...

I tried both ways and get the message "UNAUTHORIZED ACCESS DETECTED" and nothing more.

My CG Doc says gross ton: 10 GRT, too, Harv and net ton: 8 NRT, but the breadth has 10.9, length 30.3 and 4.8 depth.

AndreF wrote:My CG Doc says gross ton: 10 GRT, too, Harv and net ton: 8 NRT, but the breadth has 10.9, length 30.3 and 4.8 depth.

Andre,

My CG Doc says 30.2 by 11.1 by 4.7
Gross Tonnage 10
NRT 7

When I put up my original calculation, I just used close approximations for the required dimensions. I wasn't too far off now was I?

Not at all, reel close. I just wondered what the exact dimensions were. Interesting.
Bertram said draft was 3.6 as I recall.

I don't know why those links won't continue to work. Very strange. I tested them after posting and it worked for me then, but not now.

Here is a different link to a version of the same PDF document. Maybe this will bring better luck

http://www.qualitymaritime.info/Press/G ... fied_0.pdf


EDIT:
OK the above link goes to an earlier revision of the measurement discription but the formula and method appears to be the same. BUT If you must have the latest rev. of the measurement instructions here is how to find it:

1) do a google search for: USCG Marine Saftey Center

2) select the one that comes up with the address "Homeport uscg.mil....." down on the bottom line. In my search this was the very first one on the page.

3) Under the "services" heading on the "USCG Marine Saftey Center Homeport blah..blah..blah..." page select "tonnage measurement"

4) On the next page that comes up there are some PDF files available on the right hand side of the page. Here you will find the "simplified tonnage guide"

This seems to be the most recent version of the document.

Nothing to it!

Too bad there is nothing "simplified" about finding it!

Whew! What a hassle. You'd think they would want to make it easy to find this sort of information. Instead they hit us with "Unauthorized access" crap.

I Thought I was helping out here, instead it turned into a big mess! Oh well, your tax dolars at work!

Peter

The "depth" measurement is not the same as the draft. It is the distance from the rail to the bottom of the keel.

Peter

I went thru about 10 of my 20 plus surveys done on 31 Bertrams. Documented boats only 3 of 10, the rest were state registrations.
Gross tons 9, Net tons 6, were the numbers I had taken from documentation certificates on all three.

1974 FBC - USCG Certificate of Documentation for Offical Number 975140 states - Gross Tonnage 11GRT - Net Tonnage 9 GRT.

CLay