help me understand tonnage better?? (for licenses, etc)

[reed1v]

Originally Posted by Cadence

I believe just getting a 100T ticket would be all you would want. I am not sure what the knowledge of determining tonnage is of use to you, unless it is on a test. A head boat Capt. or delivery Capt. generally only have that. If it is for a couple of retirement bucks get a job with a tow boat co. Under 24ft. doesn't even require a tow boat license, last I checked. Run a commercial fishing boat no license required.

Yup. Plus most folks just get the six pack; although a 100 ton does give one more freedom of employment. Beyond that you need a lot of documented sea time.

[StuM]

Originally Posted by black_sails

Hence my desire to come in just under each tonnage limit with my catamaran sketches and then figure out what I can do with a boat like that for different jobs.

To give you an idea for cats, I cams across a site somewhere which listed tonnages for various Lagoons.

From memory, the 380, 400 etc where around 25 GRT and the 440 was a bit over 40 GRT.

[captlloyd]

My friend, you need to do a lot more research concerning running boats for commercial purpose. First issue is boat itself. If you are limiting your license to 6 paying passengers or less, (6 pack), you are eliminating a lot of Coast Guard requiments for the boat itself. Above 6 passengers and your boat has to start meeting some serious requirements, possibly even some stability tests . If you are above 6 passengers and are designing your own boat, expect a stability test. I am not trying to discourage you, just let you know there is a lot of hoops to jump through.

[capt-couillon]

GRT is total volume of the vessel... NRT is cargo capacity ie: GRT minus engine spaces, crews quarters etc.

[adlib2]

Originally Posted by black_sails

I will freely admit that i'm quite a newb when it comes to anything beyond recreational boating where I never needed to worry about licenses and such at all at any level accessible to me. When I look through some of the licensing rules for the USCG and elsewhere though I get totally confused at what kind of boat is even in what category. I read about Gross Register Tonnage, simplified calculations for smaller vessels, some kind of net tonnage calculation on larger vessels (or luxury yachts where they try to make "exempt space"), and ITC tonnage.

Even looking at official forms I have to be honest that I don't understand it, because following the rules the answers I get don't seem to make sense. Is there a For Dummies version or explanation showing for instance a specific ship, and all the ways it can be calculated? (exclusively for legal/licensing purposes, not interested in historical or volume or weight, just what will answer whether time spent on X boat counts me towards a 25 GRT, or 50 GRT, or 100 GRT, or 200 GRT licensing class for instance. I mean on a theoretical level/if I don't have the information provided by the owner, i'm trying to understand how the calculations vary and why by seeing examples of them applied to different vessels.)

Might not be helpful; my Canadian registered vessel has gross and net tonnage engraved on a bronze plaque along with Reg No mounted adjacent to the mast.
Is there something similar on US vessels besides Hull No on the transom?

[catman]

i was told many years ago when i got my catamaran rated for tonnage that it is an antiquated system of measuring the carrying capacity of boats.
the term tonne was the measure uf a barrel of wine and thay used to calculate how many tonnes of wine your ship could carry by calculating the entire interior volume of the vessel.
old fashioned and in need of a more reasonable method of assesing a. crafts worth.
Catman

[belizesailor]

Originally Posted by black_sails

A rectangle inside the curves minimizing tonnage or outside the curves maximizing tonnage?

I can't seem to figure out how to calculate it at all though. First thing I did was go here, https://www.uscg.mil/hq/msc/docs/CG-...6-04_v1_0b.pdf though for some reason I can't get the interactivity to work. No matter, I go through manually, and the problem is self obvious when I get to #7 'additional dimension for large deck structures' because all my designs have more enclosed cabin than cat hull volume. Unless some part of an enclosed bridgedeck is exempt the cubic volume goes up very quickly. Unless there is some secret reduction factor.

Alternately if I just have basically an open deck tonnage is very little. So it seems skewed against houseboats and enclosed cabin cruisers.


...

Outside the curves if using the simplified system because you only use length, beam, depth.

Deckhouse structures on a cat can be excluded.

Think of it like the cargo vessels for which it was intended: how much cargo can be put down in the hull (below decks).

[Kentb]

As a new captain, I have been having trouble wrapping my mind around the application, but not the concept.
In the small boat world, everything is mostly discussed in terms of length overall. Catamarans and Trimarans of course being different.
I have my 50 ton license, but pretty hard to determine what that means.
I applied for a job where they wanted a 100 ton license. Still got the job, but in fact the 41' boat I am running is a 17 ton boat.
INTERESTING thing: Look at modern passenger and carferrys on the great lakes. They are all less than 100 tons. Reasons: I know one is for the captains salary and ease of finding 100 ton captains. Another may be the level of USCG requirements and inspections.(but I am not certain of that).

[belizesailor]

Originally Posted by Kentb

As a new captain, I have been having trouble wrapping my mind around the application, but not the concept.
In the small boat world, everything is mostly discussed in terms of length overall. Catamarans and Trimarans of course being different.
I have my 50 ton license, but pretty hard to determine what that means.
I applied for a job where they wanted a 100 ton license. Still got the job, but in fact the 41' boat I am running is a 17 ton boat.
INTERESTING thing: Look at modern passenger and carferrys on the great lakes. They are all less than 100 tons. Reasons: I know one is for the captains salary and ease of finding 100 ton captains. Another may be the level of USCG requirements and inspections.(but I am not certain of that).

Yes, I expect many vessels are built with liscencing requirements in mind. A 100 Ton captain is WAY cheaper than an Unlimited.

[catman]

enter " tonnage " on Wikipedia and you get the history andexplanation.
Tuns refers to casks of wine originally used to calculate capacity.
Catman

[css145hs]

Originally Posted by belizesailor

Outside the curves if using the simplified system because you only use length, beam, depth.

Deckhouse structures on a cat can be excluded.

Think of it like the cargo vessels for which it was intended: how much cargo can be put down in the hull (below decks).

For a cruising cat, would you still treat it as a monohull on the forms because there is volume in the connecting saloon and its not simply beams (which is how the USCG forms seem to describe it should be treated)?

For a daggerboard cat without an integral keel, I'm looking at an 8' hull side (excluding daggerboard), 52' long, 25.5' wide so.... 52 * 25.5 * 8 * 1 (K factor) * 0.5 (S factor) / 100 = 53GRT

I know the GRT/Tonnage has nothing to do with weight, but for reference point, she only weights 9T... does it sound like I'm doing anything wrong? She draws 2 feet below the waterline, but I'm using 8' for below and above waterline hull height. I'm ignoring the saloon completely.

[Gruz]

https://www.youtube.com/watch?v=7Bn-kYJAqg4

[catman]

i am not sure why but when they did. a tonnage survey on my catamaran they used all of the internal volume, salon included.
For my 40’ Fountaine Pajot Fidji, the tonnage came out at 20 tonnes.
The catamaran is considered light dispacement but still had a high tonnage rating.
Should have changed it to a cargo ship and hauled wine.
The surveyor used the blueprint that i was able to get from F/P and do the calculations
in Victoria, BC even though the catamaran was located in St Martin.
I had to get the tonnage done so that i could get a Canadian Registry for it.
Maybe its time they actually looked at a catamaran or trimaran a used some common sense in their ratings, that where created for monohulls.
Cheers, Cataman

[StuM]

One FP Belize 43 I found under US Registry is/was listed as 43 gross, 35 net.
(That's what I used for registration purposes).


Belize is 43', 8.5t lightship displacement.
So 53t sounds in the ballpark for a 52', 9T cat.

[css145hs]

Thanks StuM and Catman. It seems I'm doing it right then by treating it as a monohull in the calculations, and using the freeboard as depth.