Cape Dory 36- Gross tonnage?

[bertha]

Hi all- before I go get the measuring tape out and try to do the math on calculating the gross tonnage of our Cape Dory 36 I thought I would see if anyone else had done this.

Thanks for any help!

[tjr818]

The book says the the displacement is 16,100, does that help? I think GT is a volume expression and displacement is weight, but I don't really understand the relationship. 16,100 divided by the weight of seawater (64 lb/cf) gives 252, but I have no idea if that is the number you are looking for. I think the documentation application has a formula for tonnage.

[Jim Walsh]

Hi all- before I go get the measuring tape out and try to do the math on calculating the gross tonnage of our Cape Dory 36 I thought I would see if anyone else had done this.

Thanks for any help!

I know of a CD36 which has been documented. The gross tonnage on the certificate is 16 and the net tonnage is 14.

[bottomscraper]

For what it's worth this is what is on the documentation for Mahalo. The boat was documented when we got it and has remained that way, we only changed the owner and the home port.

Length (ft.): 36
Hull Depth (ft.): 8
Hull Breadth (ft.): 11
Gross Tonnage: 21
Net Tonnage: 16

[Neil Gordon]

>> I think GT is a volume expression and displacement is weight, but I don't really understand the relationship.<<

There's no relationship between the two. Boats that weigh (i.e., displace) the same but have different volume will have different gross and net tonnage.

[mgphl52]

>> I think GT is a volume expression and displacement is weight, but I don't really understand the relationship.<<

There's no relationship between the two. Boats that weigh (i.e., displace) the same but have different volume will have different gross and net tonnage.

And it all goes back to wine!

[Neil Gordon]

Anyone know if the calculation of net tonnage is affected by having a wheel rather than a tiller?

[Jim Walsh]

Anyone know if the calculation of net tonnage is affected by having a wheel rather than a tiller?

I can affirm that the precise calculation requires the "loose or locked prop" factor.

[Neil Gordon]

Anyone know if the calculation of net tonnage is affected by having a wheel rather than a tiller?

I can affirm that the precise calculation requires the "loose or locked prop" factor.

Precise calculating requires single malt.

[mgphl52]

Anyone know if the calculation of net tonnage is affected by having a wheel rather than a tiller?

I can affirm that the precise calculation requires the "loose or locked prop" factor.

Precise calculating requires single malt.

Negative! Wine, not whiskey...

[bottomscraper]

The simplified measurement formula on link below. I still can't figure out how they came up with 21 GT for Mahalo!

https://www.dco.uscg.mil/Portals/9/DCO% ... 123757-680

[John Danicic]

Just to add to all the confusion.

My Mariah, a 1984 CD36 is listed on its Certificate of Documentation as:

Gross Tonnage = 11 GRT Net Tonnage = 10 NRT Length = 36.1 Breadth = 10.7 Depth = 8.1

I was told she was Federally Certified direct from the factory. Always wondered about the depth number......

[Neil Gordon]

>>Always wondered about the depth number......<<

It's not draft. It's depth as a measure of cargo carrying capacity, i.e., how big is the hold? Does that help?

[John Danicic]

Neil:

That does make sense now. The cabin height is about 6.5 feet sole to cabin liner and a 1.5 foot or so deep bilge.

Not sure what kind of cargo I could transport on Lake Superior that would fit in such a space.

Oh wait, didn't Canada make something legal recently?

But when all is said and done, that would not be a good idea for a cargo. The last time I encountered the US Boarder Patrol on the Big Lake, they had not three but four, 250 hp Hondas hanging off the end of their 45 foot patrol boat. The old Perkins could never out run those. Better stick to the "Recreation Operational Endorsement".

[Keith]

I asked the coast guard about this when I first documented Moon Dance 7 years ago. I believe that the gross tonnage is the weight of the water that it would take to fill the interior volume of the hull. The formula for a displacement sail boat like ours is (.375 x length x breadth x depth)/100. note depth is not to be confused with draft.

Example: the CD 30 has a displacement of 10,000 lbs or 5 tons and a draft of 4' 2", beam of 9' and a length of 30' 2 1/2 " but the gross tonnage is 9 GRT and the coast guard lists the length at 30.2 ' the breadth at 8.8' and the depth at 6.8'.

I think that the bottom line is that the Coast guard already knows the numbers for our boats so if you want to document your contact the coast guard.

Keith