Tonnage on Mainship 390

Recently purchased a 390 Mainship 2003. Working on Coast Guard Documentation. Can someone advise what their certificate states for gross tonnage and net tonnage? An old form showed 22 GRT and 18 NRT. Is this correct? Thank you so much.

Use the numbers on the old document. USCG tonnage has little to do with real weight.

David

29T Gross, 27T Net on my documentation for a '99

Welcome to the forum. Hope you'll post some pics of your new ride.

Greg.

Welcome aboard. Net tons is equal to 100 cubic feet of cargo carrying capacity. It has nothing to do with actual weight. Net tonnage is volume minus the machinery spaces basically. The tonnage quoted in the replies seems a bit on the high side. A previous boat I had was a 46’ and I think that it was 22 net tons. I would imagine that yours would be in the neighborhood of 18 net tons give or take. If you have line drawings of the boat you can calculate it fairly closely. But having said that, just use what it was listed previously. The different tonnage really makes no difference unless the boat is less than 5 net, then it cannot be documented.

It really doesn't matter what the real tonnage is or what some other MS 390 owner says it is. You will have trouble if you don't use what was on the previous document.

David

My 2003 390 says gross tonnage 22.

as others have said, use whatever was on the original documentation. If you change anything but the ownership and the name of the boat you're opening yourself up for a paperwork nightmare. Those were the words used by the broker during the purchase.
John

johnma said:

My 2003 390 says gross tonnage 22.

as others have said, use whatever was on the original documentation. If you change anything but the ownership and the name of the boat you're opening yourself up for a paperwork nightmare. Those were the words used by the broker during the purchase.
John

Click to expand...

I could believe gross of 22, but not net. Not that it really matters...

This question reminded me of a tonnage discussion in 2004 on another forum. I can't vouch for any accuracy, but for those interested:

TWL: Vessel Documentation

marke627 said:

Recently purchased a 390 Mainship 2003. Working on Coast Guard Documentation. Can someone advise what their certificate states for gross tonnage and net tonnage? An old form showed 22 GRT and 18 NRT. Is this correct? Thank you so much.

Click to expand...

Up here in Canada on our 2003 Gross Tonnage 12.50 Net Registered Tonnage 6.41 Canadian Certificate of registry

Comodave said:

I could believe gross of 22, but not net. Not that it really matters...

Click to expand...

Tonnage is cargo carrying capacity. Gross is measured form the hull, Net is measured from the volume of the cargo spaces. Even with Gross Tonnage, In no way is Mainship 390 hull volume capable of carrying 44,000 lbs.

Shrew said:

Tonnage is cargo carrying capacity. Gross is measured form the hull, Net is measured from the volume of the cargo spaces. Even with Gross Tonnage, In no way is Mainship 390 hull volume capable of carrying 44,000 lbs.

Click to expand...

For admeasurment, tonnage is not a weight measurement but rather a volume measurement. Back in the colonial days, I guess, a ton of cargo took up 100 cubic feet or so. So tonnage became known as 100 cubic feet. It is still used to admeasure a boat for documentation purposed. Gross tonnage is the total volume of the boat including engine spaces and any other non cargo carrying spaces. Net tonnage would be the gross tonnage minus the engine and non cargo spaces in volume, not weight. Tonnage has absolutely nothing to do with weight. So the 44,000 pounds has nothing to do with tonnage. Sounds strange, doesn’t it?

Length: 39' 9"
Beam: 14' 4"
Draft: 3' 8"

(40 x 15 x 4) = 2,400

For a boat with a simple sailing hull, gross tonnage (GT) = (.5 * L * B * D) / 100
--> (.5 x 2,400)/100 = 12

For a sailing boat with keel, GT = (.375 * L * B * D) / 100
--> (.75 x 2,400)/12 = 9

For freighters with angled or cylindrical hulls, GT = (.67 * L * B * D) / 100

--> (.67 x 2,400)/100 = 16.08

I'd guess more likely 10-11 Tons.

My CG documentation says 21 gross 17 net
2004 MS 400

My 2003 390 documentation shows 17 Net tonnage, 22 gross tonnage.