US tonnage survey

I'm sure he's talking about a vessel for which Simplified Measurement can not be used and it must be Convention measurement.

5. MEASUREMENT SYSTEM APPLICABILITY A vessel is eligible to be measured under the Simplified measurement system if it is either: 1) under 79 feet in length; or 2) a non-self-propelled or recreational vessel. Some vessels that are 79 feet or over in length may also require measurement under the Convention measurement system. This includes vessels that engage on foreign voyages, as well as recreational vessels that engage on voyages outside the Great Lakes and have keel laid dates after December 31, 1985. The Convention measurement system does not apply to vessels less than 79 feet in length, whereas vessels of any length can be measured under the Standard and Dual systems. For complete requirements on tonnage measurement system applicability, refer to Navigation and Vessel Circular (NVIC) 11-93, Applicability of Tonnage Measurement Systems to U.S. Flag Vessels.

6. MEASUREMENT SYSTEM HEIRARCHY For most vessels 79 feet and over in length, the Convention system is the primary tonnage measurement system under the law in the United States. However, law permits vessels to also be measured under the “optional” Regulatory system regardless of length, if requested by the vessel owner, for purposes of applying domestic laws in effect prior to July 19, 1994. For vessels less than 79 feet in length, the Regulatory system is used in all cases.

And here is the Navigation and Vessel Circular,

https://www.dco.uscg.mil/Portals/9/DCO Documents/5p/5ps/NVIC/1993/CH-3_11-93.pdf

Now, as to someone to do it reasonably, I don't even know what that is, but I know Jonathan Howe does tonnage surveys and I'd be surprised if Malcolm Elliott doesnt.

Anything over 79 feet can get into the requirements if it travels to foreign waters and fits certain other requirements.

You wanted an answer to your question to know why simplified measurement would not be acceptable. I answered and provided detailed information on the rules.

Try Malcom Elliot with Florida Nautical surveyors. BUT, the easiest is to contact the yacht manufacturer as they most likely already have one on your yacht. Whether it's applicable or not, if a new one needs to be done, it will cut down on a lot of time if they have the old one.

And many older boats do not have builder's certificates available. It's unfortunately an expensive task that can run from $2000 or $3000 to $30000 or $50000. The higher is on very large boats and when there is debate on whether areas are to be included or not. Builders do a lot of strategic design to come in under key sizes.

Tonnage calculations beyond the simplified method are a specialized field, just like admiralty law. There are a lot of “tricks of the trade” that can factor in to reduce your numbers, best to use a Naval Architect firm to do the calculations. Sometimes drawings/modifications are required as well.

While what you've said is largely true, the need to reduce the numbers is only relevant to a small percentage of boats, generally at 150' or more. Builders work hard to come in under 500 tons ITC. That's why so many 161', 164' and similar sizes. Also, in Europe, licensing requirements for captains and crews change dramatically at that same magical 24 meters (79') and you see a lot of work to work around that length. The 24 meters is evaluated by rules for determining "Convention length." The definition of convention length is:

Either 96 percent of the length on a waterline at 85% of the least molded depth measured from the top of the flat keel, or the length from the fore side of the stem to the axis of the rudder stock on that waterline, whichever is greater. In vessels designed with a rake of keel, this length is measured on a waterline parallel to the design waterline.​

For normal US Documentation as Bill is seeking, certain surveyors (not all) are able to meet the requirements. It only goes to more work and possible involvement of a naval architect if it's greater length (pressing against the 500 Ton number) or there are some unusual features of the boat affecting what is to be considered within the "total molded volume."

100' should be rather simple unless some very unusual design. You're not pressing against any of the magical tonnages that lead to manipulation and you're not trying to squeeze under 24 meters. It will be interesting to see what your other quotes are. $4000 doesn't sound that unreasonable, but $5000 seems to be pushing it a bit. Of course, that's without seeing the boat and it's design.

I can assure you that Naval Architects get involved in tonnage calculations for reasons other than the 500 grt limits.

I can appreciate your layman's grasp on the concept of gross tonnage as a yacht owner, but you are not a technical expert. Even simple statements like the 96% length of waterline quote have driven huge technical discussions behind the scenes and rule bending options, like false bows, redefining compartments, playing off molded depth and the relationship of rudder centerline to waterline length. Some builders have invested and figured out acceptable solutions, others are still trying to work the 24m rule criteria in their product portfolio. I have seen discussion that have taken hours just to agree on length as the rule applies!

A tonnage calculation for a 100' yacht can be relatively basic or complex due to a number of factors, like is it a single deck or raised deck pilothouse or a tri-deck MY, etc. Plus the translation of what the different void or machinery spaces represent. Having a lines plan digitized and computer modeled is another thing, sometimes you can get that from the mfg, other times you can't. But their is work and time involved and expertise at rule interpretation and how it applies to a specific yacht.

What are going rates for engineers / architects - $200/hour? At $5000 that's only 25 billable hours, seems like a fair amount in the overall scheme of things.

It's only 79' at the water line! lol Now you don't need it!
Where is the vessel's length supposed to be taken from for this tonnage calculation anyway?