I am, of course, Googling as well. But anybody with better Google-fu who wishes to help well have my thanks.
Never mind. I’ve found what I sought.
Please share with the rest of the class. 
Well, I phrased the OP very badly, as I should really have asked about a specific class of ship. But checking various sources after I figured out better search terms, I found ships of that size with crusing speeds of about 20-30 knots.
(A Panamax ship is one of the largest size that can still pass through the Panama canal.)
Further, modern cargo ships more or less got one speed. They are designed to go (say) 25 knots and that’s about it. They cannot economically speed up or slow down. So over long distances, they got two speeds. “stop” and “go.”
Thanks, Paul. It doesn’t matter for my purposes, but it’s interesting to know. Do you have a cite?
Your question doesn’t really compute. You need to say what sort of panamax. Bulkies and tankers tend to do about 13-15 knots. Coal etc are not time sensitive cargoes. Container vessels go faster, and if you came up with 20-30 knots, you were probably looking at cites for them.
And Rick, why the !#$ did you charter that thing? We’ve got over 3m under the keel we’re not using! I’m losing money here. You’re fired.
But boss, I got all the width I could fit through the locks.
Please don’t fire me.
Well OK, you can keep your job for now, but only because we’re sending her through the Malucca Strait. This’ll be the first voyage ever where I’m hoping some goddamn pirates try something!
But seriously, at least in the circles I am familiar with, you might say a vessel was within panamax if it will fit through the canal, but if you refer to “a Panamax Vessel” you would mean a vessel with both a beam and draft designed specifically to be the maximum that will fit. So I wouldn’t think of a warship that can fit through the canal as being a “Panamax Vessel” as such.
OOOO, if we find some pirates, can I fire the big guns?
Well when I was at Pearl Harbor, you can see the scratches in the armor where it rubbed the sides of the canal. Looking at the specs in Wiki, it lists the beam as 33m and the width of the canal as 33m. Also the guy that gave the tour of the Mighty Mo told us the design was given the size of the canal as the primary design criteria.
I see the draft of the Missouri listed as 8.8m, I didn’t see the depth of the canal listed, but I only skimmed the Wiki article.
Still with a draft that is listed as the same as the width of the canal, I think we can call that a Panamax vessel.
The max draft of the canal is about 12.5m.
I don’t doubt that the Iowa class battleships were built to be the max beam that would fit through the Panama canal. But it’s a matter of terminology. An Iowa class is panamax, but it is not “a Panamax”. If we hark back to the OP, it is clear that it is asking about the class of vessel known as a panamax. The whole OP doesn’t make sense if it is simply referring to any vessel that is panamax, since as your initial response highlights, anything from a slow old bulkie to a warship can be panamax.
You can call it a Panamax, but I can’t because I work in the industry and in the industry, it’s a term of art. It has a particular meaning. If someone is talking about a vessel and says “its a Panamax” I know they mean something about 33m beam, 12.5m draft and about probably around 65,000 deadweight.
“about probably around”. Anyone’d think I was leaving myself wriggle room.
Shit I left 20,000 tons on the table also.
You are of course correct.
I do have one more question.
If we spot the pirates, do I get to fire the big guns?
“We no pirates. We only pirates when you not in ship with big gun. When you in ship with big gun, we fishermen with few AK47 for self defence against pirates. Them pirates bad men. We not pirates.”
BOOM!
oops. I’m sorry boss my finger slipped.
They are currently building new locks for the Panama Canal that will handle larger ships. These are going to be in addition to the current locks. Completion is scheduled for 2015.
The new ones will hold ships up to 49 m wide, 366 m long and 15 m draft. So is the term Panamax going change definition or are they going to call them New and Old Panamax or something like that?
In a word, uh-uh.