All ships have dual plugs so a converter is not needed. I remember the Rotterdam V very well and loved her, but she sure was lacking the amenities we are not used to....sailed her many times back in the 80's.
You will love the Rotterdam VI and Alaska.
I'm not sure but I don't believe butane curling irons or even butane lighters are allowed on planes, even in your checked baggage, or on the ship but I would check out HAL's web site "Know Before YOu Go". Cruise Planning & Advice, Preparation | Cruise Tips and Info | Holland America Line
Hard to find, but I found this on page 6 of the above booklet "
Holland America Line cautions against
the use of garment bags with hanger hooks protruding
from the top. We also suggest that you consider placing
articles in clear plastic bags inside your baggage to minimize
handling by airport security screeners. Pack shoes on top
of other contents in your baggage to expedite the screening
process. Finally, make sure that you label the inside of your
carry-on and checked baggage with your name and contact
information. Bear in mind that the screening process for any
point of embarkation is similar to that at an airport. As such,
all weapons and dangerous devices are prohibited and may
result in denied boarding. For complete, updated information
regarding travel, please check the official website of the
Transportation Security Administration at
Where are you flying from? Wherever it's from check the rules of the airline and the Customs/Immigration as to what is allowed on the plane. If it's not allowed on the plane I don't think it's allowed on the ship.
I thought butane curling irons were a thing of the past. I once had one and it never worked properly - I was always having to buy refills.