The whole game with every vehicle actually lacks the "sense of speed" :-\

/upvoted

We tried both available boats and their max speed and compared it to proper real boats of their classes.

For speedboat class
max in real - about 70-75 km/h
max in ARMA 3 - 68 km/h

For assault boat class
max in real life - about 30-35 km/h (in this case weight is matter, for full boat its about 20 km/h)
max in ARMA 3 - 32 km/h

This issue will be looked at as general thing about speed and visual feeling of speeds.

Thank you for your report and keep the issue monitored to see when it is tweaked.

Are you sure those speed number for the real boats were not in knots? That would make a huge difference. 68kph is only 36.7kt. As you can see this possible error would explain the seemingly odd slow top speeds of these vessels.

If we assume you made the mistake I think you did we should see 126kph for the speedboat and 59kph for the assault class.

Please recheck your sources to be sure you didn't take knots as kilometers. It's not the same thing and an easy mistake to make.

I did a quick google-search and found some wiki-links:

http://en.wikipedia.org/wiki/CB90-class_fast_assault_craft
In the right box it says: 40 knots / 74kph

Another type:
http://en.wikipedia.org/wiki/Jurmo_class_landing_craft

The small boat (tube) does about 30-70 knots (53-130 kph) Depending on type and loadout:
http://en.wikipedia.org/wiki/Rigid-hulled_inflatable_boat#Performance

I believe, there is a knots<->kph mistake like sarlac said...

I'm just bumping this item.

I feel that the perception of speed is fine. If anything, it sometimes feels like it's going faster than it says it is. In reality, you won't have very good perception of speed in a boat, unless you're very close to shore. To some extent that might translate to the game as well, making it feel slow when you're far from shore.

As far as the actual speeds are concerned, I've only ever noticed the assault boat standing out as a bit sluggish. Posting a Wikipedia link about RIBs is a bit off though. The boat in the game seems to be a standard inflatable with an inflatable keel, as used by many armed forces. These won't perform nearly as well as a RIB. A small 4-5 metre inflatable is very sensitive to weather conditions and load, but is also very sensitive to engine power.

I assume the "500 fivestrike" label on the engine is a bit of a developer joke, like the "FTW" badges on certain cars in the game. However, even with a 25 hp engine at full throttle, a boat like that should be able to do maybe 20 knots. That's 37 kph, while the ingame boat maxes out at somewhere around 31. And for boats in actual military use, you can expect at least a 40-60 hp engine.

As a final note, some of the boats have a very small difference between cruise speed and turbo/max/full speed. Again the assault boat is perhaps the most noticeable, with the difference being around 3-4 kph. The only thing that really goes up when you max out the assault boat is engine noise.
And speaking of "fivestrike". Assuming the engine is supposed to be a modern four-stroke, it seems just a little bit noisy, but I might just be nitpicking now.

I wish the assault boats were a bit faster/speedier as well. Currently even when pressing "Turbo" an assault boat barely goes above 27 kph. This is an issue if for example you want to do some long range insertion missions.

To me it really looks like a knots / kph conversion mistake, as 25 - 27 knots would be absolutely doable. A Zodiac WB 400 with a 25 HP engine should easily be doing 25 - 30 knots, which would be around 50-56 kph.