Top Speed In General
 

In general what should the top speed of a 21ft V-hull boat with a stock 365hp 454cu Bravo I outdrive and trim tabs be? I understand it depends on weight in the boat, of the boat, water conditions, hull design, etc. Just looking for a range.
Thanks.

From 50 to 80mph , but very dependent on what kinda boat , could even be faster then that , but your not giving us much to work with here

Advertised top speed of a Pachanga 22(20'6") with 330 HP was 66 in 1987. Had an alpha drive so that helped a little.

A '21 Superboat will run around 80 MPH with 365HP.

65-75 is most likely

Ran 68 in that exact setup with a 22ft Checkmate

Its a Century Ultra, considered 23' but that is with the swim platform, I think its more like 21'.

1996 22' Scarab(20' w/out platform) ran about 62-64 with 330 HP/Bravo. Probably would have seen 67-68 with 365 HP.

87 wellcraft 23' nova-tall heavy boat- 330horse/bravo 55mph
This shows how weight effects mph

26 Infinity (25' with out the plat form) 454 Mag 350 HP Bravo 1 Mirage prop. 1" above std "X" dim 69.3 I gues a 21' -22' would go mid 70's. Mine is a relatively light boat for a 26'

57 mph GPS

I'm getting like 45 mph by the speedo with a full tank and two people? Is 57 the GPS speed of the exact same boat?

Don't trust the Speedo. Bring a GPS on board for real speed readings.

I've got the exact same boat, 330/454 The speedo reads 66 mph....and the 'hand held heartbreaker' (gps) :cool-smiley-026: reads 60.4....

I've also got another 22 Pachanga with the stock 350 Mag/270hp, it's interesting that the small block Pachanga runs 62.9 on gps. I guess the additional weight of the big block absorbs the additional 60 hp.

Both boats spinning 23p props, the small block does not like the Mirage Plus (I guess too much blade area) runs the best with a 23 LazerII
The 454 blows out the 23 Lazer badly, pretty much useless. It likes the 23 Mirage Plus and pulls great out of the hole.

As for your question, I'd guess that old Century should run 60-62 when everything is right and the boat has not 'gained weight'

Kurt

ran 72mph in a 1992 22' striker with a 330 hp

What year is the Century? It is a light boat.

Wow! Sounds like you got a runner and a lemon! :D

Its a 1989.

1860lbs w/o engine so add 1000lbs so about 3000lbs total with 350hp at the prop should go pretty good. I agree it may have gained some weight over the years and lost some hp. Mid-upper 60s.

Loves those old Centurys...

Once bought a boat that looked like a runner. It wouldn't even plane. I noticed that it dripped pretty much nonstop from the bilge plug. After I pulled the floor, I discovered the waterlogged flotation foam. After removing a thousand pounds of water, it ran better.

I'd also do a compression test and toss a dial indicator on the rockers. No wind or worn lobes are common culprits. I'd also look at other simple things- like is the throttle opening all the way and do the vacuum secondaries work. Check prop pitch too. If someone just tossed one on to sell it because the right one was trashed, that could be a problem.

Thanks for the pics of the other Century Ultras, I have only seen 2 others ever I can't find much info. or photos of them. I really like mine just have a few issues to work out. Its got a 23P prop on it. It is in mint condition with only 280 original hours and the engine seems to run very strong. I suspect the throttle may not be opening all the way that is the first thing I am going to check. I wish I could post a picture but can't seem to find the attachment button when replying.

a 23p what???......my boat came with some 3 blade stainless 21s.......turned out to be Merc "general duty" 21 stainless props......changed to 3 blade Merc 21 Mirages, again stainless......Wow! totally different boat...planed much faster, less wetted surface and more top speed......freed the boat right up......all 23s are not the same.....post a number offf the prop.

hit "go advanced" and you'll see a "manage attachments" button........

There is no number, it is a 3 blade and is stamped 23P and its stainless.

My buddys Ultra 1 with the 365 hp did around 72 but it was not fun to ride in at that speed.

Not fun on calm water, rough or both? 72 seems really fast I assume that was speedo speed?

Speedo, in 1 foot chop, it's very tail heavy with the big block and she was chine walking. My buddys with the 270 hp small block was better balanced. The current owner has it for sale on craigslist in Grand Rapids Michigan almost everyday.

get ahold of a 23 Mirage, buy a used one or borrow......the Mirage is the benchmark standard high performance prop for boats of (our) age/era.......probably 90% of OSO members have had a Mirage at one time or another.......tell us how the boat works with a Mirage and we'll be better able to tell you where to go with it.......doug

Round ear prop or is one edge straight and blunt?

round ear not clever style