Estimated cruise speed

riprunner · #1 03-16-2005, 06:15 PM

Anyone know what the estimated cruise and top end of a 1987 23 Seacraft with a brand new 5.7/350HP straight inboard?

MarkR · #2 03-16-2005, 07:22 PM

Wow, that's alot of power. What transmission is coupled to that 350HP?

I can tell you that it's more than 30knts. There is a '75 CC in my harbor with a 300HP Horizon I/O that approaches 35knts.

The prop. will be a big factor as well. 16" x 17"??

ocuyler · #3 03-16-2005, 07:55 PM

If you're looking for speed, there's no reason that set-up wouldn't do 40 plus, propped correctly. I'd love to be the one testing it...

riprunner · #4 03-16-2005, 08:52 PM

I actually had no idea it would produce that much speed. We needed a new engine and this one had 350hp, sounded good at the time. I know that IO's are much faster than straight inboards due to drag restraints in inboards. I was thinking a 25 knot cruise. Do you really think I could get that much speed?

ScottM · #5 03-17-2005, 08:34 AM

You'll definitely get a 25 knot cruise, no problem. I think Mark was talking top end when he said over 30 knots. However, with 350hp and the right prop, I wouldn't be surprised if you could get an economical cruise in the high 20's. The again, for longevity's sake, you might want to cruise a little slower because you're at the 1hp per cubic inch threshold.

RalphD · #6 03-17-2005, 10:23 AM

I have an older carbureted 454 crusader (350 hp) in my '79 23' inboard w/ a 17x17 prop. I have had the boat up to 37 mph with the current, by myself, and half filled with fuel. I don't see how you could go much faster anyway, as the boat becomes a bear to handle.

For cruise, I get between 26 and 29 mph at 3,000 rpms depending on current, wind, loading. The 4-barrel kicks in at around 3,100 rpms so I don't go over 3,000 much.

ocuyler · #7 03-17-2005, 11:09 AM

There's your answer...

MarkR · #8 03-17-2005, 02:33 PM

Scott is correct when he clarifies my speed of 30knts @ 4400rpm, Wide Open. I cruise at 19knts @ 2900 rpm. by the way 16"x15" with 5* cup. I'm Looking for a 16"x16" four blade if anyone has one lying around.

The I/O walks by me with that Horizon. I'm only guessing 35knts, could be more

ScottM · #9 03-17-2005, 02:42 PM

Quote:

The I/O walks by me with that Horizon. I'm only guessing 35knts, could be more

Mark, sounds about right. My buddy's Silverhawk with that setup runs about 35-36 knots WOT.

Gary Hill · #10 03-18-2005, 07:03 AM

I just repowered with a 350 VORTEC Carb 315 HP and I have a 17 X 17 with a little cup, which gives me the same speed's RalphD is talking about with a full tank and three people onboard, my 4-barrel cuts in around 34-35K rpm's. It's a 76 CC Inboard.