3200scr best cruise speed?

[geoffm70]

Just wondering, is there a general consensus on what the best/efficient RPM/MPH for a 3200 SCR, 5.7 Mercs, Bravo 2, forgot the prop pitch, but its unchanged from original? Just finished crossing the Georgia Strait (Vcr-Nan), 35 nautical miles and took 1.5hrs. 23knots at 3650rpm seems to be her sweet spot, but maybe I'm wasting fuel?

[mmwjr]

Sounds about the right rpm to me for those engines.

[geoffm70]

Thanks, was wondering because we're getting royally hosed at 2.00/liter for marine gas up here. At 3650rpm she costs about $250/hour these days.

[mmwjr]

Wow so about $8 per US gallon. It’s about $5 per gallon where I’m at.

[geoffm70]

Cad exchange is about $0.75 to usd, so apples to apples, its about us $6.75/g. Alcohol, tobacco and gasoline, are all heavily taxed here, best guess, it's to pay for health care?

[ScowHound]

Just returned First Cruise crewing on '95? 3200 SCR w 350's. Crew of 3 + gear. Approx 2 hrs at 3450 Rpm, 50 ish miles as the crow flies? We refilled and stopped pump at 100 USG, just shy of full (but it made for easy math$$$) (The soon to be replaced, poor design fuel sending unit is another subject). Returned home port, haven't fueled yet. Seems high usage to me. She ran smoothly though 3450-3600 rpms. So my relevant question is what RPM do the 4Bbl secondaries kick in, because I'm sure we had to be into them. That said, math here would be 2 gals per mile, which is not unheard of for this model/scenario, what I consider to be the entry into "big boat" category. My guess is the secondaries come in somewhere around/above 2600 RPM? On the return trip while at helm, I tweaked the trims, found the trim guages are for the outdrive trim (buttons on the throttle handles), which explains why they don't change with the trim TABS adjustment. The trim guages however are out of adjustment, as they only read down and further down lol. So I'll start a thread on trim guage adjustment. But obviously, proper and minimum trim is crucial for efficiency, so I mention it here. Not sure what props we're running, assume original, but she seems responsive relative to RPM from what I've experienced. I didn't want to run her to max to find out, as it's not my boat, and belts needed tensioned, etc from pre-return inspection. Hope the thread informed someone, look forward to any insights from folks who know this boat better.-
Scow

[Mongoose]

I have a 1994 3200 w/350 carbs and I think stock props (18.25x19p). I felt her best cruising was 3200 rpms which got me about 20 mph. That was without trimming up at all. I'm sure I could squeeze more out of her, but I'm still a noob at this.

'Goose

[Derby Time]

We have a 3200 with carbed 350's and stock 19 pitch props. We can plane without tabs no problem even with 6-8 people on board. We can run 30mph at 3,500 rpm with tabs up and trimmed out.

Your fuel consumption seems a bit off to me, but have not done the math so only really have a feel on that.

I've run 23 pitch props and was surprised how well it did. My only complaint was that it was really too fast at idle for slow maneuvering, but would still pretty much pull the rpms and would run 40mph. Does anyone have any experience with 21 pitch?

[geoffm70]

my prop pitch is 19 and anything under 3600rpm falls off plane no matter the trim?!? But 3600rpm and 23 knots, she runs great, just 200 to 225 liters per hour! WTF, really?!?

[mmwjr]

Originally Posted by geoffm70

my prop pitch is 19 and anything under 3600rpm falls off plane no matter the trim?!? But 3600rpm and 23 knots, she runs great, just 200 to 225 liters per hour! WTF, really?!?

If you are not on plane the boat is plowing through the water which is very inefficient.

[geoffm70]

I think the issue must be the weight of the contents in the boat. Why else would the same boat plane at 3200rpm and mine 3600? Last half out, no water, no waste, less than a 1/4 tank fuel, she was 18,200lbs.

[mmwjr]

Originally Posted by geoffm70

I think the issue must be the weight of the contents in the boat. Why else would the same boat plane at 3200rpm and mine 3600? Last half out, no water, no waste, less than a 1/4 tank fuel, she was 18,200lbs.

Other gear, prop pitch/diameter as well as cup,… lots of variables.

[Derby Time]

Something is off there. Maybe hull buildup, drive resistance, loss of prop diameter or cupping due to rebuilds? How much fuel? I rarely have even 1/2 tank. It's heavy and starts going bad in very little time these days. If you are running full that would be close to an additional 700 lbs heavier toward the aft half of the boat.

[Derby Time]

Whoops! Our related responses basically crossed there.

[mmwjr]

Originally Posted by Derby Time

Whoops! Our related responses basically crossed there.

Lol 😂

[Derby Time]

Originally Posted by geoffm70

I think the issue must be the weight of the contents in the boat. Why else would the same boat plane at 3200rpm and mine 3600? Last haul out, no water, no waste, less than a 1/4 tank fuel, she was 18,200lbs.

That is a lot of weight! Something like 7,400 over dry. The fuel would only be like 700 lbs. Does that seem possible to you? I'd be surprised if we have 500lbs over the dry weight plus liquids. That would put us at a little over 12,000 lbs.

[geoffm70]

Last trip was fairly smooth, less than 1ft chop and no trim tabs, very little leg trim and just over half tank tank fuel (36nm of fairly open water, Georgia Straight) and maybe 5gal fresh. Took 1hr20min at 23knts/3600. Hull and legs/props are clean. Have 1/4 tank left (thereabouts).

[geoffm70]

Originally Posted by Derby Time

That is a lot of weight! Something like 7,400 over dry. The fuel would only be like 700 lbs. Does that seem possible to you? I'd be surprised if we have 500lbs over the dry weight plus liquids. That would put us at a little over 12,000 lbs.

What the yard said, maybe they're off? I added a swim grid, have the normal equipment she came with in '94 and she was very light. In fact, this was 5 weeks ago, day she went back in, no water, less than 1/4 tank, just me (210lbs) on board, WOT, she hit 40.2mph!