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Cruising Speed/RPM 1987 Mariner 3297

GAS engine, transmission and generator repair and maintenance discussion forum.
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rybad
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Vessel Info: 1987 Carver Mariner 3297 w/ Crusader 270's
Location: Grosse Ile, Michigan
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Cruising Speed/RPM 1987 Mariner 3297

Postby rybad » June 21st, 2018, 11:54 am

Hi guys.. I'm on my 4th year with an 87 Mariner 3297 and will be doing some longer runs this Summer than normal, so I wanted to get some feedback IF there are any late 80's Mariner owners, or at least similar hull design.

I have twin Crusader 270's with Voyager electronic ignitions (replaced old points distros). Our usual long trips have been around 70-90 miles RT. I have an issue where my port throttle does not scale the same rate as my starboard. They start even, but mid way I have to throttle-up the port to keep sync. Towards the top end (3200-3400) it gets closer, but still does not even out. I can get to about 4100 WOT on each. Last summer, port side blew head gasket (hour meter reads 750, but three have been several owners, and not sure if its original hour meter, or original gasket on engine).

I replaced Head Gasket, and could never seem to get port to run/feel right. Well, this summer, it "seems" to have settled in. I did have the heads re-done when I replaced the head gasket, so I don't know if it had to break-in a bit or what. I also replaced the carb on that side (when I was trying to get it right after the head gasket replacement). So I don't know if the throttle scaling has anything to do with the new carb, or if port is just getting tired. I did a compression test, and all cylinders where all within 5 PSI and if I recall, was 140-150ish PSI (cant recall exactly, but I remember it seemed within spec by the book). To maybe help, I just installed two digital tachometers, so hopefully I will get a more accurate reading. I did not run new wire to the distro though, just used old wiring to new tach.

Aside from that, I was wondering if anyone knows what the cruising speed/rpm (I realize will vary by conditions etc.) of this hull design with my engines. I am trying to determine my GPH for several longer trips. I normally push her at 3200 RPM, but thats primarily because that is the range I grew up with.. seems like most of my boating experience had the crusing RPM at 3200. Realizing that even 100 RPM variance can make a huge GPH change, and (until now) have had no accurate RPM guage, I just want to see what others are running. I dont need to "beat the fleet" but I dont want to run like a snail either. I'm happy at 20 KTS. but more concerned about econemy, and I dont know the sweet spot yet on this vessel.

I'm starting to look into fuel-flow guages, but didnt know those could be installed easily on such an old boat.

Any input, suggestions etc.. would be greatly appreciated.

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RGrew176
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Re: Cruising Speed/RPM 1987 Mariner 3297

Postby RGrew176 » June 22nd, 2018, 3:18 am

I have an 81 3007 Aft Cabin so it's not an apples to apples comparison. I do have the same engines as you do, 270 Crusaders. I am turning 18" dia x 18 pitch 4 blade propellers. My WOT is 4000 RPM and both engines achieve 4000 RPM.

Last season I tracked many facets of my boating. Last season I made 2 trips to Put In Bay, Several trips to Detroit Beach Boat Club on fuel runs. Several boat rides around Grosse Ile. Several other shorter runs. I ran at many throttle settings from 1400 RPM up to 3200 RPM. A few times I took her up to WOT.

My numbers for the season are as follows:

The 2017 season is over. I thought it would be interesting to crunch some of the numbers. Now looking forward to 2018.

2017, My Season By The Numbers

Launch April 22, 2017

Pulled November 2, 2017

195 days in the water.

102 days spent aboard.

54.0 hours on the engines.

473 miles traveled during the season.

555.7 gallons of fuel used.

Top 5 Expenses

1. $2355.18 Transmission repair.
2. $1935.08 Fuel
3. $1700.00 Summer dockage
4. $1640.49 Winterization expenses (paid for 2016 & 2017 winterization)
5. $689.00 Winter storage.

$10025.50 Total Expenses for 2017.

Crunching The Numbers

.851 Miles Per Gallon average for the season.

10.290 Gallons Per Hour average for the season.

Cost of operation.

$51.41 Per day boat was in the water.

$98.29 Per day I spent on board.

$27.47 per day for the year.

Priceless the fun times aboard cruising to my various destinations.
Rick Grew

2022 Stingray 182 SC

2004 Past Commodore
West River Yacht & Cruising Club
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Re: Cruising Speed/RPM 1987 Mariner 3297

Postby bud37 » June 22nd, 2018, 10:11 am

Most times I don't think you will get two older engines to perform exactly alike, props could be slightly different, boat loading one side from the other, older throttle cables, you have a new carb on one side.
The fuel flow meters/systems are in my opinion a good addition for anyone wanting to optimize the running of their boat, interesting to watch as you make adjustments ( sometimes a bit scary :-D ) and keep track of tank levels ,If you are handy easy to install.....
The above is strictly my opinion always based on years of doing...remember to support local business , it pays back.

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