3700 performance numbers

[itsabowtime2]

Looking at a 1999 3700 with the Horizon engines. Can anyone share what the best cruising RPM's are and slowest planning numbers. GPH numbers would be fantastic.

And any trouble spots one should look at. I would get a survey completed but any insight into areas to pay close attention to would be appreciated. Thanks.

[CGG]

love that boat!

[dronthelake]

As you go above 1000 RPM the MPG steadily drops. At 1000 RPM I get abou 1.45 MPG. At 1200 RPM it drops to 1.25 MPG.

[itsabowtime2]

Thank you. Any idea what the best cruising would be at. With my twin I/O powered boat it is 3400 RPM's.

[dronthelake]

1998 3700 SCR, 7.4 MPI, 24,000 lbs with full tanks and gear

We cruise slow at 1200 to 1400 rpm on a fresh water lake. I log every weekend's mileage and engine hours. Over the last few months we cruised 190 miles. Last weekend I topped off the tanks with 155 gallons ($4.36 for 87 octane). The left tank took an extra 24 gallons as it also feeds the generator. Assuming the engines burn roughly the same amount of fuel they would have consumed 131 gallons. Our average speed was 5.3 mph at 1.45 gpm (11.15 gph).

On plane the boat feels the smoothest at 3600 RPM. Very noisy but good ride. If I recall it would be sucking in a lot of fuel getting less than .75 MPG. These boats are heavy and the 7.4 engines are thirsty beasts.

1200 rpm - 6.8 (0% tabs)
1400 - 7.7 (0%)
1600 - 8.7 (0%)
1800 - 9.3 (10%)
2000 - 9.9 (20%)
2200 - 10.4 (50%)
2400 - 11.0 (100%)
2600 - 12 (100%)
2800 - 13 (100%)
3000 - 20 (100%) To achieve this speed/rpm and stay on plane I have to accelerate to at least 25 mph then slowly back off.
3200 - 21 (75%)
3400 - 23 (50%)
3600 - 25 (30%)
3800 - 27 (20%)
4000 - 29 (20%)
4200 - 31 (10%)
4400 - 32 (10%)

Based on 24 gallons the Westerbeke 7.2 generator burns .47 gph.

[itsabowtime2]

Originally Posted by dronthelake

1998 3700 SCR, 7.4 MPI, 24,000 lbs with full tanks and gear

We cruise slow at 1200 to 1400 rpm on a fresh water lake. I log every weekend's mileage and engine hours. Over the last few months we cruised 190 miles. Last weekend I topped off the tanks with 155 gallons ($4.36 for 87 octane). The left tank took an extra 24 gallons as it also feeds the generator. Assuming the engines burn roughly the same amount of fuel they would have consumed 131 gallons. Our average speed was 5.3 mph at 1.45 gpm (11.15 gph).

On plane the boat feels the smoothest at 3600 RPM. Very noisy but good ride. If I recall it would be sucking in a lot of fuel getting less than .75 MPG. These boats are heavy and the 7.4 engines are thirsty beasts.

1200 rpm - 6.8 (0% tabs)
1400 - 7.7 (0%)
1600 - 8.7 (0%)
1800 - 9.3 (10%)
2000 - 9.9 (20%)
2200 - 10.4 (50%)
2400 - 11.0 (100%)
2600 - 12 (100%)
2800 - 13 (100%)
3000 - 20 (100%) To achieve this speed/rpm and stay on plane I have to accelerate to at least 25 mph then slowly back off.
3200 - 21 (75%)
3400 - 23 (50%)
3600 - 25 (30%)
3800 - 27 (20%)
4000 - 29 (20%)
4200 - 31 (10%)
4400 - 32 (10%)

Based on 24 gallons the Westerbeke 7.2 generator burns .47 gph.

Thank you. Awesome info to have if we move forward. The one we are considering has the 380hp horizon engines but I assume the numbers will be similar.