Wot on 2014 - 31 CB

[NEDBETTY]

Does anyone know the WOT top speed on a D for 300 horse
On a 31CB

 

[Wee Venture]

WOT RPM is nominally 3500. Speed will vary a lot based on load, windage, bottom condition, trim tab deployment, etc. For our R-31CB loaded for cruising with a RIB in the davits, it’s about 16 knots on a good day.

John

 

[Gin]

Not sure there is any real difference in the D4-300 for 2014 through my year, a 2019. But FWIW, I get just about 3600 at WOT. Spend is dependent on the usual factors (up river, down river, wind, passengers, fuel and water, among others). But it would be rare for me not to get 20 knots plus at WOT.

Gini

 

[Wee Venture]

Not sure there is any real difference in the D4-300 for 2014 through my year, a 2019. But FWIW, I get just about 3600 at WOT. Spend is dependent on the usual factors (up river, down river, wind, passengers, fuel and water, among others). But it would be rare for me not to get 20 knots plus at WOT.

Gini

Ours is a 2018 model year. As I understand it, Volvo recommends being within 100 RPM +/- of 3500 WOT. More than that either way and you may be over or under propped. I recorded 3470 RPM WOT under conditions of calm water, 90 gallons fuel, water tank and holding tank half full, provisioned for cruising, trim tabs deployed to keep bow down. You have a sedan, Gini, which may be one reason you’re faster. I envy your speed but we opted for the CB. We also live on our boat; in spite of our best efforts and intentions it’s fairly loaded down with stuff.

John

 

[Heronboy]

I second Gini’s numbers.

 

[NEDBETTY]

Thanks!!!

 

[BB marine]

There is one posting of D4 R31S in a thread that I started. viewtopic.php?f=2&t=17591#p115098


2018 R31S, D4 300 HP, factory prop
70% long trip cruising, 25% trolling, 5% short day excursions
2.5hp outboard mounted on stern railing, King Marine cockpit enclosure
100% in salt water
Bottom clean
Engine operation: 700 rpm 25%, 1800-2200 rpm 25%, 2800-3000 rpm 25%, 3000-3250 rpm 25%

Averages
1500 rpm 1.8 gph 6.7 kts, 3.67 nmpg
1800 rpm 2.7 gph 7.5 kts, 2.83 nmpg
2000 rpm 4.0 gph 8.2 kts, 2.05 nmpg
2200 rpm 5.1 gph 8.6 kts, 1.70 nmpg
2800 rpm 9.3 gph 13.9 kts, 1.51 nmpg
3000 rpm 10.7 gph, 15.5 kts, 1.45 nmpg
3200 rpm 12.4 gph, 16.9 kts, 1.38 nmpg

I'm assuming the 3200 rpm is high cruise speed the fuel burn does not match up to 300 hp D4 fuel burn WOT 14.5 GPH WOT.

D4 300 hp should be turning 3500 + 150 rpm/-100 to meet factory recommendations. A lighter loaded boat would want to see 3600 to 3650 rpm and a full loaded boat would not want to see under 3400 rpm WOT. With these numbers the engine is properly loaded and not over propped.

 

[Gin]

As John noted above, I do have the sedan model, so efficiency and speed may be a hair better than the command bridge. And under nearly ideal circumstances (boat newly delivered, partially loaded with gear, two people, 3/4 full fuel tank, empty water tank, fresh bottom paint, etc), I actually logged WOT at 3620 to 3640. Pleased to see Brian’s advice that WOT can go up to 3650. My more usual WOT reading, though, hovers right at 3600 once the boat is trimmed and has settled in at that throttle.

I haven’t methodically logged rpm, gph, kts, and nmpg, but I look forward to doing that. The boat is on the hard right now for new bottom paint, anodes, a prop check, etc. It would be interesting to make that log when it goes back in the water, before I take it back to its berth. It would be running with a fresh bottom paint, a full fuel tank, water tank almost empty, and 80% or more of the gear off the boat (it’s a good time to reorganize it, so most everything is off the boat). Then I could do it again under more realistic cruising conditions - full water, full gear, maybe even with the dinghy on the stern davits.

The trick will be trying to minimize the effect of the Columbia River. Current is a constant. The tidal current can either aggravate the current (on ebb) or minimize it (on flood), and how much it does either depends on time of year (the river current kicks up with spring runoff and when the Bonneville dam starts dumping lots of water). Maybe the best I can do is to time the test for max flood and take the readings both with and against the current to yield a meaningful average. Assuming I do that soon, I’d like to run the numbers again around August or September, when the river level drops and daily current is slowest. Should make for an interesting comparison between my own numbers, as well as those of other R31 owners.

Gini

 

[bill46]

Agree with John, 16 Kn normal 3500. 31CB. Use MPH since ICW is miles. Seen 20MPH usually with current.