Cruise speed 43 my

[Bertozzi]

I have a 43 my with 671 310 horse engines I am told this has a 9 knot Hull was wondering at what rpm what my speed should be around

[Freestyle]

Dead calm, clean bottom, depth 16 feet or more, mine cruised per GPs at 8.2ish at 1350 rpms and got 1nm per gallon including generator burn for thousands of miles. It would push water on the bow with anything much faster. Slow down to 7.4 knots and burned 1.3 nm per gallon or a little better.

Bruce

Freestyle
1986 62 CPMY (54MY with ext)
Tampa

Formerly owned 1976 43 DCMY (2001-2011)

[Bertozzi]

Sounds about what I’m doing I have a spare set of props I want to redo just wanted to make sure they were ok

[gbharrington]

Actual real life hull speed is probably ~6 knots. My own cruise experience is 2.2 smpg @7.5 knots. That's 1250 rpm, Cummins 903s, good sea conditions, 24x26 props. I am confident that I could make 3 smpg if I could tolerate 6 knots.

[Jammin']

43DC at about 8.7 kts and 1400 rpm, 671n with n70 injectors made about 1.22 mpg.

[wpc691]

43MY, 3208T, 302hp, 1250rpm, 7 knots plus or minus, 2.2 smpg

[SKYCHENEY]

Our 1975 43DC with 310hp J&T 671n's would cruise 16kts @ 90%, tabs full down. But, back then the price of diesel was 69 cents/gallon so we never worried about fuel burn.

[spartonboat1]

I have a 43 my with 671 310 horse engines I am told this has a 9 knot Hull was wondering at what rpm what my speed should be around

My 43' DCFB is a 1972 with the same power. I use the rule of thumb of 200 rpm below max, and I have never been able to achieve the rated 2,500 rpm max. Instead, I always see 2,450 at max throttle. I had the prop blades professionally traced/tracked, but was a poor job in my opinion, although by a Hatt shop. So unsure if the blades are the issue.

Using 2,450-200= 2,250, but I do not exceed 2,200. Note: For many years, the right engine started to heat up at 2,000+, so ran at 1,950. I later learned that the hose from the water pump to the heat exchanger was "kinked", so I installed an "ell" and two hoses and the over-heat went away, allowing higher throttle settings, i.e. 2,200. See another post about 16+ water depth. You will note that when running in shallower water, which can be 15-20 feet, you will lose 1.0-1.5 kts! Your hull generates a bow wave that reaches the "bottom" and pushes back. When running at full throttle in more than 18-20', your speed will not be affected.

Also, running with or against the sea, say 1-3' waves, will affect speed. With will add speed, against lessen speed.

So again, per the other post, 16+ feet depth, no current running, fairly calm seas, I expect 12.5-13"kts" at 2,200rpm (not mph), GPS measured. I find that my knot meters seem inaccurate or are overstating speed.

Maybe that is slower than others see for this hull and power, but is a fairly stable speed. Finally, early in season, seem to run faster - don't know why. I am barrier coated, so the hull should not bee absorbing water. Fuel load also affects speed- full will reduce by 1kt compared to about 100 gals. These are 375gal tanks.

My experience at 22 years ownership.

[jrbrein]

The theoretical hull speed of the 43' DC is just shy of 8 knots. The square root of the waterline times 1.34.

My boat is a 1982 43' DCFB with 6-71 N's (J/T modified - 310 HP each engine), 24" X 24" 4 bladed cupped with twin disc trans 1.97 to 1.

My wide open throttle under load is 2500 RPM both engines and in calm conditions, 20' plus depth with 1/2 full fuel and water and the diver just cleaned the bottom. My GPS speed over ground is 17.8 knots.

When running at 2250 RPM I get around 14 knots. Trim tabs all the way down.

I like to drive the boat at 8 - 10 knots. Trim tabs all the way up.


Jon