VP D4 320

Does the Volvo Penta D4 reduce load or power output based on loading (weight) of the boat? I had a full boat this weekend 6 adults, 170 gallons of diesel, full fresh water 80 gallons, black tank empty but WOT would only get up to 3000 RPM. No warning codes, all fluids at correct levels just felt "de rated".

Also, could not get "Engine Load %" reading on Garmin.

Ranger Tugs, like many boats, are very weight sensitive. Assuming you have had a different experience in the past with similar loads, the first two things to verify would be: 1) Condition of the bottom. Marine growth there can give you the results you experienced.
2) Condition of the primary fuel filter. (Although my experience is if it gets clogged your engine will demand fuel and then just shut way down to a lower RPM when it is starved for fuel because of the clogged filter.)

My opinion is the propping on by boat manufactures is not alway done correctly. The engines if properly propped should turn to governor. The D4 should turn WOT 3650 to 3700 rpm with full fuel water and gear. This will keep the engine loaded properly at all rpm ranges and properly load the engine. Things that will lower the rpm are dirty bottom, extra weight ( passengers, coolers, gear, weather and sea conditions ) these things are normal conditions that a boat owner and a boat manufacture should take into consideration when propping a boat/engine. If the boat/engine is propped correctly when it is normally loaded with full fuel, water and gear it will turn recommended rated RPM making full rated horse power plus 150 rpm. Why over? Because the recommended rpm for a D4 260, 300, 320 hp is 3700 max rpm to no lower than 3400 rpm to be loaded properly. This means that when it is normally loaded ,clean bottom, full fuel, full water it will turn max rated. And when it is loaded heavily, bottom dirty, it will turn minimum recommended rated. Why do boat manufactures over prop? Marketing!! When the boat manufacture sea trials a boat and decides what prop should be used the fuel tank is 1/2 tank or less, no water, clean unpainted bottom, no gear on board except coast guard package, A captain and a deck hand and possibly a Volvo rep. and away they go. They are looking for best hull performance and maintaining a rpm in the recommended range. Looking closer to 3500 rpm for rated HP and best performance over water. Volvo Penta rep. puts stamp of approval. Boat performance is awesome and that performance is what goes into advertising and marketing. Example: This is from Soundings magazine.
"Messmer and I took the R-31 for a short sea trial in February at the Miami International Boat Show. We piloted the boat from the flybridge, but she can also be driven from helm stations in the pilothouse and cockpit. Standard bow and stern thrusters complement the 300-hp Volvo Penta D4 diesel, which pushed the R-31 up on plane with minimal bow rise — not surprising for such a light boat. At a 7-knot displacement speed, the D4 burned 1.5 gallons an hour for a 4.7-nmpg mileage rating. The engine gauge showed a fuel burn of 15 gph at 24 knots for a 1.6 nmpg rating.

Those are awesome numbers and I believe true at the time of the sea trial. Volvo D4 is making rated Hp at recommended rpm and the boat is showing awesome fuel economy and speed. Now the boat is delivered to a new owner. The new owner loads it up with gear, fuel and water. The performance is still close to what was advertised and max rpm is barely making 3500 rpm and more like 3400 rpm. Close to being over propped. Now gear the boat for a trip and bring some extra passengers along and all of a sudden the rpm is 3200 rpm or lower at WOT. The engine is now being operated at over prop conditions at all rpm ranges. That is something most folks don't think about. If the engine cannot make WOT recommended rpm it is over propped and over loading the engine at all rpm ranges. It is not operating at designed load for any rpm. When I hear someone say my engine will not turn WOT recommended rpm but that's ok because I don't ever run WOT. That is an incorrect thought. There are no gears to drop down to in a boat like a car or truck. I have used the analogy of a truck climbing a hill. When a truck is climbing a hill and the rpm drops because the engine is being over loaded. What happens? The transmission shifts to a lower gear and the engine load is reduced and the rpm comes up. What would happen if it did not? The engines life expectancy would be reduced. Now the same engine is in a boat. The only way to reduce the load on the engine or maintain the proper load on the engine is by propping it correctly. If you prop it so that it will turn the minimum max rpm 3400 rpm to get great performance when loaded light. What happens when it is loaded heavily (Climbing the hill !! ) The rpm drops and the engine is overloaded and basically is always over loaded if max rpm drops below 3400 rpm. You are climbing a steep hill! The engines longevity could reduced if this is how you operate your boat/engine.

Unfortunately this is done all the time by boat manufactures. Engine manufactures warn boat owners in the owners manual. Do not operate the engine if it can not make recommended RPM at WOT.

This is not to point finger at Fluid Motion. This is pointing the finger at boat manufactures and boat owners.

Brian,

Thank you for the info! That’s a lot to digest.

We have a 2021 R29 S (LE so it has the weight of the generator in the stern) with the D4 320 and when we are loaded for a cruise (two adults and two dogs at 60lbs each) (food and clothes for weeks) we get performance numbers we expect given the Ranger Tug spec sheet. Full fuel and half water we get full throttle RPMs of about 3550. When we have half tank of fuel we turn 3590 to 3600. We will see RPMs in the 3650 to 3700 range at the end of the cruise when the water tank, fuel tank and refrigerator get closer to empty. (Fuel tank is seldom, if ever, less than one third.) We have a clean bottom without bottom paint - boat is stored on a trailer when not being used. We do not have the extra wind resistance of the CB. We cruise the fresh water Great Lakes. Thus, for our use, the boat comes with the proper pitch propeller.
If I didn't get the right performance numbers, propellers are not difficult to change (with a propeller puller for the inboards) and the original can always be saved for a spare.
I am just guessing, because I wasn't there for your weekend cruise, but if you normally get performance in the designated RPM range, I expect there was a combination of lots of passenger weight (perhaps toward the stern), a head wind blowing against the command bridge, and a dirty bottom.