Mrecruiser 3 litre 270HP -low on power, high on fuel

[Nigel52]

I have a QS905WE with Mercruiser 3 litre 270HP inboard and since new top speed has never better 24 knots and at 20knot cruising speed using 55 litres/hr. When googling this below is what I get; hugely different. On the Facebook Quicksilver group others with the QS855 (same hull) and the older VW 260HP engine they are saying 30Knots top speed and 37 litres at 20 knots. (if only)

Anyone have any suggestions how I determine if something is wrong?


The Quicksilver Activ 905 Weekend (QS905WE) with a 270HP inboard engine is a versatile and powerful boat. Here are some key details:

Top Speed​

• The top speed of the Quicksilver Activ 905 Weekend with a 270HP inboard engine is approximately 30-35 knots1.

Fuel Consumption​

• At cruising speed (around 20 knots), the fuel consumption is roughly 30-35 liters per hour2. This can vary based on load, weather conditions, and how the boat is operated.

 

[Keith-i]

Are you reaching correct rpm? Is it correctly propped?

 

[Nigel52]

Are you reaching correct rpm? Is it correctly propped?

Came with standard duo prop which I have not changed. I need to check the rpms next time I am out as currently out for mid-season scrub and new anodes. What rpm at a given speed should i be getting.

 

[Keith-i]

It should reach the maximum rated rpm at full throttle. If not then it is over-propped. If it gets to top rpm before the throttle is on the stops then it’s under propped.

 

[Nigel52]

It should reach the maximum rated rpm at full throttle. If not then it is over-propped. If it gets to top rpm before the throttle is on the stops then it’s under propped.

Thanks, I need to do some checking

 

[Nigel52]

Out on the water today Oct 27th and at 3640 rpm. Speed 25 kn and 57 litres/hrs. At cruising speed 18.5 kn, 3180rpm and 43.2 litres/hrs. Boat had scrub on August. I think this is about right for boat and engine.

 

[Hot Property]

I have a QS905WE with Mercruiser 3 litre 270HP inboard and since new top speed has never better 24 knots and at 20knot cruising speed using 55 litres/hr. When googling this below is what I get; hugely different. On the Facebook Quicksilver group others with the QS855 (same hull) and the older VW 260HP engine they are saying 30Knots top speed and 37 litres at 20 knots. (if only)

Anyone have any suggestions how I determine if something is wrong?


The Quicksilver Activ 905 Weekend (QS905WE) with a 270HP inboard engine is a versatile and powerful boat. Here are some key details:

Top Speed​

• The top speed of the Quicksilver Activ 905 Weekend with a 270HP inboard engine is approximately 30-35 knots1.

Fuel Consumption​

• At cruising speed (around 20 knots), the fuel consumption is roughly 30-35 liters per hour2. This can vary based on load, weather conditions, and how the boat is operated.

The boat is probably close to 4 tonnes and I think the figure of 30-35 litres and hour at 20 knots is very optimistic.

My saver 690 was around 2.3 tons with a 200 Verado fitted.

I got 30 litres an hour at 20 knots.

Flat out at 34 knots took 85 litres an hour....

 

[Nigel52]

I have done various tests on the boat and discussed with the Quicksilver dealers and Mercruiser at the Southampton Boat show and we are looking at a top speed of 25-27 knots depending on load. At 3180 rpm 18.5 knots 43.2 litres per hour and at 25 knots, 3640 rpm 57 litres per hr.

 

[Hot Property]

I have done various tests on the boat and discussed with the Quicksilver dealers and Mercruiser at the Southampton Boat show and we are looking at a top speed of 25-27 knots depending on load. At 3180 rpm 18.5 knots 43.2 litres per hour and at 25 knots, 3640 rpm 57 litres per hr.

Sounds about right....

 

[madabouttheboat]

I have a QS905WE with Mercruiser 3 litre 270HP inboard and since new top speed has never better 24 knots and at 20knot cruising speed using 55 litres/hr. When googling this below is what I get; hugely different. On the Facebook Quicksilver group others with the QS855 (same hull) and the older VW 260HP engine they are saying 30Knots top speed and 37 litres at 20 knots. (if only)

Anyone have any suggestions how I determine if something is wrong?


The Quicksilver Activ 905 Weekend (QS905WE) with a 270HP inboard engine is a versatile and powerful boat. Here are some key details:

Top Speed​

• The top speed of the Quicksilver Activ 905 Weekend with a 270HP inboard engine is approximately 30-35 knots1.

Fuel Consumption​

• At cruising speed (around 20 knots), the fuel consumption is roughly 30-35 liters per hour2. This can vary based on load, weather conditions, and how the boat is operated.

Those speed and fuel figures would have been produced with almost perfect optimal conditions. Very lightly loaded boat, perfectly clean hull etc. they will be very difficult to duplicate on a boat loaded with owners kit, with a few extras and options added, with fuel and water tanks full and even a month or so worth of growth in a hull will have a significant effect. If you can get anywhere vaguely near them you are doing very well. If you can’t reach full rated RPM you may need to downsize the prop, which would have been optimised for a new, lightly loaded, clean hulled boat.

 

[ontheplane]

Who on earth told you the 3 litre was 270hp.

The older 3 litre carb motor was 135hp

The newer MPi ones will be more but given the 4.3 carb was 190, EFi was 220 and MPi was 240 / 250 hp the 3 litre being 33% smaller is likely to be 200 at most in MPi form.

Is it an EFi or carb engine?

 

[ontheplane]

I have a QS905WE with Mercruiser 3 litre 270HP inboard and since new top speed has never better 24 knots and at 20knot cruising speed using 55 litres/hr. When googling this below is what I get; hugely different. On the Facebook Quicksilver group others with the QS855 (same hull) and the older VW 260HP engine they are saying 30Knots top speed and 37 litres at 20 knots. (if only)

Anyone have any suggestions how I determine if something is wrong?


The Quicksilver Activ 905 Weekend (QS905WE) with a 270HP inboard engine is a versatile and powerful boat. Here are some key details:

Top Speed​

• The top speed of the Quicksilver Activ 905 Weekend with a 270HP inboard engine is approximately 30-35 knots1.

Fuel Consumption​

• At cruising speed (around 20 knots), the fuel consumption is roughly 30-35 liters per hour2. This can vary based on load, weather conditions, and how the boat is operated.

The VW 260p is a diesel as well not a petrol - hence the reduced fuel burn

 

[Nigel52]

Excuse me but this is strange statement. This is a mercruiser diesel engine and the spec sheet is clearly available on the website. So yes a 3.0 litre giving 270 hp.

 

[ChromeDome]

The engine is stated to be a 3.0 Iveco-based V6 diesel (as seen in Daily vans) with a max rpm at 4200.
Peak torque is an impressive 594 nm at 2200 rpm.

The speed potential of a planing boat of this type is dictated by available HP and the load. Any sort of growth on the hull will add to the load on the engine. A few barnacles on the sterndrive can cost several knots!


Hence, a prop calculator can give you a good indication:

If 270 horses are to push a clean, well trimmed (angle), planing boat to 35 knots the GW (boat+engine+crew+fuel+water and everything else onboard) of the vessel needs to be <2400 kg. To make it to 30 knots the GW needs to be <3000 kg.

You've seen a max of 24 knots and 3640 rpm at wot, which sounds like a GW of 4800 kg, OR the engine not achieving the rpm (from 3400 as per below) where it makes the most HP (200 kW). Of course, it is necessary to know for sure that the tacho is correct.


These graphs are from the Mercruiser brochure - sorry for the blurred image.

Fuel consumption is related directly to how many horses you call to work. If you demand them all to pull, you need to feed them all.

As you understand, the easiest (and free) way to increase speed is to remove (dead) weight.

If the GW allows and all 270 horses are alive and ready to work, hitting the top speed at 4200 rpm will happen when the combined gear ratio is right.

Example:

The sterndrive gearbox will reduce the 4200 engine rpm as per the ratio in there. For now, let's say this is 2.00:1, so the prop shaft rpm will be 2100.

When turning 2100 rpm a prop with an 18.3" pitch will produce a speed of 31.6 knots (not factoring slip in).

If the engine doesn't reach 4200 rpm at WOT and normal GW, a prop with a different pitch is needed. One inch change of pitch changes engine rpm by 200 (less pitch=more rpm and vice versa), but as most prop manufacturers offer steps of 2", you'll get a 400 rpm change as a minimum.

As you say 3640 rpm at WOT the engine must be struggling, and the pitch ideally should be reduced by 3" to add 600 rpm, or alternatively, by 2" and remove some weight. If going 4" down, you'll add 800 rpm to reach 4400. You'd need to avoid WOT for longer periods, but fine if you plan to add more load. In any case, a lower pitch will give you better acceleration in general.

The prop design (and Quicksilver by Merc are known to be good) will deliver 90% of the performance, the prop material (e.g. stainless vs alu) may add the last 10%.

Disclaimer: The calculation is indicative and rule-of-thumb based. Nothing beats real-life testing.

 

[Grubble]

Excuse me but this is strange statement. This is a mercruiser diesel engine and the spec sheet is clearly available on the website. So yes a 3.0 litre giving 270 hp.

It would have been handy to mention that in your opening post, because a 3 litre Mercruiser is a petrol engine, rather than the TDI that you have. The data sheets you posted are for petrol outboards, which helps with the confusion.

 

[ChromeDome]

It would have been handy to mention that in your opening post, because a 3 litre Mercruiser is a petrol engine, rather than the TDI that you have. The data sheets you posted are for petrol outboards, which helps with the confusion.

Merc decided to make brochures that cover several engines, petrol and diesel. The OP second file linked to indeed is for Verado - irrelevant in this context.

The fact that both their old 4-banger and the new V6 diesel are 3 litres is just a coincidence.

Different by appearance also:

 

[Grubble]

Merc decided to make brochures that cover several engines, petrol and diesel. The OP second file linked to indeed is for Verado - irrelevant in this context.

The fact that both their old 4-banger and the new V6 diesel are 3 litres is just a coincidence.

Different by appearance also:
View attachment 185252

If the OP had posted a picture of his engine, I don't think anyone would have been confused. I think the OP has just been looking at performance data for his boat with random engine combinations, rather than the actual engine itself - hence the confusion.

 

[ontheplane]

Yeh my bad sorry - I thought it was a 3 litre Petrol!!!

 

[Hot Property]

Disclaimer: The calculation is indicative and rule-of-thumb based. Nothing beats real-life testing.

It's a black art vaguely related to a plethora of variables!

I've had outboard powered boats of various sizes over the years, and until the Admiral issued an ultimatum last year, I had 11 props on my garden wall from a knackered 9" ally one from a Suzuki 15 worth tuppence, to a shiny 15" Stainless steel Enertia one costing £700.

As chrome dome states, you can't beat real life testing.

Fortunately I have boaty friends with their collections of props so I can try before I buy......

Good luck

 

[ChromeDome]

The black art aspect really comes into play when you look to squeeze the last bit of performance out of a setup.

When you're chugging along at a good 30 knots and a friend comes along in his Mercury 225 hp 16' steering console with hydraulic outboard lift, running only on the very last bit of the hull, you know what detail-orientated persistence can lead to. A bit over 60 knots in this video.

You can't see it, but it requires constant correction on the throttle and steering wheel to keep it balancing...