Fuel consumption for a Nicholson 32/perkins perama

[lilianroyle]

I’ve just bought a Nicholson 32 with a Perkins perama 32hp.
I’m about to move it for the first time. On the engine what would be a comfortable cruising speed to estimate passage times and what kind of fuel consumption should I expect.
Thanking you in advance!

 

[B27]

The fuel consumption will vary with how fast you go, if the wind is against you, if the water is flat or choppy.
Also whether the hull is clean of weed and slime.
Typically I'd expect to do about 5 knots and use 2 or 3 litres per hour with a clean boat in benign conditions.
If you push the speed up to 6 knots, you might double the consumption.
Worst case, a 32hp motor with drink about 8 litres an hour and a weedy hull could reduce your speed to 3 knots or less.

I have seen small boats which have been growing weed on a mooring for a year make a 100hp workboat struggle.

You should also check the fuel in the tank is clean and that you have spare filters etc.
It's good to have some sort of dipstick to check the level in the tank at intervals, personally I like to have a reserve of clean fuel in cans.

Ideally, the fuel consumption will be very low, because you'll sail the boat most of the way?

 

[38mess]

I think the Perkins M30 perama is 29hp. I have the same engine in my work boat. It's a bit smaller than your boat but it weighs in at 4 ton. I guess I use around 2ltrs per hour ar 2k RPM which pushes me along at 5.5 knots in flat water with no tides and little wind.
I used to passage plan for 5knts in the Bristol channel in my 30 ft yacht.

 

[Tranona]

As above the "normal" Perama is a 3cyl 1100cc approx rated at 29hp, same as the Volvo 2030. There is also a larger 1400cc approx 3 cylinder that is rated anywhere from 32hp to 39. Physically larger and the same as a Volvo 2040. The lower ratings reflect lower rpm . I had one that was rated at 35 at 2600rpm. none of this will affect fuel consumption as that is a function of the power used and will average around 2l hour if propped correctly. However it will affect the revs you use. The smaller 29hp is rated at 3600rpm and cruises at 2400rpm, but the larger engine obviously produces the same hp but at lower rpm and will cruise at 1900rpm.

So first check what the maximum rpm of the engine is and cruise at somewhere between 60-70% of that. This should give you about 5.5 knots if propped correctly. Be aware that there are some awful re-engine jobs with wrong propeller particularly, but the figures above are typical of good installations.

 

[johnalison]

As above the "normal" Perama is a 3cyl 1100cc approx rated at 29hp, same as the Volvo 2030. There is also a larger 1400cc approx 3 cylinder that is rated anywhere from 32hp to 39. Physically larger and the same as a Volvo 2040. The lower ratings reflect lower rpm . I had one that was rated at 35 at 2600rpm. none of this will affect fuel consumption as that is a function of the power used and will average around 2l hour if propped correctly. However it will affect the revs you use. The smaller 29hp is rated at 3600rpm and cruises at 2400rpm, but the larger engine obviously produces the same hp but at lower rpm and will cruise at 1900rpm.

So first check what the maximum rpm of the engine is and cruise at somewhere between 60-70% of that. This should give you about 5.5 knots if propped correctly. Be aware that there are some awful re-engine jobs with wrong propeller particularly, but the figures above are typical of good installations.

Yes, I think #2 was a bit pessimistic. I've not sailed a Nic 32 but cruised in company with one. We have a VP 2030 and at 4 + tons can motor at 6.5 but plan for 6 and I think the Nic would be just a bit less, say 5.5-6, with a similar fuel consumption of 2-2.5/hour.

 

[B27]

I always prefer to plan fuel on the safe side and have plenty left over if the sea is flat or there's a following wind.
Likewise boat speed, I might motor at 5.5 knots normally, but actual passage averages from harbour to harbour are easily reduced by faffing with sails, avoiding traffic, slowing down to gawp at the dolphins or whatever.
'Classic' boats like the Nic have short waterlines when upright and motoring.
Best to get the sails up!

 

[westhinder]

I had a Rival 34 with a Perkins Perama M30. At 2200 rpm it consumed 2l/h and gave us 5 knots through the water unless we were punching into wind and waves. Reliable engine.

 

[scottie]

When I was a boy the rule of thumb was that a diesel produced 20 hp per gallon per hour and for petrol it was 10hp
This gave a crude calculation for tankage with safety margin
It is interesting how many people managed to get vastly improved and unproven figures however
Sorry to use imperial measurements as metric had not been invented in that century

 

[Tranona]

When I was a boy the rule of thumb was that a diesel produced 20 hp per gallon per hour and for petrol it was 10hp
This gave a crude calculation for tankage with safety margin
It is interesting how many people managed to get vastly improved and unproven figures however
Sorry to use imperial measurements as metric had not been invented in that century

Not difficult to get pretty accurate fingers for consumption with popular engines like the ones here. The 2l/h for aPerkinsm30/Volvo 2030 by keeping records of fuel used over long periods. With mine (2030 in a 5.5 tonne boat) were consistent +/- 2l/h over the 3000+ hours I ran it. Confirmed by many posting here with similar figures (Posts#5&7 as examples)

 

[LittleSister]

When I was a boy the rule of thumb was that a diesel produced 20 hp per gallon per hour and for petrol it was 10hp
This gave a crude calculation for tankage with safety margin
It is interesting how many people managed to get vastly improved and unproven figures however
. . .

Because a marine diesel will only be consuming whatever fuel is required to maintain the engine speed you have set, which will most of the time be well below what the engine is capable of producing at those revs, let alone its maximum power rating.

The rated power of the engine has relatively little influence on the fuel used. You could double the size of the engine and it wouldn't make a lot of difference to the fuel consumption powering that particular boat along at a particular speed. The boat and the speed are the main factors (together with adverse or favourable wind or waves, and any significant fouling of the hull and/or prop).

 

[B27]

A diesel running efficiently uses about a litre per hour for every 4.5HP of mechanical power actually produced.
That is a matter of the efficiency of normally aspirated diesel engines and the energy content of diesel fuel.
So, if the engine is fully loaded by the prop 32HP gives about 7.1 litres per hour, then you may want allow a bit for an overloaded engine not being so efficient as you push it towards smoking a bit. Also 32HP at the crankshaft will be after losses in the engine like water pumps and all that.
So 8 litres is a fair guesstimate for the worst case of an engine that may not have world class efficiency.

In normal cruising with a clean hull, running at a speed where we don't make much wash, of course the engine is loaded a lot less.
You set the revs with the 'throttle' and the governor puts in just enough fuel to maintain those revs.
If you're happy to potter along at speeds where wash is barely noticeable and where the water is flat etc, you can see very low numbers.
If you find yourself punching the tide into a headwind you can see much higher numbers.

But if you passage plan on low numbers assuming the best, you may join the ranks of those who've come unstuck.
It would be sensible to know that the hull is reasonably clean before attempting to go very far, and not to assume too much speed, because a lot of yachts won't motor flat out for too long without cooling problems.

There are a lot of heavily fouled yachts on our river right now!

 

[DoubleEnder]

I had a 34 foot boat weighed 5.5 tons. Long keel but less beamy than a Nich 32. We had a Beta 20 engine which is 740cc 3 cylinders, and a two bladed prop. Over about 700 hours of motoring ( I kept a log of fuel as I had no fuel gauge) we averaged about 1.75 litres per hour. The bottom was always clean or cleanish.
But most of that motoring was in calm or light headwinds doing relocation runs from winter to summer berths, plus the usual in and out of harbour stuff. Not very much punching in to tides or strong headwinds.

 

[scottie]

so it all depends on the power absorption of propeller!

 

[38mess]

It is interesting how many people managed to get vastly improved and unproven figures however
Sorry to use imperial measurements as metric had not been invented in that century

My figures are pretty accurate and proven. It's a commercial boat and everything is logged including fuel consumption. Looking at my fuel book for a 8 hour day, 6 hours of that is steaming around and it's a bit better than 2lts per hour, on Saturday we used 10ltrs which seems to be the norm. Great little engines

 

[B27]

so it all depends on the power absorption of propeller!

Obviously the power has to pass through the propellor, but the 'power absorption of a propeller' is not a fixed quantity, it varies hugely according to the slip factor it's running at. If you are motorsailing, it may take very little torque to turn the prop at a given speed. If you are aground it may take everything the engine has to turn the prop at the same speed.
A few barnacles on the prop will absorb some power too!

 

[Tranona]

A diesel running efficiently uses about a litre per hour for every 4.5HP of mechanical power actually produced.
That is a matter of the efficiency of normally aspirated diesel engines and the energy content of diesel fuel.
So, if the engine is fully loaded by the prop 32HP gives about 7.1 litres per hour, then you may want allow a bit for an overloaded engine not being so efficient as you push it towards smoking a bit. Also 32HP at the crankshaft will be after losses in the engine like water pumps and all that.
So 8 litres is a fair guesstimate for the worst case of an engine that may not have world class efficiency.

Completely irrelevant because you would never run continuously at full power.

Not sure why you constantly put out observations that are so unrelated to the real world. There are now 5 posters with similar boat/engine to the OP who are reporting typical average fuel consumption of +/- 2l/h. Why should the OP's new boat be any different?

 

[yotter]

We have a 34 foot boat at 6 tons, VP2030 (29HP) and cruise at 2500 rpm, 2 litres an hour. It will be more in a seaway or headwind. We sail whenever we can.