Nimbus 280 Fuel Efficiency?

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sir jasper

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Just acquired a Nimbus 280 coupe with the Volvo TAMD 31p (150hp) motor. The economy so far has been disappointing. At a cruising speed of 10 knots (2900 rpm) the consumption is approximately 2 litres per nautical mile (2.25mpg) – this consumption has been constant for over 200 nautical miles. The condition of the boat is excellent; the engine has run for 270 hours & has been recently serviced, the hull is freshly antifouled & very clean.

Can any kind forum member shed some light on what the “expected” speed/economy values should be for a 280 coupe?
 
I would have thought 10-12knts would be just about the worst speed you can pick for fuel economy and I am amazed you are getting 2lt/nm to be honsest.

At that speed you will be pushing water as the boat tries to climb onto the place but never gets there.

You either need to throttle back to displacement speed (probably around 6knts on a 28 footer) or get the boat on the plane and then throttle back.

10knts at 2900 rpm doesnt seem like much if you ask me. From memory the AD31 is supposed to rev to 3700 so it sounds like the boat is a little underpowered imho.
 
She would be better cruised at 12 to 16 kts.
At about 3200/3400 revs I reckon.
Dunno about mpg/ litre etc.
Should use about 4 galls an hour at that speed /revs imho.
As Whiteghliter says.

2900 revs is not the right setting.
For Best perfomance/ ecomomy.
 
We have a Nimbus 280 - though it is the aft cabin 'Familia' version. It is powered by the Volvo D3 160.

We keep a log of fuel used, and voyages done, brimming before we leave, then recording that used by topping up on arrival. On trips Poole to Brixham the consumption usually comes out at around 145 Litres. I accept the speeds are not great, on one journey I recall we left on the half nine bridge, and were entering Brixham Marina just on 4PM.

I generally try and keep to an engine revs at around three thousand. I've never reckoned this boat will go "on the plane" - whatever that is! Certainly I've tried 'playing' with it, but doubt it was ever designed to do that. I would class it as a displacement type.
 
Dear all,
Thanks for the advice.

PhilipF, from your passages to Brixham it looks as though you’re getting very similar consumption figures to my own (Poole – Brixham 70ish nautical miles / 145 l = 2l per mile).

Kawasaki/Whitelighter, I’ll try increasing the revs to 3200/3400 & see if it makes a difference.

Does anyone know of an after market fuel economy meter that can be fitted?
 
They are Semi Dispacement hulls.
However , Yours and sir jaspers will almost plane or feel like they are.

PhilipF, you have a newer and different Generation engine.

The D3 is miles ahead of the TAMD30/31 units fitted earlier.

Your 160 hp should deliver about 18kts no sweat if I am right.
Only guessing however.
I am interested to know what You achieve 'flat out'.
Because I was toying with the idea of fitting a 'D' series to My old Tub.

Your thoughts would be interesting
Cheers
K
 
> Your 160 hp should deliver about 18kts no sweat if I am right.
Only guessing however.
I am interested to know what You achieve 'flat out'.<

Yes, I should have given more detail: Pushing the throttle lever as far as it will go while under load, the engine revs would be showing 3500 on the meter, but it is always reckoned the cruising speed should be set at around ten per cent lower than that, so that is why my 'running speed' is three thousand. To answer your 'flat out' question: At the 3500 rev setting, I did see 15 kts, I assume this was off the GPS read out, not 'through the water', but I cannot actually remember.

But as I say one would not be normally running at that setting. In any case, other factors come into account - is the current with you or against you example, being but just one. It is what you get from the boat by normal usage is to my mind the crucial factor.
 
Yep, I appreciate Your calculations ref current/tide etc.
3500 max.
Then I would 'cruise' at 3200 .
This I my observation with the 'D' series in other vessels with the same engine.
OK, not with a Nimbus 280 however.
Strangely I have only ever driven My own Nimbus.

Given, that last Year I did a few delivery trips and handovers for quite a few boats.
Various makes.
About 40 different boats in all but none where Nimbus.
Bit rare up in My part of the World!

Here is a thing.

D3 in a Regal.
OK outdrive.
160 hp.
OK pure planing hull.
Cruised lovely at 25 planing.
Used beggar all fuel.
Off the plane.
It was a bit lumpy(the Sea!) used loads.
That is it with fully planing hulls.
Give Me Semis all day long!

Cept when I lived on a dreadfull Council estate.
The peeps in the Semi next door were awfull.

But the peeps next door in this House are ok!
 
Hi Sir Jasper,

If you take a look at this website, it gives the technical specification and a graph of the estimated fuel consumption of the Volvo TAMD 31p engine:-

http://www.volvo.com/NR/rdonlyres/E...800AEC8FF63F/0/TAMD31P_PD_SLD_HS1_1994_en.pdf

As I'm also considering the purchase of a Nimbus 280 Coupe, I would appreciate your general comments on your boat, e.g. how does it perform in roughish weather; what is the build quality like; how easy is it to manoeuvre when berthing; are you generally pleased with the boat; how easy is it to maintain the blue hull colour; etc, etc?

Cheers, Allan
 
Yep - 10kts on a 28' cruiser is an awfully uneconomic speed. Waterline length will be (say) 24' so displacement speed (1.34 x sq.rt) is 6-7 kts max. I get ~4 mpg at displacement speed with 2 x 370hp so you should do a lot better on 1 x 150.
 
Hi Allan,

Appreciate the link, very useful.

Only got my hands on the Nimbus 4 weeks ago, in that time we’ve covered approx 300 Nm.

I’m a new comer to motor sailing, my previous craft have all been yachts. My initial observations on the Nimbus are:

Very well made & thoughtfully designed.

Great sea going boat (hand holds in all the right places), handles the rough stuff with ease.

Close quarters handling is a breeze, don’t be put off by its single prop.

The blue hull appears to have a light fast finish with no visible fading.

The accommodation is generous for two (very comfortable double cabin), but a tad tight for four.

Hope the above initial observations are of use.

..................................................................

Hi Observer,

Thanks for the input, it does appear that I need to increase the revs.

I’ll try cruising at 3300rpm for the next 250l.
 
More speed from my Nimbus 27

Apologies that this is an old thread and an even older topic, but I am guessing that the members on this thread could help me the most with my query.

I want to understand why I get such poor performance from my Nimbus Familia 27. I bought her this year, she is 20 years old on the TAMD31a variant engine. She needs a lot of work to bring her back, but I am on it.

Ignoring efficiency for now, I would like to get a higher top speed. I can only reach 13kts right now, on flat seas with just two aboard.

My Nimbus has not been cared for that well, and I suspected all manner of issues to do with the engine, turbo, gears etc... But last week I fitted a replacement for the faulty Tachograph and can see that on full throttle, at 13kts, I am running at around 3700 revs. From what I can see the revs are right for full throttle (I think)?

If I have the running rev's at the this level, am I right in thinking that the motor and gearbox are working well, and that I should look elsewhere for whats holding me back?

And where should I look next?

Any help welcome
 
Lichfield said:
Apologies that this is an old thread and an even older topic, but I am guessing that the members on this thread could help me the most with my query.

I want to understand why I get such poor performance from my Nimbus Familia 27. I bought her this year, she is 20 years old on the TAMD31a variant engine. She needs a lot of work to bring her back, but I am on it.

Ignoring efficiency for now, I would like to get a higher top speed. I can only reach 13kts right now, on flat seas with just two aboard.

My Nimbus has not been cared for that well, and I suspected all manner of issues to do with the engine, turbo, gears etc... But last week I fitted a replacement for the faulty Tachograph and can see that on full throttle, at 13kts, I am running at around 3700 revs. From what I can see the revs are right for full throttle (I think)?

If I have the running rev's at the this level, am I right in thinking that the motor and gearbox are working well, and that I should look elsewhere for whats holding me back?

And where should I look next?

Any help welcome
Click to expand...

Sounds about right, a TAMD31a is only 130hp the later p and D3's discussed above were 150hp and 160hp, I think Nimbus claimed 18-20knts for this boat but I don't know anybody who has achieved it. You might gain a knot or two with a cleaner bum and a newly refurbished prop but that will be it, 3700 rpm is the correct max revs so if that is WOT that is as fast as it will go, although its worth checking you have the right prop fitted.
 
Following what Whiteliter says I would get a GPS and see what speed you are doing at 1500 revs, then up the revs by 100 a time and see if the hull speed increases. You may find that over 2500 revs all you are doing is making more noise and the hull speed only increases fractionally to the point where you are doing 3300 revs and perhaps have only increased the speed by 1 knot. If your boat was to go on the "Plane" the bow would drop and the speed would increase significantly. Which it may not do unless your boat had twin engines. Someone mentioned hull speed, thats your most economical speed. F
 
Nimbus Familia - raise top speed

Thanks Jim@sea and Chris_d

I guess the good news is that I can get to 3700 revs, so engine, gears etc must be pretty good.

Cleaning up the bottom, and the prop is where I will concentrate. And I will try Jim@sea's idea. It certainly seems the case that pushing the throttle has diminishing returns right the top end, creates more noise but not much extra speed.

I have never got her on a plane, and that's what I am really hoping. I have played with trim tab settings, but I guess I should take a more organised approach to these, there may be a midway setting that works to get her up.

Thanks
 
This is an interesting post.

On a Sealine S28 with twin KAD32's, 2900rpm = 21kts, and about 2.2mpg as well. So approximately the same consumption per mile, but I'm getting there somewhat faster (in good conditions. In a blow, I know which boat I would prefer to be in, and it's not the S28).

Consumption with these engines seems to be a function of revs.
 
FlowerPower said:
Consumption with these engines seems to be a function of revs.
Click to expand...

yes and no....as always!

fuel consumption on a diesel is a function of prop horsepower and drag/load aren't purely proportional to speed on a planing hull.

for your boat I would expect to see a strictly proportional relationship between about 14 knots and the max full time revs. it's a very well balanced hull with relatively little change in attitude with speed.

on the nimbus hulls discussed earlier it will be much more proportional through the whole rev range, with a small hump (in consumption/mile) around 9-11 knots because it's a SD rather than planing hull.

many smaller, fully planing hulls, have a huge hump around 8-9 knots.
 
Lichfield said:
Ignoring efficiency for now, I would like to get a higher top speed. I can only reach 13kts right now, on flat seas with just two aboard.

My Nimbus has not been cared for that well, and I suspected all manner of issues to do with the engine, turbo, gears etc... But last week I fitted a replacement for the faulty Tachograph and can see that on full throttle, at 13kts, I am running at around 3700 revs. From what I can see the revs are right for full throttle (I think)?

I
Click to expand...

I have (well until today,just sold Her) an old Nimbus 27
With a TAMD30a 105 HP
Same underwater as Your Familia.
With a clean bottom and everything tickety boo the following speeds and revs etc occur
W.O.T which gives 3590 revs
16.5 kts
Cruising revs 3250
12/14ts

Speeds are over the ground not through the water
At cruising revs cosumption was 3.5 galls an hour
W.O.T 5.5 galls an hour
These figures have been consistent and checked regularly through my 8 tears of ownership
Once at cruising speed a couple of seconds of trim tab application gives a slight raising of the bow and 100 revs are gained
I would double check the prop diameter and pitch is correct as per origional spec
Can't remember what mine was
The manuals etc are now with the new owner
However I can check tomorrow
I would say your turbo will be kicking ok for you to reach the revs you mention
She should do 16 flat out imho
 
Last edited:
Getting top speed from my Nimbus Familia 27

Thanks Kawasaki

I'd seen your earlier posts, knew you had a similar boat (until today)

The prop dimensions etc would be great info. I have no manual to go by, only what I can glean from online sources - and those are thin on the ground for this boat.

Just to check this ....
Once at cruising speed a couple of seconds of trim tab application gives a slight raising of the bow and 100 revs are gained
Click to expand...
Does this mean that you go to cruising speed with tabs all the way down, keeping the nose down, and then you raise the nose by raising tabs a notch?
 
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