45ft ish catamaran owners: a question about fuel consumption

Whitelighter

Whitelighter

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Can I ask anyone with a reasonably recent mid 40s cat some questions about motoring:

Is it possible to comfortably motor at Hull speed or just above (7-8knts)
Do you tend to motor on one engine or does the turning force mean it’s better to use 2?
What sort or fuel burn do you see at a decent speed (7-8knts)
What sort of size fuel tanks do most cars this size have

Thanks in advance
 
My 40 footer will do 7 knots but I wouldn't say that it's comfortable as that's around 3000 rpm which is well above what I cruise at. I would guess that a 45 footer will be a lot more relaxed at 7 but I think 8 will still be quite boisterous.

I don't usually motor on one engine although I have done so when I've had a technical problem. I can't say that either I, or the autopilot, notice any difference except that it's slower.

I haven't really checked fuel but it seems to be economical. I've got two 175 litre diesel tanks.

Richard
 
Crossed the pond last year on a 50' Lagoon with 2 x 80hp Yanmars. There was a marginal advantage in fuel economy running one engine to maintain 5.5 knts, burning 6l/hr.
During the run-in from Bordeaux to Cascais using max revs a lot we burnt up to 16l/hr giving 8.5knts through the water. Ouch! A 4 figure fuel bill for a 600 mile trip. How I pity moboers.
 
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Ok thanks.

Do sensible cruising speed should be more 6-6.5knts from a fuel burn POV.
80Hp motifs sounds sporting - I think the upgrade for one of the cats I’m idly considering is 57Hp, standard I think is 40-45Hp

In my current 50ft boat at 8 knots we burn about 32l/hr. let’s not discuss 20knts....
 
Whitelighter said:
Ok thanks.

Do sensible cruising speed should be more 6-6.5knts from a fuel burn POV.
80Hp motifs sounds sporting - I think the upgrade for one of the cats I’m idly considering is 57Hp, standard I think is 40-45Hp

In my current 50ft boat at 8 knots we burn about 32l/hr. let’s not discuss 20knts....
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32 LPH ?? , am I reading that right ?
 
We have a single 110 HP Turbo Yanmar in our 12.5 metre motorsailer.

Over the last 4,000 NM we have averaged just under 4 LPR. Usually with some assistance from the sails.

2,200 RPM-my prefered cruising RPM if the wind will not serve- 3.2 LPH.

But, thread drift, as not a 45 foot cat................................
 
More drift but my 10.3M motor cat has 2 x 75HP Yanmars. I motor almost exclusively on one engine doing 7 Knts @ 2200 rpm and burning 3.5 lph. If I employ both engines @ 2200 she makes 8.5 Knts for double the fuel burn.
 
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I moved a 42 foot Fontain Pajiot cat from Lefkas to Barbados winter before last. When motoring it was normally at about 6.5 knots on two 30 hp engines running at 2200 rpm: that burnt about 4-4.5 lph. As above, running on one engine meant running it at about 2600-2800 rpm with a boat speed of 5.5 knots: no noticeable handling problems (did a fair bit of one engines running as we had diesel bug problems that often knocked out an engine....).
The cat had a 600 litre diesel tank. I also carried 200 litres in jerrycans on the leg from Tenerife to Barbados: didn’t actually need them as we arrived with 300 litres left.
 
We are a 38' cat, 7t cruising weight (including 400l water, 260l fuel, 2 x 20hp engine, 3 bladed Volvo prop.

We would seldom motor with 2 engines (at any revs). The times when we use 2 engines, in tight confined spaces, to anchor, and retrieve and if we MUST punch into big seas. Basically 2 engines gives an increase of speed of maybe 20% but a doubling of fuel consumption. The idle engine will be in gear, and hopefully the prop folded (we can usually see it).

Its a no brainer.

If you want to achieve maximum speed for given revs - keep the hull and prop clean and reduce the amount of water you carry - even a little fouling makes a disproportionate impact.

If the wind are light and we MUST move on then we might run the engine on the windward side and motor sail

We have a 200 litre tank and might carry 4 x 20l full drums, re-fueling here can be a bit far apart. The tank has a sight tube down the side.

Jonathan
 
Smaller Cat 32' with 13.5 engines.

one engine at 2200 revs gives me 5.7kts and 1.2 l/hr.

two engines at 2500 gives 7.5 kts but more like 1.7 l/hr each engine.

Depends very much about sea state.

In the canals I run one engine at 1500 giving 4.2kts. but need both on for locks.
 
jhr said:
Jez: have you tried asking Rick? Or is this on his behalf? :-)
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I’ve asked rick but he seldom purely motors so doesn’t have a huge amount of data (or more over he doesn’t keep much of a record) though have got some info from him.

The question is more me, considering a cat but would likely motor unless he wind is obviously in the right direction.
 
Whitelighter said:
I’ve asked rick but he seldom purely motors so doesn’t have a huge amount of data (or more over he doesn’t keep much of a record) though have got some info from him.

The question is more me, considering a cat but would likely motor unless he wind is obviously in the right direction.
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Adding an extra fuel tank would not be a big issue, in terms of space, in a cat. As far as I know and without exception they all have huge bow lockers and you could easily add extra tankage, under or very close to the mast. The only issue is weight, as cats are very weight sensitive. To offset extra fuel weight consider a desal unit, and carry less water, and use the desalinator when you are motoring.

Jonathan
 
Irish Rover said:
More drift but my 10.3M motor cat has 2 x 75HP Yanmars. I motor almost exclusively on one engine doing 7 Knts @ 2200 rpm and burning 3.5 lph. If I employ both engines @ 2200 she makes 8.5 Knts for double the fuel burn.
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3.5 lph at 2200 rmp for a 75HP Yanmar.............. that's impressive, I have the same engine and I burn around 6 lph at those revs
 
BigJoe said:
3.5 lph at 2200 rmp for a 75HP Yanmar.............. that's impressive, I have the same engine and I burn around 6 lph at those revs
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I didn't believe it either when the previous owner told me but that's what I'm getting after putting up around 250 hours on each engine in the last 12 months - engines have 3,900 hours total.
 
[QUOT

The question is more me, considering a cat but would likely motor unless he wind is obviously in the right direction.[/QUOTE]

In that case you may well motor most of the time.
 
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