Larson 240 cabrio (2006)

A Sea Ray 240 Sundancer with a KAD 32 ought to be getting very close to 30 knots. That ought to give you a cruising speed of 20 - 25 knots.

I've had small petrol and small diesel boats and the truth is, other than a quick blat on the odd occasion it's flat calm, you tend to cruise everywhere in the low 20's anyway - it just gets too bumpy going much faster.

But for us the big difference is that with a petrol boat we'd have a good whizz about on the Saturday, blow through £200 worth of fuel (bear in mind that even at 20 knots these things are using 40+ litres an hour, that's £70/hour or more at £1.75/litre so £200 is very easy) and then on the Sunday we'd think 'perhaps today we'll just anchor up in a bay somewhere for the day'.

With a diesel boat we don't even think about it. In fact out of curiosity I just looked on the Volvo site for the fuel figures for the KAD 32 and annoyingly they don't have them but they do for the newer (but similar horsepower) D3 and at 3,500rpm (fast cruise, max is 4,000rpm) its using just over 20 litres an hour. So almost half and at about £1/litre the fuel cost isn't that far off half.

So call it £65 for a day out rather than £200 - we don't even think about whether we can afford/justify it. When it gets low we just call into the fuel dock and brim it again.

As I said before, that doesn't 'prove' that diesel boats are better. If you keep the boat on a trailer at home for example and use it for the odd sunny Sunday stopping at the petrol station on the way to brim it then you probably are better off with a petrol. And certainly the petrol boat will be faster, smoother and maybe quieter (they're far from silent, so that last one isn't a deal breaker).

Plus for a fixed budget you'll get a newer boat so maybe it will require less maintenance, or you could get a bigger boat of the same age and have more space. And there are arguments that petrol engines are simpler, easier to maintain, less to go wrong etc. All valid.

But for me, I just want to go boating without worrying that a day out is going to cost me a three figure sum. Yes, in the grand scheme of boat ownership costs maybe that isn't that much really. But it is the one cost that clocks up as you use the boat, and that does tend to focus the mind each time you dock and pour yet another £300 in!
 
hg2016 said:
sorry, didn't thank you for the links you sent. very interesting, nice boats. Love the Monterey and the performance sounds great too. I'm really surprised Great post and very helpful.
Click to expand...

Just on this point, bear in mind that this forum has a search facility. So you can search, for example, 'Monterey 250' and it should show you any discussions on that boat. I mention it because I seem to recall someone asking about these before, and someone who had one commented with his experiences - performance and generally.

It's quite a useful resource if a boat has been discussed before.
 
Ari, Some good points but your figures for petrol are, I feel, over pessimistic.
Actual test figures from boattest.com for Sea ray 240 with 5.7 V8 petrol
20knts = 3000rpm = 31.8 lphr
At £1.39 per l = £44.20 per hour (current cost at Parkstone bay Marina)
So 4.5hrs to blow £200, that’s 103 miles I don’t think many do that as an average day out.
Your £200 at £70/hr is gives 2.85 hr run time, apply that to actual figures above and the cost is £126.28
Diesel at Parkstone Bay is £1.05
If you are a berth holder at MDL both fuels about 20p per liter cheaper (at Cobbs Quay anyway).
 
Fair enough. The last time I saw petrol costs at a dock it was £1.75 but since I don't have a petrol boat that's a sample of one! :D

Agree entirely that IF you have a local fuel dock and IF the fuel is relatively cheap there then that's clearly going to advantageously skew the figures.

What I do know is that switching from petrol to diesel made a genuinely massive difference to our fuel costs, enough that we just stopped worrying about what we were using (or the logistics of getting it - we had to 'can' it to the boat and decant it, or travel somer distance and then pay through the nose for it).

Personally I wouldn't go back to running a petrol boat if I could help it, but as I said before, I'm certainly not saying 'don't buy a petrol boat', it all depends on what you want and your own circumstances.

The oft used expression 'Your mileage may vary' is particularly appropriate to this thread! :D
 
That's good stuff Ari and dpb and, I'll give the search facility a try. These points of view from different folk is exactly what I'm after and its pricelessly helpful. Keep em coming boys. The swingometer is just tipping towards diesel at the moment. Lets keep this thread smoking.
 
Hello Jamie,
can you tell me a little info about your diesel searay. what was the make and hp of the engine, the performance you got from it etc. And did you have any expensive repair issues with it.
Thanks for your input.
 
Diesel for me any time. I don't say that from the view of economy but from the view of access to fuel. Where I go cruising petrol is hard to find unless you want to get a taxi to take you to the nearest fuel station with a bunch of jerry cans. I see lots of my friend lugging heavy cans down to the marina every weekend just to fill up, eventually getting fed up and turning to diesel.

I also think that the re-sale on a diesel will be better as well in my opinion.
 
Hi HG
Firstly, don't sweat the diesel vs petrol age old argument too much on your size of boat...
The truth is that you have perhaps inadvertently chosen a good set up. You can probably ignore the earlier comparison to the 5.7 Mercruiser fuel economy too. You engine is a million miles away from the normal 5.7 Mercruiser. The 5.0 Mpi is an incredible thing. 260 hp and almost diesel like fuel economy.
I have the same engine and propped correctly, you will find the above statement true. I manage to cruise at 24mph at 2200/2300 rpm and 19.6 litres per hour economy. A figure lots of diesel boat could find enviable.
Given the huge weight saving over a diesel, hugely cheaper service costs (which can be done very easily yourself for about £100 per annum) and vastly superior performance over the diesel version, I'm sure you will enjoy it plenty. After all....that's what it's all about !
Top tip for the Mpi....remember and change the diz cap and rotor every few years....they are a known weak point.
Keep the electrics well protected with wd40 too.
I've had a wee bit of grief with rouge faults but mainly down to a poor battery.
Someone will be along shortly to tell you that they are no good because they are raw water cooled.....nonesense. As far as I know, there hasn't been a case of a Mercruiser engine block corroding through....they have been about for decades and aren't the most popular worldwide engine choice for nothing. Just change the manifolds and risers every few years if you are in the salt and all will be fine !
Enjoy !
 
https://www.dropbox.com/sh/ljoy4y8qsscsgfh/AADJhGAutM1WchoxnMh7Bi8Aa?dl=0

You might take some relief by looking at the link here. This is a comparison between the Merc 5.0 mpi and equivalent powered VP Diesel. You will also take comfort from the following, which should be considered;
You most likely wouldn't get such a high powered diesel in your boat...if you did it would be twice the price initially
The diesel equivalent in that boat would surely be a kad 32 with 170hp. Although a great engine, it's a 4 cylinder and a bit rattly and noisy at planing speeds. Don't expect a conversation in the cockpit at high speed....especially with the hoods up
With the right prop, you will likely be at around 2500-3000 rpm max with the mpi (see photo for economy)...with the diesel, you would likely be between 3000-3500 rpm at planing speed. See picture above, even though it's for a higher horsepower engine, bear in mind the kad32 is older tech than the modern D series and would likely compare in figures.
Nearly 100hp extra on tap !
Only downside I can see with your boat and suggested financial outlay is that you might have been lucky enough to get a Sealine S23 with a kad32 in it.....the difference in quality may just swing it and balance out the above.
Horses for courses, as they say !
 
I just looked on the Volvo site for the fuel figures for the KAD 32 and annoyingly they don't have them but they do for the newer (but similar horsepower) D3 and at 3,500rpm (fast cruise, max is 4,000rpm) its using just over 20 litres an hour. So almost half and at about £1/litre the fuel cost isn't that far off half.
Click to expand...

KAD32 figures are not on the web site :)

lHRL90.jpg
 
QBhoy said:
You might take some relief by looking at the link here. This is a comparison between the Merc 5.0 mpi and equivalent powered VP Diesel.
Click to expand...

I'm not saying that a V8 260 MPi isn't a thing of beauty, because it is, and it sounds great.

But a D4-260 at 3500rpm is absolutely flat out, and actually producing 260hp.
The Merc V8 at 3500rpm is nowhere near flat out, and will be producing waaay less than 260hp, and will be going more slowly.

So, not really a good comparison.

(In real life, two boats, one with a Merc V8 260, another with a D4-260 would have vastly different gearing & props, such that both engines could reach rated speed at WOT. A more meaningful comparison would be to compare consumption at 20kts, 25kts. 30kts etc. I'd expect the D4-260 to be ultimately slower, but only because it's heavier).

.
 
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Hi flowerpower...
Not sure your analysis makes sense, when thought about.
Probably find that they would be doing the same speed at these rpms...just the Merc will have way more left to go
The D series and kad series can't really compare in your favour because the d series will be much better on fuel. In any case, I have added the closest d3 comparison (way down on horse power compared to 5.0) in the link
https://www.dropbox.com/sh/ljoy4y8qsscsgfh/AADJhGAutM1WchoxnMh7Bi8Aa?dl=0
 
Also
If you look at my post detailing my speed and revs...
With regards to you mentioning the 3500rpm on the 5.0...I'm pretty sure my boat would be running about 45mph plus. Different type of boat to be fair, but just an example.
 
QBhoy said:
Hi flowerpower...
Not sure your analysis makes sense, when thought about.
Probably find that they would be doing the same speed at these rpms...just the Merc will have way more left to go
Click to expand...

It's not about RPM's going into the gearbox and prop - it's about the power.

If it helps, think about an extreme example:
- Imagine an F1-type engine that produced 260hp at 15,000 rpm
- You fit this to your boat, with a gearbox and props that mean that it can just about hit 15,000rpm flat out.
- It sounds amazing at this speed, and everyone else on the lake is jealous :)

- But at 3500rpm it will be producing hardly any power: that plus the gearing needed means the speed you will be going at will be much slower than your V8 at 3500rpm, and way slower than a D4-260 at 3500rpm

- All three boats will be in the same ballpark for top speed (apart from drive/prop optimisations - the DPH drive isn't suited to very high speeds - and the weight factor) because flat out, they are producing the same power. It's just that they will be pulling different RPM's at similar speeds.

- In the real world, the lightest boat with the most efficient drive and prop will win.

Remember, the props don't have any idea what is turning them: it could be an F1 engine, a V8, a diesel, or 6000 hamsters in wheels.
The props only know how hard they are being turned, and how fast they are going.

.
 
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Totally understand what you mean...just that a Nissan micra 1.0 and a Ferrari 5.0 will both sit at 70mph on the motorway and not be using all their horse power once at that speed. Like you say, it's all about the gearing.
 
Totally agree with FP. In reality, and in the sort of boats we are talking about, all that matters at 22 knots cruise is:

Is the engine 'comfortable'? (ie reasonably quiet and within its prescribed cruising rev range, not revving its nuts off flat out to maintain that speed).
How much fuel are we burning and what did it cost? (Not per revs, just here's the speed we want to cruise at, what is it actually costing us?)
Did the boat get on the plane okay? (No point having a super efficient low revving diesel at 22 knots if you have to send everyone to the bow every time you want to get on the plane).
 
I also agree it's about cruising speed and what it performs like overall. That's what I'm getting at with the 5.0 mpi
Mine cruises at 24mph at around 2200/2300 rpm and 19.6 litres per hour. This is what my whole argument is based on.
Anyway, it's all about enjoyment more than anything....but if you can save yourself 15k in the process at time of purchase...all the better.
 
QBhoy said:
I also agree it's about cruising speed and what it performs like overall. That's what I'm getting at with the 5.0 mpi
Mine cruises at 24mph at around 2200/2300 rpm and 19.6 litres per hour. This is what my whole argument is based on.
Anyway, it's all about enjoyment more than anything....but if you can save yourself 15k in the process at time of purchase...all the better.
Click to expand...

Petrols work really well on the smaller / lighter boats where you can throttle right back and still be planing at a decent speed.
When your boat weighs 8000kg(!) it's a different story.

Somewhere in the middle is a transition point: buying a 24ft cabin cruiser, I think you could swing either way, so to speak.
30ft+ plus and twin engines, I would prefer diesels.

Of course, the Americans have an entirely different take on the above.
I suspect that the following boat would raise eyebrows in Newtown Creek for a number of reasons:
skater-36-88959.jpg
 
We ran boats with a single 5.7 V8 petrol for 14 or so years ( TBI then EFI). Totally reliable, cheap service costs as the engines are so widely used in the USA. On average around 8 gph or thereabouts, so not horrendous fuel costs considering we did around 50 or so engine hours, or less, per year.

The only reason we moved to a diesel was I got fed up with filling up and carrying around multiple 20 litre jerry cans of petrol

So we bought a boat with a D4-300. Easy to fill up at the fuel berth and it seems to use less fuel. Reliability of the EVC system ( which I know is used on some petrols as well, so not really a "diesel" thing) has not been good and the far higher cost of service parts is eye watering, 2 expensive oil filters, air filter, crankcase breather filter, 2 fuel filters compared to 1 cheap oil filter and one cheap fuel filter. I'd switch back to petrol tomorrow if I didn't have to carry the jerry cans ..
 
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