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Old 23 September 2011, 01:49   #1
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Which engine for chugging about in?

I am either going to get a 6m RIB with a 90HP or 6.5 with 115HP or slightly larger. I would like an engine just out of warranty so I know it has been serviced properly BUT I want something frugal with fuel equally capable of chugging around at 8 knots in Chichester Harbour as well as occasional blasts out in the Solent!

I was very impressed with the Suzuki 90HP yesterday, sooo quiet but would really like to go up a size in boat to a 6.5m. If i get a Humber 6.5 a 115HP is recommended by Humber but the fuel shoots up on one of those as it doesn't have lean burn and is a bigger engine block They probably don't go back 4-5 years anyway.....

Any suggestions for a good reliable engine that will never really get thrashed? 125HP maybe, other wise I'll get a 90HP something and a 6M RIB!
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Old 23 September 2011, 02:03   #2
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I would like an engine just out of warranty...
I was very impressed with the Suzuki 90HP yesterday...115HP is recommended by Humber but the fuel shoots up on one of those as it doesn't have lean burn and is a bigger engine block
The 'lean burn' 1502cc Suzuki DF90 was launched at the Southampton Boat Show 2008 so all those engines are still in their 5 year warranty.

The Suzuki DF100/115 are 1950cc and not advertised as lean burn as you say. But, they also weigh 35kgs more...

If most of your cruising is lowish speed (you say it'll never get really thrashed) do you need the extra hp/weight/cost/fuel consumption?
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Old 23 September 2011, 02:54   #3
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Sounds to me like you need a small diesel inboard (merc 140/170hp?)

90hp would be fairly pants on that size of RIB and certainly not attractive if you were reselling. The diesel would happily creep around all day and still be fine for faster cruising. Fuel efficiency would be very good. Obviously you'd be paying a premium for it, but resale values should be good?
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Old 23 September 2011, 03:39   #4
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Or buy an 8-ish Hp aux & use that for the slow speed stuff?
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Old 23 September 2011, 03:46   #5
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Sounds to me like you need a small diesel inboard (merc 140/170hp?)

90hp would be fairly pants on that size of RIB and certainly not attractive if you were reselling. The diesel would happily creep around all day and still be fine for faster cruising. Fuel efficiency would be very good. Obviously you'd be paying a premium for it, but resale values should be good?
Can second that. Have a Parker 630 with the old 1.7l Merc tdi.
My fuelconsumption is 17h/l when blasting WOT in heavy weather out in the North Sea. The total average FC incl going offshore in a blast is 8.6l/h. Excluding offshore it is 5.9l/h.

Its both less fuelconsumption, and cheaper fuel. Further, you'd get Diesel anywhere.
In addition the feeling of being in a real ship :-)

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Old 23 September 2011, 04:42   #6
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My fuelconsumption is 17h/l when blasting WOT in heavy weather out in the North Sea.
Now that's impressive

Or, a typo...
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Old 23 September 2011, 05:01   #7
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Forgot to add, no meaningful restrictions on transport or storage of fuel either...
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Old 23 September 2011, 05:02   #8
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Now that's impressive

Or, a typo...
No typo. Bookkeeping.
To be fair I need to mention the revs - 4100 WOT, 3400/3700 cruise. The FC is pretty much inline with the data supplied from Mercury
The max rated revs of that engine are 4400, but I've never seen them :-(

However, averaging 18kn over ground (against 25-30kn wind and against a 2kn tide with 2.5m breaking waves) over 2hours at 3500 revs is good enough to me

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Old 23 September 2011, 05:06   #9
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DNV - maybe lost in translation more than a typo. Your use of "h/l" reads as Hours per Liter but it is obvious, even to Leapy () that this should read "17 l/h", i.e. liters per hours.
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Old 23 September 2011, 05:10   #10
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DNV - maybe lost in translation more than a typo. Your use of "h/l" reads as Hours per Liter but it is obvious, even to Leapy () that this should read "17 l/h", i.e. liters per hours.
you couldn't be more right...

rather lost in space than lost in translation. yes I mean LITERS per HOUR.
shouldn't post when on antibiotics...
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Old 23 September 2011, 05:10   #11
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In addition the feeling of being in a real ship :-)
Travelling slowly in a cloud of smoke

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Old 23 September 2011, 05:31   #12
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Travelling slowly in a cloud of smoke

you mis-typed fragrance

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Old 23 September 2011, 06:14   #13
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Travelling slowly in a cloud of smoke

Mine does that too!
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Old 23 September 2011, 06:14   #14
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Sounds to me like you need a small diesel inboard (merc 140/170hp?)

90hp would be fairly pants on that size of RIB and certainly not attractive if you were reselling. The diesel would happily creep around all day and still be fine for faster cruising. Fuel efficiency would be very good. Obviously you'd be paying a premium for it, but resale values should be good?
Willk - thats certainly a sensible suggestion, although Zagato has been looking at new Humbers with a budget of around £20k if I followed correctly. He'd get a reasonable condition, but old, diesel rib for that but I doubt he can get a new diesel? I'm not sure about your resale argument either - on a new diesel; but if he spent 20k (or even 15k) on an older diesel rib he could resell it in 3 yrs time with minimal losses compared to loosing at least 1/3rd on the humber. If he splashed out 30+k on a new diesel he'd still loose more £ in 3yrs than he would on the humber...

Or does it need to be a rib at all? If it going to spend most of its time at 8 knots in relatively sheltered water there may be better suited craft?

Or to really break out the popcorn then maybe something from the Leeway stable which I get the feeling are built very light (and to a budget) so would get better performance from less horses?

Zagato - very roughly speaking everyone gets the same sort of fuel economy with an outboard. OK some are marginally better than others but the main factor is the guy sitting at the console and his enthusiasm not the engine! Buying an "underpowered" engine could be false economy on fuel though as it will be harder to pull back on the throttle and keep going at a sensible cruising speed. Also sitting at 8 kts with a deep V hull is just about the worst possible speed for fuel economy. I am acutely aware that everyone here has a compulsion to stick the biggest engine they can on their rib partly as some sort of willy waving contest and partly because its what everyone else does so it must be needed. I certainly don't buy into that and 20 years ago people were quite happily cruising around fast with much smaller engines. BUT will 115 on a 6.5m really give you the benefit to justify the extra hull length over the same engine on a 6m which will be a bit cheaper?
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Old 23 September 2011, 06:23   #15
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The 'lean burn' 1502cc Suzuki DF90 was launched at the Southampton Boat Show 2008 so all those engines are still in their 5 year warranty.

The Suzuki DF100/115 are 1950cc and not advertised as lean burn as you say. But, they also weigh 35kgs more...

If most of your cruising is lowish speed (you say it'll never get really thrashed) do you need the extra hp/weight/cost/fuel consumption?
No I definitely don't want the extra weight/mpg but would really like the bigger 6.5m boat which I presume would really struggle with a 90 even though i'm not going to be tearing about. I used to have a 6m 450KG Drascombe sailing boat that flew with a 6HP on the back so all this HP does seem odd as a newbie. I suppose it's about getting it on a plane but i am quite happy to do 10-15 knots as long as it is comfortable speed in waves (Suppose the idea with RIBs is to get cut across waves rather than go with them!)

I had a Yanmar diesel on my yacht which was very good so might look into that - It would mean building it all in though and I do prefer outboards!

So I want a 6.5M RIB and a Suzuki 115HP is recommended by the manufacturer, what other second hand engines would fit the bill or am I always going to have the extra weight/MPG - the 90 was a lovely smooth quiet engine, could only just hear it ticking over

Anyone know of any reputable second hand engine dealers I could call? Thanks
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Old 23 September 2011, 07:04   #16
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With a 6.5m Humber you could go for a twin setup say something around the 70-90hp mark. Nice and light like a Zuki 4 stroke or a DI 2 stroke like the etec or tldi.
Just a thought.
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Old 23 September 2011, 08:23   #17
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[QUOTE=Polwart;422434]

Zagato - very roughly speaking everyone gets the same sort of fuel economy with an outboard. OK some are marginally better than others but the main factor is the guy sitting at the console and his enthusiasm not the engine! Buying an "underpowered" engine could be false economy on fuel though as it will be harder to pull back on the throttle and keep going at a sensible cruising speed. QUOTE]

Having been there with my old SR4 / 25Hp combo, yes, 2 up and it was a bit of an essay in WOT running.... It would cruise happily at 18 knots, and when pushed (one up, empty tank, flat water etc etc) would hit the dizzy heights of 21. Having said that we did some decent cruises in it, just not maybe as fast as the bloke with the 50 on his!

Unfortunately I can't give a decent comparison to the new boat yet (bearing in mind my driving style hasn't changed perceptively) as pretty much all the running so far has been at 25:1.... Even at that I am getting a recorded 1.1 L/mile, the first 2 hrs of which was at displacement speed.
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Old 23 September 2011, 19:28   #18
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No I definitely don't want the extra weight/mpg but would really like the bigger 6.5m boat which I presume would really struggle with a 90 even though i'm not going to be tearing about.
I don't think it would "really struggle" it's just a matter of finding the right prop and you obviously wouldn't get the same top speed. Pure guesswork but I'd think a 90 on a 6.5m might give 28-30 knots flat out? 115hp on my old 5.8 Humber used to just crack 40kt if I chucked everything out to save weight. I seem to remember the "minimum HP" quoted on the 5.8 was 40hp - presumably the minimum to get it up on the plane. May be worth checking the minimum recommended for the 6.5?

What it wouldn't do is haul a full boatload of people and as also said above the resale could be a problem. Personally I like an excess of power in normal use which gives you an unstressed engine and the "yeehaa" factor when you want it. I think most RIB buyer probably lean the same way.

Perhaps the biggest problem as already suggested is that 8 knots is a lousy speed for everything in a RIB, the boat attitude is horrible (nose up in the air just off the plane), the wash will sink people in dinghys, the fuel consumption is terrible and it's probably labouring the engine to do it for a long period.
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Old 24 September 2011, 10:57   #19
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+1 to what Boggy says about 8kn. It's in about the worst speed range for a RIB, you will be constantly holding the engine back as it tries to get the boat planing. If it's an Etec it will probably overheat at those speeds around the 2000rpm mark. If 8kn is your target speed, I'd be looking at a different kind of boat, probably displacement.
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Old 24 September 2011, 11:14   #20
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Thanks for the advice 70HP is quoted as minimum for a 6.5M Destroyer. The whole of Chichester Harbour is 8knots takes about 1.5 -2 hours to get out to sea - in my yacht anyway under motor!

Quite a few RIBs in the harbour - sailing clubs RIBs, Harbour Master, etc I wonder how they get on trundling about all day. I'll give them a call

I won't be selling the boat, I like to buy something and keep it, so would have it 20 years or so. I could always try a second hand 90 and flog it and move up to a bigger engine if i need it but would rather try and get it right first time. If a 115 is 35KG more than a 90 then that also works against it - it's a monster of an engine I don't really want something that massive hanging off the back. As long as I can get the boat up to a decent cruising speed for the hull and deal with any unforseen nasty weather changes I will be happy - I'm not a tearing around sort of bloke, doesn't do anything for me, maybe I am looking at the wrong type of boat, but I REALLY WANT an ORANGE RIB, stable,safe etc. I'm going to get one even if i have to row it
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