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Old 19 April 2004, 14:54   #1
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Country: Brazil
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Single or twin diesels?

I've run all the numbers, and without a doubt diesel is the way to go for my tour boat. The manufacturer swears that the best motor setup they've installed is twin Mercruiser 1.7L dti's (120hp per motor). This would give me plenty of low-end torque, great maneuverability, and excellent fuel economy. The owners are claiming 15lts per hour for both at cruising speed, about 27mph. My original thought was to go with the Merc D-Tronic 250hp. I've heard nothing but good things about the 1.7's, but not much info on the D-Tronic model.
My problem is that I can't get over the fact that we're talking about 2 120hp motors for a total of 232hp at the props! Merc and Flexboat here both claim that because the motor is designed to operate at higher rpm's, the torque generated compensates for the lower hp rating since I'll be operating only at cruising speed or less. It kinda makes sense, but I thought I'd run it by you folks to get some unbiased feedback.
Two advantages are that there will be less strain on the legs (Alpha 1), which is where many problems seem to occur, and that the D-Tronic costs 4,000 USD more than the 2 1.7's combined. The biggest con is the age-old "twice the motors, twice the headache" theory, but labour is cheaper down here.
Am I far off with my logic? What would you put on this boat?

7.6 mtrs without rear deck
1,900 lbs. w/ no motor or fuel
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Old 19 April 2004, 15:01   #2
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Here's another. And BTW it's rated for 22... 15 in seats, 5 in the bow, 2 crew.
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Old 19 April 2004, 15:04   #3
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If it will really give the performance that you need then it sounds like a good choice as from what you say the money is right and you've got dealer support.

I would definitely want a serious sea trial with this engine setup and a fully loaded boat before committing to anything though!

John
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Old 19 April 2004, 15:50   #4
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Quote:
Originally Posted by John Kennett
I would definitely want a serious sea trial with this engine setup and a fully loaded boat before committing to anything though!
Unfortunately the nearest boat in this configuration is a plane ride away, but I think it's worth for an investment this size.

I've seen a few members post an interest in the twin Merc 1.7 setup, but haven't seen anyone on here that's actually done it. It would be great to find someone who has this setup on these forums.

So I take it no alarm bells are going off with this setup John?

Thanks
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Old 19 April 2004, 16:09   #5
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Hi folks

I belive the 1.7TD 120HP is quite a wide engine, almost as wide as my Yanmar 240HP.

If this is the case, assuming your 7.6M is not much wider then my 7.8 will they fit without staggering ?.

I always though this setup would be very good for cruising, will be very interested if you go this route to see how it works out, but to date I dont know anyone who has done this in a 7M class RIB.

Keep us posted

Regards Gary
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Old 19 April 2004, 16:19   #6
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Quote:
Originally Posted by Garygee
Hi folks

I belive the 1.7TD 120HP is quite a wide engine, almost as wide as my Yanmar 240HP.

If this is the case, assuming your 7.6M is not much wider then my 7.8 will they fit without staggering ?.

I always though this setup would be very good for cruising, will be very interested if you go this route to see how it works out, but to date I dont know anyone who has done this in a 7M class RIB.

Keep us posted

Regards Gary

we have just taken on an order for a Parker 7.5 mtr rib from our Baltic range with twin Mercruiser 1.7 TDI for delivery to a UK customer . This is an interesting project and will keep the forum posted on the built including photos

Andre

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Old 19 April 2004, 16:58   #7
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I was planning to do this a while ago and width was an issue. Here's a pic of the two engines side by side. It may be of help.
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Old 19 April 2004, 17:33   #8
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I too have entertained this idea. It is a serious contendor on my next RIB list but you guys have put more thought into it. How wide is a yanmar 240, i know putting two of those in a RIB causes a serious problem - like you need to remove one to service it.
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Old 19 April 2004, 17:52   #9
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Quote:
Originally Posted by Daniel
How wide is a yanmar 240,....
699, not including the power steering cylinder.
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Old 19 April 2004, 18:03   #10
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Always a wealth of knowledge. I've voted for you

Given that most RIB's 7m+ have a beam of about 1500mm it would seam one would be having similar problems with a pair of 1.7's as with yanmar 240's. I know which i'd rather have. Don't suppose you have the cost and weight of both to hand anyone?
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