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Old 23 September 2018, 03:24   #1
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8m+ In board v Outboard

Hi,

Looking for a quick bit of advice please...

Iím currently looking at 8m+ Scorpion RIBS and Iíve seen some great looking boats with Inboards and Outboards (Petrol and diesel)

Are there any key performance / handling differences I need to consider please ?

Iíve previously owned a 7.5m Vipermax and 25ft Four Winns, so Iíve experienced both in some forms, but Iíve never been on a RIB with an Inboard.

Would it be right to assume they are slower out the hole but more sure footed as the weight is lower at the stern ? Are inboards innately heavier ?

I like the look of the more ďopenĒ stern of an inboard, and diesel would mean a lot less drama at fuel time (thereís no petrol pumps at our local marinas!).

Thanks in advance !
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Old 23 September 2018, 04:02   #2
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Diesel:

-More economical
-Better avaibility of fuel at the quayside
-Fit a diesel heater in your console to keep the batteries warm and take advantage of the 60/40 fuel duty split = cheaper fuel

Petrol:
-Better "performance" eg hole shot
-More space in the boat
-Generally easier to work on. Much easier to take engine off / repair / change etc
-Generally quieter
-Generally lighter (might be a consideration for towing etc)

It's swings and roundabouts. I've run both in the size range you're talking about. In the Solent I had an 8m with a 250 Suzuki petrol on the back. No issues with fuelling as everywhere sells petrol, loads of room, great performance boat. When I moved to Norfolk I had a Redbay 7.4 diesel. Nowhere sells petrol at the quayside so that was a huge advantage, plus the boat was very heavy do felt very safe in the North Sea.
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Old 23 September 2018, 04:57   #3
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The 8m+Scorpions are fantastic ribs.The main advantage of diesel is fuel availability,especially in remote areas and cost with 60/40 rate plus the ability to cope with rough conditions Fast Farward will go through anything,the harder you push her the better she goes ,mainly due to her weight.The disadvantage is her towing weight,which is bang on the legal limit when fuelled up and lack of cockpit space.
The outboard engined Scorps.have the advantage of more room and lighter weight ,but those big outboards don't half drink the fuel!
Both are fantastic sea boat that with cope we much harder conditions that the crew!
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It looks massive on the trailer,but tiny in a big sea!
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Old 23 September 2018, 05:42   #4
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Agree with both posters.........except:
outboards quieter?? not been my experience.

Also, Anglesea. Irish Sea. Go diesel.
You dont want to be towing that about do you?
Go by sea-it's quicker anyway-and more enjoyable.
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Old 23 September 2018, 06:55   #5
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Thanks guys ! Appreciated !

Iíd not considered the cockpit space, thatís a slight concern but hopefully with an 8.5m, I wouldnít notice too much lost space from my old 7.5m. I think the flat engine lid gives a lot of usable moored space too...

Once sheís in anglesey sheíll be slipped by tractor 100 yards away so her weight shouldnít be too big a factor...

Time to go and see the 8.5m diesel Iíve been stalking !
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Old 23 September 2018, 14:10   #6
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Consider carefully the engine/drive package. There have been many cracked engine blocks and failed drives, some packages are hugely more reliable than others. Brian can give you details of his good and bad packages, I'm sure. Also, the Achilles heel of diesel power is getting the turbo up to speed when in sizable waves. You need engine speed to drive the turbo but in some wave conditions it's not possible to get the engine up to speed because it doesn't produce enough power to climb the next wave without the turbo so you get stuck not able to climb the hump to get on plane. Eventually a good wave set comes along and the turbo spins up and you're away but now you're too fast for the conditions so you throttle back, fall off the turbo and start over again. It can be a real pest. To overcome this you need lots of power. Willk has a big power plant in his Redbay, it might be worth a chat with him. I have a Volvo Penta which uses a supercharger up to the point of the turbo spinning up. It's designed to overcome this low power at lowish revs issue. It does work but it works best with an open exhaust which reduces the back pressure and gets the turbo spinning early.

Lots to think about before you jump in with both feet.
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Old 23 September 2018, 16:41   #7
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Quote:
Originally Posted by jwalker View Post
Consider carefully the engine/drive package. There have been many cracked engine blocks and failed drives, some packages are hugely more reliable than others. Brian can give you details of his good and bad packages, I'm sure. Also, the Achilles heel of diesel power is getting the turbo up to speed when in sizable waves. You need engine speed to drive the turbo but in some wave conditions it's not possible to get the engine up to speed because it doesn't produce enough power to climb the next wave without the turbo so you get stuck not able to climb the hump to get on plane. Eventually a good wave set comes along and the turbo spins up and you're away but now you're too fast for the conditions so you throttle back, fall off the turbo and start over again. It can be a real pest. To overcome this you need lots of power. Willk has a big power plant in his Redbay, it might be worth a chat with him. I have a Volvo Penta which uses a supercharger up to the point of the turbo spinning up. It's designed to overcome this low power at lowish revs issue. It does work but it works best with an open exhaust which reduces the back pressure and gets the turbo spinning early.

Lots to think about before you jump in with both feet.
What he said!

Friends diesel inboard Scorpion local to me, lovely boat (8m ish), handles nice , looks good, fast, however............... getting up on the plane, itís embarrassing! Itís not turbo lag, more like turbo sleeping! Lol
Couple other inboard ribs I know on the Solent, 20 knots flat out, not great for getting any distance in a reasonable time. The general merits of petrol / diesel are well explained in the earlier posts, but my overriding experience is inboards can bite you if not looked after, bellows / legs etc can properly cost if not maintained right
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Old 23 September 2018, 16:55   #8
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I love the slightly heavier feel of my 9m diesel Ribtec, it certainly feels a lot more solid going through a sea than most of the 8m outboard RIBs I've driven. As per JW, turbo lag can be a slight problem given the typically fairly large turbos they run with in marine spec, but if the engine is of a suitable power for the boat, and it's correctly propped, I don't find that a massive issue. You won't have the always available instant power of a big outboard though, especially at lower revs, but I think it's something you learn to deal with in most cases.

Fuel consumption/costs a definite advantage, along with probably greater range than an equivalent sized petrol RIB. On mine at least the engine bay lid makes a wonderful flat area for sunbathing, use as a table, inflating towed toys, etc. - very multipurpose!

Some people think that diesel engines will be cheaper to maintain, but parts are typically very expensive, definitely for Yanmar! If you're only doing typical leisure use rather than high hours commercial stuff where the fuel saving and longevity make a bigger difference, a diesel may end up no cheaper to run. Definitely research the specific engine (and drive) you're looking at, as some of the diesel installations are better than others. I assume most 8m Scorpion diesels are on the Yanmar/Yamaha 315hp engines, unless looking for a very recent example? I love my Yanmar 315 - a fairly simple engine to work on and no fancy electronics. Some minor parts and service items are shared with the Toyota block it's built on and thus very cheap, but the Yanmar-specific marinised components are pretty expensive. If it's running a Bravo 3 drive, the big diesels have a reputation for eating those, so check it carefully. Mine has been fine so far, but I put a drive shower on it as soon as I bought it to help with cooling, regularly change the drive oil, and try to drive it such that the prop doesn't leave the water too much as the sudden big torque as the prop re-enters the water can cause issues with the drive shafts and UJ's. Do budget for the drive servicing as well, they need to be looked after!

I guess the best answer is try to get a ride/demo on 2 similar boats and see which one you prefer - some people hate the slower pickup of the diesel and the general heavier feeling.
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Old 23 September 2018, 16:55   #9
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Quote:
Originally Posted by M.Thornton View Post
The 8m+Scorpions are fantastic ribs.The main advantage of diesel is fuel availability,especially in remote areas and cost with 60/40 rate plus the ability to cope with rough conditions Fast Farward will go through anything,the harder you push her the better she goes ,mainly due to her weight.The disadvantage is her towing weight,which is bang on the legal limit when fuelled up and lack of cockpit space.
The outboard engined Scorps.have the advantage of more room and lighter weight ,but those big outboards don't half drink the fuel!
Both are fantastic sea boat that with cope we much harder conditions that the crew!
That grey rib is my old boat. How is she doing mike?
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Old 23 September 2018, 16:58   #10
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I run a 250ho outboard in my 8.1. Itís a rapid boat, but the fuel meter scares the out of me. At a steady pace I am using similar fuel to my mate and his 70. But flat out is another thing.

I will be getting diesel next time if possible.
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