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Old 23 September 2002, 16:12   #1
Country: UK - England
Town: Salisbury
Length: 5m +
Join Date: Dec 2001
Posts: 459
5 M rib with 50hp underpowered ???

Any views on whether a 5 metre rib with a modern 50 hp two stroke would be too underpowered, boat weighs all in at 280kg including engine ? Would only ever have two adults and two youngsters on board at most. Would guess max speed would be about 30/35 MPH ?

Wouldnt need to pull up a mono or anything, just a bit of pottering around with the odd blast around the solent on a flat day, again I wouldnt ever go out in the rough stuff.

Has anyone got any experience of a similar set up, I prev had a 5.2 metre with a 75hp which flew and had ample power.

Boat is an Arimar made in italy I believe, any thoughts on this model ? What attracts it to me is the ample seating set up and lots of locker storage.

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Old 23 September 2002, 17:07   #2
Country: UK - Wales
Town: Milford Haven
Boat name: Various
Make: Commercial
Length: 10m +
Engine: Screw / Voith / Jets
Join Date: Sep 2002
Posts: 791
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I had a Narwhal 5m rib with a 70hp engine on the back, and if anything it was slightly overpowered - wild at flat out speeds it was

At peak speed with 3 people on board, we clocked it with gps on slack water at about 33knots.... dunno exactly what that is in mph.

To be honest, I can't imagine a 50hp engine being too much slower... depending on the hull, you might get anything between 25 and 35 knots (nice and exact there!!).


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Old 23 September 2002, 17:21   #3
Country: UK - England
Town: Margate / Ramsgate
Boat name: Ballistic
Make: Ballistic
Length: 7m +
Engine: Yam HPDI 250
Join Date: Feb 2002
Posts: 2,775
Previous RIB was a Tornado 4.7 with a 30!

It was fine 3 up (only had three seats) and more than up to the rough (ish) stuff if a little wet and bumpy. No idea of speed, dident own a GPS at the time. I could just tow a skier (in fact my friend could tow me - i'm the only one good enough to get up on that boat and he is too lardy!)

5m and 50 sounds fine to me, but then i went and got a 5.5, with a 130!
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Old 24 September 2002, 01:19   #4
Country: UK - Scotland
Town: Highlands
Boat name: Quicksilver
Make: Quicksilver
Length: 3m +
Engine: Mariner 15hp
Join Date: Aug 2001
Posts: 1,771
I wouldnt ever go out in the rough stuff.
I should change that to read: I wouldn't ever plan to go out in the rough stuff. I have no idea if the engine size is okay, it seems so from the comments so far, but I know that many people on Ribnet will always argue for a large margin of safety.

For example, always carry TWICE the amount of fuel you think you will need.

Keith (best power to weight ratio on Ribnet) Hart
Small boat - BIG truck
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Old 24 September 2002, 03:14   #5
Country: Greece
Town: Athens
Boat name: Sofia - Konstantina
Make: Wave
Length: 5
Engine: Outboard 2-stroke 115 Mercury
Join Date: Apr 2001
Posts: 82
According to my formulas (see my previous posting "top speed")
if the boat plus engine weights 280 kilos and you allow 300 more
hundred kilos for passengers, fuel and other equipment, then your speed should be 32 - 34 knots.


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Old 24 September 2002, 04:29   #6
Country: Ireland
Town: ireland
Make: lencraft rib
Length: 5m +
Engine: yamaha 80hp four str
Join Date: Feb 2001
Posts: 42
I have a 5 m with a yamaha 50hp 2 stroke which I use off west coast of Ireland.I have similar top speed as you indicated 38mph
with 2 up on flat water.If I was changing engine 70 hp would help only with 3 up +.If swell is interesting speed and engine
is not an issue getting home safely is!
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Old 24 September 2002, 04:43   #7
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Country: UK - Isle of Man
Town: Peel, IOM
Boat name: Saffron
Make: Scorpion
Length: 8m +
Engine: I/B Diesel 315hp
Join Date: Nov 2000
Posts: 2,197
"Keith (best power to weight ratio on Ribnet) Hart"

I am reminded of Keiths sign-off above.
What I don't remember seeing, however, was Keith's calculation of power/weight ratio AFTER taking Quicksilvers crew into account !!!

Did I miss it or is it best left to our vivid imaginations?
Or has Mr. Cynicism crept in and sat down at my keyboard?
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Old 24 September 2002, 05:05   #8
Country: UK - England
Town: Upavon, Wiltshire
Boat name: Dromedary
Make: Ribtec
Length: 6.55
Engine: Honda 130
Join Date: Apr 2001
Posts: 183
I use to have a 5M Dunlop which I had converted to a RIB (they did not exist then and she had a Suzuki 85 and was very good so I would think a 50 may be a bit small

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Old 24 September 2002, 05:51   #9
Country: Greece
Boat name: SUN KISS II
Make: Nuova Bat 9 Falcon -
Length: 5m +
Engine: Outboard Mercury 115
Join Date: Jun 2001
Posts: 639
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My previous rib was a Gommorizzo 450 (200 kg),with a Yam 50 plus Yam Malta (donkey). It was not a deep vee hull and the tubes were always in touch with the water. Never had any problem with 2 adults and 2 children (100+60+25+25 kg)+ stuff. I 've spent a whole summer carrying 4 adults AND 4 children which is twice as much you want. Didn't expect to go as fast as with 1 passenger, but I was happy with it
Michael a.k.a "Bat Falcon"

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Old 24 September 2002, 06:20   #10
Country: UK - England
Town: London + Brighton
Boat name: TIPS
Make: Avon Adventure *FOR SALE*
Length: 5.6m
Engine: 115 Yamaha 4-Stroke
Join Date: Apr 2002
Posts: 50
Used to have a Zodiac YachtLine 4.9m Rib (quite heavy for its size) with a 60hp Merc 2Stroke. After upping the pitch to 17 we could hit about 37knots with two adults in. I think 50hp will be fine for a 5m Rib.


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