5 M rib with 50hp underpowered ???

[matiboy]

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.

[Alex Brown]

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!!).

-Alex

[Daniel]

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!

[Keith Hart]

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

[dimitris]

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.

Regards

Dimitris

[mccabe]

Hi,
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!

[Brian]

"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?

[Scubakid]

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

John

[batfalcon]

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

[TIPS]

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.

Mark

[Jizm]

I have a tornado 4.8 with a yamaha 60 and it seems to have around the same top speed whether I have 1,2,3,4 or even 5 people on board! accelaration differs but not too much. I wouldn't think that 20cm and 10hp could make a massive difference, noticable but hardly worth worrying over!

[DJL]

50HP certainly won't be underpowered but it obviously won't be as nippy as if you had a 75 or 90HP

I have a 60HP on my 4.7m RIB. I get a max speed of 33kts with 1-2 people and that only drops to 31kts with 8 people on board (I would not recommend 8 people in a 4.7m RIB). Prop choice will be quite important. The prop which came with the boat gave me much better top speeds but wan't as good in rough weather/water sports.

Daniel (the 2nd) Loughlin

[Keith Hart]

Hi Brian

What I don't remember seeing, however, was Keith's calculation of power/weight ratio AFTER taking Quicksilvers crew into account !!!

Difficult one that Brian. It depends whether I'm out in the boat before or after dinner!

Keith (these brackets seem to be catching on) Hart

[Alan]

Sorry to point this out Keith me old mate but do you really think that in the grand scheme of things the amount of dinner you've had makes a difference??

[Keith Hart]

Alan

If you'd ever seen the amount of dinner that I eat, you wouldn't be asking that question.

Keith (burp) Hart

[Alan]

Should the brackets thus read....

Keith (He can eat his own bodyweight) Hart?



Alan

[matiboy]

50 Hp should be ok for general sunbathing use !

(given my current 15 hp gets 4 of us on the plane in the little avon and I reckon will do about 25 mph, I reckon 50 hp should shift us )

Do I assume correctly that this 50 HP would on the flip side offer better fuel consumption than say I was running a bigger 75 on the same boat ???

Keith you realise I only sold my 6 metre rib and bought this 3.1 metre Avon just to capture your award of smallest boat on rib.net !!!

[Flanker]

Try the link below. For $20 US you will be given a complete analysis of what to expect. There is a sample report on the site to see if it is what you are looking for. You get unlimited on line reports for 20 days, maybe you could do some for others for a beer.

http://www.propworks.com/becomeamem.htm

Pete