Engine size for rib

[stul]

hi
Have Narwall 4 metre Rib,what is the largest safe engine I can use.have been running a 40 hp Idears and advice most welcome
stul

[Poly]

if boat was made since the recreational craft directive (1994?) then it should have a plate on the transom stating maximum weight and engine size

Below is an extract from a recent MAIB investigation - which shows the recommended safe power. Multiply the answer in kW by 1.341 to get HP.

But if this is bigger than the manufacturers rating it will cause you insurance issues.

[AndrewH]

Originally Posted by stul

hi
Have Narwall 4 metre Rib,what is the largest safe engine I can use.have been running a 40 hp Idears and advice most welcome
stul

I have a Narwhal NK400R and the label on the toobs states that the maximum o/board power is 50 hp with a max transom weight of 100 kg

HTH

Andrew

[stul]

Originally Posted by Polwart

if boat was made since the recreational craft directive (1994?) then it should have a plate on the transom stating maximum weight and engine size

Below is an extract from a recent MAIB investigation - which shows the recommended safe power. Multiply the answer in kW by 1.341 to get HP.

But if this is bigger than the manufacturers rating it will cause you insurance issues.

Thanks
for info will have to work it out,engine date is 1990,hard to read info on tubes
thanks Stul

[stul]

Originally Posted by AndrewH

I have a Narwhal NK400R and the label on the toobs states that the maximum o/board power is 50 hp with a max transom weight of 100 kg

HTH

Andrew

Hi Andy
Hard to read info on toobs or tubes,50 engine max would go well with that,how old is your Narwhal,ps my engine is mounted about 3inches off centre to startboard side is your mounted in the centre?thanks for interest
Stul

[AndrewH]

Originally Posted by stul

Hi Andy
How old is your Narwhal
Stul

Can't be sure but I believe about 1996/1997

Originally Posted by stul

Hi Andy
ps my engine is mounted about 3inches off centre to startboard side is your mounted in the centre?thanks for interest
Stul

- Bizarre - Mine is slap bang in the middle of the transom. I wonder if any one else here could shed light on that?

[stul]

Originally Posted by AndrewH

Can't be sure but I believe about 1996/1997



- Bizarre - Mine is slap bang in the middle of the transom. I wonder if any one else here could shed light on that?

Andy
had a bit of advice about this off a guy called Fast Fred,from usa,see "Fitting A engine" queston below
thanks Stul

[Rene]

you can very easily calculate the max engine size off your boat using the current CE marking regulations.

Max engine size i HP = (Lenght * Width * 10 - 33) * 1,341

Length is the max length off the boat without engine
Width is the max outside width off your both.

This is the current CE regulations, so if your boat is CE marked this is the rules that apply to your boat

Best Regards
Rene

[codprawn]

I see it doesn't take into effect actual hull surface area - how deep the V is etc etc - who came up with this?

[ADS]

Codprawn, has a point, my old 4m shallow v Avon was downright dangerous on its maximum 40HP, had to back right off to be able to turn at any great speed or it went sideways. However a 4m Avon Searider deep v will take a 50-60hp no problem.

[jyasaki]

Originally Posted by AndrewH

- Bizarre - Mine is slap bang in the middle of the transom. I wonder if any one else here could shed light on that?

It is done to counter the prop's torque steering. Never heard of quite that much; usually just an inch or two.

jky

[Poly]

Originally Posted by Rene

you can very easily calculate the max engine size off your boat using the current CE marking regulations.

Max engine size i HP = (Lenght * Width * 10 - 33) * 1,341

Length is the max length off the boat without engine
Width is the max outside width off your both.

This is the current CE regulations, so if your boat is CE marked this is the rules that apply to your boat

Best Regards
Rene

This is the formula I posted earlier. But it is important to realise this is the maximum power that the manufacturer could spec to get a CE mark on it. That is NOT the same thing as the manufacturers max spec not the same thing as the max safe power. So e.g. my boat gives a max power of around 38 HP with the formula, but the manufacturer states 30 HP.

[Rene]

Hi Polwart

You are off course correct.
That is the MAX enigine size according to CE marking.

The supplier off the boat might spec. the max engine lower than that. And even that might bee to much.

I have just never earlier seen a boat where the supplier spec. a lower HP that then formula in the CE marking.

I have however seen a lot off supliers spec a HIGHER MAX engine than the spec. but that is off course not legal, and the boats will fail a proper CE marking.

I really don't get people trying to make fraud CE markings on boats.

Latest the Balistic 7.8 marked at max engine 250 HP, when the real value is 225 HP

Best regards
Rene

PS. Safety first...

[Poly]

I would suspect that the reason my manufacturer specs a lower power than the formula gives (with rounding or a few cm on the hull length he could have got it to 40HP) is that the transom might not be strong enough (or well enough mounted) to take the thrust.

Its interesting that weight doesn't feature in the formula.

To be honest I have a 20HP on my boat and its fast enough. A 30HP would maybe get another 5 knots, but the dealer suggested it would be unnecessary and give crap handling at FOT. A number of people whose opinion I value reckon its about the right power for the size of the boat, and any bigger would be over powered.

[donutsina911]

Originally Posted by Rene

Latest the Balistic 7.8 marked at max engine 250 HP, when the real value is 225 HP

are you sure about that? Not disputing what you say, just that there are shed loads of 7.8's out there with 250's (mine included), a few with twin 200's and a couple with 300's....

[Rene]

Originally Posted by donutsina911

are you sure about that? Not disputing what you say, just that there are shed loads of 7.8's out there with 250's (mine included), a few with twin 200's and a couple with 300's....

There are 2 different rules in wich you can calculate the max engine power off your boat.

1) is the formula stated by Polwart and myself, thats the easy one. That rule apply to all RIB's no question asked. This is the "normal" way to calculate max enigine on any CE marked boat.

2) States that you can put a bigger engine on your RIB if you follow some standards. I don't have them all, but maybe Polwart does.

but here goes....
a) the factory that is building the boat (not the importer or reseller), is to supply the boat as key finished. (this means incl. engine all consoles, a-frames and electronic)

b) the factory have to make a sea trial in whích they have to complete different taskes with the boat within a specific area.

c) You as the owner can not change anything on the boat that will change weight distribution. (add a new bigger battery, add a new seat or even remove the a-frame)

The list is longer, but if you as the owner of the boat change anything you will make the CE marking invalid.

And since boating dynamics in SA, dosn't supply the boat finished with consoles and engine mounted you would be breaking the CE marking by putting a 250 HP engine on the back off your balistic 7.8

max HP = ((7.8 * 2.55 * 10) - 33) * 1.314 = 217,9926 HP

That means that if I have the width right (from memory) you can not even put a 225 one it.

Or maybe the factor from KW to HP is wrong, I really thought the max Hp on balistic 7,8 was 225, but I might be wrong on that.

Regards
Rene

Polwart - You wouldn't happen to have a copy off the complete ISO standard for RIB's that I could bye / borrow from you ?

[Poly]

Originally Posted by Rene

Polwart - You wouldn't happen to have a copy off the complete ISO standard for RIB's that I could bye / borrow from you ?

I'm afraid not. The quote I posted was an extract from a Marine Accident Investigation Branch report (which considered whether the wrong size of engine contributed to an accident - they concluded it did not). The ISO specs are downloadable but cost about £100

And - as far as I can see you are correct on the kW-HP conversion.

[donutsina911]

Originally Posted by Rene

There are 2 different rules in wich you can calculate the max engine power off your boat.

1) is the formula stated by Polwart and myself, thats the easy one. That rule apply to all RIB's no question asked. This is the "normal" way to calculate max enigine on any CE marked boat.

2) States that you can put a bigger engine on your RIB if you follow some standards. I don't have them all, but maybe Polwart does.

but here goes....
a) the factory that is building the boat (not the importer or reseller), is to supply the boat as key finished. (this means incl. engine all consoles, a-frames and electronic)

b) the factory have to make a sea trial in whích they have to complete different taskes with the boat within a specific area.

c) You as the owner can not change anything on the boat that will change weight distribution. (add a new bigger battery, add a new seat or even remove the a-frame)

The list is longer, but if you as the owner of the boat change anything you will make the CE marking invalid.

And since boating dynamics in SA, dosn't supply the boat finished with consoles and engine mounted you would be breaking the CE marking by putting a 250 HP engine on the back off your balistic 7.8

max HP = ((7.8 * 2.55 * 10) - 33) * 1.314 = 217,9926 HP

That means that if I have the width right (from memory) you can not even put a 225 one it.

Or maybe the factor from KW to HP is wrong, I really thought the max Hp on balistic 7,8 was 225, but I might be wrong on that.

Regards
Rene

Polwart - You wouldn't happen to have a copy off the complete ISO standard for RIB's that I could bye / borrow from you ?

The CE plate rates the RIB at 250, is to be MCA coded with this set up (surveyed by Searider) and insured as such - I'm confused.

Even more confusing is that Boating Dynamix indicate on their site that 300 or 2 x 250 is the max.

http://www.boatingdynamix.co.za/RIB_boat.htm

Will ask JBT at Ribex....

[donutsina911]

awesome rib with 2 x 250 e-tecs....