Outboard motor advice needed for 4.2m RIB

[tom_aimes92]

Hi there.

We have a RIB, which needs a good new outboard motor, however we are unsure on whether to purchase a 25 HP 4 stroke (Mercury F25E) or a 20 HP 4 stroke (Mercury F20E)

The RIB (Valiant brand):
Length: 4,2 meters approx.
Weight: Don't know, but max weight on it is 700 kg.
Max HP: 25 HP

Use scenario:
Shorter trips along the coast
Wakeboarding at decent speed (thinking 30 km/h).
Should carry typically 1-3 adults.

Ideally, we want to go with the 20 HP Mercury (or another brand). Our one and only concern is whether the 20 HP will be enough for our use scenario. We also ponder over what max speed we can achieve with the 20 HP.

What do you folks think? Is the 20 HP enough, and what max speed might we achieve with it, when let's say 2 adults are onboard with no equipment?

Cheers.

[beamishken]

Originally Posted by tom_aimes92

Hi there.

We have a RIB, which needs a good new outboard motor, however we are unsure on whether to purchase a 25 HP 4 stroke (Mercury F25E) or a 20 HP 4 stroke (Mercury F20E)

The RIB (Valiant brand):
Length: 4,2 meters approx.
Weight: Don't know, but max weight on it is 700 kg.
Max HP: 25 HP

Use scenario:
Shorter trips along the coast
Wakeboarding at decent speed (thinking 30 km/h).
Should carry typically 1-3 adults.

Ideally, we want to go with the 20 HP Mercury (or another brand). Our one and only concern is whether the 20 HP will be enough for our use scenario. We also ponder over what max speed we can achieve with the 20 HP.

What do you folks think? Is the 20 HP enough, and what max speed might we achieve with it, when let's say 2 adults are onboard with no equipment?

Cheers.

Is it the one with the offset console and the little bench seat in the stern? If its the model I think it is even maxed out with the 25 will be quite pedestrian I had one for a short time with a 25 yam & it was disappointing, no idea why they are rated to 25 max, a 40 would be more the mark.

Sent from my SM-G950F using RIB Net mobile app

[Salty Pete]

Being a person who knows nothing.
I have a 3.8 M with a 30 HP. 4.2 M is not much bigger. I got a calculator entered 4.2 - 3.8 and the calculator said. "Not much bigger."

So, one would think that a 4.2 M could handle a 30 HP outboard.

Could it be the weight? Outboard engines are providing more HP per weight and when the boat was made a 25 HP outboard may have been the max. weight for the boat.

It can carry 700 Kg my 3.8 says it can carry 637 Kg. Divide 637 by 3.8 and multiply by 4.2. My calculator says, "that's about right mate."

Displacement weight of mine is 82 Kg. Using the same calc. your weight would be about 91 KG.

The recommended HP on my 3.8 is 25 - 30 HP. I reckon 25 for a nice quiet family boat. But I like the 30 HP, to have the boat airborne between waves.

[mhb100]

Originally Posted by tom_aimes92

Hi there.

We have a RIB, which needs a good new outboard motor, however we are unsure on whether to purchase a 25 HP 4 stroke (Mercury F25E) or a 20 HP 4 stroke (Mercury F20E)

The RIB (Valiant brand):
Length: 4,2 meters approx.
Weight: Don't know, but max weight on it is 700 kg.
Max HP: 25 HP

Use scenario:
Shorter trips along the coast
Wakeboarding at decent speed (thinking 30 km/h).
Should carry typically 1-3 adults.

Ideally, we want to go with the 20 HP Mercury (or another brand). Our one and only concern is whether the 20 HP will be enough for our use scenario. We also ponder over what max speed we can achieve with the 20 HP.

What do you folks think? Is the 20 HP enough, and what max speed might we achieve with it, when let's say 2 adults are onboard with no equipment?

Cheers.

I think something is wrong here, the valiants I know around 4m were rated max 40HP with a recommended 25HP for general use. They also had a max engine weigh limit of around 100kg.

I think you need to check out your model details to check first. Which model do you have 400DR, 400 vanguard, etc?

Personally I’d not want to put less than 30hp on it

I think you would be disappointed with less

[treerat]

I used to run a 40 on a 4.1 rib, its wasn't a Valient (Rimini) but wouldn't have wanted anything smaller - had a 25 on the 3.8 sib and it was great fun.

Sticking smaller on larger and heavier seems odd to me.

[Inglenook]

I have a 4m Valiant (looking to sell) and it has an EX RNLI 40hp Mariner on the back. I can wakeboard but, it is a bit of a struggle to get up and Im only 12stone and that was with 3 onboard but once up its fine. Anything less and i think you will be disappointed.

[Locozodiac]

The motor you go with will depend entirely on the number of passengers you'll be boating with on regular basis. A boat is rated for max number of passengers and max HP motor. If will be boating with less than max passengers don't need to go for max HP motor rated for.

For instance my 4.50 Rib with 2 up which it's the max passengers I like going boating with powered with a long shaft 2 stroke Tohatsu 18 HP motor powers the combo at 41 Km/h on flat calm no wind water conditions. My total boat/motor/fuel and passengers is 500 Kg. BTW, my Rib is rated for max 7 passengers and a 50 HP motor. 20-25 HP motors well propped to rev around middle to it's max wot rpm range set by the manufacturer will do the trick depending on the number of passengers you'll be constantly boating with ?

The good thing is that I always run same half ton fixed load with a maximized less pitch prop from the factory delivered one which achieves an excellent fast hole shot with a nice top end speed.

Happy Boating

[tom_aimes92]

Thanks all for this great feedback - plenty of excellent points for me to reflect on.

Apparently, the RIB turns out to be 3.6 meters in total, and it's a Valiant LodeStar model AA360002N. Perhaps the 20 HP 4 stroke Merc is enough given this size..?

Thinking we'll usually be 2 adults on the RIB for wakeboarding and smaller trips.

I agree that more HP will be more fun. The issue with going 25 HP and beyond is that you need a license for that where I live, which means that guests without a license can't steer the RIB, which is unfortunate.

Cheers