5HP RIB tender performance

[Deelirious]

I was wondering what sort of setup and performance others are getting out of their small RIB tenders with a 5hp outboard.

I have a small 2.4m alloy RIB and recently upgraded the outboard from 2hp to a 5HP Yamaha short shaft. Judging from some youtube footage I have seen as well as reported from friends with similar setups I was expecting the boat to plane easily with myself in it and a little gear although I was not expecting it to plane with 2 people in it.

The boat only just planed with myself in it and no gear and was very sensitive to weight. The engine has a 7.5 x 8 inch pitch prop on it and I was running a fuel that was approximately 2 years old (not sure) mixed at 50:1 and the manufacturer recommends 100:1 ratio.

What do other people run and get performance wise and,
what sort of improvement could I expect from fresh fuel, correct oil mix and a smaller pitch prop say 7.5 by 7 inch pitch?

Cheers
Ed


Before you ask the fuel came from an old jerry under the house that I leave for running the mower and whipper snipper etc and I do not know how old it really is.

[Noelm]

You will proabaly get improvement from the prop change, but doubt you will get anything noticable from the fuel change, except being better for the engine to run the right clean fuel and oil mix. I personaly think 100:1 is a tad too lean for a small outboard that is going to be run full throttle most of the time (my opinion only of course)

[spelchek]

I've gt a polycraft tuff tender (~80kg) with 6hp yam 2strk. Pretty similar performance to what you describe Deelerious. MAkes it onto the plane with just me onboard - but sluggush with more weight. I'm actually considering an upgrade to 8hp - i think the extra 2 horses will give it that little bit more 'oomph' that I'm after. The 8 hp yammi is same weight as the 6hp - I dfinately don;t want anymore weight in the tender outboard as I have to lift it from the boat and into the tender on the duckboard.

[sharkymark2]

I had a 5 hp suzuki with a 10' light weight ally and it used to easily get up on the plane

[Camhawk88]

A rib has a lot of water friction to overcome to get onto the plane. Im surprised the 5hp got it there. A smaller pitch prop will probably get you up a bit better.

[Deelirious]

Thanks for the feedback guys. I've ordered a smaller pitch prop and once I've given that a go with some fresh fuel I'll let you know how I get on.

[GBC]

I've gt a polycraft tuff tender (~80kg) with 6hp yam 2strk. Pretty similar performance to what you describe Deelerious. MAkes it onto the plane with just me onboard - but sluggush with more weight. I'm actually considering an upgrade to 8hp - i think the extra 2 horses will give it that little bit more 'oomph' that I'm after. The 8 hp yammi is same weight as the 6hp - I dfinately don;t want anymore weight in the tender outboard as I have to lift it from the boat and into the tender on the duckboard.

A 9.8 tohatsu is a powered up 6 h.p. And still weighs 26 k.g. Definitely plenty of oomph for its size.

[spelchek]

Cheers GBC. I shall investigate. No experience at all with tohatsu OB's - anyone here care to recommend or rubbish them? (Probably both I'd bet LOL).

[GBC]

I've got one for the car topper and love the thing. It is an old school two stroke though so don't expect miracles. Typically jap built with good metals and close tolerances as you'd expect though. Just feed it fresh fuel and flush it and it will do the rest. They are a very common engine, also rebadged as nissan overseas and mercury here.

[Crocodile]

Hello Deelirious,

You say that you have trouble planning, is that because the bow is going skywards?
Weight shift may solve the problem.
Are you using tiller extension to get your weight forward?
Have look at this; http://www.youtube.com/watch?v=QscORQGjP_M
It may even provide a more comfortable sitting posture.

[GBC]

Funny you put that up. That is the 'big' 3m spindrift dinghy rated to 6 h.p. My cartopper i mentioned before is the small 2.4m version rated to 4 h.p.

The 9.8 goes o.k. on it :P. It is an amazingly stable little platform which handles the chop just like a real cat.

[Deelirious]

Update,
I gave the RIB a run on Saturday with the smaller 7.25 by 6.5 inch prop, the smallest yamaha prop for the 5HP. It had a lot more thrust and about the same top end speed 13kn as the larger prop as the engine revved out a bit higher at the top end.

The boat still bogs down in the arse when trying to get on the plane and one of the reasons for this I think is that the boat is so short.

I love the idea of the spindrift dingies and maybe in the future I will trade from the RIB to one of these but at the moment weight is critical and even a 5 or 10kg more in the hull weight would make the option of a tender unviable.

The next thing to try is a long tiller handle as suggested above to keep weight forward in the boat while trying to get on the plane and I think this will make a big difference because with the short handle your weight is back while putting on the throttle and although you can then move forward the boat is already bogged down at the back by the time you do this.

In the meantime I will dream about upgrading to a spindrift!!

[Deelirious]

GBC,
These sound like a great little boat. what sort of load will the 2.4m boat plane with using a 4hp outboard? Can it plane with an adult (what sort of weight) and gear? An adult and kid, two adults etc?
Cheers

[GBC]

Dunno. They are only very light boats (40 odd k.g.?) they don't actually plane in that they are a proper little cat hull so load carrying isn't an issue. I have only tried my hull with the 9.8 and I can confidently say it is badly overpowered. It will take off and run with hardly any throttle so I think they have their ratings about right. I dare say the 3.0m version would handle the h.p. A bit better, but I am happy with the more portable lighter version.
there were a few done up as impoundment comp boats so you'd be able to track down some owners fairly easily who have stuck to the rules and put the correct sized donk on. I'd say it'd go fine with an adult and a couple of kids and only 4 h.p. But that is only a guess.