engine for 4.3M RIB???

jpn · 20 July 2010, 07:15

Getting a 4.3M rib, 20deg deadrise at transom, I was thinking of a 30HP 2stroke Yammie, would that be enough for top speed of 25knts...or do I need a 40HP. I prefer a lower HP so it will not be too dangerous for young kids to be at the helm...off course with an adult by the side...

gotchiguy · 20 July 2010, 08:22

Quote:

Originally Posted by jpn

Getting a 4.3M rib, 20deg deadrise at transom, I was thinking of a 30HP 2stroke Yammie, would that be enough for top speed of 25knts...or do I need a 40HP. I prefer a lower HP so it will not be too dangerous for young kids to be at the helm...off course with an adult by the side...

I ran a 4.2m for 3 years before my current boat and to be honest, the fact that children will be driving oughtn't have too large an effect on your purchase. If you were to get a 50hp and the first time a child drove it then all you have to do is get a piece of string and rig up a little restrictor job (assuming it is remotes) or if tiller I'm sure I've seen a solution for that somewhere on here...

spartacus · 20 July 2010, 12:12

Quote:

Originally Posted by jpn

Getting a 4.3M rib, 20deg deadrise at transom, I was thinking of a 30HP 2stroke Yammie, would that be enough for top speed of 25knts...or do I need a 40HP. I prefer a lower HP so it will not be too dangerous for young kids to be at the helm...off course with an adult by the side...

Used to have a Zodiac Pro 7-man now renamed the 420. It had a 20 degree deadrise too. It was perfectly matched to a long-shaft Yamaha 40hp, 3 cylinder, 2-stroke (40V model). The transom was rated for 50hp, but in 3 years of looking I never came across a used (50G model) for sale that didn't look as if it was on it's last legs.

Personally I'd opt for a larger HP engine, as you'll eventually hanker after more speed. As long as an adult is supervising, I don't see this being an issue.

9D280 · 20 July 2010, 12:36

I had a 25 on the back of an Avon SR4, which topped out around 21 Knts. From memory it's nearer 30 Degree deadrise (can someone form the "Gaffa Crew" confirm or correct that?), so I suspect 30 will get you to 25 Knots easily enough.

gotchiguy · 20 July 2010, 21:35

Quote:

Originally Posted by 9D280

I had a 25 on the back of an Avon SR4, which topped out around 21 Knts. From memory it's nearer 30 Degree deadrise (can someone form the "Gaffa Crew" confirm or correct that?), so I suspect 30 will get you to 25 Knots easily enough.

My 50 only gave me 32.1knts on my Pro 4.2...

...t'was 4 stroke though I admit...

jpn · 20 July 2010, 23:42

Thanks for the info mates.....from what I have gathered, 30 will work, 40 would be ideal, 50 will be the best option....

Brand new 30 or 40....or used 50....hmmm hope to find a good deal....

gotchiguy · 21 July 2010, 07:35

Quote:

Originally Posted by jpn

Thanks for the info mates.....from what I have gathered, 30 will work, 40 would be ideal, 50 will be the best option....

Brand new 30 or 40....or used 50....hmmm hope to find a good deal....

Often manufacturers use the same engine but with a modifeied ECU to provide a different horsepower. For instance, I know that my Suzuki DF50 was exactly the same as a DF40 bar a re map (and maybe different air restrictors). In a case like this, the price difference between the two engines should be pretty small in the scheme of things I would have thought. The price differential between an Optimaz 115 and a 125 is only £200 I read the other day on here.

To be honest, secondhand engines are a good way to go, as long as you get a well maintained and serviced engine it should give you years of troublefree boating to come

9D280 · 21 July 2010, 08:11

As Gotchiguy says, usuially two or three engines are built from the same lump. The net result of this is that you may find if the 50 is the restricted 60 & 70, you will get a very lardy 50. If however it's the unrestricted one that shares it's hardware with the restricted 40 & 30, you'll get an engine about as light as it's going to get. Same goes for all engine sizes, and the "separation lines" in the brochure are dfferent for each manufacturer.

Honda 50 is ridiculously light for a 4- stroke - I could even hang one on my prehistoric 110Kg rated transom - and get an Aux on as well!

So, whilst looking, also a good idea to look a couple of engine sizes either side to get a feel for how overweight or not it may be.

gotchiguy · 21 July 2010, 08:19

Quote:

Originally Posted by 9D280

As Gotchiguy says, usuially two or three engines are built from the same lump. The net result of this is that you may find if the 50 is the restricted 60 & 70, you will get a very lardy 50. If however it's the unrestricted one that shares it's hardware with the restricted 40 & 30, you'll get an engine about as light as it's going to get. Same goes for all engine sizes, and the "separation lines" in the brochure are dfferent for each manufacturer.

This is what I was thinking whilst writing, but obviously forgot to include

Searider · 21 July 2010, 13:49

My SR4M with a 30hp 3 cyl yamaha 2 stroke makes 26 knots.

Still planes 3 up.