Originally Posted by il corvo
its a shame that a rib of that size is rated to such a low hp. i'm sure as time goes buy rib manufactures are loosing their balls!
Or they realised that if they stick a label on it saying Max 60HP people will think that means "MUST HAVE" 60HP on it or it will be "too slow!" and then some newbie will take it out with a 60 (or maybe more!) on and flip it on the first wave because he doesn't know how to use it. I'm sure in 1970s they didn't need to explain how they arrived at their Maximum value - they may have had some internal calculations that said the transom wont fall off. They may have just stuck a big engine on, loaded it to the max and made sure it was OK. Now they need to convince other people that the big engine is OK. Being over powered was certainly considered by the MAIB when they looked at the Milly incident.
avon SR4 rated to 50hp, even my tiny avon s3.45 rib is rated to 30hp (even though its got a 40 on it)! i know 4 strokes weigh more but a rib of that size should be rated to 60hp easy especially when it's gonna drag consoles, seating 4 or 5 people around and all the crap crew tend to bring too. with only 40hp it's gonna struggle a little.
A SR 4 needs some decent punch to shift the half a ton of water its filled the hull with when stationary. I'd say a 50HP is the wrong hands with now crew weight etc on a SR4 on flat calm waters once its cleared the ballast is quite twitchy sometimes and yet people come here saying "Is it OK to put 55, 60, 70, 75" on my 50HP rated boat... Sure stick 6 divers and gear on and it'll probably be far less twitchy. But you can't label it up to say "60HP if 6 fat crew in board, 40HP if single handed"
I don't know the boat in question. I looked up its spec and found the 420 not the 430. The 420 is rated to 40HP, 8 people. It didn't look comfortable for 8 people with a console on. I wouldn't wanna be on it planing with 8 people on it. Without a console, as a basic people carrier short distances to dive sites or loading and unloading keel boat racers after Sunday lunch 8 would be fine. But doesn't need to plane. Doesn't need 60HP (probably doesn't need 40). Two crew on the bench - 40HP will be fine for planing with.
If bigger was needed - the 460 is rated to 60HP and 9pax.
Did he say he was going to use it with 5 crew plus "crap" and a console? Or are we making assumptions on other people's MO? The fair weather boater doesn't bring 5 people's gear. In my experience if I'm doing some serious adventuring there is probably 2 people plus 50kg of gear max. If I'm doing some family day tripping there may be 4 people with 25kg of gear.