speed and rpm

[alsere_42]

Hi i have a new 4.10mtr alley craft scout runabout it has a 30hp yamaha four stroke on it and it does according to the gps 41kmh. it gets up on the plane straight away and seems to cruise ok,im not used to a four stroke as its so quiet after the 2strokes, the tacho is sitting on 5000rpm at top speed does this sound right ?? the compliance plate recomends a 30hp with a max of 40hp...

[mirage]

5000 rpm sounds a bit on the low side. Don't know about a 30 hp but the larger engines, 100 and above seem to have a max rpm, wide open, at around 6000 rpm. My Suzuki DF175 4stk is 6000.

Check your handbook, maybe it could do with a finer pitch prop to get the rpm up around its max, which would give you more speed and probably better cruise economy if it is labouring on a course pitch prop.

Cheers, Scotty.

[alsere_42]

thanks mirage,but i dont have the hand book so i might ask the yamaha dealler here in cairns unless some else can help thanks Alan...

[Blackened]

G'day
Jump on the yamaha website and this will give you a good guide to the maximum rpm range for your 30hp 4 banger. My little 9.9 2/ merc is 5500-6000 RPM at WOT. If yours isn't reaching the max rpm range at WOT then you'll more than likely need to come down in prop pitch.
Dave

[Seahorse]

i had a 4.2m stacer with 30hpmerc. sold today. when i was out on saturday i got out my hand held gps and clocked a 41.5kmh.
thats pretty good i think