Yamaha 80 2 str need little help

[Psychol]

Hey guys have few questions to pro ..

Finaly i put together my winter project Fletcher Arrowsport 16 ft with 80 yamaha 2 stroke , the prop on engine was little damage so i decide to exchange for new one ,so i pick up basicly this same pitch and diam .. i choice Solas Aluminium prop with 13.5 diam and 15 pitch , i was hoping i get around 50 knots but i didnt pas 45 knots top speed on 5800 rpm , 5800 i thing that's is very high any way , so my main question is (cos i cant find any proper info about (speed-tourk-acceleration etd ..) to choice right propeller to get max max speed , i dont care about pulling ski or something just want get everything from this engine to the limits - i say the boat will be around 450 kg with engine - i was reading little bit about fletchers and this company putting maximum engines of 50-60 hp on that model of boat -and them max speed is around 45 knots -

I was driving before rib with this same engine and prop , 5.45 meter lencraft - and on 5400 rpm i was doing 38-39 kt - but weight on this rib will be around 1000 kg

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another question is (i no it is out of this topic)

but after my last spin on full throttle and couple good bangs from wave and swell , engine on 5500 rpm start loosing power not much - but i was thinking meaby is low of oil so i come back to harbour for check ,the oil was plenty but the bulb for pumping petrol was quoit soft it is possible the engine was loosing petrol to carbs duo of short jumping on waves ?

sorry for my great grammatical . and long messi text , but I'll be very grateful for any answer or to give me few tips , thanks guys .

 

[steelespike]

Re: Yamaha 80 2 str need little help

45 kn converts to 51 mph. anything over 50 will be harder to get.
The motor is rated for 5,500 most looking for speed would run over that.You may want to check
in the Yamaha foruum for max rpm suggestions.
I would imagine these other boats you mention are running ss props of sofisticated design.
without that info the speeds don't mean much.Do you have your motor mounted as high as possible?there are props that allow maximum height.Do you carefully adjust trim to the best speed? Is your speed by gps?

 

[Psychol]

Re: Yamaha 80 2 str need little help

thanks steelespike

hmm .right i will try ss prop , but i dont like them much cos if u hit the ground you can say goodbye 2 your gear box ,any way the max rpm on yam`s are 4500-5500 - everything over that is call emergency revs . i was trying tilting the engine of course there is a big difference - also i forget say i have a hydro stabilizer on leg on my engine -what u thinking about them ? distance between of end of gear box and bottom of boat will be around 50 cm , so its deep enough ... the speed is showing by yamaha speedometer its that good ? or it is better to check on gps ?

finaly i thinking anyway the hull will be design to do 45 knots max

 

[steelespike]

Re: Yamaha 80 2 str need little help

ss prop do transmit more impact than al but the prop hub should soak up some of it.
If you do run where hard contact is likely you should stick with al it is less expensive to repair.
There are al props that do very well.The Turning point Hustler is one.
Use the antivent(cavitation) plate (just above the prop) to measure the height.Should be even with or slightly higher than the bottom.The less motor in the water the less drag.
Raise the motor to a point just before venting becomes a problem.
This could net a couple of mph.
The hydrofoil will help hole shot but must be clear of the water at speed or could reduce speed.If your not having any venting issues your motor is likely to low.