Prop torque lean

[simon p]

After replacing the 60 yamaha 4 stoke with a 2016 80 suzuki on the 4.8 center console mclay i am getting guite a bit of prop torque with the boat leaning to the left ,the motor is running a 17 inch prop but seems to be 500 rpm short of its rev range ,the motor is not too deep as it is 3/4 of an inch higher then the keel (the mclay has a internal keel).
Before i go to the expense of a different size prop eg 15 inch to get the revs higher ,maybe should lift the motor higher but i am a bit cautious of the boat riding to flat and not being able to lift the bow enough for rough water,shifting weight to the right etc does not work .

[Moonlighter]

Firstly you can’t prop a Suzuki the same as a Yamaha because they run a very different gear ratio and are designed to swing a larger diameter prop. So if you have a prop of the same dia and pitch as you had on the Yamaha, it is WRONG. and will likely cavitate due to too small diameter.

Secondly, getting the motor lifted to the right height will not cause the issues you seem to think it will re boat not lifting the bow etc. getting the motor height correct will make the hull perform to its best, its as simple as that.

So its hard to know where to start - normally the best starting position is to get the engine height set right. You should be able to see the anti-vent plate skimming the surface at cruise speeds, it shouldnt be buried in the flow. But it seems strange that with a 17” pitch you cant hit max revs. Which may again point to motor set too deep.

A 80hp on a 4.8m plate boat like a Mclay should really power along well. So something doesnt sound right at all here.

Have you talked to your dealer about the issues? What do they say?

Towards the top of this forum is a sticky thread dealing with props and engine height. Have a read of that as well.

[simon p]

thanks for the response Moonlighter ,performance part is pretty disappointing for a 25 % increase in power i only got a 10% increase in speed ,from 50 klm to 55 klm on a dam ,speaking to a dealer the next size down is a 15 pitch but he was more concerned for the motor over revvings with this prop,the prop people said they could supply a 15 pitch that was extra cupped taking it to a 16 inch ,but because the boat preformed well with the 60 hp ,i was hoping for a cheaper solution .
will lift the motor higher as you suggest and hopefully not suffer from ventalation

[Moonlighter]

Yes try that.

Your rev target should be to get 6000rpm at full throttle, trimmed out.

Here is a link to a Suzuki Australia performance report for a similar size (although maybe a bit lighter construction) boat like yours. It may give you some useful idea

It shows then running a genuine (OEM) Suzuki 13.75 x 17 alloy prop. Is that the same diameter and pitch as yours?

Is yours the Suzuki OEM prop or an aftermarket one?

They managed to get 64km/hr at 6000rpm, so even being a bit heavier boat, you shouldn’t be too far off that IF THE MOTOR is set up at the right height and is running properly.

It would also be worth checking that the throttle is actually opening fully on the engine when you have it pushed all the way forward. Might need adjusting.

https://www.suzukimarine.com.au/outb.../product/df80a

By the way, it is the selling dealers responsibility to set the motor up properly, at the right height, and with the correct prop so the motor performs to its best. At their expense. (Unless of course you chose or supplied an aftermarket prop yourself).

[simon p]

Resized_20190524_065912.jpeg well lifted by one hole to the middle hole of the five ,about 1 inch from the bottom of the keel ,yet to test it,doesen't seem that much ,prop doesen't have suzuki on it that i can see ,no other brand either ,the motor was fitted by the dealer but not water tested as it was on consignment with 16 hrs on it.
interesting that 7 klm/h was achieved in the 500 rpm from 5500 to 6000 as that will make the top speed a lot better

[Moonlighter]

See how the test goes. Let us know.

What dia is that prop - looks to have some numbers on it?

Already been dredging some new channels? LOL!!

[simon p]

props 13.75x17
nah not dredging ,just effortless digging for yabbies ,i think the prop has done some oyster shucking for the previous owner as well cause it's got a touch up glob of paint on the body near the fin.

[simon p]

long time revisiting this post i know , but i only just put the boat in the water ,the motor was lifted to the middle bolt hole of the five and that made the prop torque lean to the left stop ,
no effect on the motor revs though ,still only 5500 rpms so i bought a cupped 15 pitch prop which lifted the revs to 5700 but with only a minor increase in speed if any .
thinking i might lift the motor one bolt hole higher as the vent plate is still not visible ,can only see the top of the ( nose ) that the vent plate is attached to,just don't want any overheating problems.
happier that the lean was solved as that was very annoying,thanks Moonlighter.

[Moonlighter]

I doubt you would have overheating issues - and in any case, the Suzuki temp alarms will activate before any damage is done. But as I say, seems very unlikely. If you have gone too high you will probably find that the prop loses grip when accelerating out of the hole.

Another way to test if engine is too high after you have lifted it another hole is to do some sharp turns at med/fast cruise speeds with engine trimmed mid-way, if it lets fo real easy trim it in and try again, if it still lets go you might have gone too high.