prop torque after motor upgrade

[sjp2]

After replacing the 60 yamaha 4 stoke ,113/8 prop (i think) 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 i should lift the motor higher but i am a bit cautious of the boat riding too flat and not being able to lift the bow enough for rough water,shifting weight to the right etc does not work,

and the 25 % increase in hp only resulted in about 10 % increase in speed ,if that .

[Moonlighter]

The way to determine if the engine is too high or low is to run it on the plane at a good fast cruise speed, trimmed out to where the engine revs max at that throttle position, and look over the stern and check where the anti vent plate is - it should be skimming the surface.

I will bet its too low.

[catshark]

i thought 15 inch was the fave for that HP range suzuki.. did the dealer match up the prop/suggest this size upon sale..

[stevej]

What did you expect from the upgrade
Speed is revs x prop specs minus a bit of slip

A bugger engine can swing a bigger prop though

The other thing is you went from a 996cc engine to 1500cc a 50 percent in capacity
That’s where your extra tourqe is comming from

It’s also 47kg heavier mainly up high

[sjp2]

Catshark - dealer said the 15 would probably cause the motor to over rev,only about 500 rpm out .
stevej - expected and got a 12 year younger motor (with bigger balls),and the rest you state is all true ,but solving it a different matter cause i feel a bit uneasy with the boat on a lean ,one of the reasons i sold my trailer sailer.

[stevej]

Moving the engine up and down would be the easiest options to try
Mount a GoPro on the rear don’t get a mate to lean over as all that is doing is adding another 60plus kg over the rear where it wouldn’t normally be

Is it leaning at all speeds or just at the slightly higher speed

I have had a crusiecraft explorer and it would lean into the wind at top speed 65kph

Try the easy options first

[gazza2006au]

SJP maybe u have over powered the boat and its doing a speed the hull was not designed for and its flopping to one side? i donno just a thought

[sjp2]

will try the easiest option first ,move it up a peg ,the lean starts about 20 ks .
Gazza i hope not

[stevej]

They are a kiwi aluminium hull ?

What’s the deadrise if it’s quite a fine hull without a planing plank then Gazza might be right

[Noelm]

I think I see trim tabs in your future.

[Fed]

Raising the motor should make it worse.

[stevej]

https://www.boatsales.com.au/boats/d...24&pss=Premium

this the boat ?

[catshark]

not bad looking boat and 80 Hp would be some muscle on this boat

[sjp2]

lean starts at about 20 to 25 ks ,it doesn't get to top hull speed and fall over ,maybe the sailboat comparison was too extreme .
yes same boat ,built in 2005 but center console with 4mm hull and 4mm floor .

[Chimo]

sjp2

Do you have a foil on the motor?

I know some on here do not like the thought but I have used them on most of my boats and always found a benefit to the boats stability and low speed planing.
At higher speeds with the boat sitting higher and the motor trimmed back and out the foil should not creat drag as it should be mostly above the water surface.

Did you check the height of your anti ventilation plate when planing at moderate / higher speed as this will give a good indication of the correctness of you motor height setting?
Prop adjustments with your chosen expert can happen after this aand be most effective at that stage.

cheers
Chimo