motor over revs

[mjbpjk]

Hi guys
im just after some advice in regards to my new boat.

Im yet to use the boat as i don’t pick it up till tomorrow but the mech where im buying it from tells me its a bit of a weapon and ill have to take it easy.

As most would know from my past posts im getting a Stacer 489 seahorse with a 4st merc 60.

on the water test with the original prop im told the boat pulled strongly to just over 45mph which i think is around 72kmh or 40knts.

im told for this type of boat that is really quick! I guess ill find out Saturday morning just how quick that is.

Im told to take it easy and not go full stick even when run in as the motor still wants to over rev.

Bearing in mind I probably don’t need to go any faster is it worth going to a different prop or do I just show some restraint and not open her right up. The dealer says it will be a great set up as is cos it has a great hole shot and should travel well when loaded, but most of the time ill be by myself

Any thoughts would be great

Cheers
Pete

[Wahoo]

Hi Pete
something dont sound right, this is a new boat and your mec took it for a run and said to take it easy, but the motor is over reving, :-/:o


Daz

[litenup]

Pete, if it exceeds the max rev range as specified by the manufacturer, then its wrong. Dealer should not set it up to over rev, as it will void warranty if there are any problems. Two props may be a solution, one with higher pitch for when the load is light so it doesn't over rev. Cheers Pete.

[Dan5]

Hey you had better check that speed for yourself there matey that sound's a little like dealer hype.I have a 4.5 with a 60 4strk yammie and 30.5kts top's it out.I also had a 4.8 with a 70 4strk that did 32kts wot.Forty knots is pretty quick from a 60 on a 4.89 just test it for yourself first mate then see how it "really" goes.Dan..............

[Wahoo]

Hey you had better check that speed for yourself there matey that sound's a little like dealer hype.I have a 4.5 with a 60 4strk yammie and 30.5kts top's it out.I also had a 4.8 with a 70 4strk that did 32kts wot.Forty knots is pretty quick from a 60 on a 4.89 just test it for yourself first mate then see how it "really" goes.Dan..............




thats what i also thought Dan :-/


Daz

[mjbpjk]

Hi Pete
something dont sound right, this is a new boat and your mec took it for a run and said to take it easy, but the motor is over reving, :-/:o


Daz

Daz the mech took it for a water test yesterday and said it runs great but may over rev at WOT . That was by him self, however once loaded with fishing gear, fuel and another passenger im told it should be ok.

it may just be a little light one up and so i should be carefull not to over rev if this is the case.

I guess my 1st post was a little confusing sorry for that.:-[
im not sure if i should opt for a bigger prop to avoid this as im usually one up.
is this condition bad if i dont WOT

cheers Pete

[Hamish73]

any outboard will only overrev if you want it to.
Just dont twist the throttle as hard.
All this is dealer dribble until you test it for yourself.
IMO if it does 40 knots, it's probably overpropped, in which case it shouldnt over rev.
I wouldnt want to be in a tiller steer boat at 40 knots ::)

[mjbpjk]

Hey you had better check that speed for yourself there matey that sound's a little like dealer hype.I have a 4.5 with a 60 4strk yammie and 30.5kts top's it out.I also had a 4.8 with a 70 4strk that did 32kts wot.Forty knots is pretty quick from a 60 on a 4.89 just test it for yourself first mate then see how it "really" goes.Dan..............

Thanks Dan,

I thought that to as it seems very quick, im keen to see for myself.

When I arrived at the dealer the staff there approached me and said they hear my boats goes extremely well and really surprised the mechanic how it performed ( as this was the first boat of its kind they had sold ). Then the head dealer a really nice bloke told me perhaps it may go to well and he wanted me to talk to the mech so I don’t go crazy and have an accident or something. The seemed genuinely surprised at the performance and stressed it take it easy.
But all will be reviled on Saturday.

thanks again for your input ill let you know how I go

cheers Pete

[mjbpjk]

[quote=Hamish73;676003
I wouldnt want to be in a tiller steer boat at 40 knots ::)[/quote]

That would be insane i know but ive got a side console fitted as i like a little more comfort when cruising

cheers Pete

[Dan5]

Good luck with your testing mate maybe it does do 40kts and we'll have to eat some humble pie!!!Cheers Dan.........

[Hamish73]

That would be insane i know but ive got a side console fitted as i like a little more comfort when cruising

cheers Pete
ahh, ok. I checked the website and assumed it was the bare bones model. Still a light boat to be doing those speeds. make sure you take you digi camera and a gps ;)

[mikeyh]

A couple of points worth thinking about......
Any engine at WOT uses ***tloads of fuel....proportionately much more in NM/L than at "cruising revs". Except for short bursts you should always be sitting at less than full revs...much kinder on the engine (look what happens to Formula 1 & racing engines...and they are just somewhat better built than your average OB :)) and also your fuel bill....

In terms of setting up the boat ..if you are mostly by yourself, the correct prop will allow you to achieve WOT with your normal load....whatever this speed may be. IMO changing props is a pain in the a, not to mention the $$ of having 2 props...unless the 2 load situations are so hugely different. If you set it up for the usual situation and you have a heavier load at times...the boat will just be a bit slower.

as for the 40kn in a tiller steer..I'm with Hamish

cheers, Mike

[BM]

Correct setup should see a boat able to over-rev in an unloaded condition and be at the upper end of the WOT range when typically loaded.

There is nothing wrong with an over-revving engine (within reason) but a lugging (under revving) engine is deadly....

Think about it people, if you want to do some heavy duty skiing actvities you will buy a prop suited to skiing. This will give you great "pull" off the line but it may also terribly over-rev the engine. But the astute prop buyer knows this and has the intelligence to apply the knowledge to the way he operates the boat and therefore, when the ski prop is on he knows to be careful of his upper rpm.

Similarly, if your rig can over-rev a bit unloaded, when its loaded with gear, 2 or more guys etc etc you still need it to perform somewhere near its maximum. This means unloaded it will over-rev.

But we would expect that you are not so SILLY as to go beyond the manufacturers stated RPM.. Which of course should be very clearly spelled out to you by the selling dealer and if they don't then they are seriously wayward in their duties.....

Cheers

[Noelm]

a lot of people get all caught up with speed, the speed your boat does has nothing to do with the motor setup and longevity (sort of) what you should de is cover the speedo, and use a tacho only, the WOT RPM is what will decide if it is going to last you for years and years or be "lugged to death" by a big prop in just a few years.

[BM]

Yep, couldn't agree more Noel.

As far as I am concerned the tacho is "the" instrument to pay attention to (at least in the setting up of the boat).

[Noelm]

yep, that's the go, normal load full max RPM acheived relatively easily, if lightly loaded, then it MAY be able to obtain more RPM than manufacturer recomended, but a couple of hundred over will not hurt it in any way, and is indeed desireable to ensure a long and healthy life (for your motor, not you!) I don't know how many boats I have sorted out over the years that have been grossley over propped by the owner thinking that it will get a better cruise speed at lower RPM, thereby saving fuel, WRONG!!! the motor is forever going "uphill" and will get bad fuel economy, and it's life expectancy shortened considerably.

[warti]

I used to have a 480 stacer with a 60 four stroke merc and it maxeded out at 60 kays an hour and felt like it could go faster without being dangerous. That was with no gear in it. Loaded up with gear though it was a pig. Poor hole shot performance but no big deal up here.

[BM]

Sadly Noel,

There are plenty of sales staff at dealers who don't understand propping and recommend the entirely wrong props also... :(

[Seahorse]

i got 489 stacer runabout with 75hp 2 stroke merc. cruises nicely at 25knots. had it flat stick at 35knts.
thats on a pretty good day.
but i guess urs is a tiller?

greg