What affect does the wrong prop have on an outboard?
Submitted by Josh on Sun, 2015-10-18 13:23
Hi all
Just chasing some advice from those in the know.
I took a boat out for a test run this morning, and it had a 5 blade stainless prop on a 115 Merc 2 stroke, 5 and a half meter stabi craft pontoon style boat.
The engine only managed a max rpm of 4700-4800.
Does this mean that there could potentially be damage to the gearbox/engine from the wrong prop?
I look forward to the advice
Cheers
Rob H
Posts: 5798
Date Joined: 18/01/12
yes sounds to be over
yes sounds to be over propped.
The effect is similar to driving your car in 5th gear up a hill foot flat to the floor when you could change to 4th.
But with a boat, the hill never ends.
Damage is not to gearbox but to the powerhead itself along with the hip pocket with fuel and soggy performance.
The damage is generally not catastrophic but a shortening of life span and problems (esp in 2 stroke) with sparkplug, oiling up etc.
If you find the outboard specs or google them it will give a range it should operate in.
Testing should be done with the maximum normal load (not average load) and preferably toward the upper limit of RPM.
Better to be slightly under than over propped.
A 5 blade on a 115?
Solas tell me though do not recommend more than a 3 blade under 150hp
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
dodgy
Posts: 4578
Date Joined: 01/02/10
Sounds like someone was
Sounds like someone was looking for more lift from the prop. I bet a 3 blade will make it porpose.
Does anyone know where the love of god goes, when the waves turn the minutes to hours?
Josh
Posts: 283
Date Joined: 14/09/10
If I trimmed it out to just
If I trimmed it out to just past neutral it really got good porpoise going at cruising speed
Josh
Posts: 283
Date Joined: 14/09/10
I think they were using it
I think they were using it for skiing, to drag big skiers out of the water, if I do get it, first step will be straight to the prop shop!
Rob H
Posts: 5798
Date Joined: 18/01/12
if you were going to prop it
if you were going to prop it for that, they could not have got it more wrong.
The anology would be trying to pull your boat up the ramp in 3rd gear
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
Josh
Posts: 283
Date Joined: 14/09/10
yeah, I am not too sure how
yeah, I am not too sure how much they actually knew about the boat, other than it floats and goes fine. Partially reflected by the 80 or so Engine hours