Which Prop size 18,19,20 21 Deg

Hi All,
l Have a new boat, 493 f Haines Cubby Cabin, it has a 90 HP Mercury OPTY Max with 18 deg prop, it pulls 60 kph top end, when l had my old boat with with a 75 hp mercury it has the same size prop as my 90 and it pulled 63 kph top end.
l want to go faster: ?
which prop will give me better fuel economy: ?
Which prop do l go for: 19 - 20 - 21
Boat uses: touring, towing a ski tube.
Number of persons carried: (2) adults, (2) 16 year olds

Regards
Wheelybin.

 

Probably the one it came with.

-Tom

 

With the boat fully loaded the way you run it, compare your full throttle RPM with the Mercury's recommended WOT RPM for your outboard.

 

how long is a piece of string, you need to experiment and find which one lets the motor achieve full revs or close to it. never over prop an outboard or the overload will destroy it. pitch is measured in inchs not degrees. you could try the ausfish website, there might be someone on there with the same outfit.

 

Hi Sub-Tom,
Went out for a run today, by my self took it up to full RPM and got prop spin.
an alarm went off when l reached 6000 RPM.

Regards
Wheelybin.

 

Ya, so, you still want to do all those other things on your list too, don't you?

If you want the best performance for each of your assorted activities you'll likely need a different prop for each one and change every time you change your activity.

Your call...

-Tom

 

if its going over the rev limit ....which is what ....then you want more pitch ..going up 2 inches in pitch will drop it back 400 rpm approx

 

Hi Sub-Tom & Pistnbroke,
Went to the MercuyMarine.com, site and entered all my boat and prop details, and it spat out that l need a Mercury Lazer ll ether 19 or 20 pitch props for my situation.
My current prop is a Mercury Vengeance 18 pitch

Went to the Ausfish.com site but it currently down.

Regards
Wheelybin.

 

well you dont need to go with the fancy name...I had 20 p on a 115 and 19 on my 90 ....many dealers have props they use to try on engines when they do a water test ..you might be able to persuade them to let you borrow some against a deposit..those fancy names ones are just for posing at the ramp. Buy one on e bay and then sell your old one