mercury 115 opti prop selection

seafreak · 30 November 2008, 12:24

my opti 115 is now all run in and running fine.on w.o.t. max revs are 5250, on looking at mercurys specs for this model it states max rpm at wot should be 5000-5750. i am happy with acceleration /top speed/fuel economy, is there any point in me experimenting with props to achieve 5750 at wot.i am just concernd for engine longevity/ reliability.

Nos4r2 · 30 November 2008, 12:43

Quote:

Originally Posted by seafreak

my opti 115 is now all run in and running fine.on w.o.t. max revs are 5250, on looking at mercurys specs for this model it states max rpm at wot should be 5000-5750. i am happy with acceleration /top speed/fuel economy, is there any point in me experimenting with props to achieve 5750 at wot.i am just concernd for engine longevity/ reliability.

What's the load onboard when you get 5250rpm?
You probably won't go any faster if you get 5750 at WOT-but you'll use more fuel. I might be tempted to go down 2" if I was getting 5250rpm with a light load though as it'll be straining a bit with a load onboard.

seafreak · 30 November 2008, 12:49

hi, load was usual for my boat; 75ltrs fuel 3 adults and 2 med size kids

Hightower · 30 November 2008, 12:51

If you're happy as you've stated, then stick to the lower revs as it'll give you the best MPG. Going for a higher RPM WOT might well give you better top speed (although not always) with improve acceleration, however your fuel consumption with go up and might well be dissapointed with the results against spending all that money on a new prop.

If you want to experiment then I would recommend having a look at the prop thread and seeing if anyone would lend you a prop just to trial.

http://rib.net/forum/showthread.php?t=22455

seafreak · 30 November 2008, 12:58

thankyou hightower.

Nos4r2 · 30 November 2008, 13:04

I'd stick with what you've got too-that's quite a big load for a 5.5m boat anyway so you'll prob rev quite a bit more lightly loaded.

Steve_B · 30 November 2008, 20:14

I have 5.7m Rib with the Mariner Opti 115.

With 4/5 adults, which is my usual loading, I get around 5200rpm and about 35-36kts.
However, with just 2 aboard, she will pull 5600+rpm and get 42kts. This is with the standard ali prop.
The biggest issue is the leading edge of the prop. If it has the slightest dink and therefore blunt edge, the rpm can drop on WOT. Take a bit of time to clean it up and a dab of paint and away she goes. I average about 1.3miles/ltr at around 30kts
Hope this helps
Steve