Slow etec 50 hp

[Marian Mudcrab]

Etec is running a viper s/steel prop
13.7/8 × 15 , wot 6100 rpm for around 28 mph. It's on the back of a 14.5 feet outlaw. Just wondering what a 13.1/4 x 17 would do? Looking for a little bit more speed! Already raised the motor helped a little.

 

[jimmbo]

Welcome to iboats

What is the WOT range for your engine? If you are currently above the range, more pitch might give you a small increase(between 1/2mph and 1 1/2mph) in speed, along with lower rpms and slower Hole Shot. That is assuming you were putting higher pitched Viper. Changing to a different Make/Model of Prop, can throw a real Monkey Wrench into what differences in Performance occurs

If you want more speed, get rid of all unnecessary Weight, like Wives, kids, and Mother-in-law, especially the Mother in Law. Girl Friends and Mistresses can remain aboard.
Also make sure stuff is properly placed to Balance the Boat. And Engine Angle-Trim can make a big difference.
Viper is pretty much a standard SS prop, it will have slightly thinner Blades, and a bit more cup than the entry level SS by OMC/BRP.

 

[Marian Mudcrab]

Thanks for the reply jimmbo! The boat has everything stored in the right places. I don't carry any unnecessary items or people! Haha!

Welcome to iboats

What is the WOT range for your engine? If you are currently above the range, more pitch might give you a small increase(between 1/2mph and 1 1/2mph) in speed, along with lower rpms and slower Hole Shot. That is assuming you were putting higher pitched Viper. Changing to a different Make/Model of Prop, can throw a real Monkey Wrench into what differences in Performance occurs

If you want more speed, get rid of all unnecessary Weight, like Wives, kids, and Mother-in-law, especially the Mother in Law. Girl Friends and Mistresses can remain aboard.
Also make sure stuff is properly placed to Balance the Boat. And Engine Angle-Trim can make a big difference.
Viper is pretty much a standard SS prop, it will have slightly thinner Blades, and a bit more cup than the entry level SS by OMC/BRP.

 

[Marian Mudcrab]

The wot on this outboard is 6080 Running with me and 40 litres of fuel.(flat water) at 28 mph. I understand that pitching up will give more speed but decrease rpm . What I can't find out is will a smaller prop diameter increase the rpm? So my line of thinking smaller diameter plus larger pitch some more speed but still be in recommended 5500 to 6000rpm?

 

[Marian Mudcrab]

The wot on this outboard is 6080 Running with me and 40 litres of fuel.(flat water) at 28 mph. I understand that pitching up will give more speed but decrease rpm . What I can't find out is will a smaller prop diameter increase the rpm? So my line of thinking smaller diameter plus larger pitch some more speed but still be in recommended 5500 to 6000rpm?

 

[roscoe]

Really just wasting money at this point. Is it really worth it for 1 mph ?

You aren't going to get 3, or 7, or 10 more mph.

 

[jimmbo]

Smaller Diameter, may mean less Blade Area, and while it may increase the rpm, it can also increase the % of Slip. A lot of Prop Lines have the dia getting smaller as the pitch goes up. I rarely worry about Diameter, preferring to let the Prop Engineers do that.
Is the Engine in Good Shape? Good Compression, Good Spark? Timing fully advancing, and the Throttle Bodies opening fully?
From what I can find the WOT range is 5500 - 6000rpm. If you are getting 6080 by yourself, you are just about optimal, going to a 17 will drop you to about 5680, which is less desirable . By being less than 100 rpm over, you are not losing much power, and it will allow you to have the Mistress bring along a friend, and you will be perfect rpm wise.

 

[Marian Mudcrab]

Really just wasting money at this point. Is it really worth it for 1 mph ?

You aren't going to get 3, or 7, or 10 more mph.

Smaller Diameter, may mean less Blade Area, and while it may increase the rpm, it can also increase the % of Slip. A lot of Prop Lines have the dia getting smaller as the pitch goes up. I rarely worry about Diameter, preferring to let the Prop Engineers do that.
Is the Engine in Good Shape? Good Compression, Good Spark? Timing fully advancing, and the Throttle Bodies opening fully?
From what I can find the WOT range is 5500 - 6000rpm. If you are getting 6080 by yourself, you are just about optimal, going to a 17 will drop you to about 5680, which is less desirable . By being less than 100 rpm over, you are not losing much power, and it will allow you to have the Mistress bring along a friend, and you will be perfect rpm wise.

 

[Marian Mudcrab]

Jimmbo and Roscoe thanks for your input! Very helpful information. Cheers Mudcrab.