Optimising Zodiac Futura 2c with 40HP Yamaha 2 stroke

jamesess · 02 June 2019, 21:54

hi all,

Just bought a Zodiac Futura 2c 3.8m and a Yamaha 40v short shaft tiller and was wondering what the best setup is. The outboard currently has a 10" diameter and 12" pitch prop on it and was wondering what size would be a good upgrade if I am looking for more speed, and will only usually have 1 or 2 people in, 11" x 17" maybe? I don't know the engine RPM nor the top speed but I can buy a tach and find out if that's what's necessary.
Any tips or tricks on getting the most from the boat as I am new to this would be much appreciated.

Many Thanks

James

jeffstevens763@g · 02 June 2019, 22:01

You need the tach James find out your WOT RPM and work from there assuming your set up perfect it will be easy to get optimum of course depends what you want I'm down 2 inches on pitch so I get more response in rough water to maintain the plane for example.

jamesess · 02 June 2019, 22:04

Quote:

Originally Posted by jeffstevens763@g

You need the tach James find out your WOT RPM and work from there assuming your set up perfect it will be easy to get optimum of course depends what you want I'm down 2 inches on pitch so I get more response in rough water to maintain the plane for example.

wise words ill get a tach and see what I'm getting next weekend, is 10" diameter normal as eBay seems to have the 40hp props at 11+"

jeffstevens763@g · 03 June 2019, 09:34

Quote:

Originally Posted by jamesess

wise words ill get a tach and see what I'm getting next weekend, is 10" diameter normal as eBay seems to have the 40hp props at 11+"

well my suzuki 25 has a 10 1/4 dia prop 10,11,12, pitch. ive had 40 hp engines and can't for the life of me remember the dia but easy to find out look on propeller EU.com you can find your engine which will have a selection of props to choose from

Locozodiac · 03 June 2019, 17:54

Factory motors delivered with a installed prop are usually medium pitched ones as factory wants to be safe as won't know which boat type that 40 HP motor will be powering it.

If wanting to play with prop pitches correctly, install a high quality induction hour/tach brand say Hardline, Tiny Tach. Soon after the break in period has ended, report max wot revs the motor achieved with 2 up, afterwords if needed can go for a spot on prop maximization. A 40 HP on an inflatable boat with 2 up should perform pretty well.

During first wot water trial on flat calm water cond, motor should be free of having back, side or over transom water splashes. Will need to play with motor/transom different heights to correct those symptoms if having any, but that's a different chapter...

Happy Boating

pagick · 03 June 2019, 18:27

Just to give you an idea of what to expect from your boat and how I tried different props.
My Futura mk2 2013 had its first season with a used Mercury 40HP efi 4 stroke with very good compression. It would run it at 30mph with a good holeshot with two on board.
I swapped out that motor for a new Evenrude etec 60hp 2 stroke the next season (37mph).
And I just went thru this process of propeller testing the last few weeks with the help of this forum. Someone wisley recommended to try different pitches without changing prop models to get the correct pitch info, which I did. Before, I bought a "recommended" prop that changed both pitch and blade shape. But it just gave results that have too many variables and poor results that were of no help towards what to try next. I think our SIBs just don't respond like a smooth hard bottom boat to some props. Lots of drag.
P.S. Check your tube pressure, re-check after your boat is in the water for 10 min.(shrinkage) Its best to use electric pump with auto shutoff pressure gauge. Soft boats are slower. 3.4 psi on all tubes.

jamesess · 03 June 2019, 22:41

right, I have bought a tach so will find out what WOT RPM I am getting and go from there. Looking at diameter and Pitch alone there seems to be a variety of options but 11" diameter seems standard so not sure why I have 10" what do you think the advantage is to go up in diameter should I have 10" x 17" or 11" x15" for example, prop list for Yamaha 40hp 2 stroke below:

https://imgur.com/zuDIMiY

pagick · 04 June 2019, 00:23

Quote:

Originally Posted by jamesess

right, I have bought a tach so will find out what WOT RPM I am getting and go from there. Looking at diameter and Pitch alone there seems to be a variety of options but 11" diameter seems standard so not sure why I have 10" what do you think the advantage is to go up in diameter should I have 10" x 17" or 11" x15" for example, prop list for Yamaha 40hp 2 stroke below:

https://imgur.com/zuDIMiY

I don’t have info on the performance change on diameter. But I hope someone has info. In fact my inexpensive props I tried were 1/3” smaller than my original
Prop. But they were super inexpensive. $68. Each delivered.
Original prop 13.3 x 17p 6100rpm great hole shot
First new prop 13.0 x 19p 5900rpm very good hole shot (keeper)
Second new prop 13.0 x 21p 5200rpm very bad hole shot

jeffstevens763@g · 04 June 2019, 09:07

as a rule and in my experience 1 inch of pitch is = 150-200 RPM 1 inch of diameter is = 2 inches of pitch.
if you look on propeller EU.com choosing the right prop there's lists for different engines so when you find your WOT RPM which i guess will be well up you also need to know the optimum rev range of the engine