M40C - best prop to use on a ZapCat

nova_gts

Seaman
Joined
Jul 20, 2008
Messages
50
The scenario:
I'm running a Sea Wolf 1300 Predator (13' inflatable catamaran - just under 200lbs).
I have a Tohatsu m40c - Sea Wolf originally told me I needed a 10.375 X 14P stainless semi cleaver. When I got that it didn?t work and they admitted they were thinking I had the M40d2, that my 2cyl motor wasn?t as powerful as the 3cyl motor and I should probably should back it down to a 12P prop.

Question:
Is there that big of a difference in the two motors? Is mine just old and in need of repairs? What prop should best fit my needs?
 

pvanv

Admiral
Joined
Apr 20, 2008
Messages
6,500
Power is power - they are both 40 hp. The 2-cylinder has better throttle response. the D2 can be a wee bit smoother. The ONLY way to get the correct prop is by trial and error. First, dial-in the best transom height and tilt. Then read the tach at WOT. If you are over revving, you need more pitch. If under, you need less. If you don't have actual tach data, you are only guessing.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Yep, can't possibly dial best prop pitch by wild guessing nor testing without a induction tach. Those 40C are very powerful on light applications, you plan racing or just having fun at speed ? Which number is stamped on prop body 11-13 ? Need to buy an induction Hardline tach with programmable firing sequence to tach at wot while lightly loeaded current factory delivered prop, depending on your max wot rpm readings can maximize a less prop pitch to suit best your boating scenario.

Happy Boating
 

nova_gts

Seaman
Joined
Jul 20, 2008
Messages
50
Well the HP ratings could be the same, but Torque and power curves could vary.
I had a ebay Tach that I'm not 100% sure was correct, but I was getting up around 8k RPM's (according to that) with the factory just under 11P prop.
When I went to the 14P I wasn't getting enough speed to plane onto the Hi-Jackers and I believe I was seeing right around 4K RPM's
 

pvanv

Admiral
Joined
Apr 20, 2008
Messages
6,500
Well the HP ratings could be the same, but Torque and power curves could vary.
I had a ebay Tach that I'm not 100% sure was correct, but I was getting up around 8k RPM's (according to that) with the factory just under 11P prop.
When I went to the 14P I wasn't getting enough speed to plane onto the Hi-Jackers and I believe I was seeing right around 4K RPM's
I think your tach was wrong. The ESG should prevent going up to 8000. Correct WOT RPM is 5200-5800.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
The following data is needed :

-Use, general use, fast boating, racing ?
-Cat is used with one mate up front (bow area) ?
-Transom height S or L ?
-Leg size S or L ?
-Trim hole when tested ?
-Tach model, brand ? assume induction, programmable or non programmable unit ?
-With standard factory prop which was the max wor rpm achieved ?
-Post pics of rear OB/transom area.

M40C does not have a rev limiter, 8K is an exageration, probably tach is not set right, or reads right ? With a 40 well set, propped right, in excellent working order that light Cat should fly..

Happy Boating
 

nova_gts

Seaman
Joined
Jul 20, 2008
Messages
50
-Use, general use, fast boating, racing ? Fast boating
-Cat is used with one mate up front (bow area) ? yes - me (160lb) + gf (120lb) - maybe a cooler + gear (20lb)
-Transom height S or L ? the transom is standard - the MFG told me to try to get the center-line of the prop right around the center-line of the hi-jacker tubes
-Leg size S or L ? what is this? the motor is short shaft
-Trim hole when tested ? I tried all sorts of combinations, the second from the top seemed best
-Tach model, brand ? assume induction, programmable or non programmable unit ? I was using a ebay one that was programmable for # of cylinders - it seemed kind of unreliable. I think I still have a tiny Tach also - do you have a recommendation if i get a new one?
-With standard factory prop which was the max wor rpm achieved ?
-Post pics of rear OB/transom area.

M40C does not have a rev limiter, 8K is an exageration, probably tach is not set right, or reads right ? With a 40 well set, propped right, in excellent working order that light Cat should fly.. I guess I was trying to see what other people are experiencing so i should know if I'm in the right ball park. I get about 40mph on GPS with the factory Prop.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Tohatsu seems is delivering factory props with different pitches for worldwide markets. New M40C comes with 13 pitch props, on a light 430 Sib top air inflated with just one up only achieves 4800 wot rpm from max stated 5800. Have told factory to deliver new M40C with 11 pitch props instead to pull wot revs towards max.

Those cheapo induction tachs sold on line are crap, are what you paid for. Would suggest buy a nice https://www.hardlineproducts.com/pro...ourtach-meter/ check Iboats, Amazon..

If already counting with an induction programmable Tiny Tach unit, program it to 2P (2 sparks per revolution ) to real accurately.

Follow installation procedures., install it on tiller arm, next to throttle grip. With the right tach you could maximize a prop for best combo performance with 2 up and some gear. Float Cat alone, trim OB manually to rest at (90 deg) and AV plate parallel to water level. OB must sit right in middle transom and well clamp tight. Go for a wot spin loaded as described and report achieved max wot rpm with current factory delivered prop which is ? check number stamped on prop body. Can work from there flying that Cat to Mars...

Happy Boating
 
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