Tiny Tach - Propeller testing

[harrison]

ChrisP, that looks good and not a bad price to boot. Useful being able to replace the battery.

The cheap copy tiny tachs are great for short term testing but have found not reliable enough for long term use.

[Fly360]

I think I’ll pick up one of the TTO Trail techs. The tach model also has the hour meter function right? Also what kind of battery does it take?

Also is there a rule of thumb with finding an rpm sweet spot? Or is it just anywhere within the manufacturers recommended range? I have a 6hp 4 stroke and my next motor will be a 25hp 4 stroke.

[harrison]

Fly,
We’ve had a few TTO’s, all reliable but the batteries are non replaceable. Never had one die though...expect to last a minimum 4 years/300 odd hours. They also log hours.

The one from Amazon, recommended by ChrisP, has a replaceable battery though.

Have found most motors that rev up to 6000rpm are probably happiest cruising all day at around 4000 to 4500rpm. Certainly this will be where they return best fuel economy.

[chris moody]

I agree, @harrison I've always found outboards to give surprisingly good fuel economy if you keep at or below 4000 rpm.

On one boat I used to use I was managing 1 litre per nautical mile (nm) from just planing right up to 4000 rpm, but at 6000rpm I was burning 2.4 litres per nm. That's a massive difference in the fuel bill.

On my little Ribcraft 4.8 I am averaging just under 0.5 litres per nm which I think is excellent.

.

Fly,
We’ve had a few TTO’s, all reliable but the batteries are non replaceable. Never had one die though...expect to last a minimum 4 years/300 odd hours. They also log hours.

The one from Amazon, recommended by ChrisP, has a replaceable battery though.

Have found most motors that rev up to 6000rpm are probably happiest cruising all day at around 4000 to 4500rpm. Certainly this will be where they return best fuel economy.

[Shaun]

This is the Tiny Tach
.
IMG_0088.PNG

I have one of these and they work really well. simple and easy to install.

[harrison]

Fly,
We’ve had a few TTO’s, all reliable but the batteries are non replaceable. Never had one die though...expect to last a minimum 4 years/300 odd hours. They also log hours.

Just checked on TTO site, manufacturer states battery life as 5 years plus.

[chris moody]

I agree, @harrison I've always found outboards to give surprisingly good fuel economy if you keep at or below 4000 rpm.

I can’t speak for other outboard manufacturers but Suzuki do a fuel chart for their outboards.
The optimum fuel efficiency for my 20hp efi with the 11” pitch 3 blade prop is at 4500rpm iirc.

Martin.

[harrison]

As I'm almost certainly going to need a specially reworked propeller for the Takacat, with a modification called cupping, rather than an off the shelf standard prop, I'm going to also order a couple of spare props. Once I have the test data from the Tiny Tach with each propeller, I can get Steel Developments to adjust the pitch and add the desired amount of cupping to my specifications. But first I need to find the maximum rpm achievable with each propeller at wide open throttle.

This is going to be loads of fun getting the Takacat tuned for maximum performance.

Chris, this sounds interesting and keen to hear your findings.

Are you looking to get more grip/lift from the cupped prop and/or run nearer the surface? I know the cat racers use surface breaking cleaver props to good effect. A bit extreme I know.

Will be interesting to hear how these tweaked/custom props perform on the smaller hp motors.

Good luck tuning the Takacat, sounds like you’ll soon be taking on the Thundercats.

[chris moody]

The aim @harrison is to remove the propeller ventilation which happens more on twin hulls. Apparently cupping is the way to cure this ventilation. I’m getting some ventilation, probably for around half to two thirds of a second, soon after getting up onto the plane. Once that ventilation is over it runs fine whilst on the plane with no further ventilation occurring, until the next time I go from displacement mode to planing mode.

If I can get away with running the outboard higher than usual that will be a bonus, less drag more speed.

[Fly360]

Fly,
We’ve had a few TTO’s, all reliable but the batteries are non replaceable. Never had one die though...expect to last a minimum 4 years/300 odd hours. They also log hours.

The one from Amazon, recommended by ChrisP, has a replaceable battery though.

Have found most motors that rev up to 6000rpm are probably happiest cruising all day at around 4000 to 4500rpm. Certainly this will be where they return best fuel economy.

Good to know about the battery.

As far as rpm goes I usually have my 6hp near WOT out of necessity but my next motor will have plenty of reserve power and I’ll have to find it’s sweet spot with the right prop. The tach will be invaluable for that.