F-Ribs And Sibs - Inflatable Boat Community

I have just ordered a Tiny Tach. This is a small tachometer / rev counter that I will be using to determine what pitch of propeller is needed to get the optimum performance out of my sib and outboard combination.

My engine is a Tohatsu 9.8 2 stroke. This model is designed to operate within the range of 5000 to 6000 rpm when at full throttle. If it cannot reach 5000 rpm, or it’s exceeding 6000 rpm, when running at full throttle, then I’m not getting maximum performance and I’m probably causing damage to the engine by over stressing it or over reving it.

When I receive the tiny tach I will be adding to this thread and explaining the process I’m going through to select the correct pitch prop to get the optimum performance.

This will be an interesting read !

The Tiny Tach was ordered yesterday, and is on its way from China. Should arrive in about three weeks time.

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.

This is the Tiny Tach
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Nice one Chris.

I’d also vouch for adding a little tach/hour meter on a portable motor. Invaluable when running in, prop testing, keeping record of hours or just indicating that nice sweet spot for cruising/max efficiency.

Over the years we’ve had good experience with the TTO Trail Tech models. While not cheap have proved reliable and with a clear readable display.


https://rover.ebay.com/rover/0/0/0?mpre ... 2922850228



Also have the hour meter only version under the hood on our main engine....great for logging run time in between services.

So this is simply a wire that wraps around the spark plug cable, bit like an electricians clamp meter, taking data from within the cable ?

Funny you should mention that, because I found my engine seemed to be happier at a slightly lower speed than max

@chris moody worth adding a linbk to the tach? I got an e-bay chinese one but it only lasted 1 trip - didn't seem to like the water at all - will be interesting to see how yours gets on

cheers,

Paul.

Andy wrote: ↑

13 Jan 2019, 13:49

So this is simply a wire that wraps around the spark plug cable, bit like an electricians clamp meter, taking data from within the cable ?

Yeah, dead simples. Just wrap and go.

It only has to last for a couple of trips while I am propeller testing. It’s not going to be a permanent instrument, I just need the data from it to enable me to determine what work I need done on the propeller.

As it was less than a tenner, I’m not expecting it to be waterproof or last.

mm289 wrote: ↑

13 Jan 2019, 13:55

@chris moody worth adding a linbk to the tach? I got an e-bay chinese one but it only lasted 1 trip - didn't seem to like the water at all - will be interesting to see how yours gets on

cheers,

Paul.

I bought this one from Amazon.
Engine Hour Meter Inductive...

It was £20 but it arrived next day and has worked faultlessly all year.