4-stroke EFI run in rev limiter?

[Moonlighter]

Moonlighter thanks - I've tried different positions with the trim pin and best one is second slot from the transom.
Then it takes like 6 seconds to reach a plane - that's with myself, wife and 2 kids on board.

We are not particularly heavy people but I know during summer at the river we will probably have another passenger or so.

Had a chat yesterday with a coastal dealer - his advice is also for me to look at a 9 pitch prop rather than the 10 pitch I got with the motor.


Thanks,
Jacques

Ok good that you have tried the various trim pin positions and found the best.

Heck though, 2 adults and 2 children and only a 15hp engine - that is a load for a small engine like that!! Especially on the inflatable boat that pushes a lot of water and creates so much drag!

Every 1” change in prop pitch normally gives you around 150-200 rpm change, assuming that you stay with the same diameter and propellor model. So, I wouldn’t expect a major difference going from a 10” pitch to 9”. Perhaps consider an 8”?

Re the engine height, can you put a piece of 1.5 x 1” timber or similar on the top of the transom before sitting the engine on there and still get the clamp bracket to tighten up? This will lift the engine height by an inch and might help too?

Have you given it a run by yourself to see how it goes and what max rpm you can get then?

[JacquesR_ZA]

Thanks Moonlighter - appreciate!

Unfortunately didn't try with myself only in the boat.

I'll check with my dealer on an 8".

My campsite neighbour runs the same duck with a Chinese 2-stroke and it goes a lot easier onto a plane.
And they're much bigger people as well...

[Boberstop]

Jacques: Mine came with a 4 blade 9 pitch prop.

[JacquesR_ZA]

So I've learned some interesting things during our summer holidays.

Took the rig down to our coastal area - subsequently where altitude is basically 0-meters above sea level and achieved 5500rpm with the same 10" prop I've used inland at 1500m above sea level at none more than 5000rpm. Getting the duck to plane also at 3 sec's, same passengers, rather than the 6 sec's at altitude.

Then also tried my newly acquired 8" prop and quite easily it reached 6000rpm and the ECU's rev limited to preserve the motor. Plane also in 3 secs, but notably slower travelling speed at 6000rpm.

So can confirm that using at altitude took away 500rpm of top end power and 3 sec slower planing.

I'll also try the 8" prop at altitude on our inland dam and report back.

Me thinks I should maybe have bought a 20 or 25hp, but then must do a skippers license by law.


Kind regards,
Jacques

[Boberstop]

So I've learned some interesting things during our summer holidays.

Took the rig down to our coastal area - subsequently where altitude is basically 0-meters above sea level and achieved 5500rpm with the same 10" prop I've used inland at 1500m above sea level at none more than 5000rpm. Getting the duck to plane also at 3 sec's, same passengers, rather than the 6 sec's at altitude.

Then also tried my newly acquired 8" prop and quite easily it reached 6000rpm and the ECU's rev limited to preserve the motor. Plane also in 3 secs, but notably slower travelling speed at 6000rpm.

So can confirm that using at altitude took away 500rpm of top end power and 3 sec slower planing.

I'll also try the 8" prop at altitude on our inland dam and report back.

Me thinks I should maybe have bought a 20 or 25hp, but then must do a skippers license by law.


Kind regards,
Jacques

Hi Jacques, when I got done with my boat last fall I had maybe 6 hours on it. The surging was going away, and it was runnin good nearly at 3/4 throttle. It's winter here where I live (9) degrees right now. Won't be in the water till April. Good to hear from you.

[Murray]

For every 1000’ (305meters) elevation gain you loss 3% hp.
In your case 1500 meters is approx 15% loss of hp.
15% of 15hp=2.25hp lost due to elevation, so when your boating at 1500m above sea level your 15hp is really only 12.75hp.

With a carburetor one would be looking at jetting the carburetor for high elevation running, in your case with EFI not an option. I think your on the right track with the propellers, you will likely end up with two props, one for high elevation and one for lower elevations. It would be interesting to see how your engine performs on a 14’ aluminum boat compared to your inflatable. I think you will be pleasantly surprised.

[Moonlighter]

There is another very important issue being forgotten here - boating in fresh water Vs saltwater!!!

Saltwater has far, far more buoyancy that fresh. Its denser.

In saltwater, the boat will float higher, less surface area in the water = less drag = faster to plane and faster speed.

[JacquesR_ZA]

Hi Jacques, when I got done with my boat last fall I had maybe 6 hours on it. The surging was going away, and it was runnin good nearly at 3/4 throttle. It's winter here where I live (9) degrees right now. Won't be in the water till April. Good to hear from you.

Great - yep, 9 degrees is not nice to get out on the water!
Mine has now reached 11 hrs of service.

Thanks Murray, Moonlighter - interesting facts!