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I did a few more runs today with two adults and a medium load.

Ballast in: 4800 RPM and 20.4 MPH.
Ballast out: 4900 RPM and 24.0 MPH.
Aluminum 14x11 x 3 blade prop. Average readings going both ways. Anti-fouling bottom paint. Wedges installed.

I was really hoping for a couple miles per hour more...any ideas?

13x11 prop? 13x13 prop? 14x9 prop?

So you have reached the speed advertised by the macgregor marketing?


I'd go with 13x11

Running good non ethanol fuel ? Mine does 28 on GPS with 2 people no ballast with a couple coolers but I wouldn't say lightly loaded ??? I notice a big difference with good fuel ?

Altitude and fresh vs salt makes a difference. My motor starves for O2 at our 6000 feet.

Starscream wrote:I did a few more runs today with two adults and a medium load.

Ballast in: 4800 RPM and 20.4 MPH.
Ballast out: 4900 RPM and 24.0 MPH.
Aluminum 14x11 x 3 blade prop. Average readings going both ways. Anti-fouling bottom paint. Wedges installed.

I was really hoping for a couple miles per hour more...any ideas?

13x11 prop? 13x13 prop? 14x9 prop?

A 14 X 9 will give you 5400-5500rpm, make sure its double cupped if aluminum.

Yes premium fuel, non-ethanol. Fresh water. A few hundred ft. ASL.

28 MPH would be nice. Bahama Bound do you know your prop size and RPM at 28MPH? Do you have anti-fouling?

Based on a previous post by Mastreb which puts planing speed at 20+ knots, I suspect (hope) that I must be just under that magic point and maybe a prop change will put me up on top? I am right around that 20knot mark unballasted. With the old BF50A I would run about 8mph full ballasted, and that would increase to about 15 or 16 as the ballast came out. With this new motor, the difference is much less, only about 3mph. I wonder if that is indicative of anything?

I have a 90 Suzuki on 26 M. Only get 13 k with a 4 blade 13.5x15. I only get 5 k rpm. What prop did you end up with?

From experience a 15 pitch is way too much...I think the 4-blades make it worse.

A 14x11 - 3 blade prop gets me about 4800 RPM and 20 knots unballasted. It doesn't seem fast enough for a 90HP and I am hoping for some input from the forum members for a logical next step with regards to prop choice. I have one vote for a 14x9 double-cupped aluminum prop but I am also thinking of a 13x11. Hoping Bahama-Bound posts his prop choice since he is getting 28mph with the same engine.

I honestly would have thought you'd see higher speeds with the Etec90.

The Yamaha 70 can do about ~19mph (~16kts?) with ballast in and ~23-25 (~19-20kts?) with ballast out on my

I honestly expected the M to go faster

Actually the M is much slower under power since it is a displacement hull.

It "squishes" the water out from under the hull vs ridding on top like the X.

Victor

Starscream wrote:From experience a 15 pitch is way too much...I think the 4-blades make it worse.

Not to sideline this too much, but you have to be careful about generalizing when it comes to props. The Suzuki has a 2.59:1 reduction ratio, but a higher engine speed range of 5300-6300 rpm, resulting in a prop speed of 2046-2432 rpm. The ETEC 90 has an engine speed of 5000-5500 rpm and a reduction ratio of 2.00:1 for a prop speed of 2500-2750 rpm.

The higher prop speed of the same hp ETEC means either smaller diameter prop, or lower pitch, or both, to best utilize the full shaft hp of the engine than the Suzuki, which can swing a bigger prop at lower speed to do the same thing. Similar to the Bigfoot engines. And the new ETEC Pontoon series.

I don't know where the crossover point is, where larger prop with shallower pitch meets smaller prop with steeper pitch, though.

If it were me, I'd go for the 14" x 9" pitch, but I'd buy it from someone who will let me return it for the 13" if it's not right. Like the OB dealer who sold the engine in the first place.

Starscream wrote:From experience a 15 pitch is way too much...I think the 4-blades make it worse.

A 14x11 - 3 blade prop gets me about 4800 RPM and 20 knots unballasted. It doesn't seem fast enough for a 90HP and I am hoping for some input from the forum members for a logical next step with regards to prop choice. I have one vote for a 14x9 double-cupped aluminum prop but I am also thinking of a 13x11. Hoping Bahama-Bound posts his prop choice since he is getting 28mph with the same engine.

Like I said I believe I'm living kinda a lie .I just looked again and mine is Apollo xhs stainless 13 1/4 x17 .my motor came with 15 and 17 pitch prop and the first couple times I ran it with the 17 .I loved how it performed but thought it might be bad for the motor so I put the 15 on it and was not happy at all .switched back to the 17 p . I should be WAY over propped .! But I gotta tell ya I was grinning ear to ear .made the boat come alive .handled great ! I think I was in the low 20s with ballast .

fdnynapes wrote:I have a 90 Suzuki on 26 M. Only get 13 k with a 4 blade 13.5x15. I only get 5 k rpm. What prop did you end up with?

And I agree with Starscream that you have too much prop on there, given the empirical data. With a rated engine speed of 5300-6300 rpm, there's definitely too much prop for what you're trying to do, and I also agree that 4 blades only makes it worse. By way of generalization.

I use a 4-blade with one less inch of pitch when pulling a wakeboard, by the way, for the extra 'traction'.

We sent our 4 blade 13.75x15 to a shop and removed 1" pitch. Mast down, empty, no ballast max RPM 6250 @ 31 Mph. Needs another 1" removed Mast up.

Loaded Mast up no ballast we now get a max of 5800 RPM. The prop hit a sand bottom and probably slightly damaged it.

4 blade is the best prop for these boats from what I've experienced.

Victor

Watching this post with interest... the old hat stroker on the back makes the admirable green, especially with a following 5kt breeze! Also the noise can be aggravating when churning away for 4 hours at a time as we cruise between islands looking for wrecks to dive in the Greek Cyclades.
I'm sort of selling the dream quite well of island hopping on the plane, 1 hour to cover a 20 mile hop, a fraction of the fuel cost (11 litres/hour??? + oil & island price $2/l) virtual silent running (she loves our friends yam 4 stroke 50)
so quick question, how is the noise and smell factor compared to a 50 4stroke?