Top Speed?

[NiceAft]

This has been graphed out before; the challenge is trying to find those posts. So far, I haven’t had any success.. Hopefully, those who posted a fuel consumption chart will see this.

[Inquisitor]

I suspect there are several. It would be interesting to see what other people have come up with... but, I didn't even look because, it will be highly dependent on engine, hull growth, how the boat is loaded, even how much drag there is of all the rigging. In another thread, we talked about merely tilt of the motor made significant differences in mileage and speed. IOW... my curves would only be valid for my boat.

[NiceAft]

Yes, but if there are enough charts, one might be able to correlate some similarities.

[Be Free]

Here are my measurements for a moderately heavily loaded with a BF40D (fuel injected). Bottom is clean but paint is a little rough. 12x10 3 blade Solas. Ballast is out, mast up, no jib, main under sail cover. No appreciable wind or chop. No current. Fresh water. Speed measured by GPS. Fuel flow reported by engine.

RPM GPH Knots nMPG
800 .2 2.3 11.5
1000 .2 2.9 14.5
1500 .4 4.2 10.5
2000 .6 5.3 8.8
2500 .7 6.2 8.9
3000 1.0 7.2 7.2
3500 1.5 8.1 5.4
4000 2.0 10.0 5.0
4500 2.7 12.4 4.6
5000 3.5 14.0 4.0
5500 4.3 15.3 3.6

[Chinook]

Interesting numbers. Looks like the sweet spot for best performance is right around 2500rpm, producing 6 knots. That's predictably right in the hull speed range. My experience is similar, although at 2500rpm I would normally expect a slightly slower speed (5 to 5.5 knots). I attribute that to extra weight, with the boat set up for extended cruising and dinghy in tow, fully ballasted.

[rsvpasap]

https://www.boat-fuel-economy.com/fuel- ... calculator

[ris]

Boat is a 2003 X with a Honda BFP 60 hp. This Honda 60 has a 70 hp foot so the prop is 14 inches instead of 12 like the Honda 50 or regular 60. All three runs were made on a lake with winds of less than 5 mph. There were 850 pounds of people on the first run beside the two who did all three test runs. My son helped me as the 2nd person who changed the props.

First run prop is 14 inch X 7 pitch (extra 850 lbs).
RPM. MPH
2000 6.8.
3000 7.8.
3500 8.6.
4000 9.5.
4500 10.7.
5000 12.6.
5500 14.6 WOT.
14 X7 without extra weight and fuel per hour
RPM MPH GPH (fuel)
2000 6.1 .5
2500 7.3 .8
3000 8.5 1.2
3500 10.2 1.6
4000 12.8 2.0
4500 15.2 2.6
5000 17.2 3.7
5650 19.2 5.1

Prop is 14inch X 9 pitch
RPM MPH
2000 6.5
3000 9.1
4000 15.5
5250 21.5 WOT

Prop is 13 3/4 inch X 13 pitch
RPM MPH
2000 8
3000 10
4000 no data
4500 19.5

I know we missed some data and ran with the exta people on the 14X7 prop. which is the one I needed data on the most. Our plan is the next time we load the boat for travel we will run the boat for trawling and try all three props. Cannot remember if we filled ballast. Not much of a engineer. We do run the boat about 8 mph as we travel unless on the one of the Great Lakes heading for the next marina then it is 12.5mph

Richard


x

[Inquisitor]

Boat is a 2003 X with a Honda BFP 60 hp. This Honda 60 has a 70 hp foot so the prop is 14 inches instead of 12 like the Honda 50 or regular 60...

First run prop is 14 inch X 7 pitch (extra 850 lbs)
RPM MPH
5500 14.6 WOT

Prop is 14inch X 9 pitch
5250 21.5 WOT

Prop is 13 3/4 inch X 13 pitch
4500 19.5

Richard

Hmmm! Interesting... This sounds as close as I am ever going to get comparing a Honda to my Mercury 60 hp, BigFoot. It also suggests why I can't pull anywhere near my 6000 rpm red-line.

The best I can do with very light gear (1 battery, no galley, interior mostly gutted, not even cushions) and no sailing gear flapping in the wind, I was only able to get 5220 rpm at WOT. This gave a nice speed of 20 mph. Since, I'll never be configured this light again, I imagine, I won't be able to even break 5000 rpm in my more normal configuration.

My prop is a 14 x 11.

Are there any equations, charts, rules of thumb that might suggest a pitch that gains me 1000 rpm?

[kurz]

I use with my Merc 60hp big foot efi 2011 Prop 14x10

So I can get to max rpm.

In idle the boat is slow if course...

Boat is 26m

[Inquisitor]

I use with my Merc 60hp big foot efi 2011 Prop 14x10

So I can get to max rpm.

In idle the boat is slow if course...

Boat is 26m

PERFECT... how good/bad would you estimate your Mod'd weight over stock? +10, +100, +200... etc.

Thanks.

[ris]

The prop for the Honda is a 14 X9. I had the pitch changed to a 14 X 7 which loaded gives us about 350 RPM higher. On a aluminum prop they will repitch from a 9 to a 7 pitch, if it is stainless they will only change it one pitch. Or that is what they do at prop shops in central Florida. You will get better speed for a given prop with stainless but you pay for it. We still have a 14 X9 and a 14 X 7 prop that we can swap if one is damaged.

Richard

[Inquisitor]

The prop for the Honda is a 14 X9. I had the pitch changed to a 14 X 7 which loaded gives us about 350 RPM higher. On a aluminum prop they will repitch from a 9 to a 7 pitch, if it is stainless they will only change it one pitch. Or that is what they do at prop shops in central Florida. You will get better speed for a given prop with stainless but you pay for it. We still have a 14 X9 and a 14 X 7 prop that we can swap if one is damaged.

Richard

You bring up an interesting problem keeping a spare.

Does anyone have any experience with the Piranha propellers? They'd be lightweight and since they disassemble, they'd take up less room and you could have spare blades... 4 blades for a 3 blade prop. Reviews on Amazon seem good and its roughly the same price of aluminum props.

[Starscream]

You bring up an interesting problem keeping a spare.

Does anyone have any experience with the Piranha propellers? They'd be lightweight and since they disassemble, they'd take up less room and you could have spare blades... 4 blades for a 3 blade prop. Reviews on Amazon seem good and its roughly the same price of aluminum props.

Yes, we carry a piranha composite as a spare, disassembled somewhere in the bilge. Lightweight, and easier to store.

I've had mixed performance results. We run an evinrude 14X11 aluminum prop for best performance, topping out at 5,500rpm and about 25mph. The 14X11 Piranha (old model, no strakes on the blades) over-revved way too early and didn't come close to top our usual speed. So we changed it for a 14x13, but that one came with Piranha's new prop strakes and I wasn't able to get over 4k rpm, and also way down on speed. I could have asked them to change it again, to a 14x11 with the strakes to see if that was optimal, but I just kept the 14x13. I figure I can use it as a cruising prop, or in an emergency.

I hit a submerged rock hard enough to warp the aluminum prop, a big bang! Didn't need to change it out though, just dropped the revs a bit and headed home. I'm not sure what one would have to do the destroy the aluminum prop enough so that it had to be changed on the water.

[kurz]

I use with my Merc 60hp big foot efi 2011 Prop 14x10

So I can get to max rpm.

In idle the boat is slow if course...

Boat is 26m

PERFECT... how good/bad would you estimate your Mod'd weight over stock? +10, +100, +200... etc.

Thanks.

It is fully equipped with AL gear and beer...
Empty ballast tank: 26m 2000kg. Then add people on the boat and 100kg water etc.

[Be Free]

I hit a submerged rock hard enough to warp the aluminum prop, a big bang! Didn't need to change it out though, just dropped the revs a bit and headed home. I'm not sure what one would have to do the destroy the aluminum prop enough so that it had to be changed on the water.

I've hit rocks that curled the edges of my aluminum prop. Once I took a pretty good chunk out of one. Bringing the revs down to where the vibration was reasonable always brought me back home.

More than once I broke the shear pin on an older engine. I always carried spare pins and changed many of them on the water. I'm not sure that the modern equivalent of "spinning a hub" is an improvement. The only option would be to change the prop. Spare shear pins were a whole lot cheaper than spare props.