Top Speed?

[Dogginit]

Recently purchased a 26M with Mercury four stroke 50hp engine. Motor has been under repair as it sat for a couple years not being used. We have replaced filters, fuel pump and two injector coils through licensed power mechanic. The top speed I have been able to achieve with empty ballast tanks is only 15 km/hr (9.3 miles per hour) and Ihave yet to achieve a decent plane. As I I have no context to to compare with....what speeds have other 26m's achieved with the same motor and conditions? I am not sure if I am underpropped or if fins on the motor will help or if I need to dig deeper into the motor and consider other options. My boat has very few mods or extra weight.

[Jimmyt]

What is your RPM at full throttle? Is your throttle linkage properly adjusted to give full throttle? What prop are you runnng? Where is your trim set? It should plane with a 50, lightly loaded and no ballast. At least Roger said it would

[NiceAft]

Once, when fully empty, with no ballast, and only me at the helm, I got my 2005 with a Honda 50 hp 4 stoke, up to 30.5 km/h; it was a calm day. Close to 6,000 RPM. That’s the red line.

Fully loaded, with ballast and one other person on board, we’re talking 22.5 km/h; again at full throttle.

[Tomfoolery]

I have an , which has a flatter bottom at the stern than the , and it's only gotten up to 16 mph with no ballast. That's with a Honda BF50.

As has already been asked, what's the engine rpm at WOT? And what diameter, pitch, and blade count is the prop? The prop has to be matched to both the engine and the boat, and is the most likely culprit assuming the engine is operating as it should.

[adudinsk]

I have a 75HP Merc 4 stroke.
(carb'ed)
Fully loaded.. 2 people... gear... ballast..24 gallons fuel..

In less than glass water.. (way less).. wide open.. 18mph..


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[BOAT]

i have video proof of speeds over 18.5 knots in the ocean loaded with supplies from a week at Catalina - ballast empty - RPM 5350

the WOT RPM on 'boat' is 5650 per the Evinrude software displaying on m chartplotter. the red line for 'boat' is 5500 RPM - if i actually push the throttle all the way open to 5650 i have reached speeds in excess of 19 knots

these speeds are achieved on very smooth water in zero wind and at great expense to fuel mileage.

just last week we did three leg trip from oceanside to dana point to newport harbor. we left for dana point at noon and sailed in 3 knot winds until 4pm so with such lousy wind we were still 15 miles from dana point. because of the restricted military area you must avoid and the freakish north winds we had last week we only went 10 miles under sail on a 26 mile trip. dana point is an anchorage and i hate to anchor in the dark so with 2 hours of daylight left we started the motor. we made the remaining 16 miles in less than an hour.

now, we were not WOT but 16 knots was easy to maintain. with that north wind our top speed at WOT was only 17.5 knots so the 22MPH speed we get under good conditions fall off quite a bit with headwinds.

even with a strong crosswind with the wheel cranked 1/4 turn we have always been able to achieve more than 15 knots with empty ballast.

at high speeds we do not use full ballast because 'boat' makes too much spray that comes over the sides when we hit chop when the ballast is full so we leave the gate open when under power.

[kurz]

wow BOAT 18kn seems very god for me. So the Evinrude seems to be much stronger than the other.
With my 60HP merc I get max 16kn max. Is to say loaded with much things.

But when I see your speed I can understand that Roger got 22 milies (19kn) that he says in the brochure. Mabe without mast...

Interesting point: I use more or less the same fuel if I do 9.2kn (4500 rpm) or 12kn (5000rpm), takes half a liter for 1 mile...

[BOAT]

stop this video at 00.14 and see the GPS speed on the ipad that is wifi linked to the chartplotter on the pedestal (this is how I monitor the course from inside the boat and how I monitor the anchor when at night)



here is a picture at 00.14: it shows 18.2 K over M



also study the wake shape in the video - clearly the entire front half of the boat is out of the water - you can tell from the wake and the side spray

there was no wind that day - the wind has the most effect on speed if you have a clean bottom

also bottom paint - we have none = bottom paint will take a full knot off your speed - this was confirmed by mastreb

the motor has the big prop that captain Mike Inmon put on it at the factory. we are running the ballast open when under power so at that angle the ballast should be dry - we ran like that for almost an hour between Avalon and the Los Angeles breakwater

[Dogginit]

Thanks everybody..it is clear that I have some sort of issue. I'm working with my mechanic to test out different prop sizes and check the throttle linkage as well. RPM gauge would be nice but my boat does not have one, which makes this much more difficult.

[NiceAft]

What does Mercury suggest as to the perfect prop for a Mac with your motor.

[adudinsk]

To help dial it in, get a $10 cheap-o tach that you wrap a wire around a spark plug wire.. not perfect.. awkward to use.. but you will be able to see the RPMs (rip'ems) accurately, and cheaply.

They have usually a short "sense" wire.. but for a one off test.. not bat.

Amazon has MANY for around $8 plus shipping

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[Ixneigh]

Now I don’t feel too bad with my 15k WOT on a loaded boat. I did change to a flatter pitched prop which helped get the engine to a higher rpm. Etec 60 8 years old

Ix

[Inquisitor]

I'm in the process of refurbishing my M and the Mercury 60hp BigFoot came back from the shop. I took it out on the lake with NOTHING in it... not even cushions, anchors, mast, rigging... na-da. Just admiral, me and a picnic and one full 12 gallon tank. Achieved 20 mph (17.4 knots), but only achieved 5220 rpm. I doubt it'll break 5000 once loaded up back to normal. Been considering a little less pitch to get closer to 6000 red line, but really not after top-end... but more interested in high speed but efficient long distance cruise.

[NiceAft]

The most efficient speed is hull speed. In an , that is about 6 mph.

If your thinking about long distance at high rpm, forget efficiency. Your better off figuring how far you can go on a tank of fuel, and calculating your trip that way.

[Inquisitor]

The most efficient speed is hull speed. In an , that is about 6 mph.

If your thinking about long distance at high rpm, forget efficiency. Your better off figuring how far you can go on a tank of fuel, and calculating your trip that way.

I'm sure you're right. I didn't really convey what I meant. I want to derive a speed and fuel rate curves versus rpms for my M. https://www.followingseas.media/blog/20 ... burn-curve

Most all the time I've never come close to running out. After a day of pulling kids around on tubes, the stupid float tank gauge always showed near full. This gave me a false sense of the engine is super efficient. Then one fine trip, we did a lot of ICW motoring and we ran out - WITH THE GAUGE SHOWING NEAR FULL. Let's just say I use a stick on her when I need to be fuel efficient.

From seat of the pants experience and basic knowledge of hull speed and planing characteristics, we know...

• that up to hull speed we get a pretty linear speed versus throttle position.
• there's probably a huge fuel rate bump getting up on plane
• there'll probably be a completely different set of curves in the planing range
• there's a point at the top end (say... 90% to 100% throttle position) where we don't get any real speed gain, but we get a lot more noise and probably a lot worse fuel consumption.

This all gets mashed up with things like engines have sweet spots where they run more efficiently or are being lugged. I also wonder how getting a red-line permitting prop will make a difference. Intuitively, I know 6000 red-line will be even more fuel inefficient, but having another knot or two of speed might become a safety benefit when fuel consumption isn't a concern... like running for shelter or running to a fine happy-hour spread.

Now with the new addition (viewtopic.php?f=9&t=27999 I can create such curves without having to bring out the stick.