Wot speed results

Some people have questioned my wot speeds and I was even amazed at the speeds I was getting out of my 1993 20hp 2 stroke mercury on a 1648 flat bottom,I would get near 29mph with over 1000+ lbs of weight in the boat with the standard 13 pitch prop. With just me in the boat I get over 30+ mph. So I just switched out the 20hp carb for a 25hp carb that came off a 1994 merc outboard, I am flabbergasted at how fast this engine is now. I tested it today,I know people will think I'm crazy. Now I'm pushing a 14 pitch aluminum solas prop ,with the same weight over 1000+lbs I'm getting at the highest wot speed 32.7mph with 2 separate gps's. By myself I'm hitting near 35mph,extremely scary fast because it porpoises so bad. This again is with 2 different gps's,even my buddy couldn't believe how fast my boat moves. I just wanted to update my speeds here. I know and understand people will question my speeds as I did myself as well, but after doing it over and over and over I got the same speeds every time. This 1993 engine has so much more power than any other 25hp mercury outboard I have ever run,I can't explain why or how either but I have no complaints, lol. Please chime in if anyone has comments, ty.

You can get a tiller extension to sit farther forward. Will help with porpoising, but won't turn very sharp.

Be careful you aren't over-reving, or your motor may not live much longer.

Personally, I'm waiting on the videos of some of these test runs you are doing. :mrgreen: Back in the early 90's, my little brother had a 1648 with a 25 hp mariner. That boat was very fast, even compared to other similar boat and motors. He could easily outrun all of his friends or other boats he encountered on the rivers. We didn't have a gps back then to check it with, but I would have bet money it was making 30mph, and possibly more.

Very hard to take a pic of my gps when it's really rough out,I tried. I just down loaded an app for speed on my phone so next time I go to the lake I will try to get the speed. You think I'm not amazed,I am insanely amazed how fast this boat is. I won't run it without weight in the front again,way to scary and I almost lost the boat a couple times on turns so I will try to take a video hitting the 32mph with 1000lbs of weight. Remember, I'm using a 14 pitch prop also,I could actually push a 15 pitch prop if I wanted. I thought going to the 14 pitch prop I would lose torque out of the hole,I lost nothing over my 13 pitch prop suprisingly. I think a 15 pitch prop would be pushing it though, the 14 seems to be just right. I can hear the Rev difference big time between the 20 and 25hp carb,the power difference is tremendous. I will try and get a nice flat day to do the video. I was consistently staying at 31.5 mph but I hit 32.7 a few times but the average speed was 31.5. Depends on the wind and how rough it was. Imo getting any speed over 30mph is amazing to me with the amount of weight in the boat . Next week,possibly monday if it's a bit calmer I will go.

scoobeb said:

Very hard to take a pic of my gps when it's really rough out,I tried. I just down loaded an app for speed on my phone so next time I go to the lake I will try to get the speed. You think I'm not amazed,I am insanely amazed how fast this boat is. I won't run it without weight in the front again,way to scary and I almost lost the boat a couple times on turns so I will try to take a video hitting the 32mph with 1000lbs of weight. Remember, I'm using a 14 pitch prop also,I could actually push a 15 pitch prop if I wanted. I thought going to the 14 pitch prop I would lose torque out of the hole,I lost nothing over my 13 pitch prop suprisingly. I think a 15 pitch prop would be pushing it though, the 14 seems to be just right. I can hear the Rev difference big time between the 20 and 25hp carb,the power difference is tremendous. I will try and get a nice flat day to do the video. I was consistently staying at 31.5 mph but I hit 32.7 a few times but the average speed was 31.5. Depends on the wind and how rough it was. Imo getting any speed over 30mph is amazing to me with the amount of weight in the boat . Next week,possibly monday if it's a bit calmer I will go.

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Quite honestly I would be less concerned with speed and more concerned with weight distribution or motor trim and getting that porpoising stopped.

It only porpoises with me in the boat and no weight in the front. I knew it was going to porpoise as it did the last time I ran it while doing my 20hp carb test. I just did a wot run by myself with no weight in the front for wot speed results with the 25hp carb comparing it to the 20hp carb speed,no other reason. When I go by myself I bring a 150qt cooler and put it in the front part of the boat and I fill it with cement blocks at around 150lbs . That is the perfect weight I use to stop the porpoise. I have no issues with weight distribution. Like I said it was only for wot speed results to see how fast it would go with minimal weight. I knew it was going to porpoise,it was just very scary going near 35mph and it doing that. I'm all set with weight distribution, I know how sensitive these boats are to weight distribution if it's wrong. 31-32mph is plenty fast enough with me in the boat. I'm very happy and satisfied.

scoobeb said:

It only porpoises with me in the boat and no weight in the front. I knew it was going to porpoise as it did the last time I ran it while doing my 20hp carb test. I just did a wot run by myself with no weight in the front for wot speed results with the 25hp carb comparing it to the 20hp carb speed,no other reason. When I go by myself I bring a 150qt cooler and put it in the front part of the boat and I fill it with cement blocks at around 150lbs . That is the perfect weight I use to stop the porpoise. I have no issues with weight distribution. Like I said it was only for wot speed results to see how fast it would go with minimal weight. I knew it was going to porpoise,it was just very scary going near 35mph and it doing that. I'm all set with weight distribution, I know how sensitive these boats are to weight distribution if it's wrong. 31-32mph is plenty fast enough with me in the boat. I'm very happy and satisfied.

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Somehow I misunderstood. I was reading you had 1K# of weight in the boat. "Now I'm pushing a 14 pitch aluminum solas prop ,with the same weight over 1000+lbs"

I pushed over 1000lbs of weight in the boat 32.7mph but with some 200lbs in the front seat is part of the 1000lbs + weight.


Ok,let me make this easy and simple. I bought a 1993 20hp 2 stroke mercury outboard and with a 13 pitch prop it moves over 1000lbs of weight near 29mph. With just me in the boat and no 200lb person which is a bit over 800 lbs it goes a bit over 30mph but it porpoises horrible. Then I tested a 2002 25hp 2 stroke mercury with a 13 pitch prop on it,I did the 1000lbs test which was a hair over 30mph,800 lbs it was 32 ish. Now I just upgraded my 1993 20hp 2 stroke mercury using a used 25hp carb and jumped up to a 14 pitch prop and with 1000lbs of weight it was 32.7mph and with 800 lbs of weight it was near 35mph but again porpoises horrible. I sold my 2002 and kept the 93. It has insane power for a 25hp. My 93 had better top end and torque than the 1993 when tested equally. Why I don't know. They were both great motors but I like the 93 style better. I just wanted to switch out the carb and see if it was worth the $90 I spent on the used carb and it was.

What is your RPM?

Haven't got a clue,honestly. I know I'm definitely under the 6000 rpm max though because the over Rev limiter would kick in if I was. That is my next thing,buy a tiny tach. If I had to guess by sound,just an educational guess would be 5500-5700. Pure guess though.

The standard prop is a 13 pitch aluminum prop,that is what comes on all the 20/25hp 2 stroke mercury outboards that I have ever owned. So the rpm range for the 25hp is 5000-6000rpm so I would guess the standard prop at wot pushes the motor at it's highest rpm,say 5800-6000 depending on load,so a 14 pitch prop would drop as they say near 200 rpm every pitch gained and every pitch dropped to a smaller size adds 200rpms. Like I said those numbers in the last post is pure guesses. Once I get the tiny tach I will hopefully be spot on with rpm. Is there a tach that is better for the price then a tiny tach??? I'm open to any suggestions. Something for around say 50-100$ and easy to instsll.

Do you know what your lower unit gear ratio is? I'd like to input some of these numbers into a prop calculator to see what kind of prop slip you may be getting at random rpms.

I found a site that says its 2.25. Plugging that in with a speed of 32.7 mph, a 14 pitch prop, and assuming 6000 rpms (top of WOT range), you are getting 7.5% prop slip. Which would all be reasonable numbers.... although it seems hard to believe such a heavily loaded boat would reach max rpms without having to drop at least one pitch from the factory size. Are these Mercurys just beasts? I have heard that they are faster than other manufacturers but I have always been an OMC guy because I feel more comfortable working on them so I dont have much first hand experience other than my 70hp Force which I hate lol.

This 25hp merc is special I tell you, I have ran a 25hp everything and every major brand and I have yet to see a 25hp 2 stroke 2 cylinder run like this particular outboard. I don't know why it's so powerful. My buddy is 140 lbs and I want to see what it runs with just him and another 140 lbs in weight in the front of the boat. I bet he will barely touch water ,lol. It screams. I am going to try a video that shows how fast it goes. I don't know if I can do both gps and video but I will try. The boat screams for a flat bottom jon boat. Imo 30+mph in any jon boat is fast and can get scary,lol.

I went 27mph with a 20hp 4 stroke Suzuki on a 1436 Crestliner, that was a 11 pitch prop and me at 300lbs,friend,200lbs,boat 200lbs,engine ,97lbs,gear,floor etc,add say 100lbs more. So near 900lbs in a 1436,now this was the stronger 1436 not the thin tin can one,I was in shock hitting 27mph. So with a powerful 25hp pushing a 14 pitch prop, I think anything is possible. If I wanted to this motor could easily push a 15 pitch prop to as crazy as it sounds. I lost absolutely no hole shot from a 13 to 14 pitch prop as crazy as it sounds.

I just don't know how to explain the power this engine produces. Funny to,the outboard sits quite low in the water,the anti ventilation plate is near 2 inches below the bottom of the hull so there is even some extra drag with these numbers,probably not to much but I bet a little . Like I said I can't explain it.

The very low motor is probably the key. Your boat aerodynamics and the low motor have you just about 100% airborne would be my guess. The lack of stability at speed would also be a symptom of this. In boat hull design it's called the pad...smaller pad = less drag. It's the area of the boat that remains in contact with the water at speed.... boat racing folks could probably tell you more... not an expert but I'd imagine the info is out there somewhere... A flat bottom boat with a typical wedge shaped front end is going to create a lot of lift.

https://www.screamandfly.com/content.php?219-The-Bottom-Line-How-a-Pad-Makes-a-Vee-Hull-Faster

https://www.boatdesign.net/forums/boat-design/what-faster-flat-boat-hull-vee-pad-hull-7378.html

My boat is completely flat bottom though.

My boat has tons of stability,I run it wot everywhere I go,it just porpoises if no weight is in the front. When I have some sought of weight in the front or say someone sitting on the middle seat I can make some insane sharp turns without issue,even in rough water. I usually take it a but easier in rougher water but I fly on straight runs and most turns that aren't 2 sharp. I don't do anything crazy.

Those articles are just an example of what a pad is. It's the part of the boat that touches the water at speed. A flat bottom boat gets a lot of air under it. When a boat porpoises it can be caused by a boat going fast enough to raise the prop too close to the surface so that it looses thrust... then the boat drops back down till it repeats.


A lower motor allows even more of the boat to get out of contact with the water. You are likely just barely touching the water at speed... that's why it goes so fast.... Have somebody take a movie of you going by at speed...